photochemistry: volume 33

Photochemistry

Volume 33

A Specialist Periodical Report

Photochemistry

Volume 33A Review of the Literature Published betweenJuly 2000 and June 2001

Senior ReporterA. Gilbert, Department of Chemistry,University of Reading, UK

ReportersN.S. Allen, Manchester Metropolitan University, UKA. Cox, University of Warwick, UKI. Dunkin, University of Strathclyde, Glasgow, UKA. Harriman, University of Newcastle upon Tyne, UKW.M. Horspool, University of Dundee, UKA.C. Pratt, Dublin City University, Ireland

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ISBN 0-85404-435-3ISSN 0556-3860

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Contents

Chapter 1Introduction and Review of the Year 1By Andrew Gilbert

Part I Physical Aspects of Photochemistry 11

Photophysical Processes in Condensed Phases 13By Anthony Harriman

1 Introduction 13

2 General Aspects of Photophysical Processes 13

3 Theoretical and Kinetic Considerations 16

4 Photophysical Processes in Liquid or Solid Media 184.1 Detection of Single Molecules 184.2 Radiative and Non-radiative Decay Processes 194.3 Amplitude or Torsional Motion 214.4 Light-induced Proton-transfer Reactions 234.5 Quenching of Excited States 24

4.5.1 Energy-transfer Reactions 254.5.2 Electron-transfer Reactions 25

4.6 Photophysics of Fullerenes 27

5 Applications of Photophysics 29

6 Advances in Instrument Design and Utilisation 296.1 Data Analysis 296.2 Instrumentation 30

7 References 31

Photochemistry, Volume 33© The Royal Society of Chemistry, 2002

v

Part II Organic Aspects of Photochemistry 51

Chapter 1 Photolysis of Carbonyl Compounds 53By William M. Horspool

1 Norrish Type I Reactions 53

2 Norrish Type II Reactions 552.1 1,5-Hydrogen Transfer 552.2 Other Hydrogen Transfers 58

3 Oxetane Formation 60

4 Miscellaneous Reactions 614.1 Decarbonylation and Decarboxylation 614.2 Reactions of Miscellaneous Haloketones and Acid

Chlorides 664.3 Other Processes 66

5 References 69

Chapter 2 Enone Cycloadditions and Rearrangements: Photoreactions ofDienones and Quinones 74By William M. Horspool

1 Cycloaddition Reactions 741.1 Intermolecular Cycloaddition 74

1.1.1 Open-chain Systems 741.1.2 Additions to Cyclopentenones and Related

Systems 751.1.3 Additions to Cyclohexenones and Related

Systems 771.2 Intramolecular Additions 80

1.2.1 Intramolecular Additions to Cyclopentenones 811.2.2 Additions to Cyclohexenones and Related

Systems 81

2 Rearrangement Reactions 842.1 �,�-Unsaturated Systems 84

2.1.1 Isomerisation 842.1.2 Hydrogen Abstraction Reactions 862.1.3 Rearrangement Reactions 87

2.2 �,�-Unsaturated Systems 882.2.1 The Oxa Di-�-methane Reaction and Related

Processes 882.2.2 Other Rearrangements 89

Contentsvi

3 Photoreactions of Thymines and Related Compounds 913.1 Photoreactions of Pyridones 913.2 Photoreactions of Thymines etc. 913.3 Miscellaneous Processes 94

4 Photochemistry of Dienones 954.1 Cross-conjugated Dienones 954.2 Linearly Conjugated Dienones 96

5 1,2-, 1,3- and 1,4-Diketones 975.1 Reactions of 1,2-Diketones and Other 1,2-Dicarbonyl

Compounds 975.2 Reactions of 1,3-Diketones 985.3 Reactions of 1,4-Diketones 100

5.3.1 Phthalimides and Related Compounds 1025.3.2 Fulgides and Fulgimides 106

6 Quinones 1086.1 o-Quinones 1086.2 p-Quinones 108

7 References 110

Chapter 3 Photochemistry of Alkenes, Alkynes and Related Compounds 119By WilliamM. Horspool

1 Reactions of Alkenes 1191.1 cis,trans-Isomerisation 119

1.1.1 Stilbenes and Related Compounds 1191.1.2 The Dithienylethene System and Related

Compounds 1221.2 Miscellaneous Reactions 127

1.2.1 Addition Reactions 1281.2.2 Electron-transfer Processes 1281.2.3 Other Processes 128

2 Reactions Involving Cyclopropane Rings 1292.1 The Di-�-methane Rearrangement and Related

Processes 1292.1.1 The Aza-di-�-methane Rearrangement andRelated Processes 132

2.2 Miscellaneous Reactions Involving Three-memberedRing Compounds 132

3 Reactions of Dienes and Trienes 1353.1 Vitamin D Analogues 139

Contents vii

4 (2� � 2�)-Intramolecular Additions 139

5 Dimerisation and Intermolecular Additions 1405.1 Dimerisation 141

6 Miscellaneous Reactions 1416.1 Reactions Involving Cations and Radicals 1416.2 Miscellaneous Rearrangements and Bond Fission

Processes 144

7 References 146

Chapter 4 Photochemistry of Aromatic Compounds 155By Andrew Gilbert

1 Introduction 155

2 Isomerisation Reactions 155

3 Addition Reactions 156

4 Substitution Reactions 164

5 Cyclisation Reactions 168

6 Dimerisation Processes 178

7 Lateral Nuclear Shifts 181

8 Miscellaneous Photochemistry of Aromatic Systems 183

9 References 188

Chapter 5 Photo-reduction and -oxidation 194By Alan Cox

1 Introduction 194

2 Reduction of the Carbonyl Group 194

3 Reduction of Nitrogen-containing Compounds 201

4 Miscellaneous Reductions 205

5 Singlet Oxygen 212

Contentsviii

6 Oxidation of Aliphatic Compounds 213

7 Oxidation of Aromatic Compounds 217

8 Oxidation of Nitrogen-containing Compounds 223

9 Miscellaneous Oxidations 232

10 References 232

Chapter 6 Photoreactions of Compounds Containing Heteroatoms Otherthan Oxygen 242By Albert C. Pratt

1 Introduction 242

2 Nitrogen-containing Compounds 2422.1 E,Z-Isomerisations 2422.2 Photocyclisations 2442.3 Photoadditions 2542.4 Other Processes 261

3 Sulfur-containing Compounds 275

4 Compounds Containing Other Heteroatoms 2874.1 Silicon and Germanium 2874.2 Phosphorus 2904.3 Other Elements 292

5 References 294

Chapter 7 Photoelimination 307By Ian R. Dunkin

1 Introduction 307

2 Elimination of Nitrogen from Azo Compounds andAnalogues 307

3 Elimination of Nitrogen from Diazo Compounds andDiazirines 3083.1 Generation of Alkyl, Alicyclic and Heterocyclic

Carbenes 3083.2 Generation of Aryl and Heteroaryl Carbenes 3113.3 Photolysis of Diazo Carbonyl Compounds and

Sulfur Analogues 313

Contents ix

4 Elimination of Nitrogen from Azides 314

5 Photoelimination of CarbonMonoxide and CarbonDioxide 316

5.1 Photoelimination of CO from OrganometallicCompounds 318

6 Photoelimination of NO and NO2 321

7 Miscellaneous Photoeliminations andPhotofragmentations 3227.1 Photoelimination from Hydrocarbons 3227.2 Photoelimination from Organohalogen Compounds 3227.3 Photofragmentations of Organosilicon and

Organogermanium Compounds 3247.4 Photofragmentations of Organosulfur,

Organoselenium and Organotellurium Compounds 3277.5 Photolysis of o-Nitrobenzyl Derivatives and Related

Compounds 3277.6 Other Photofragmentations 329

8 References 330

Part III Polymer Photochemistry 337By Norman S. Allen

1 Introduction 339

2 Photopolymerization 3392.1 Photoinitiated Addition Polymerization 3402.2 Photocrosslinking 3452.3 Photografting 351

3 Luminescence and Optical Properties 352

4 Photodegradation and Photooxidation Processes inPolymers 3694.1 Polyolefins 3694.2 Polystyrenes 3704.3 Poly(acrylates) and Poly(alkyl acrylates) 3704.4 Polyesters 3714.5 Polyamides and Polyimides 3714.6 Poly(alkyl and aromatic ethers) 3714.7 Silicone Polymers 3714.8 Polyurethanes and Rubbers 372

Contentsx

4.9 Poly(vinyl halides) 3724.10 Photoablation of Polymers 3724.11 Natural Polymers 3734.12 Miscellaneous Polymers 373

5 Photostabilization of Polymers 374

6 Photochemistry of Dyed and Pigmented Polymers 375

7 References 375

Part IV Photochemical Aspects of Solar Energy Conversion 405By Alan Cox

1 Introduction 407

2 Homogeneous Photosystems 407

3 Heterogeneous Photosystems 408

4 Photoelectrochemical Cells 410

5 Biological Systems 411

6 References 412

Author Index 415

Contents xi

Introduction and Review of the Year

BY ANDREWGILBERT

The chapter and reference numbers of the reports cited in this Introduction andReview can be found by using the Author Index. As usual, this subjectivereflection on the literature published within the review period follows the orderof the chapters in this volume and so begins with themore physical aspects of thesubject.Phenyl-substituted polyacetylenes are important materials for light-emitting

polymeric devices and a significant conclusion from their detailed theoreticalstudy is that polyacetylenes have a smaller optical band gap than polyenes of thesame chain length (Shukla et al.). The enormous increase in interest in thephotochemistry of dendrimers, which havemultiple chromophores, arises princi-pally because such systems can be used as models for the natural light-harvestingcomplexes. Thus several groups have reported the fluorescence properties oforganic-based dendrimers (see references 80—85 in Part I) and Balzani et al. havedescribed a dendrimer which hosts 32 dansyl groups. In other studies, opticallyactive dendrimers have been synthesised which are capable of enantioselectivefluorescence sensing at modest levels (Gong et al.), and picosecond laser flashphotolysis has been used to monitor twisted intramolecular charge-transferstates in dendrimers (Drobizhev et al.). A further area of increasing interest is theconstruction of molecular-scale wires for use in molecular opto-electronic devi-ces, and indeed ultrafast energy transfer has been observed in such systemsfashioned from zinc porphyrins (Kim et al.). The spectroscopic investigation ofsingle or isolated molecules has been the subject of considerable attention forsome time and Enderlein and Sauer have described a new algorithm for single-molecule identification by time correlated single-photon counting techniques,while Bereshkovski et al. have developed an analytical approach using single-molecule fluorescence spectroscopy to evaluate rate constants for slow confor-mational exchange.A new approach for measuring the rate constant of oxygen quenching of long-

lived triplet excited states is based on the time-resolvedmeasurement of resultantsinglet molecular oxygen (Kruk and Korotkii), and a new technique, the so-called ‘piston source method’ has been used to measure the absolute concentra-tions of singlet molecular oxygen in solution (Dun et al.). New treatments havealso been presented for the analysis of kinetic data, particularly those of non-exponential decay processes (Wen and McCormick, inter alia).


1

Publications on the more organic aspects of photochemistry are now con-sidered. The photochemistry of acetone continues to attract interest and com-putational procedures have been used to probe its photodissociation (Liu et al.),and Aloisio and Francisco have reported its photochemical behaviour in thepresence and absence of water. Irradiation of the ketone (1) provides an efficientroute to the cyclopropyl ketone (2) and this method, which is initiated by aNorrish Type II hydrogen abstraction, can be used to synthesise such bicycliccompounds as (3) (Wessig and Muhling).

The formation of the oxetanes (4) and (5) from the photoaddition of benzo-phenone to cis- and trans-cyclo-octene is subject to a remarkable temperatureeffect (Adam et al.), and the specific addition of benzaldehyde to ethenes (6) hasbeen used in a synthetic approach to preussin (7) (Bach et al.). Barton esters suchas (8) have been used in new photochemistry of boronic esters [e.g. (9)] to give(10) as the major product isomer (Cadot et al.) and Horton et al. have described anew photolabile linker (11) which, in the presence of tributyltin hydride, liberatesindole. The photoaddition of cyclic amines to 5-(R)-(1)-menthyloxy-2(5H)-furanone has been developed into a new method for the synthesis of chiralcycloaminobutyrolactones (Wang et al.) and dienamides (12) are reported byBois et al. to undergo efficient photocyclisation in the presence of sodiumborohydride to give (13) which is considered to be a convenient intermediate inthe synthesis of (S)-(�)-pipecoline.

Photochemistry2

As in previous years, the photochemistry of molecules as guests in host systemscontinues to attract a high level of interest. Examples in the review period includethe formation of the dimer (14) with 100% ee from irradiation of the inclusioncomplex of the enone (15) with (16) as the host (Tanaka et al.), and the report ofthe host-dependent outcome of the photoinduced rearrangement of (17) (Zim-merman et al.). Macrocyclic systems can be formed from phthalimide derivativesboth by photoaddition of 2-phenylpropene to appropriatelyN-substituted com-pounds followed by cyclisation [e.g. (18)] (Zhu et al.), and by photocyclisation ofsuch molecules as (19) giving (20) (Yoon et al.). Novel indol-2-ylfulgimides (21)have been synthesised by Heller et al. and their cyclisation with 336 nm radiationyields the stable photochromes (22). A useful source of the cyclopentanone (23)for conversion into the natural product �-necrodol can be obtained from theproduct (24) of the copper triflate assisted intramolecular (2��2�) cycloadditionin the diene (25) (Samajdar et al.) and irradiation of racemic norbornadiene (26)with r-circular polarised 290 nm radiation is reported to excite the (�)-enan-tiomer selectively and yield the (�)-quadricyclane (27) (Nishino et al.)

Introduction and Review of the Year 3

Wakita et al. have synthesised the stable silabenzene (28) and report that this isconverted with 320 nm radiation into the silabenzvalene (29). The first exampleof using �-cyclodextrin for asymmetric induction in the intramolecular metaphotocycloaddition of arene—ethene bichromophores has been described byVizvardi et al., and Morley and Pincock have reported an unprecedented intra-molecular photoaddition of a carbonyl group to a naphthalenemoiety from theirstudy of the ester (30) in methanol solution.

6�-Photocyclisation in stilbene derivatives continues to provide a convenientaccess to a variety of polyarenes (inter aliaMartinez et al. and Sato et al.), and Irieand co-workers have reported on the photochromism of a number of derivativesof 1,2-bis(methylthienyl)-perfluorocyclopenteneand related systems. The forma-tion of (31) from irradiation of the linked bi-naphthyl compounds (32) underoxygen provides the first example of trapping a triplet biradical intermediate inaromatic cycloadditions (Kohmoto et al.), and the previously unknown species4-iminocyclohexa-2,5-dienylidene (33) has been observed by nanosecond transi-ent absorption spectroscopy from irradiation of 4-halogeno-anilines (Othmen etal.). Saito et al. report that the sequential irradiation of 1,2:5,6-naphthalenetetracarboxylic dianhydride (34) in an argon matrix provides the first prepara-tion of dec-5-ene-1,3,7,9-tetrayne (35).

Photochemistry4

Diastereo- and enantio-meric excesses of the order of 96% are observed in theproduct (36) from irradiation of chiral esters such as (37) in the solid state(Cheung et al.), and evidence has been provided from a study into the magneticfield effect on the photoinduced electron transfer between benzophenone andstarburst dendrimers that those of higher generations act as both an electrondonor and as a supercage in the photoprocess (Akimoto et al.). Using �-benzoyl-propionic acid derivatives as substrates, Wessig et al. have obtained resultswhich give an insight into the factors which determine the stereochemistry of theNorrish-Yang reaction, and a new route to vicinal diamines by photoreductivecoupling of pyridine- arene- and alkyne-carboxalddimines has been described(Campos et al.). From studies into the excited state dynamics of methylviologen,it has been shown for the first time that a hydrogen bonding solvent can act as anelectron donor in ultrafast intermolecular electron transfer (Peon et al.), andcontrol over competitive photochemical and photophysical pathways to allowmaximisationof electron and proton pathways can be gained bymanipulation ofthe species in the novel complex of 8-hydroxy-1,3,6-pyrenetrisulfonate anion (38)and methylviologen using ionic micellar aggregates (De Borba et al.).


Interest in the photophysics and photochemical reactions of fullerenes con-tinues unabated at a high level and covers a wide variety of topics. Furthermore,there appear to have been numerous attempts to incorporate such compoundsinto essentially every type of photosystem. Indeed the molecular dyads compris-ing fullerene and porphyrin terminals seem to attract the most interest and havebeen the most intensely studied (see references 495—505 in Part I). Reports haveappeared describing the one-step multiple addition process of secondary aminesto C60 to give the corresponding tetra(amino)fullerene epoxide in moderate toexcellent yields (Isobe et al.), and the photoinduced properties of C120O, which isa dimer of C60 linked through a saturated furan ring (Fujitsuka et al.). Electrontransfer to give the C60·� and C70·� species has also been a subject which hasattracted considerable attention (Part II, Chapter 5, references 89—113), and thephotophysical properties of self-assembled supramolecular ensembles fromfullerene derivatives have been recorded (Deviprasad et al.).A new method for the production of singlet oxygen consisting of passing

molecular oxygen over an irradiated sensitiser (e.g.Methylene Blue) formed froman impregnated pigment on a support such as silica, alumina or titania has beenreported by Matsuura and Suzuki. p-Xylene has been converted into p-tolual-dehyde with 100% selectivity using the 10-methyl-9-phenylacridinium ion as theelectron acceptor sensitiser with visible light (Ohkubo and Fukuzumi) and�-amino radicals produced photochemically from tertiary amines (e.g. N,N-dialkylanilines) undergo diastereoselective addition to (39) which can then leadto tetrahydroquinolines such as (40) in a tandem process (Bertrand et al.).

Maier and Endres have identified the products from irradiation of the carbene(41) in matrices at 313 nm as the (s-E)-(E)-conformer (42) of triplet pent-2-en-4-yn-1-ylidene which is converted into 3-ethynylcyclopropene (43) with 436 nmradiation, and novel triplet anthryl(aryl) carbenes (44) have been generated fromthe corresponding diazo compound in rigid matrices and characterised by ESR

Photochemistry6

spectroscopy (Itakura and Tomioka). The first report of the direct observation ofa carbine—ether ylide has been made from studies into the laser flash photolysisof methoxycarbonyl-2-naphthyldiazomethanewhich yields the ether ylide (45) asa transient (Wang et al.), and novel surface modifications of platinum by thephotoysis of 3- and 4-pyridyl �-diazoketones (46) are considered to have poten-tial as a basis for general surface alterations (Pitters et al.). A synthesis of novelmesoionic amides such as (47) by irradiation of the azidotetrazolium salts hasbeen reported by Araki et al., and studies into the photolysis of M(CO)6 insupercritical fluids have provided the first observation of organometallic noblegas complexes [e.g. M(CO)5(Kr)] (George et al.). The first experimental measure-ments of triplet ethene near its equilibrium geometry have been made (Qi et al.)and the cinnamyl radical (PhCH�CHCH2O·), generated from the correspond-ing 4-nitrobenzenesulfonate, is reported to undergo unprecedented ring closureto give the oxiranyl benzyl radical (Amaudrut and Wiest). Papageorgiou andCorrie suggest that the photoylic release of carboxylic acids (RCO2H) from1-acyl-7-nitroindolines (48) would provide a convenient method to generateneuroactive amino acids, and in a remarkable process that involves a ringcontraction and loss of a nitrogen atom, irradiation of the benzodithiadiazine(49) gives the radical (50) in almost quantitative yield (Vlasyuk et al.).

In marked contrast to stilbene, the photostationary E/Z-ratio of azobenzenein zeolite cavities is closely similar to that in cyclohexane (Kojima et al.). The keyintermediate (51) in an enantioselective synthesis of the antitumor alkaloids(�)-narciclasine and (�)-pancratistatin has been obtained by a stereo- and


regio-controlled photocyclisation of the arylenamide (52) (Rigby et al.), and asimilar photoreaction of the dienamide (53) and its enantiomer in the presence ofsodium borohydride and methanol has been used in the synthesis of (S)-(�)-pipecoline and of (S)-(�)- and (R)-(�)-coniine (Bois et al.). The �-ketoamides (54)undergo �-hydrogen abstraction and loss of methanesulfonic acid on irradiationto give the enolate diradical (55) which cyclises regioselectively to form (56): thisis the first example of C—Obond formation in the Norrish-Yang reaction (Wessiget al.). The (2��2�) photodimerisation of cinnamic acid and its derivatives isvery well documented in the literature and has now been reported for thecinnamoyldopamines (57) and (58) but, in contrast, (59) photodimerises byethene addition to the benzene giving (60), which is the first example of this typeof process in the solid state (Ito et al.).

The considerable number of publications reviewed in Part III of this reportreflects the enormous and continuing activity in ‘polymer photochemistry’. The

Photochemistry8

volume of reports concerning light emitting diode systems has increased yetagain and from this measure the topic has become one of the largest specialisedareas in photochemistry and photophysics, with poly(phenylenevinylene)s(PPVs) creating the greatest academic and technical interest and attention.Much of the effort in this area is to devise polymer systems with highly efficientluminescence in specific wavelength region. Lipson et al. have shown thatpreparation and encapsulation of these polymers under argon greatly enhances(70%) their luminescence intensity, and Chen et al. report that PPVs withdentritic side chains self-organise into highly ordered structures in the solid state.Complexes of metal ions with PPVs exhibit an ionchromic effect with potentialapplications in optical switching devices (Huang et al.) and oligo-PPVs—fullerenedyads are reported to undergo rapid electron-transfer steps (Peeters). Newinitiator systems for photopolymerisation continue to be developed for generaland specialised purposes. For example, poly(ethyl methacrylate) with highacetone insolubility is produced using bis(cyclopentadienyl)titanium dichlorideas the initiator (Sato et al.), and a star-shaped polymer of tetrahydrofuran isformed by photoinduced cationic polymerisation in the presence of pentaeryth-ritol tetrakis(3,4-epoxybutanoate) (Mah et al.). A new method has been develop-ed by Lavrov et al. for the synthesis of C60-polyfullerenes, and Cataldo hasreported that such a polymer can be converted into a piezopolymer that is ashard as diamond. A novel photosensitive polyimide/silica hybrid has beenprepared by a sol—gel route which yields material with high tensile and thermalstability (Cao et al.), and Wurtz et al. have described a new method on thesub-micrometre scale for curing nanometric polymer dots. A series of novelpolyfluorinated epoxides have been synthesised which, following a cationic cure,give a segregated surface with low free energy (Matuszczak and Feast), andpolyesters doped with 1,4-phenylenebis(acrylic acid) undergo (2��2�) cycload-dition to give a photochemical set (Vargas et al.). Sykora et al. have synthesised afunctionalised polystyrene which allows the attachment of transition metalcomplexes such as ruthenium-polypyridine for use as a system for light harvest-ing energy through electron transfer, and a new photobioreactor incorporatingdiluted whey as the substrate has been evaluated: it is reported that on sunnydays the yield of hydrogen production corresponds to a conversion efficiency ofapproximately 25% (Modigell and Holle).Sadly, this volume of Photochemistry is the last that will benefit from Alan

Cox’s considerable talents as a reporter. Alan has had a long and somewhatvaried history of contributions to this series. He joined the team for Volume 10reporting on the Photochemistry of Transition Metal Complexes to which headded chapters on the Photochemistry of Transition Metal OrganometallicCompounds, the Photochemistry of Main Group Elements and Photo-reduc-tion and -oxidation for Volume 14. Alan continued reporting in these four areasup to Volume 22 when the inorganic aspects of photochemistry were droppedfrom the series. However, in that Volume he also took on the reporting of thePhotochemical Aspects of Solar Energy Conversion. Alan continued contribu-ting his two chapters up to and including the present volume but also added thePhotochemistry of Aromatic Compounds to his portfolio for Volumes 29—32


inclusive. The depth and breadth of Alan’s reporting over the years reflect hisconsiderable insight across the various areas of science into which Photochemis-try has spread over the years. All of us involved in the reporting and productionof the volumes of Photochemistry wish Alan well in his ‘retirement’ and I extendmy gratitude to him for his precise and concise reporting and for always meetingthe deadlines!

Photochemistry10

Part I

Physical Aspects of Photochemistry

By Anthony Harriman

Photophysical Processes in Condensed Phases

BY ANTHONY HARRIMAN

1 Introduction

This review follows the format adopted in recent years, with minor modificationaccording to the volume of work presented in particular areas. It appears thatinterest in single-molecule photophysics is less than in previous years but thatthere has been an increase in the number of publications concerning fullerenes.Several research groups are making serious efforts to design molecular-scalephotochemical devices and there has been a tremendous upsurge in interest inthe synthesis of dendrimers containing multiple chromophores. No attempt hasbeenmade to cover all the literature pertaining to the application of luminescentdyes for the detection of solutes in solution and only a few such highlights aregiven. There has been a progressive increase in the use of quantum chemistry togain an improved understanding of photophysical processes and it is clear thatsuch approaches, especially quantum dynamics andmolecular dynamics simula-tions, will make major contributions to photophysics research in the near future.Increased interest has also been shown in intramolecular proton-transfer reac-tions, since the ultrafast instrumentation often needed to follow such processes isnow available.The chapter is organised to cover all important processes leading to the

deactivation of an excited state in a condensed phase. Special attention has beengiven to the various fullerenes because of the exceptionally high interest paid tothese compounds over the past few years. Other sections consider theoreticalconcepts, instrumental methods for monitoring photophysical processes andapplications. The huge number of journals now in the market place precludescomplete coverage of the subject.

2 General Aspects of Photophysical Processes

Various aspects of excited state behaviour have been reviewed or highlightedduring the relevant period. Thus, several general reviews of organic photochem-istry have appeared1,2 and the importance of luminescence spectroscopy has beenstressed.3 The photophysics, photochemistry and optical properties of poly-imides have been discussed in terms of charge-transfer effects.4 Related work hasillustrated the importance of ultrafast transient spectroscopy for elucidating the


13

primary photophysical processes inherent to tailor-made organic chromophoresin solution.5 The special effects exerted by intense laser pulses have been high-lighted6 while the use of the phase of the incident light to establish couplingmechanisms has been reviewed.7 Specifically, this latter work has examined howthe phase of a transition dipole matrix element can be measured by the in-terefence between competing quantum mechanical paths.The effect of organised media on the photophysical properties of organic

molecules has been considered with particular reference to relating dynamics ofthe probe molecule to the microscopic properties of the host medium.8 Lightharvesting for solar energy conversion, especially with regard to semiconductor-based solar cells, has been reviewed in a comprehensive fashion.9 An interestingaccount10 has been given of n,�* photochemistry for compounds other thanaromatic ketones while the effect of ultrasound on the photopinacolisation ofbenzophenone has been reported.11 It appears that ultrasound can modify thecourse of bimolecular processes originating from triplet excited states. Variousaspects of photochemical isomerisation have been reviwed, with special atten-tion given to the so-called ‘hula-twist’ mechanism12 and to isomerisation fromthe triplet excited state.13 The more common singlet state induced photo-isomerisation has also been reviewed.14 The photophysics of phenyl-substitutedpolyacetylenes, these being important materials for light-emitting polymericdevices, have been subjected to detailed theoretical examination.15 An importantconclusion to emerge from this work is that polyacetylenes display a smalleroptical band gap than found for polyenes of the same chain length.Fluorescence excitation spectra have been reported for some organic radicals16

and a new technique, the so-called ‘piston source method’, has been introducedto measure absolute concentrations of singlet molecular oxygen in solution.17 Areview has appeared18 that covers the basic principles involved in the solvationdynamics of triplet excited states in viscous liquids or glassy solids. It appearsthat there are many cases where the phosphorescence signals are stronglyinfluenced by local dipolar reorientation dynamics and the mechanisms for sucheffects have been discussed in detail.The photophysical properties of tetrapyrrolic pigments continue to attract

attention19 and increased interest has been given to deactivation of the upper-lying excited singlet states.20—22 The underlying mechanisms whereby light-emit-ting polymeric devices operate have been reviewed23—25 and the role of electron-transfer reactions in photoinitiation of polymers has been examined.26 Consider-able attention has been given to the photophysics of transition metal complexes,especially with respect to metal-to-ligand, charge-transfer excited states.27—33 Adirect obsevation34 has been made of the charge-transfer-to-solvent reactivemode in the photoexcited alkali metal anion Na�. A theoretical evaluation hasbeen made of photoluminescence from semiconductors.35

The intramolecular magnetic interactions between two nitrosyl nitroxideradicals separated by a thiophene residue have been probed and compared withthe corresponding phenylene-linked compound.36 Closely-related systems havealso considered the photoswitching of intramolecular magnetic interactions inradical-substituted chromophores.37—39 Photoinduced spin states have been re-

Photochemistry14

ported40 for compounds known to undergo a light-induced phase change and themechanisms for such magnetic interactions have been considered.41 The poten-tial for generating molecular-scale magnets has been highlighted.41

The use of confined environments, such as zeolites and clays,42—46 has receivedconsiderable attentionwhile many aspects of bimolecular photochemistry occur-ring in crystals have been reviewed.47 A general kinetic model has been proposedto account for the optically and thermally stimulated luminescence observedwith samples of pure quartz.48 There is continued interest in using luminescentcompounds to detect analytes in solution.49—56 Similar attention has been given tothe analytical applications of chemiluminescence.57 The design of liquid mem-branes bearing light switches has been highlighted.58 In such systems, a liquidmembrane is used to separate two different solutes, usually dissolved in aqueoussolution. Selective transport across the membrane is facilitated by doping themembrane with a light-activated carrier molecule. The general technique ofsonoluminescence has been reviewed, especially with regard to single-bubblesonoluminescence.59—65

A light-drived moleular rotor, capable of unidirectional rotation, has beendescribed.66 Other interesting molecular-scale photochemical devices have beenconstructed from catenanes and rotaxanes67 while a fluorescent probe hasbeen reported tomimic the functions of a simple logic gate.68 Ways to control thehelix content of short peptides by photochemical means have been reviewed69

whilst the design of ‘off-on’ luminescent systems has receivedmuch attention.70—72

A reversiblemolecular shuttle has been produced73 where translationalmotion iscontrolled by hydrogen bonds. Related molecular switching events have beendescribed74—77 A review has covered the application of near-field fluorescenceimaging to the detection of single pigment molecules using an open-endedprobe.78

Recent years have seen a major initiative made into placing a large number ofchromophores in close proximity, primarily to build models for the naturallight-harvesting complexes. A variety of approaches have been advocated andthe effects of spatial crowding on the photophysical properties of the chromo-phores have been documented. Thus, the fluorescence properties have beendescribed for nano-sized star-like molecules,79 organic-based dendrimers,80—85

and doughnut-like assemblies.86 A dendrimer has been described that hosts 32dansyl groups87 and optically active dendrimers have been synthesised that arecapable of modest levels of entioselective fluorescence sensing.88 Other den-drimers have been reported to display ‘off-on’ luminescence switching effects inthe presence of certain solutes.89—92 Photophysical probes for organised assem-blies have been described93 while artifical light-harvesting arrays have beenassembled by way of non-covalent associations.94—97 The photophysical proper-ties of large aggregates of tetrapyrrolic pigments have been reported98,99 and thefluorescence behaviour of other nano-sized aggregates has been recorded.100—103

Parallel to the studies devoted to the preparation of photoactive dendrimers,there has been a concerted effort to construct linear molecular-scale wires forfuture use in molecular opto-electronic devices. Thus, ultrafast energy transferhas been observed to take place in long molecular wires formed from zinc

I: Photophysical Processes in Condensed Phases 15

porphyrins.104 Related meso,meso-linked porphyrin arrays have been de-scribed105,106 and the use of ethynylene bridges to couple together porphyrin-based chromophores has been highlighted.107 Related porphyrin-based arrayshave been formed108 by fusing adjacent porphyrins at the pyrrole positions.Many different dendrimers have been reported to contain photoactive transitionmetal-based chromophores.109—113 The emission properties of a molecular rec-tangle have been described.114

Great interest has also been shown in the design of novel light-emittingpolymeric devices and the photophysical properties of appropriate model com-pounds and oligomers have been measured. In particular, the importance ofinterchain exchange effects has been stressed115 while the significance of tripletexcited states has been considered.116 The luminescence properties of highly-conjugated oligomers have been reported with a view to better establishing themechanism for light emission from the corresponding polymeric devices.117—127

3 Theoretical and Kinetic Considerations

Theory has always been an integral part of photophysical investigations and thecurrent availability of cheap but powerful computers has greatly aided thedetailed examination of experimental data. There is a growing use of quantumchemical calculations to interpret decay kinetics and to explore how the solvententers into photophysical processes. Experimental verification has been pro-vided for the theoretical prediction of a kinetic transition in a reversible bindingreaction driven by the difference in effective lifetimes of bound and unboundspecies.128 A hopping model has been proposed to account for thermally stimu-lated luminescence in disordered organic molecules.129 The model is based on thepremise that such emission arises from radiative recombination of long-livedgeminate pairs of charge carriers. A theoretical model has been presented thatallows determination of the donor—acceptor distribution functions in Forster-type energy transfer.130 Unlike previous approaches to this problem, the newmodel makes no a priori assumptions about the nature of the distribution and itis reported that the method has particular application to measuring the acceptordistribution in luminescence sensing protocols. The possible role of inversionsymmetry in intramolecular vibrational relaxation has been considered131 andthe dynamics of vibrational motion in electron donor—acceptor complexes hasbeen addressed by ultrafast transient spectroscopy.132

The photodynamics of ethylene have been explored by ab initio quantumchemical calculations of the conical interesction.133 It is reported that the twistedgeometry of ethylene corresponds to a saddle point, rather than being a localminimum. Other reports have shown the value of the conical intersectionmethod134,135 while a theoretical analysis has been made of the absorption spectraand dynamics of photosynthetic reaction centres.136 This latter work is based ona microscopic exciton-vibrational model that includes temperature effects andthat takes into account the inherent inhomogeneity of the reaction centre com-plex. An approximate analytical solution has been provided for photochromic

Photochemistry16

and photorefractive gratings observed with certain materials.137

A configuration-interaction description has been given for intersystem cross-ing and spin—orbit coupling in conjugated polymers.138 An analytical routine hasbeen described for non-linear least-squares fitting of fluorescence quenchingdata139 and a quantum dynamics approach has been applied140 to analyse frac-tional wave packet behaviour in random phase fluorescence interferometry.Theoretical studies have been used to probe the photophysics and structure ofadenine,141 various aromatic amino acids142 and 7-azaindole.143 Semi-empiricalAM1 calculations have been used to calculate potential energy surfaces relatingto isomerisation of unsymmetrical carbocyanine dyes.144 It was found that theisomerisation potential surface was highly dependent on chain length and on thenature and position of the terminal groups. The results of this study alsoindicated the importance of steric hindrance around the isomerising bond.Related studies have addressed the triplet potential energy surface for hexa-triene.145 Twisting around the C-7—C-6 and C-4—C-7 bonds in coumaric acid hasbeen studied by ab initioMO calculations146 while related calculations have beenapplied to the problem of photochromiticity in substituted dithienylethenes147

and to the photoreactivity of fulgides.148

A theoretical study has considered the mechanism of energy transfer in metalcation-containing cryptates149 and separate work has focussed on the nature ofthe Kekule vibration in styrene for the S1 state.150 An ab initio study hasconsidered the mechanism for photoisomerisation of acrylic acid151 and hasshown the importance of the triplet state as a reactive intermediate. Theoreticalinvestigations have explored the spectroscopic properties of charge-transfercomplexes152 and have described anharmonic effects in electron-transfer pro-cesses.153 A computational study has considered the factors that govern thetriplet state reactivity of 1,4-pentanone154 while other studies have examined howthe fluorescence properties of highly conjugated organic molecules are affectedby changes in molecular geometry.155 The reaction pathway for electrocyclicreactions has been studied by ab initio multistate, second-order perturbationtheory.156

The ground- and excited-state structures of intramolecular donor—acceptorcomplexes have been examined by DFT calculations157 while large-scale confor-mational exchange has been studied by molecular dynamics simulations.158 Therole of molecular symmetry in intersystem crossing processes perturbed by anexternal magnetic field has been considered159 and a dynamical theory has beenproposed160 to account for time-resolved fluorescence spectroscopy. Propagatorcalculations have been described for the electronic spectra of photochromicspiro-oxazines.161 The ultrafast energy- and electron-transfer reactions occurringin bacterial photosynthetic systems have been explained in terms of a micro-scopic model162 and contributions of short-distance donor—quencher pairs inintermolecular fluorescence quenching have been considered.163 Incorporatingsuch effects into conventional Rehm-Weller quenching expressions is reported toexplain the discrepancies between theory and experiment. The special case ofreversible intramolecular energy transfer has been treated in terms of integralencounter theory.164


Certain aspects of photochemical ring-opening reactions have been subjectedto theoretical examination.165 The question of non-Arrhenius temperature de-pendencies in electron-transfer processes has received further study.166 Theoreti-cal studies have also addressed the low-lying excited singlet states in styrene,167

reversible intermolecular photochemical processes,168 Franck-Condon factors inpolyaromatics,169 and proton-transfer reactions.170 This latter study used a semi-classical molecular dynamics simulation to construct the relevant potentialenergy surfaces. Proton transfer was found to be greatly affected by isotopicsubstitution and to be coupled to internal vibrational modes. Potential energysurfaces have also been constructed for light-induced metal—ligand bondweakening.171

4 Photophysical Processes in Liquid or Solid Media

4.1 Detection of SingleMolecules. — The most elegant photophysical processesare undoubtedly those attributed to single or isolated molecules and this type ofspectroscopic investigation has been popular for a number of years. The reviewperiod has seen little progress in this area, however, and most research has beendevoted to looking at isolated molecules on inert surfaces. A technique has beenintroduced, based on near-field fluorescence imaging, that allows detection ofsingle molecules with a spatial resolution of about 10 nm.172 This high resolutionis attributed to the onset of non-radiative energy transfer from the fluorescentmolecule to the coated metal of the probe. A theoretical investigation has beenmade for single-molecule fluorescence detection on thin metallic layers using aclassical electrodynamics approach.173 A correlation has been made174 betweenthe fluorescence intermittency and spectral diffusion for single semiconductorquantum dots. A new algorithm has been described for single-molecule identifi-cation by time-correlated, single-photon counting techniques.175

Fluorescence correlation spectroscopy has been used to investigate single-molecule dynamics in thin polymer films.176 An analytical approach has beendeveloped to evaluate rate constants for slow conformational exchange usingsingle-molecule fluorescence spectroscopy.177,178 The statistics of photobleachingof single dye molecules have been monitored using renewal theory.179 Themethod uses a five-state model where bleaching occurs exclusively from thetriplet excited state. An exact formulism allows calculation of the distribution ofbleaching number and accounts for photostable dye molecules. Enhancement ofsingle-molecule fluorescence under metallic and dielectric tips has been ex-plained180 and linewidth measurements have been made for single moleculesdispersed in disordered media.181 A study of the dynamics of single latex beads inpolyvinyl alcohol films has been made by confocal microscopy182 and the multi-step deactivation of single luminescent conjugated polymers has been de-scribed.183 A description has been given that accounts for the effects of solutes onsingle-bubble sonoluminecence.184 The concept of single atom lasers and masershas been introduced.185

Photochemistry18

4.2 Radiative and Non-radiative Decay Processes. — A comprehensive correla-tion has been attempted between the fluorescence properties, the photochemicalstability and the lasing properties of aromatic compounds with their molecularsymmetry.186 It is reported that the molecular symmetry has a profound effect onthe ability of the compound to function as a laser dye, especially with respect tothe threshold of laser action. A somewhat related study has compared the opticalproperties, and the fluorescence quantum yield in particular, to the molecularpacking of the compound in a crystal or sublimed film.187 Other correlations havebeen made between the molecular vibrational structure and the fluorescencequantum yield for a range of organic molecules.188 The latter results haveparticular application to light-emitting polymeric devices. The photophysics ofcertain esters of 4-cyanobenzoic acid have been interpreted in terms of NorrishType II hydrogen atom abstraction reactions.189 The effect of an applied mag-netic field on the molecular photophysics of s-triazine has been considered190 interms of promoted intersystem crossing. A statistical approach to the study ofsinglet—triplet interactions in small polyatomic molecules has been advocated.191

This study made use of surface electron ejection by laser excited metastablespecies and laser-induced fluorescence spectroscopic techniques.The fluorescence properties of conjugated polyenes in non-polar solvents have

been described.192 The extraordinary hypercojugation of the methyl group in theS1 excited state of 8-methylquinoline has been reported on the basis of red-shiftedemission and polariation studies.193 Fluorescence from porphyrin aggregatespresent at extremely low concentration has been observed in certain mixedsolvents.194 The structure and reactivity of 4,4�-bipyridine in the S1 excited statehave been addressed by picosecond Raman spectroscopy.195 Very fast formationof radical species in methanol was observed to follow laser excitation. RelatedRaman studies have focussed on models for conducting polymers.196 The photo-physical properties of tryptophan in water,197 phenyl-substituted polyacety-lenes198 and pyrromethene-BF3 dyes199 have been described.The fluorescence radiative lifetime of Rhodamine 6G in a polymeric matrix

has been evaluated200 and the mechanism for photodegradation of this dye hasbeen considered.201 The photophysical properties of poly(4�-ethoxyacrylo-phenone) have been measured202 and the role of intersystem crossing in thedeactivation of the singlet excited state of aminofluorenones has been exam-ined.203 While the rate of intersystem crossing in such molecules remains slowand insensitive to the nature of the solvent, it is recognised that internal conver-sion is both rapid and solvent dependent. Phenyl-substituted terpyridine showsevidence for intramolecular charge transfer under illumination204 while the fluor-escence spectra of ketocyanine dyes depend on the nature of the solvent.205

Photophysical studies have been reported for some acridine derivatives,206 an-thracene-based carbonyl compounds207 and some asymmetrically substitutedethenes in solution.208 An unusual temperature dependence has been reported209

for anthracene in ethanol. The photophysical properties of 4-aminobenzo-phenone have been revisited,210 as has the photochemistry of triacylmethenedyes,211 Michler’s ketone212 and certain benzothiazoles.213

Considerable attention has been given to characterising the S2 excited states of


large polyatomic molecules, especially metalloporphyrins. Thus, fluorescencefrom the S2 state of tetraphenylporphyrins has been measured by ultrafastspectroscopy in various solvents.214 The energy gap between the S2 and S1 statesis somewhat dependent on the nature of the central metal cation and this caninfluence the lifetime of the upper-lying excited state. Related measurementshavemonitored S2 emission from 1,4-anthraquinones215 and pyrene.216 This latterstudy indicates that the lifetime of the S2 state in pyrene is only 150 fs. Pyrenederivatives are also known to form intramolecular excimers217 while anthraceneundergoes facile photodimerisation.218

The anomalous fluorescence properties of Terylene in a frozen neon matrixhave been reported.219 Curcumin displays solvent-dependent photophysicalproperties, possibly due to formation of an intramolecular charge-transferstate.220 Rapid decay of the S1 state of trans-stilbene, and the effects of vibrationalcooling by solvent molecules, has been monitored by picosecond Raman spec-troscopy.221 The solvation dynamics of Nile Blue in ethanol confined in poroussol—gel glasses have been measured222 and the effect of solvent polarisability onthe dual fluorescence of 1-phenyl-4-(1-pyrene)-1,3-butadiene has been de-scribed.223 It is seen that emission from a thermally populated upper-lying statedisappears at low temperature and in highly polarisable solvents such as carbondisulfide. The general effect of solvent exchange on excited state relaxationprocesses has been considered224 and solvation of acridone has been reported interms of a microscopic solvation model.225

The mechanism for the photoionisation of Methyl Viologen has been ad-dressed on the basis of transient absorption spectroscopic studies.226 The effectsof microheterogeneous media on the photophysics of certain dyes continues tobe a source of considerable activity.227—236 Phosphorescence from large aromaticketones has been described in terms of mixing between nearby n,�* and �,�*excited triplet states.237 The low-lying excited states of pyridine have been as-signed from high-resolution singlet-to-triplet absorption spectroscopy and phos-phorescence spectral measurements.238 Phosphorescence has also been recordedfor the chlorotoluenes at low temperature.239 Photophysical properties have beendescribed for some peripherally metallated porphyrazines,240 vitamin B2,241 tet-rakis(4-N-methylpyridinium)porphyrin,242 and pheophorbide-a.243 Triplet—trip-let annihilation has been observed in some soluble conjugated polymers244 and incertain fluoranthrene derivatives.245 Triplet—triplet annihilation has also beenmeasured for some tetraphenylporphyrins in liquid solution.246

A description has been given for the triplet states of a series of Pt-containingethynylenes.247 The photophysical properties of zinc porphyrins in microemul-sions have been studied.248 Hole burning spectroscopy has been applied to theelectronic states of coordination compounds in order to probe local structures.249

The luminescence properties of several new ruthenium(II) and osmium(II) poly-pyridine complexes have been described.250,251 and the efficiency of elec-trogenerated chemiluminescence from such compounds has been related to thecorresponding free energy change.252

Photochemistry20

4.3 Amplitude or Torsional Motion. — Light-induced conformational changescan provide a facile way by which to promote internal conversion. Thesegeometry changes may be small, such as slight twisting around a connectingbond, or large-scale, leading to formation of a geometrical isomer. Such pro-cesses can be extremely fast and highly efficient means for deactivating theexcited state. Because of frictional forces with surrounding solvent molecules,light-induced torsional motion provides a unique opportunity by which to studythe structure of the host medium. The photophysical properties of some 2,6-distyrylpyridines, and the corresponding hetero-analogues, have been inves-tigated in order to monitor conformational exchange processes.253 It has beenreported that photoisomerisation of certain chiral azobenzenes leads to en-hanced helical twisting capabilities.254 The ultrafast barrierless rotation ofAuramine O has been studied using femtosecond laser spectroscopy.255 Fastrelaxation within the excited state manifold occurs by way of torsional diffusionof the phenyl rings. It is believed that this twisting motion involves charge-transfer interactions.256

A report has been made of the light-induced reorientation of triacylpyryliumcations in solution resulting from excited state twisting and reverse twisting.257

The unusual fluorescence properties noted for 3,4,6-triphenyl-�-pyrones havebeen attributed to internal rotation of the aromatic rings.258 A synthetic strategyhas been devised to control the dihedral angle between porphyrin rings incovalently-linked bis-porphyrins.259 The mechanism and reaction dynamics forconformational exchange in non-planar porphyrins have been examined byultrafast transient spectroscopy.260,261

The role of a transient dipole moment in stabilising intramolecular charge-transfer states in solution has been examined262 for Coumarin 440 in solvents ofdiffering polarity. A considerable enhancement of �-electron delocalisation, anda concomitant increase in fluorescence intensity, can be achieved for 1,6-diphenyl-1,3,5-hexatriene by covalent rigidification.263 The importance of inter-nal rotation and intramolecular charge transfer has been stressed for somedonor—acceptor carbobazole derivatives264 and for some substituted carbosty-rils.265 A dual-mode molecular switch based on a chiral binaphthol compoundhas been reported.266 Several other compounds are believed to undergo internalrotation following promotion to the excited singlet267 or triplet268 states insolution. A series of donor—acceptor substituted biphenylenes has been proposedas highly selective and sensitive fluorescence probes for monitoring changes inpH.269 It is argued that protonation shows some degree of selectivity for thetwisted rotamer.Charge recombination within some planar donor—acceptor systems leads to

weak emission that can be explained in terms of a simple model based on themagnitude of the electronic coupling matrix element.270 The importance ofinternal rotation within the intramolecular charge-transfer state is highlighted.Intramolecular charge transfer, coupled to structural modification, has beendescribed for donor—acceptor substituted butadienes271 and for N-phenyl-phenanthridinones in solution.272 Light-induced intramolecular charge transfer


has been observed for the sodium salt of 4-(N,N-dimethylamino)benzenesulfon-ate in water but not in organic solvents.273

Considerable attention continues to be given to the so-called twisted intra-molecular charge-transfer (TICT) states where internal motion accompaniesintramolecular electron transfer, often leading to the appearance of two or morefluorescence bands. Picosecond laser flash photolysis studies have monitoredTICT state formation in dendrimers274 and highly-flexible long-chain mol-ecules.275 In the latter case, coordination of cations to the polyether linker canaffect the photophysical properties of the TICT state. Transient infrared spectro-scopic studies have provided additional insight into the mechanism leading toTICT state formation in 4-dimethylamino-4�-nitrostilbene.276 The photophysicsof 1-dimethylaminonaphthalene in binary solvents have been interpreted interms of TICT state formation277 while the archetypal TICT molecule, 4-dimethylaminobenzonitrile, has been shown to undergo light-induced electrontransfer with carbon tetrachloride.278 Using fluorescence anisotropy measure-ments, the mechanism for TICT state formation in this prototypic molecule hasbeen studied further.279 It is reported that the TICT mechanism gives a betterrepresentation of the experimental data that obtained with alternative modelsbased on planar ICT states or having the cyano group undergo bending modes.A comprehensive study has addressed the concept of internal conversion of

3,5-dimethyl-4-(methylamino)benzonitrile in alkane solvents.280 Intramolecularcharge transfer has been reported for a set of pyrene-2,2�-bipyridine-baseddyads281 and for various substituted 1,2-diarylethenes.282 Time-resolved fluor-escence studies have been used to follow TICT state formation in aminostyrylpyridinium dyes in both homogeneous solution and microheterogeneous me-dia.283 Incorporating the molecule into the cavity of �-cyclodextrins perturbsTICT state formation284 while the effects of added polymers on TICT-formingmolecules have been reviewed.285

The excited-state Raman spectrum has been recorded for trans-stilbene andused to discuss vibrational relaxation within the S1 state.286 Similar studies havebeen applied to the corresponding cis-isomer, where it is seen that there is anunusually high intensity of low-frequency bands for the S1 state.287 The signifi-cance of the meta-effect in controlling the photophysical properties of donor—acceptor substituted trans-stilbenes has been considered.288,289 The dynamics forphotoisomerisation of 4-(methanol)stilbene have been compared with theKramers-Hubbardmodel290 and it is concluded that the barrier to isomerisationdecreases with increasing solvent polarity. A range of novel stilbenes displayingrelatively high fluorescence yields has been synthesised291 and light-inducedisomerisation has been described in some multiply substituted alkenes.292

The effect of macromolecular isomerisation on the photomodulation of den-drimer properties has been reported for some azobenzene-subsituted photosys-tems.293 Intramolecular hydrogen bonding can affect the rate of light-inducedisomerisation294 while the photoisomerisation of certain cyclic olefins occurs viaboth singlet and triplet excited states,295with the possible involvement of charge-transfer effects.296 The photophysical properties have been recorded for linearpolyenes,297 substituted butadienes298 and hexatrienes299,300 and simple poly-

Photochemistry22

enes.301 The importance of light-induced isomerisation has been stressed in eachcase. Evidence has been presented for the involvement of neutral soliton pairs inthe relaxation pathways of photoexcited polyenes.302

Photoisomerisation of azobenzene derivatives has been shown to take place atthe air/water interface303 while a solvent isotope effect has been reported for therate of isomerisation of an azo dye.304 It is known that azobenzene undergoeslight-induced isomerisation when included inside the cavity of a zeolite305 where-as related studies have reported on the photochemical contol of the microstruc-ture of cholesteric liquid crystals functionalised with azobenzene residues.306

4.4 Light-induced Proton-transfer Reactions. — Light-induced proton transferreactions, which are often extremely fast, have been known for a long time but itis only recently, with the availability of ultrafast laser spectroscopic tools, thatthe dynamics of such processes have been resolved. Excited-state proton-transferreactions have been reported for some substituted naphthols in liposomes,307

1,1�-binaphthyl-4,4�-diol in various solvents and as a function of pH308 and2,2�-bipyridyl-3,3�-diol in polymeric media.309 The latter system is intended as aUV stabiliser for plastics. A report has appeared of the ground- and excited-statereactivity of 2,2�- and 4,4�-biphenyldiols with a range of proton acceptors.310 Atheoretical evaluation has been made of light-induced proton transfer andinternal motion in 1-hydroxy-2-acetophenone.311 The photochemistry andphotophysics of other �-hydroxy ketones has been reviewed312 and the excited-state proton transfer reactions of 2,5-diphenyl-1,3,4-oxadiazole have been re-ported.313 Photochemical proton-transfer reactions have been recorded for avariety of other organic compounds.314—318 All the above-mentioned photosys-tems involve proton transfer from the S1 state of the chromophore but it has beenreported319 that hypericin in a micellar dispersion undergoes proton transferfrom the lowest-energy triplet state.The mechanism for rapid photoacid—base reactions has been assessed by

ultrafast transient spectroscopy.320 The results have been interpreted in terms of adiffusion model that allows for electrostatic interactions and distinguishes be-tween H2O and D2O. Competition between inter- and intra-molecular protontransfer has been observed for some 2-hydroxy derivatives of 2,5-diphenyl-1,2-oxazole in media of varying acidity.321 The rapid proton transfer from pyranineto water has been followed, with several transient species being identified beforeproton transfer occurs.322

Photoinduced tautomerism has been monitored in several molecules.323—327

Such processes are necessaily fast and difficult to resolve from other inherentdeactivation pathways. Intramolecular proton transfer has been described forthe anionic form of 2-(2�-acetamidophenyl)benzimidazole.328 Light-induced S—Hbond cleavage has been detected by laser flash photolysis techniques for somesubstituted thiones in non-polar solvents.329 Light-induced proton transfer hasbeen observed for a variety of hydrogen-bonded complexes.330—334 while thenature of the solvent exerts a strong effect on the rate of intramolecular protontransfer in hydroxy-substituted flavothiones.335 Ab initio calculations have beenused to augment laser spectroscopic detection of proton transfer in 3-hydroxy-2-


naphthoic acid.336 Excited-state double proton transfer has been observed forcertain pyrimidines.337

4.5 Quenching of Excited States. — Various aspects of the interaction betweenan excited state and molecular oxygen have been considered. In particular, themechanism for photodegradation of certain cyanine and merocyanine dyes hasbeen explored.338 A new method has been proposed to determine the rateconstant for quenching of a long-lived triplet excited state by oxygen, based onthe time-resolved measurement of the resultant singlet molecular oxygen.339Thefactors that combine to control the efficiency of singlet molecular oxygen sensi-tisation by expanded porphyrins have been explored340 and the involvement ofcharge-transfer interactions in oxygen quenching of triplet naphthalene deriva-tives has been appraised.341 A separate study has considered the fluorescencequenching by oxygen of 9,10-dimethylanthracene in liquid solution and insupercritical fluids.342 The effect of a heavy atom on the photophysical propertiesof various classes of compound has been studied with a view to promoting tripletstate formation.343—346

There have been several reports of how covalently-attached stable organicradicals interact with excited states.347—349 The most popular radical has beenTEMPO and it has been shown that the lifetime of the excited state dependsmarkedly on the number of attached radicals. The lifetimes of both singlet andtriplet excited states are perturbed by the radical centres and it appears that themagnetic properties of the overall molecule is influenced by excitation.348

Quenching of room-temperature phosphorescence of polycyclic aromaticcompounds has been observed350 while hydrogen atom abstraction by tripletexcited states is a common phenomenon.351 A comprehensive study of theexciplex formation mechanism, often known as the Rehm-Weller model, hasbeen made.352 The mechanism for enhanced intersystem crossing in certaingable-type bis-porphyrins has been considered in terms of a through-bond,spin—orbit coupling interaction.353 It is reported that the lifetime of the free-baseporphyrin subunit is markedly dependent on the geometry and nature of theconnecting spacer residue. It has been reported354 that the rate of energy transfercan be controlled by selective protonation of one of the reactants. Ultrafastelectronic energy transfer has been reported to take place in linear and crossedporphyrin arrays355 while energy migration and subsequent trapping have beendetected in a polymer matrix.356 Related work has examined the photophysicsand energy-transfer reactions of 9,10-diphenylanthracene in solution.357

Investigations have been carried out to probe the conformations of tetheredpoly(ethylene glycol) chains anchored on polystyrene latex particles using fluor-escence energy transfer to establish the distance between donor and acceptorspecies.358 A newly developed semi-empirical method has been applied to the fastenergy-transfer steps occurring in photosynthetic purple bacteria.359 It is re-ported that the method gives a good representation of exciton interactions. Theconcept of photoswitching of intramolecular charge and energy transfer has beendiscussed in terms of donor—spacer—acceptor tripartite sysyems.360 The switchingfunction was achieved by incorporating optically bistable photochromic units

Photochemistry24

into the spacer. Efficient energy- and electron-transfer processes have beenreported for certain bis-porphyrins361 and for a range of naphthalene diimides.362

The development of stable dye-injection solar cells requires the identificationof appropriate sensitisers and much work has centred on the use of transitionmetal polypyridine complexes as the photoactive electron donor. However,ultrafast charge injection into the semiconductor particles has been monitoredwith coumarin sensitisers.363 Rapid interfacial electron transfer has been reportedto occur from both singlet and triplet excited states of certain ruthenium(II)complexes.364 The latter report is a rare example of photoreactivity from thesinglet excited state of a transition metal complex.

4.5.1 Energy-transfer Reactions. Intramolecular singlet energy transfer has beenreported for a series of coumarin-based molecular dyads included into �-cyclo-dextrins.365 An experimental protocol has been devised to ensure the onset ofroom-temperature phosphorescence generated during triplet—triplet energytransfer between dyes and polycyclic aromatic hydrocarbons solubilised inanionic micelles.366 Intermolecular energy transfer has been detected betweenselected laser dyes and Rhodamine 110.367 Triplet energy transfer has beenobserved between hydrogen-bonded reactants,368 although the inherent flexibil-ity of the tethers prevents a detailed mechanistic study. Energy transfer has alsobeen detected within the geminate radical pair formed by light-induced chargetransfer,369 within monolayers,370 in polymeric matrices,371—373 in solids374 and incertain pure crystals.375

Triplet—triplet energy transfer in various transition metal polypyridine com-plexes has been reviewed.376 A particularly efficient conduit for Dexter-typeelectron exchange seems to be acetylene-based bridges and long-range tripletenergy transfer has been achieved with such linkers.377 Here, electron exchangehas been detected over distances in excess of 50 A� . Much less efficient through-bond electron exchange occurs across spiro-based bridges but through-spacetriplet energy transfer has been detected in such molecular dyads.378 The syn-thesis of putative porphyrin-based dyads has been reported379 and ways toachieve structural control over the direction and dynamics of energy transfer inporphyrinic arrays have been discussed.380 A possible two-step triplet-energytransfer process has been described.381 Porphyrin-based models for the naturallight-harvesting antenna continue to attact attention382 and artificial arrayscapable of establishing a cascade of energy-transfer steps are now available.383

4.5.2 Electron-transfer Reactions. Research into light-induced electron-transferprocesses continues to be highly popular and there have been numerous at-tempts to employ such reactions for the engineering of photochemical molecu-lar-scale devices.Most work has been carried out in fluid solution. By measuringthe changes in enthalpy, entropy and volume that accompany electron transfer influid solution it has been concluded that the size of the reactants has only amodest effect on the efficiency of the process.384 This finding is in apparentcontradiction to earlier work carried out with charge-transfer complexes but thediscrepancy might relate to the nature of the reactants used in the various


experimental studies. A separate approach has considered the importance ofstereochemical factors in bimolecular electron-transfer reactions.385 Chargetransfer between strongly-coupled redox partners is often accompanied by excip-lex formation, with the reaction following non-Marcus behaviour.386 A detailedanalysis of the kinetic factors associated with diffusional electron-transferquenching has been made387 with a view to evaluating the size of the electroniccoupling matrix element for such reactions.Several experimental studies have examined the role of aliphatic and aromatic

amines as qunchers of various excited states in polar solvents.388—392 Inmost cases,evidence for light-induced charge transfer has been obtained by laser flashphotolysis and kinetic parameters for both forward and reverse steps have beenelucidated. The primary intermediates formed by electron transfer from 1-methylcytosine to anthraquinone-2,6-disulfonate in water have been monitoredby FT-EPR spectroscopy.393 Novel photosensitisers have been tested394,395 fortheir ability to operate as electron-transfer promoters in biological systems and ithas been noted that triplet 1-nitronaphthalene is able to oxidise trans-stilbene inpolar solvents.396 The same system undergoes light-induced excitation energytransfer in non-polar solvents. Ultrafast anisotropy measurements indicate acomplicated mechanism for light-induced electron transfer with ruthenium(II)tris(2,2�-bipyridine) in nitrile solvents due to diffusive solvation dynamics.397

The regioselectivity of photoinduced electron-transfer reactions involvingunsymmetrical phthalimides is controlled by the spin density distribution of theintermediate radical anions.398 Electron transfer to the triplet excited state of10-methylphenothiazines is influenced by an applied magnetic field.399 The in-volvement of fluorescent Lewis acid—base exciplexes and triplexes has beendemonstrated for numerous types of redox pairs in solution.400 Light-inducedelectron transfer across the interface between two immiscible liquids has beenreported401 and related to ion transport across the interface.It has been reported that bond cleavage triggered by electron transfer may

follow either a stepwise or a concerted mechanism.402 It is well documented thatthe nature of the solvent can exert a powerful effect on the outcome of electron-transfer reactions,403 especially when the solvent plays a direct role in chargetransfer.404 In fact, a microscopic model involving translational and rotationalmotion of the solventmolecules has been developed to account for rapid electrontransfer from N,N-dimethylaniline to oxazine when the latter is dissolved in theformer. The quantum yield of radical ion pairs formed by light-induced electrontransfer has beenmeasured by transient photoconductivity studies405 and relatedwork has addressed several aspects of charge recombination within geminateradical ion pairs.406 The effect of solution viscosity on the efficiency of bimolecu-lar electron-transfer reactions has been considered407 and ways to control elec-tron transfer using hydrogen bonds have been considered.408,409 Charge-transferprocesses have been monitored for ion pairs410 and in conjugated polymers.411—413

Directed electron transfer has been demonstrated in elaborate catenanes414

and rotaxanes,415 intended as models for the photosynthetic bacterial reactioncentre complex. The catalytic effect of molecular oxygen on the rate of intra-molecular electron transfer has been shown for a porphyrin—fullerene molecular

Photochemistry26

dyad.416 Several studies have indicated that the selective coordination of cationscan influence the dynamics of electron transfer between remote redox part-ners.417—419 Other studies have monitored light-induced electron transfer in por-phyrin-based molecular dyads and triads.420 Various aspects of intramolecularcharge transfer have been explored by reference to specific, flexibly-linkeddonor—acceptor dyads.421—424 It is often difficult to resolve the intimate reactionmechanism in such systems, because of competing diffusion, but strong indica-tions for through-space electron transfer have been observed with carefullydesigned U-shaped dyads having varying bite angles.425

In order to monitor the effects of through-bond electron transfer is is usuallynecessary to study rigidly-linked donor—acceptor systems and this has proved tobe a rich research field.426—429 Charge recombination within such dyads can resultin formation of the corresponding triplet state with an uncommon spin polarisa-tion.430 Orientational effects have been reported to be important for light-induced charge transfer between closely-spaced reactants431 while other work hasreported a novel double-electron transfer in certain donor—bridge—acceptordyads.432 Attaching the chromophores to a polymeric support might lead to theisolation of model compounds able to mimic some of the essential features of thephotosynthetic apparatus.433

Although most work in this field has centred around the use of porphyrin-based chromophores there has been a parallel effort to design molecular dyadsand triads around ruthenium(II) polypyridines.434 Indeed, such complexes can beused to drive a wide variety of electron-exchange reactions leading to long-distance triplet energy transfer along rigid spacers.435,436 A ruthenium(II)—manga-nese(II) mixed-metal binuclear complex has been proposed437 as a model for theoxygen-evolving catalyst present in green plant photosynthetic organisms. Sev-eral systems have been designed to undergo the photoswitching of electrontransfer.438—440 Usually, such systems are designed such that a conformationalexchange can be promoted by selective excitation or coordination and where thetwo conformers display markedly disparate rates of electron transfer. This is arapidly expanding area of electron-transfer research, driven by the need toidentify appropriate components for use in molecular-scale opto-electronics.

4.6 Photophysics of Fullerenes. — Research into the photochemistry andphotophysics of the various fullerenes continues unabated, aided by the prolifer-ation of specialised journals, and there have been numerous attempts to includesuch materials in virtually every kind of photosystem. Although the photophysi-cal properties of the basic clusters are now well established, fullerenes have beenfunctionalised in such a way as to make them attractive components in LEDsand in artificial photosynthetic devices, where their unusually low reorganisationenergy provides important benefits. Recent advances in the photophysics offullerenes have been highlighted,441,442 and high-resolution fluorescence spectrahave been recorded for C60 in toluene at 5 K.443 Thermally-activated processescontributing to the overall excited-state properties of fullerenes have been re-viewed,444,445 and laser flash photolysis studies have been reported for fine par-ticles of C60 prepared by re-precipitation techniques.446 Separate reports deal


with the photochemistry of the higher fullerenes447 and with the photophysics ofring-opened C60 derivatives.448 Using argon ion laser excitation, quantum yieldsfor photodegradation and singlet molecular oxygen production have been meas-ured for solutions of C60, C70, C76 and C84 at room temperature.449 The photo-physical and photochemical properties of C120O, a dimer of C60 linked through asaturated furan ring, have been reported.450 Singlet oxygen generation viafullerene-based sensitisers has been described in detail.451—453

The temperature-dependent fluorescence properties of phenylated and chlor-inated C70 have been described454 and the photophysical properties of multi-phenylated derivatives of C70 have been recorded.455 Related studies, includinglaser flash photolysis, fluorescence and phosphorescence spectroscopy and kin-etic measurements, have concentrated on a mono-benzyne—C70 adduct.456 Someunusual luminescence properties have been reported457 for hexapyrrolidine de-rivatives of C60 and the photophysical properties of several methano derivativesof C60 have been recorded.458 Other work has addressed the photophysics of cis-and trans-stilbenomethano fullerenes,459 carborane-functionalised fullerenes,460

and a C70 derivative equipped with a crown ether linkage.461 Several reports havebeen directed towards exploring the photophysics of fullerenes covalently linkedto unsaturated compounds.462,463 Because of on-going interest in using fullerenesin conjunction with conducting polymers, or light-emitting diodes, much re-search has focussed on attaching fullerenes to oligo-thiophenes,464—469 oligo-phenylenevinylenes470,471 and tetra-thiafulvalenes.472

The role of C60 adducts in light-induced electron-transfer reactions has beenreviewed473 and numerous energy- and electron-transfer processes driven bytriplet C60 have been described in solution474,475 and organised media.476 Light-induced reduction of fullerene derivatives by amines has been considered477—479

and other electron-transfer processes have been reported between C60 and vari-ous redox-active reagents.480—485

Intramolecular light-induced energy and/or electron transfer has been de-scribed for a wide variety of fullerene-based dyads.486—494 In most cases the courseof reaction has been followed by laser flash photolysis techniques and rates offorward and reverse transfer steps have been evaluated. The most interesting,and most intensely studied, molecular dyads are those comprising fullerene andporphyrin terminals and several such systems have been reported during thecurrent review period.495—505 The low reorganisation energy associated with one-electron reduction of C60 means that fast rates of charge separation can berealised at modest thermodynamic driving forces while charge recombinationfalls within the Marcus inverted region, and is therefore relatively slow. Attach-ing additional redox-active subunits has allowed extension to form moleculartriads displaying long-lived charge-separated states.506,507 Again, tetrapyrrolicpigments are the most popular chromophores for use in such systems and thefullerene residue serves as the primary electron acceptor.Interest is growing in the use of fullerene derivatives to form self-assembed

supramolecular ensembles. Several such assemblies have been formed recentlyand their photophysical properties recorded.508 Likewise, functionalisedfullerenes have been incorporated into films.509,510 These latter systems have

Photochemistry28

genuine opportunities to be built into photochemical devices where some kind ofcooperative orientation is essential.

5 Applications of Photophysics

The study of photophysics, especially time-resolved fluorescence spectroscopy,provides unique opportunities to explore complex molecular systems, to selec-tively transfer information at the molecular level, to label biological materials,and to design new analytical protocols. Perhaps themost popular applications ofphotophysics concerns the selective detection of analytes and measurement ofthe fluidity, polarity, electric surface, effective dielectric constant or compositionof microheterogeneous media. Here, we mention only a few such applications.Thus, the analytical applications offered by using cyclodextrins to induce room-temperature phosphorescence have been reviewed.511 Fluorescence anisotropycan be used as a measure of chiral recognition512 and novel fluorescence aniso-tropy tools have been developed to monitor liquid crystals513 and to estimatemicroviscosity.514 Luminescence techniques have also been developed to followthe entire range of surfactant aggregation in aqueous solution.515

Fluorescence microscopy has been applied to the problem of monitoring theconcentration of oxygen dissolved in polymer matrices.516 Fluorescence quench-ing techniques are also available to follow radical-induced cross-linking ofmonomers.517 A protocol based on the re-absorption of laser-induced fluor-escence has been adapted to measure film thickness.518 Finally, a method hasbeen proposed519 to measure the size distribution of colloidal particles by usingthe well-known photofading and subsequent recovery stategy.

6 Advances in Instrument Design and Utilisation

Photophysics research depends critically on the availability of appropriate in-strumentation and adequate computational protocols. To a large degree, pro-gress in the field is limited by new developments in the type and scope ofinstrumentation, but the importance of a steady supply of pure and tailor-mademolecules must never be underestimated. Improvements in the precision withwhich conventional measurements can be made and the opportunities to under-take new types of photophysical investigation continue to be reported; not all areexpensive or subject to the simultaneous use of several sophisticated lasers.

6.1 Data Analysis. — Improved methods have been proposed for the analysisof fluorescence anisotropy,520 fluorescence decay kinetics,521 solvation dyna-mics522 and fluorescence quenching in the presence of high concentrations ofquencher.523 New treatments have also been given for the analysis of kinetic data,especially non-exponential decay processes.524—526 A direct observation has beenmade of non-RRKM behaviour in femtosecond laser spectroscopic studies527

and improved modelling of ultrafast photophysical processes has been re-


ported.528 An experimental protocol has been established that allows estimationof fluorescence quantum yields for heterogeneous samples529 while ways todetermine rate constants from time-gated fluorescence correlation spectroscopyhave been highlighted.530 Related studies have proposed improved routines formonitoring energy transfer by luminescence techniques531,532 and correctingbackground signals in Raman spectra533 and in 2D fluorescence measure-ments.534

A kinetic treatment has been given to account for triplet—triplet annihilation indisorderedmedia.535 The importance of a detailed analysis of fluorescence excita-tion spectra has been stressed536 and an absolute calibration of laser-inducedfluorescence can be obtained from optical depth analysis.537 Extraction of par-ameters from time-resolved fluorescence specroscopy has been considered538 andnew applications have been found for fluorescence polarisation techniques.539

Two-photon fluorescence excitation spectra have been recorded540,541 and arobust local regression procedure has been introduced for baseline subtrac-tion.542 Analytical models have been presented for fluorescence correlation spec-troscopy,543 scanning-fit analysis of fs spectroscopic data,544 to account for noiseon fluorescence correlation data545 and for detailed analysis of single-photoncounting results.546

6.2 Instrumentation. — Several aspects of the instrumentation used in photo-physics research have been reviewed during the relevant period. Thus, the typesof instrumentation used for direct observation of transient species have beendescribed,547 the technique of time-resolved infrared spectroscopy has been re-viewed,548 the applications of ultrafast transient grating spectroscopy have beenhighlighted549 and the multifarious applications of time-resolved EPR spectro-scopy to supramolecular chemistry have been described in detail.550 Severalreports have concentrated on the development and use of the optical Kerr-gateeffect for femtosecond time-resolved luminescence spectroscopy.551—554 Other ap-proaches have been used to record femtosecond luminescence555,556 and infraredspectra557 while a description has been given of up-conversion spectroscopyusing square-wave excitation pulses.558

A near-field fluorescencemicroscope with a spatial resolution of about 100 nmhas been described559 and a set-up having somewhat improved spatial resolution,achieved using the technique of near-field shadowing, has been reported.560 Thedesign of a rapid-scanning, spectrally-resolved fluorescencemicroscope has beenprovided561 while other studies have led to the development of a detector fortime-resolved emission working at wavelengths greater than 1500 nm.562,563 Theadvantages of two-colour excitation fluorescence microscopy have been high-lighted.564 It is clear that fluorescence correlation spectroscopy is gaining popu-larity and recent advances in this area have been reported.565,566

The application of strong electrical567,568 or magnetic569—571 fields to perturbphotophysical properties continues to provide valuable information about theprocesses under investigation. The technique of rotational coherence spectro-scopy has been described572 and a critical comparison has been made of theoptical geometries needed for combined flash photolysis and total internal

Photochemistry30

reflectance fluorescence microscopy.573 Techniques for use in nanometre-resol-ved 2D photochemistry have been discussed574 and a review has reported ontunable picosecond optical parametric amplifiers for time-resolved Raman spec-troscopy.575 The application of photoacoustic calorimetry for following photo-isomerisation has been highlighted576 while the construction of a 40 ns time-resolved, step-scan FTIR instrument has been reported.577

7 References

1. P. Suppan, Photomed. Gynecol. Reprod., 2000, 53.2. J. Baggott,New Chem., 2000, 45.3. R. Cees, Proc. — Electrochem. Soc., 2000, 99 (Physics and Chemistry of Luminescent

Materials), 69.4. M. Hasegawa and K. Horie, Prog. Polym. Sci ., 2000, 26, 259.5. P. Plaza, P. Changenet-Barret, D. Lange and M. Martin, Actual. Chim., 2001, 37.6. D. M. Villeneuve, S. Aseyev, M. Y. Ivanov, P. Yestrich and P. B. Corkun, Proc. Int.

Conf. Lasers, 2000, 22, 260.7. J. Gordon, L. Zhu and T. Seideman, J. Phys. Chem. A, 2001, 105, 4387.8. K. Bhattacharyya, Proc. Indian Natl. Acad. Sci., Part A, 2000, 66, 199.9. T. Markvart, Prog. Quantum Electron., 2000, 24, 107.10. W. M. Nau, EPA Newsletter, 2000, 70, 6.11. A. Gaplovsky, M. Gaplovsky, S. Toma and J.-L. Luche, J. Org. Chem., 2000, 65,

8444.12. R. S. H. Liu, Acc. Chem. Res., 2001, 34, 555.13. T. Arai,Mol. Supramol. Photochem., 1999, 3, 131.14. V. J. Rao,Mol. Supramol. Photochem., 1999, 3, 169.15. A. Shukla, H. Ghosh and S. Mazumbar, Synth.Met., 2001, 116, 87.16. C. J. Wang, W. Deng, L. G. Shemesh, M. D. Lilien, D. R. Katz and T. S. Dibble, J.

Phys. Chem. A, 2000, 104, 10368.17. L. Dun, T. Cui, Z. Wang, W. Chen, B. Yang and F. Sang, J. Phys. Chem. A, 2001,

105, 281.18. R. Richert, J. Chem. Phys., 2000, 113, 8404.19. S. Takagi and H. Inoue,Mol. Supramol. Photochem., 2000, 4, 215.20. K. Tokumaru, J. Porphyrins Phthalocyanines, 2001, 5, 77.21. A. J. Vlcek Jr., Chemtracts, 2000, 13, 776.22. T. Shibata, H. Chosrowjan, N. Mataga, N. Yoshida and A. Osuka, Springer Ser.

Chem. Phys., 2001, 66, 691.23. T. Kountotsis and J. V. Masi, Proc. — Electr. Insul. Conf. Electr. Manuf. Coil

Winding Conf., 1999, 80 [Chem Abstr., 134, 258421b].24. M. T. Bernius, M. Inbasekaran, J. O’Brien and W. Wu, Adv. Mater., 2000, 12,

1737.25. Z. Peng, Polym.News, 2000, 25, 185.26. J. Paczkowski, Z. Kucybala, F. Scigalski and A. Wrzysczynski, Trends Photochem.

Photobiol., 1999, 5, 79.27. R. Schmehl, Spectrum, 2000, 13, 17.28. A. J. Lees, Coord. Chem. Rev., 2001, 211, 265.29. V. Balzani and A. Juris, Coord. Chem. Rev., 2001, 211, 97.30. A. Vogler and H. Kunkaly, Coord. Chem. Rev., 2001, 211, 208.


31. L. Sun, L. Hammarstrom, B. Akermark and S. Styring, Chem. Soc. Rev., 2001, 30,36.

32. M. D. Ward and F. Barigelletti, Coord. Chem. Rev., 2001, 216, 127.33. M. Furue, M. Ishibashi, A. Satoh, T. Oguni, K. Maruyama, K. Sumi and M.

Kamachi, Coord. Chem. Rev., 2000, 208, 103.34. E. R. Barthel, I. B. Martini and B. J. Schwartz, J. Chem. Phys., 2000, 112, 9433.35. K. Hannerwald, S. Glutsch and F. Bechstedt, Phys. Rev. B, Condens.Mater. Phys.,

2000, 62, 4519.36. K. Matsuda, M. Matsuo and M. Irie, Chem. Lett., 2001, 436.37. K. Matsuda andM. Irie, J. Am. Chem. Soc., 2000, 122, 7196.38. K. Matsuda andM. Irie, J. Am. Chem. Soc., 2000, 122, 8309.39. F. Dietz and N. Tyutyulkov, Chem. Phys., 2001, 259, 165.40. Y. Ogawa, S. Koshihara, C. Urano and H. Takagi, Mol. Cryst. Liq. Cryst., Sci.

Technol. Sect. A, 2000, 345, 175.41. T. Kawamoto, Y. Asai and S. Abe, Phys. Rev. Lett., 2001, 86, 348.42. V. Ramamurthy, J. Photochem. Photobiol. C, 2000, 1, 145.43. T. Scichi and K. Takagi, J. Photochem. Photobiol. C, 2000, 1, 113.44. K. B. Yoon,Mol. Supramol. Photochem., 2000, 5, 143.45. K. Takagi and T. Scichi,Mol. Supramol. Photochem., 2000, 5, 31.46. H. Yamashita and M. Anpo, Photofunct. Zeolites, 2000, 99.47. K. Venkatesan,Mol. Solid State, 1999, 3, 89.48. R. M. Bailey, Radiat.Meas., 2000, 33, 17.49. F. Pina, M. A. Bernardo and E. Garcia-Espana, Eur. J. Inorg. Chem., 2000, 2143.50. A. P. da Silva, D. B. Fox, A. J.M.Huxley andT. S.Moody,Coord.Chem.Rev., 2000,

205, 41.51. B. Valeur and I. Leray, Coord. Chem. Rev., 2000, 205, 3.52. L. Prodi, F. Bolletta,M.Montalti andN. Zaccheroni,Coord.Chem.Rev., 2000, 205,

59.53. A. M. Jesceanu, Roum. Chem. Q. Rev., 2000, 7, 213.54. H. Kojima and T. Nagano, Adv.Mater., 2000, 12, 763.55. L. Fabbrizzi, M. Liezhelli, G. Rabaioli and A. Taghetti, Coord. Chem. Rev., 2000,

205, 85.56. M. Granda-Valdes, R. Basia, G. Pina-Luis and M. E. Diaz-Garcia, Quim. Anal.,

2000, 19, 38.57. A. M. Garcia-Campana and W. R. G. Baeyena, Analusis, 2000, 28, 868.58. C. A. Koval, Chem. Innovation, 2001, 31, 23.59. M. A. Margolis, Phys. — Usp., 2000, 43, 259.60. K. S. Suslick, AIP Conf. Proc., 2000, 524, 96.61. Y. T. Didenko, W. B. McNamara and K. S. Suslick,Nature, 2000, 407, 877.62. K. Yasui, AIP Conf. Proc., 2000, 524, 437.63. K. S. Suslick,W. R.McNamara andY. T. Didenko,AIPConf.Proc., 2000, 524, 463.64. T. J. Matula and C. A. Frensley, AIP Conf. Proc., 2000, 524, 425.65. B. Metten and W. Lauterborn, AIP Conf. Proc., 2000, 524, 429.66. N. Koumura, E. M. Geertsema, A. Meetsma and B. I. Feringa, J. Am. Chem. Soc.,

2000, 122, 12005.67. J.-P. Sauvage, Science, 2001, 281, 2108.68. H. F. Ji, R. Dabestani and G. M. Brown, J. Am. Chem. Soc., 2000, 122, 9306.69. J. R. Kumita, O. S. Smart and G. A. Woolley, Proc.Natl. Acad. Sci.USA, 2000, 97,

3803.70. S. Uchiyama, T. Santa and K. Imai, Analyst, 2000, 125, 1839.

Photochemistry32

71. J.-P. Collin, A.-C. Laemmel and J.-P. Sauvage,New J. Chem., 2001, 25, 22.72. B. Strehmel, K. B. Henbest, A. M. Sarker, J. H. Malpert, D. Y. Chen, M. A. J.

Rodgers and D. C. Neckers, J.Nanosci.Nanotechnol., 2001, 1, 107.73. A. M. Brouwer, C. Frouchot, F. G. Gatti, D. A. Leigh, L. Mottier, F. Paolucci, S.

Roffia and G. W. H. Wurpel, Science, 2001, 291, 2124.74. L. Gobbi, P. Seller, F. Diederich and V. Gramlich,Helv.Chim.Acta, 2000, 83, 1711.75. R. Ballardini, V. Balzani, A. Di Fabio, G. T. Gandolfi, J. Becher, J. Lau, N.

Brondsted, F. Stoddart,New J. Chem., 2001, 25, 293.76. I. Willner, V. Pardo-Yissar, E. Katz and K. T. Ranjit, J. Electroanal. Chem., 2001,

497, 172.77. F. M. Raymo and S. Giordani, Org. Lett., 2001, 3, 3475.78. N. Hosaka and T. Saiki, Jasco Rep., 2000, 42, 59.79. H. Tang, L. Zhu, Y. Harima, K. Yumashita, K. Koo Lee, A. Noka andM. Ishika, J.

Chem. Soc., Perkin Trans. 2, 2000, 1976.80. G. C. Azzellini, Anal. Acad. Bras. Cienc., 2000, 72, 33.81. O. Vrnevski, G. Menkir, T. Goodson and P. L. Burn, Appl. Phys. Lett., 2000, 77,

1120.82. H. Tachibana, H. Kishida and Y. Tokura, Appl. Phys. Lett., 2000, 77, 2443.83. G. De Belder, G. Schweitzer, S. Jordens, M. Lor, S. Mitra, J. Hofkens, S. De Feyter,

M. Van der Auweraer, A. Herrmann, T. Weil, K. Mullen and F. C. De Schryver,ChemPhysChem., 2001, 2, 49.

84. L. A. Baker and R. M. Crooks,Macromolecules, 2000, 33, 9034.85. D. Cao and H. Meier, Angew Chem., Int. Ed., 2001, 40, 186.86. S. Masuo, H. Yoshikawa, T. Asahi, H. Masuhara, T. Sato, D. L. Jiang and T. Aida,

J. Phys. Chem. B, 2001, 105, 2885.87. V. Balzani, P. Ceroni, S. Gestermann,M. Gorka, C. Kauffmann,M.Maestri and F.

Vogtle, ChemPhysChem., 2000, 1, 224.88. L. C. Gong, Q. S. Hu and L. Pu, J. Org. Chem., 2001, 66, 2358.89. C.M. Cardona, J. Alvarez, A. E. Kaifer, T. D.McCarley, S. Pandey, G. A. Baker, N.

J. Bonzagni and F. V. Bright, J. Am. Chem. Soc., 2000, 122, 6139.90. S. Quici, A. Manfredi, M. Maestri, I. Manet, P. Passanita and V. Balzani, Eur. J.

Org. Chem., 2000, 2041.91. V. Balzani, P. Ceroni, S. Gestermann, C. Kauffmann, M. Gorka and F. Vogtle,

Chem. Commun., 2000, 853.92. F. Vogtle, S. Gestermann, C. Kauffmann, P. Ceroni, V. Vicinelli and V. Balzani, J.

Am. Chem. Soc., 2000, 122, 10998.93. K. Bhattacharyya,Mol. Supramol. Photochem., 1999, 3, 283.94. Y. Kobuke and N. Nagata,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 342,

51.95. T. Pullerits, J. Chin. Chem. Soc. (Taipei), 2000, 47, 773.96. R. A. Haycock, A. Yartsev, U. Michelsen, V. Sundstrom and C. A. Hunter, Angew.

Chem., Int. Ed., 2000, 39, 3616.97. A. Ambroise, J. Li, L. Yu and J. S. Lindsey, Org. Lett., 2000, 2, 2563.98. Y. Kuroda, K. Sugou and K. Sasaki, J. Am. Chem. Soc., 2000, 122, 7833.99. A. V. Udal’tsov, L. A. Kazarin andA. A. Sweshnikov, J.Mol. Struct., 2001, 562, 227.100. F. C. Spano, Synth.Met., 2000, 116, 339.101. H. Langhala, R. Ismael and O. Yuruk, Tetrahedron, 2000, 56, 5435.102. N. W. Alcock, P. R. Barker, J. M. Haider, M. J. Hannon, C. L. Painting, Z.

Pikramenou, E. A. Plummer, K. Rissanen and P. Saarenketo, J. Chem. Soc., DaltonTrans., 2000, 1447.


103. L. A. J. Chrisstoffels, A. Adronov and J.M. J. Freschet,Angew.Chem., Int.Ed., 2000,39, 2163.

104. Y. H. Kim, D.H. Jeong, S. C. Jeong, D. Kim,N. Aratazi and A.Osuka, Springer Ser.Chem. Phys., 2001, 66, 601.

105. Y. H. Kim, H. S. Cho, D. Kim, S. K. Kim, N. Yoshida and A. Osuka, Synth.Met.,2001, 117, 183.

106. A. Kashiwada, Y. Takeuchi, H. Watanabe, T. Mizuno, H. Yasue, K. Kitagawa, K.Iida, Z. Y. Wang, T. Nozawa, H. Kawai, T. Nagamura, Y. Kurono and M. Nango,Tetrahedron Lett., 2000, 41, 2116.

107. M. Ravikanth, Indian J. Chem., Sect. A: Inorg. Bioinorg, Phys. Theor. Anal. Chem.,2001, 40, 86.

108. R. Paolesse, L. Jaquinod, F. Della Sala, D. J. Nurco, L. Prodi, M. Montalti, C. DiNatale, A. D’Amico, A. Di Carlo, P. Lugli and K. M. Smith, J. Am. Chem. Soc.,2000, 122, 11295.

109. M. Sakamoto, A. Ueno and H. Mihara, Chem. Commun., 2000, 1741.110. M. Ravikanth, Tetrahedron Lett., 2000, 41, 3709.111. H. J.Murfee, T. P. S. Thomes, J. Greaves and B. Hong, Inorg.Chem., 2000, 39, 5209.112. M. Zhou and J. Roovers,Macromolecules, 2001, 34, 244.113. O. Varnavski, R. G. Ispasoin, L. Balogh, D. Tomalia and T. Goodson, J. Chem.

Phys., 2001, 114, 1962.114. K. D. Benkstein, J. T. Hupp and C. L. Stern,Angew.Chem., Int. Ed., 2000, 39, 2891.115. R. Jakubiak, M. Yan, W. C. Wan, B. R. Hsieh and L. J. Rothberg, Isr. J. Chem.,

2000, 40, 153.116. D. Hertel, S. Setayesh, H. G. Norhoffer, U. Scherf, K. Mullen and H. Bassler, Adv.

Mater., 2001, 13, 65.117. H. Detert and E. Sugiono, J. Phys. Org. Chem., 2000, 13, 587.118. N. G. Pschirer, T. Miteva, U. Evans, R. S. Roberts, A. R. Marshall, D. Neher, M. L.

Myrick and U. H. F. Bunz, Chem.Mater., 2001, 13, 2691.119. C. Botta, S. Dastri, W. Porzio, B. Bongiovanni, A. Mura, M. A. Loi, F. Garnier and

R. Tubino,Mater. Res. Soc. Symp. Proc., 2000, BB598, 86.120. L. Antolini, E. Tedesco, G. Barbarella, L. Favaretto, G. Sotgiu, M. Zambianchi, D.

Casarini, G. Gigli and R. Cingolani, J. Am. Chem. Soc., 2000, 122, 9006.121. L. Guyard, D. A. Nguyen and A. P. Michel, Adv.Mater., 2001, 13, 133.122. S. Y. Song and H. K. Shim, Synth.Met., 2000, 11, 437.123. G. Barbarella, L. Favoretto, G. Sotgiu, M. Zambianchi, A. Bongini, C. Arbizzani,

M. Mastragostino, M. Anni, G. Gigli and R. Cingolani, J. Am. Chem. Soc., 2000,122, 11971.

124. J. Sexias deMelo, E. Elisei, C. Gartner, G. Aloisi and R. S. Becker, J.Phys.Chem.A,2000, 104, 6907.

125. A. Donat-Bouillud, I. Levesque, Y. Tao, M. D’Iorio, S. Beaupre, P. Blondin, M.Ranger, J. Bouchard and M. Leclerc, Chem.Mater., 2000, 12, 1931.

126. B. Behnisch, P. Martinez-Ruiz, K. H. Schweikart and M. Hanack, Eur. J. Org.Chem., 2000, 2541.

127. G. A. Baker, F. V. Bright, M. R. Detty, S. Pandey, C. E. Stilts and H. Yao, J.Porphyrins Phthalocyanines, 2000, 4, 669.

128. K. M. Solntsev, D. Huppert and N. Agmon, Phys. Rev. Lett., 2001, 86, 3427.129. V. L. Arkhipov, E. V. Emelianova, A. Kadashchuk and H. Bassler, Chem. Phys.,

2001, 266, 97.130. O. J. Rolinski, D. J. S. Birch, L. J.McCartney and J. C. Pickup, Chem. Phys. Lett.,

2000, 324, 96.

Photochemistry34

131. G. N. Patwari and S. Wategaonkar, Chem. Phys. Lett., 2000, 323, 460.132. I. V. Rubtsov and K. Yoshihara, J. Chin. Chem. Soc. (Taipei), 2000, 47, 673.133. M. Ben-Nun and T. J. Martinez, Chem. Phys., 2000, 259, 237.134. S. Zilberg and Y. Haas, Chem. Phys., 2000, 259, 249.135. A. L. Sobolewski and W. Domcke, Chem. Phys., 2000, 259, 181.136. C. H. Chang, M. Hayashi, R. Chang, K. K. Liang, T. S. Yang and S. H. Lin, J.Chin.

Chem. Soc. (Taipei), 2000, 47, 785.137. C. H. Kwak and S. J. Lee, Opt. Commun., 2000, 183, 547.138. D. Beljonne, Z. Shuai, G. Pourtois and J. L. Bredas, J. Phys. Chem. A, 2001, 105,

3899.139. O. Nazari and M. J. Chaichi, Int. J. Chem., 2001, 11, 35.140. C. Warmuth, A. Tortschanoff, F. Milota, M. Leibscher, M. Shapiro, Y. Prior, I. S.

Averbukh, W. Schleich, W. Jakabetz and H. F. Kauffmann, J. Chem. Phys., 2001,114, 9901.

141. A. Toniolo and J. Tomasi, J. Phys. Chem. A, 2001, 105, 4749.142. P. S. Kushwaba and P. C. Mishra, J. Photochem. Photobiol. A, 2000, 137, 79.143. A. Douhal, M. Moreno and J. M. Lluch, Chem. Phys. Lett., 2000, 324, 75.144. J. Park, Dyes Pigm., 2000, 46, 155.145. J. Saltiel, O. Dmitrenko, W. Reischl and R. D. Bach, J. Phys. Chem. A, 2001, 105,

3934.146. A. Yamada, S. Yamamoto, T. Yamato and T. Kakitani, THEOCHEM, 2001, 536,

195.147. K. Kasatani, ITE Lett. Batteries,New Technol.Med., 2001, 2, 220.148. Y. Yoshioka, M. Usami and K. Yamaguchi, Mol. Cryst. Liq. Cryst. ScI. Technol.,

Sect. A, 2000, 345, 81.149. R. Longo, Chem. Phys. Lett., 2000, 328, 67.150. L. Belau and Y. Haas, Chem. Phys. Lett., 2001, 333, 297.151. W. H. Fang, Chem. Phys. Lett., 2000, 325, 683.152. M. Belletete, S. Beaupre, J. Bouchard, P. Blondin, M. Leclerc and G. Durocher, J.

Phys. Chem. B, 2000, 104, 9118.153. D. G. Evans, J. Chem. Phys., 2000, 113, 3282.154. S. Wilsey, J. Org. Chem., 2000, 65, 7878.155. S. C. Yang, W. Graupner, S. Cuha, P. Puschnig, C. Martin, H. R. Chandrasekhar,

M. Chandrasekhar, G. Leising, C. Ambroasch-Draxl and U. Scherf, Phys. Rev.Lett., 2000, 85, 2388.

156. M. Garavelli, C. S. Page, P. Celani, M. Olivucci, W. E. Schmid, S. A. Trushin andW. Fuss, J. Phys. Chem.A, 2001, 105, 4458.

157. A. B. J. Parusel, Phys. Chem. Chem. Phys., 2000, 2, 5545.158. I.W. Hwang,H. H. Choi, B. K. Cho,M. Lee and Y. R. Kim,Chem.Phys.Lett., 2000,

325, 219.159. P. Gilch, C. Musewald and M. E. Michel-Beyerle, Chem. Phys. Lett., 2000, 325, 39.160. J. Lu, F. W. Shao, K. Fan and S. D. Du, J. Chem. Phys., 2001, 114, 3879.161. Y. Shigemitsu, H. J. A. A. Jensen, H. Koch and J. Oddershede, Mol. Cryst. Liq.

Cryst. Sci. Technol., Sect. A, 2000, 345, 89.162. M.Hayashi, T. S. Yang, K. K. Liang, C. H. Chang and S. H. Lin, J.Chin.Chem. Soc.

(Taipei), 2000, 47, 741.163. S. Iwai, S. Murata and M. Tachiya, J. Chem. Phys., 2001, 114, 1312.164. K. L. Ivanov, L. K. Lukzen, A. B. Doksorev and A. I. Burshtein, J. Chem. Phys.,

2001, 114, 5682.165. L. Kurtz, A. Hoffmann and R. De Vivie-Riedle, J. Chem. Phys., 2001, 114, 6151.


166. I. S. Jeong, K. Scott, K. J. Donovan and E. G. Wilson, J. Chem. Phys., 2000, 113,7613.

167. V. Molina, M. Marchan, B. O. Roos and P. A. Malmquist, Phys. Chem. Chem.Phys., 2000, 2, 2211.

168. N. Boens, J. Szuhiakowski, E. Novikov andM. Ameloot, J. Chem. Phys., 2000, 112,8260.

169. A. Toniolo and M. Persico, J. Comput. Chem., 2001, 22, 968.170. V. Gualiar, V. S. Batista and W. H. Miller, J. Chem. Phys., 2000, 113, 9510.171. J. I. Zink, Coord. Chem. Rev., 2001, 211, 69.172. N. Hosaka and T. Saiki, J.Microsc., 2001, 202, 362.173. J. Enderlein, Biophys. J., 2000, 78, 2151.174. R. G.Neuhausser, K. T. Shimizu,W. K.Woo, S. A. Empedodes andM.O. Bawendi,

Phys. Rev. Lett., 2000, 85, 3301.175. J. Enderlein and M. Sauer, J. Phys. Chem. A, 2001, 105, 48.176. M. Casoli and M. Schonhoff, Biol. Chem., 2001, 382, 363.177. A. M. Bereshkovski, M. Boguna and G. R.Weiss,Chem. Phys. Lett., 2001, 336, 321.178. M. Boguna, A.M. Berezhkovski andG. R.Weiss, J.Phys.Chem.A, 2001, 105, 4898.179. A. Molski, J. Chem. Phys., 2001, 114, 1142.180. J. Azoulay, A. Debarre, A. Richard and P. Tchenio, Europhys. Lett., 2000, 51, 374.181. E. A. Dunley and T. Plakhotnik, J. Chem. Phys., 2001, 114, 9983.182. R. Mealiet-Renault, H. Yoshikawa, Y. Tamaki, T. Asahi, R. B. Pansu and H.

Masuhara, Polym. Adv. Technol., 2000, 11, 772.183. J. D. White, J. H. Hsu, S. C. Yang, W. S. Fann, G. Y. Pern and S. A. Chen, J. Chem.

Phys., 2001, 114, 3848.184. M. Ashokkuman, L. A. Crum, C. A. Frensley, F. Grieser, T. J. Mutula, W. B.

McNamara and K. B. Suslick, J. Phys. Chem. A, 2000, 104, 8462.185. H. Walther, J.Korean Phys. Soc., 2000, 37, 640.186. N. Nijegorodov and R. Mabbs, Spectrochim. Acta, Part A, 2000, 56, 2157.187. M. Muccini, M. Murgia, C. Taliani, A. D. Esposti and R. Zamboni, J. Opt. A: Pure

Appl. Opt., 2000, 2, 577.188. K. Henderson, K. P. Kretsch, A. Drury, S. Maier, A. P. Davey, W. Blau and H. J.

Byrne, Synth.Met., 2000, 111, 559.189. J. A. Pincock, S. Rifni and R. Stefanova, Can. J. Chem., 2001, 79, 89.190. N. Ohta, J. Photochem. Photobiol. C, 2000, 1, 195.191. S. Altunate and R. W. Field, J. Chem. Phys., 2000, 113, 6640.192. K. Fujii, T. Ishikawa, Y. Koyama, M. Taguchi, Y. Isobe, H. Nagae and Y.

Watanabe, J. Phys. Chem. A, 2001, 105, 5348.193. R. Yang and S. G. Schulman, Luminescence, 2001, 19, 129.194. C.-P. Jelien and H. Bettermann, J.Mol. Struct., 2001, 563, 119.195. G. Buntinx, L. Bussotti, V. De Waele, C. Diderjean and O. Poizat, Laser Chem.,

1999, 19, 353.196. T. L. Gustafson and J. D. Leonard, Laser Chem., 1999, 19, 381.197. X. H. Shen and J. R. Knutson, J. Phys. Chem. B, 2001, 105, 6260.198. T. L. Gustafson, E. M. Kylio, T. L. Frost, R. G. Sun, H. Lim, D. K. Wang, A. J.

Epstein, G. Lefumeux, G. Burdzinski, G. Buntinx and O. Poizat, Synth.Met., 2000,116, 31.

199. F. L. Arbeloa, T. L. Arbeloa and I. L. Arbeloa, Recent Res. Dev. Photochem.Photobiol., 1999, 3, 35.

200. H. M. Abdel Moneim, L. Z. Ismail, A. F. Gamal and Z. A. Zohady, Polym. Test,2000, 20, 135.

Photochemistry36

201. W. Holzer, H. Gratz, T. Schmidt, A. Penzkofer, A. Costela, I. Garcia-Moreno, R.Sastre and F. J. Duarte, Chem. Phys., 2000, 256, 125.

202. N. A. Weir and M. Delaney-Luu, J. Photochem. Photobiol. A, 2000, 136, 189.203. L. Biczok, T. Berces, T. Yatsuhari, H. Tachibana and H. Inoue, Phys. Chem. Chem.

Phys., 2001, 3, 980.204. T. Mutai, J. D. Cheon, S. Arita and K. Araki, J. Chem. Soc., Perkin Trans. 2, 2001,

1045.205. R. Pramanik, P. Kumar Das, D. Banerjee and S. Bagchi, Chem. Phys. Lett., 2001,

341, 507.206. A. Szymanska, W. Wiczik and L. Lankiewicz,Chem.Heterocycl. Compd., 2000, 36,

801.207. F. Tanaka, T. Furuta, M. Okamoto and S. Hirayama, Chem. Lett., 2000, 768.208. E. J. Shin, J. Photosci., 1999, 6, 61.209. G. Greiner, J. Photochem. Photobiol. A, 2000, 137, 1.210. A. K. Singh, A. C. Bhasikuttan, D. K. Palit and J. P. Mittal, J. Phys. Chem.A, 2000,

104, 7002.211. V. V. Jarikov and D. C. Neckers, J. Org. Chem., 2001, 66, 659.212. A. K. Singh, D. K. Pallit and J. P. Mittal, Res. Chem. Intermed., 2001, 27, 125.213. I. Petkova, P. Nikolov and V. Dryanska, J. Photochem. Photobiol.A, 2000, 123, 21.214. G. G. Gurzadyan, T. H. Tran-Thi and T. Gustavsson, Proc. SPIE — Int. Opt. Eng.,

2000, 4060, 96.215. T. Itoh, M. Yamaji and H. Shizuka, Chem. Lett., 2000, 616.216. P. V. R. Neuwahl and P. Poggi, Laser Chem., 1999, 19, 375.217. M. Vasilescu, M. Almgren and D. Angelesco, J. Fluoresc., 2000, 10, 339.218. H. Bouas-Laurent, J.-P. Deavergne, A. Castellan and R. Lapouyade, Chem. Soc.

Rev., 2001, 30, 248.219. I. Desperasinsko, B. Kozenkiewicz, I. Biktchantaev and I. J. Serpio, J. Phys. Chem.

A, 2001, 105, 810.220. S. M. Khopde, K. I. Priyadarsini, D. K. Pelit and T. Mukherjee, Photochem.

Photobiol., 2000, 72, 625.221. K. Iwata and H. Hamaguchi, Laser Chem., 1999, 19, 367.222. R. Baumann, C. Ferrente, F. W. Deng and C. Brauchle, J. Chem. Phys., 2001, 114,

5781.223. E. Marri, G. Galiazzo, U. Mazzacato and A. Spalletti, Chem. Phys., 2000, 269,

383.224. A. S. R. Koti and N. Periasamy, J. Fluoresc., 2000, 10, 177.225. M. Mitsui, Y. Ohshima and O. Kujimoto, J. Phys. Chem. A, 2000, 104, 8660.226. J. Peon, X. Tan, J. D. Hoerner, C. G. Xia, Y. F. Luk and B. Kohler, J. Phys. Chem.,

2001, 105, 5768.227. A. K. Singh and S. Kanvah,New J. Chem., 2000, 24, 639.228. S. Habuchi, H. B. Kim and N. Kitamura, J. Photochem. Photobiol. A, 2000, 133,

189.229. Y. Katsumoto, H. Ushiki, B. Mendiboure, A. Gracia and J. Lachaise, Colloid.

Polym. Sci., 2000, 278, 905.230. V. B. Nazarev, V. G. Avakyan, T. G. Vershinnikov and M. V. Alfinov, Russ. Chem.

Bull., 2000, 49, 1699.231. M. S. Mehata and H. B. Tripathi, Indian J. Phys. A, 2001, 75, 189.232. A. V. Deshpande and E. B. Namdas, J. Lumin., 2000, 91, 25.233. C. Rogge and S. R. Ahmad, J. Optoelectron. Adv.Mater., 2000, 2, 247.234. J. K. Thomas and E. H. Elison, Adv. Colloid. Interface Sci., 2001, 89, 195.


235. F. Marquez, H. Garcia, E. Palomares, L. Fernandez and A. Corma, J. Am. Chem.Soc., 2000, 122, 6520.

236. G. S. Andreas, C. Debus, A. J. Meixner and G. Calzaferri, J. Phys. Chem. B, 2001,105, 25.

237. S. Ohshima, A. Uthida and S. Fujisawa, Polycycl. Aromat. Compd., 2000, 19,199.

238. Z. L. Cai and J. R. Reimers, J. Phys. Chem. A, 2000, 104, 8889.239. T. Okutsu, N. Kounose, J. Tsuchiya, T. Suzuki, T. Ichimura and G. Kiryu, Bull.

Chem. Soc. Jpn., 2000, 73, 1763.240. E. G. Sakellariou, A. G.Montalban, H. G.Meunier, R. B. Ostler, G. Rumbles, A. G.

M. Barrett and B. M. Hoffman, J. Photochem. Photobiol. A, 2000, 136, 185.241. C. Lu, Z. Han, G. Liu, X. Cui, Y. Chen and S. Yao, Sci. China, Ser. B: Chem., 2001,

44, 39.242. N. N. Kruk and A. A. Korotkii, J. Appl. Spectrosc., 2000, 67, 966.243. H. Y. Yang, Z. Y. Zhang, Z. H. Han and S. D. Yao, Dyes Pigm., 2000, 46, 139.244. A. P. Monkman, H. D. Burrows, I. Hamblett and S. Navaratnam, Chem. Phys.

Lett., 2001, 340, 467.245. M. Gehring and B. Nickel, Z. Phys. Chem. (Munchen), 2001, 215, 343.246. P. P. Levin, Russ. Chem. Bull., 2000, 49, 1831.247. J. S. Wilson, A. Kohler, R. H. Friend, M. K. Al-Suti, M. R. A. Al-Mandhary, M. S.

Khan and P. Raithby, J. Chem. Phys., 2000, 113, 7627.248. D. M. Togashi and S. M. B. da Costa, Phys. Chem. Chem. Phys., 2000, 2, 5437.249. H. Riesen, L. Wallace and E. Krausz, Inorg. Chem., 2000, 39, 5044.250. F. Puntoriero, S. Serroni, A. Licciandello, M. Venturi, A. Juris, V. Ricevoto and S.

Campagna, J. Chem. Soc., Dalton Trans., 2001, 1035.251. M. R. Waterland and D. F. Kelley, J. Phys. Chem. A, 2001, 105, 4019.252. P. Szrebowaty and A. Kapturkicz, Chem. Phys. Lett., 2000, 328, 190.253. L. Giglio, U.Mazzucato, O.Musumarra and A. Spalletti,Phys.Chem.Chem.Phys.,

2000, 2, 4005.254. C. Ruslim and K. Ichimura, Adv.Mater., 2001, 13, 37.255. P. Changenet, H. Zhang andM. J. Van derMeer, J.Chin.Chem. Soc. (Taipei), 2000,

47, 715.256. P. Changenet, H. Zhang, M. J. Van der Meer, M. Glasbeek, P. Piaza and M. M.

Martin, J. Fluoresc., 2000, 10, 155.257. V. Gulbinas and R. Karpicz, Environ. Chem. Phys., 1999, 21, 102.258. K. Hirano, S. Minakita and M. Komatsuo, Chem. Lett., 2001, 8.259. N. Yoshida and A. Osuka, Org. Lett., 2000, 2, 2963.260. J. L. Retsek, S. Gentemann, C. J. Medforth, K. M. Smith, V. S. Chirvony, J. Fajer

and D. Holten, J. Phys. Chem. B, 2000, 104, 6690.261. V. S. Chirvony, A. van Hoek, V. A. Galiewsky, I. V. Sazanovich, T. J. Schaafsma

and D. Holten, J. Phys. Chem. B, 2000, 104, 9909.262. C. Vijila, A. Ramalingam, P. K. Palanisamy and V. Masilamani, Spectrochim.Acta,

Part A, 2001, 57, 491.263. B. Jousseline, P. Blanchard, P. Frere and J. Roncali, Tetrahedron Lett., 2000, 41,

5057.264. M. C. Castex, C. Olivero, G. Pichler, D. Ades, E. Cloutet and A. Siove, Synth.Met.,

2001, 122, 59.265. G. Uray, G. A. Strohmeier and W. M. F. Fabian, Proc. ECSOC-3, 2000, 521.266. M. M. Birau and Z. Y. Wang, Tetrahedron Lett., 2000, 41, 4025.267. P. H. Bong and J. H. Ryoo, J. Photosci., 1999, 6, 171.

Photochemistry38

268. P. Borowicz, J. Herbich, A. Kapturkiewicz, R. Anulewicz-Ostrowska, J. Nowackiand G. Grampp, Phys. Chem. Chem. Phys., 2000, 2, 4275.

269. M. Maus and K. Rurack, New J. Chem., 2000, 24, 677.270. R. Czerwieniec, J. Herbich, A. Kapturkiewicz and J. Nowiacki, Chem. Phys. Lett.,

2000, 325, 589.271. R. Davis, S. Das, M. George, S. Drazhinin and K. A. Zachariasse, J. Phys.Chem.A,

2001, 105, 4790.272. A. Demeter, T. Berces and K. A. Zachariasse, J. Phys. Chem. A, 2001, 105, 4611.273. L. Lin and Y. Jiang, Sci. China, Ser. B: Chem., 2000, 43, 295.274. M. Drobizhev, A. Rebane, C. Sigel, E. H. Elandaloussi and C. W. Spangler, Chem.

Phys. Lett., 2000, 325, 375.275. T. Morozumi, T. Anada and H. Nakamura, J. Phys. Chem. B, 2001, 105, 2923.276. H. Okamoto and M. Tasumi, Laser Chem., 1999, 19, 363.277. H. Chen and Y. B. Jiang, Chem. Phys. Lett., 2000, 325, 605.278. C. Ma, W. M. Kwok, P. Matousek, A. W. Parker, D. Phillips, W. T. Toner and M.

Towrie, J. Raman Spectrosc., 2001, 32, 115.279. W. Rettig and S. Lutze, Chem. Phys. Lett., 2001, 341, 263.280. I. Ruckert, A. Hebecker, A. B. J. Parusel and K. A. Zachariasse, Z. Phys. Chem.

(Munchen), 2000, 214, 1597.281. T. Soujanya, A. Philippon, S. Leroy, M. Vallier and F. Fages, J. Phys. Chem. A,

2000, 104, 9408.282. A. K. Singh and S. Kanvah, J. Chem. Soc., Perkin Trans. 2, 2001, 395.283. A. Mishra, G. B. Behera, M. M. G. Krishna and N. Periasamy, J. Lumin., 2001, 92,

175.284. S. Panja, P. R. Bangal and S. Chakravorti, Chem. Phys. Lett., 2000, 329, 377.285. A. Bajorek and J. Paczkowski, Polimery, 2000, 45, 792.286. T. Nakabayashi, Laser Chem., 1999, 19, 75.287. P.Matousek, C. Gaborel, A.W. Parker, D. Phillips, G. D. Scholes,W. T. Toner and

M. Towrie, Laser Chem., 1999, 19, 97.288. F. D. Lewis and W. Weigel, J. Phys. Chem. A, 2000, 104, 8146.289. F. D. Lewis and R. S. Kalgutkar J. Phys. Chem.A, 2001, 105, 285.290. K. L. Wiemers and J. F. Kauffman, J. Phys. Chem. A, 2001, 105, 823.291. C. A. Stanier, M. H. O’Connell, H. L. Anderson and W. Clegg, Chem. Commun.,

2001, 493.292. M. L. Balevicius, A. Tamulis, J. Tamuliene and J. M. Nunzi,NATO Sci. Ser., 2000,

79, 437.293. S. Li and D. V. McGrath, J. Am. Chem. Soc., 2000, 122, 6795.294. Y. Norikane, H. Itoh and T. Arai, Chem. Lett., 2000, 1094.295. K. Mizumo, H. Sugita, T. Hirai and H. Maeda, Chem. Lett., 2000, 1144.296. K. Mizuno, K. Nire, H. Sugita and H. Maeda, Tetrahedron Lett., 2001, 42, 2689.297. A. K. Singh, J. Indian Chem. Soc., 2001, 78, 53.298. G. Bartocci, G. Galiazzo, U. Mazzucato and A. Spalletti, Phys. Chem.Chem. Phys.,

2001, 3, 379.299. Y. Sonoda, W. M. Kwok, Z. Petrasek, R. Ostler, P. Matousek, M. Towrie, A. W.

Parker and D. Phillips, J. Chem. Soc., Perkin Trans. 2, 2001, 308.300. J. Saltiel, S. Wang, L. P. Watkins and D. H. Ko, J. Phys. Chem.A, 2000, 104, 11443.301. K. Ohta, Y. Naitoh, K. Tominage, N. Hirota and K. Yoshihara, Laser Chem., 1999,

19, 371.302. M. Garavelli, B. R. Smith, M. J. Bearpark, F. Bernardi, M. Olivucci and M. A.

Robb, J. Am. Chem. Soc., 2000, 122, 5568.


303. Y. O. Oh, H. Y. Jung and Y. S. Kang,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A,2000, 349, 91.

304. R. Wang and H. Knoll, J. Inf. Rec., 2000, 25, 361.305. T. Takagi and T. Goshima,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 344,

179.306. S. Kurihara, S. Nomiyama and T. Nonaka, Chem.Mater., 2001, 13, 1992.307. N. Pappayee and A. K. Mishra, Indian J. Chem., Sect. A: Inorg. Bioinorg. Phys.

Theor. Anal. Chem., 2000, 39, 964.308. S. K. Nayaki andM. Swaminathan, J. Chem., Sect. A: Inorg. Bioinorg. Phys. Theor.

Anal. Chem., 2000, 39, 634.309. L. Kaczmarek, P. Borowicz and A. Grabowski, J. Photochem. Photobiol. A, 2001,

138, 159.310. J. Mohanty, H. Pal and A. V. Sapre, Bull. Chem. Soc. Jpn., 2001, 74, 427.311. J. A. Organero, M. Moreno, L. Santos, M. J. Lluch and A. Douhal, J. Phys. Chem.

A, 2000, 104, 8424.312. S. Jockusch,M. S. Landis, B. Friermuth andN. J. Turro,Macromolecules, 2001, 34,

1619.313. A. O. Doroshenko, E. A. Posokhov, A. A. Verezubova and L.M. Ptyagina, J. Phys.

Org. Chem., 2000, 13, 253.314. P. T. Chou, Y. C. Chen, W. S. Yu, Y. H. Chou, C. Y. Wei and Y. M. Chang, J. Phys.

Chem. A, 2001, 105, 1731.315. W. Liu, H. Y. Zhang, D. Z. Chen, Z. Y. Zhang and M. H. Zhang, Dyes Pigm., 2000,

47, 277.316. G. Krishnamoorthy and S. K. Dogra, J. Lumin., 2000, 92, 91.317. Y. Wan, A. Kurchan and A. Kutateladze, J. Org. Chem., 2001, 66, 1894.318. Y. Kim, M. Yoon and D. Kim, J. Photochem. Photobiol. A, 2001, 138, 167.319. S. Dumas, D. Eloy and P. Jardon,New J. Chem., 2000, 24, 711.320. L. Gemosar, B. Cohen and D. Huppert, J. Phys. Chem. A, 2000, 104, 6689.321. A. O. Doroshenko, E. A. Posokhov and V. M. Shershukov, Russ. J. Gen. Chem.,

2000, 70, 573.322. T. H. Tran-Thi, T. Gustavsson, C. Prayer, S. Pommeret and J. T. Hynes, Chem.

Phys. Lett., 2000, 329, 421.323. M. Gil, J. Jaszy, E. Vogel and J. Waluk, Chem. Phys. Lett., 2000, 323, 534.324. J. D. Geerlings, C. A. G. O. Varma andM. C. Van Hamert, J. Phys. Chem. A, 2000,

104, 7409.325. S. Y. Arzhantsev, S. Taksuchi and T. Tahara, Chem. Phys. Lett., 2000, 330, 83.326. A. Douhal, M. Moreno and J. M. Lluch, Chem. Phys. Lett., 2000, 324, 81.327. J. Katalan and M. Kasha, J. Phys. Chem. A, 2000, 104, 10812.328. S. Santra, G. Krishnamoorthy and S. K. Dogra, Chem. Phys. Lett., 2000, 327,

280.329. M. A. El-Kamary, M. E. El-Khouly and O. Ito, J. Photochem. Photobiol. A, 2000,

137, 105.330. L. Biczok, P. Valat and V. Wintgens, Phys. Chem. Chem. Phys., 2001, 3, 1459.331. D. H. Chang, S. Kim, S. Y. Park, H. Yu and D. J. Jang,Macromolecules, 2000, 33,

7223.332. T. Suzuki, Y. Kaneko and T. Arai, Chem. Lett., 2000, 756.333. S. Watanabe, K. Kumagai, M. Hasegawa,M. Kobayashi and T. Hoshi, Bull. Chem.

Soc. Jpn., 2000, 73, 1783.334. J. C. Penedo, M. Mosquera and F. Rodriguez-Prieto, J. Phys. Chem. A, 2000, 104,

7429.

Photochemistry40

335. P. Elisei, J. C. Lima, F. Ortica, G. G. Aloisi, M. Costa, E. Leitao, I. Abreu, A. Dias,V. Bonifacio, J. Medeiros, A. L. Macanita and R. S. Becker, J. Phys. Chem.A, 2000,104, 6095.

336. H. Mishra, H. C. Joshi, H. B. Tripathi, S. Maheshwary, N. Sathyamurthy, M.Panda and J. Chandrasekhar, J. Photochem. Photobiol. A, 2001, 139, 23.

337. M. A. El-Kemary, H. S. El-Gezawy, H. Y. El-Baradie and R. M. Issa, Chem. Phys.,2001, 265, 239.

338. S. Yang, H. Tian, H. Xiao, X. Shang, X. Gong, S. Yao and K. Chen, Dyes Pigm.,2001, 49, 93.

339. N. N. Kruk and A. A. Korotkii, J. Appl. Spectrosc., 2000, 67, 560.340. J. H. Ha, G. Y. Jung, M. S. Kim, Y. H. Lee, K. Shin and Y. R. Kim, Bull. Korean

Chem. Soc., 2001, 22, 69.341. R. Schmidt, F. Shafii, C. Schweitzer, A. A. Abdel-Shafi and F. Wilkinson, J. Phys.

Chem. A, 2001, 105, 1811.342. M. Okamoto, O. Wada, F. Tanaka and S. Hirayama, J. Phys. Chem. A, 2001, 105,

566.343. V. G. Klimenko, R. N. Nurmunkhametov, S. A. Serov and E. A. Gastilovich, Opt.

Spectrosc., 2000, 89, 42.344. E. A. Gastilovich, S. A. Serov, N. V. Korol’kova and V. G. Klimenko, Opt.

Spectrosc., 2000, 88, 313.345. J.M. G.Martinho, A. T. Reis e Sousa,M. E. TorresOliveira andA. Fedorov,Chem.

Phys., 2001, 264, 111.346. D. M. Guldi, T. D. Mody, N. N. Gerasimchuk, D. Magda and J. L. Sessler, J. Am.

Chem. Soc., 2000, 122, 8289.347. K. Ishii, T. Ishizaki and N. Kobayashi, Chem. Lett., 2000, 482.348. K. Ishii, Y. Hirose, H. Fujisuka, O. Ito and N. Kobayashi, J. Am. Chem. Soc., 2001,

123, 3403.349. S. Takeuchi, Y. Ogawa, A. Naito, K. Sudo, N. Yasuoka, H. Akutsu, J. I. Yamada

and S. Nakatsuji,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 345, 167.350. L. D. Li, W. Q. Long and A. J. Tong, Spectrochim. Acta, Part A, 2001, 57, 1261.351. M. Ikegami and T. Arai, Chem. Lett., 2000, 996.352. M. Dossot, D. Burget, X. Allonas and P. Jacques, New J. Chem., 2001, 25,

194.353. N. Toyama, M. Asano-Someda, T. Ichino and Y. Kaizo, J. Phys. Chem. A, 2000,

104, 4857.354. N. Armaroli, J.-F. Eckbert and J.-F. Nierengarten, Chem. Commun., 2000, 2105.355. S. Akimoto, T. Yamazaki, I. Yamazaki, A. Nakano and A. Osuka, Pure Appl.

Chem., 1999, 71, 2107.356. J. Duhamel, A. S. Jones and T. J. Dickson,Macromolecules, 2000, 33, 6344.357. T. Suzuki, M. Nagano, S. Watanabe and T. Ichimura, J. Photochem. Photobiol. A,

2000, 136, 7.358. K. N. Jayachandran, L. Maiti and P. R. Chatterji, Polymer, 2001, 42, 6113.359. J. M. Liannanto and J. E. I. Korppi-Tommola, J. Chin. Chem. Soc. (Taipei), 2000,

47, 657.360. H. Port, A. Hartschuh, M. Heinrich, H. C. Wolf, J. M. Endtner and F. Effenberger,

Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 344, 145.361. E. K. L. Yeow, P. J. Sintic, N. M. Cabral, J. N. H. Reek, M. J. Crossley and K. P.

Ghiggino, Phys. Chem. Chem. Phys., 2000, 2, 4281.362. S. Alp, S. Erten, C. Karapire, B. Koz, A. O. Doroshenko and S. Icli, J. Photochem.

Photobiol. A, 2000, 135, 103.


363. J.Wachtvetl, R. Huber, S. Sporlein, J. E.Moser andM.Gratzel, Int. J.Photoenergy,1999, 1, 153.

364. S. Iwai, K. Hara, R. Katoh, S. Murata, H. Sughaya and H. Arakawa, Springer Ser.Chem. Phys., 2001, 66, 447.

365. H. Takekusa, K. Kikuchi, Y. Urano, T. Higuchi and T. Nagano,Anal.Chem., 2001,64, 452.

366. G.Melnikov, S. Shtykov and I. Goryacheva, Proc. SPIE — Int. Soc. Opt. Eng., 2000,4002, 217.

367. S. A. Azim, R. Ghazy,M. Shabeen and F. El-Mekawey, J. Photochem.Photobiol.A,2000, 133, 185.

368. S. Encinas, N. B. M. Simpson, P. Andrews, M. D. Ward, C. M. White, N. Armaroliand F. Barigelletti,New J. Chem., 2000, 24, 987.

369. N. Ichinose, T. Tanaka, S.-I. Kawanishi and T. Majima, Chem. Phys. Lett., 2000,326, 293.

370. K. Ray, H. Nakahara, A. Sakamoto and M. Tsumi, Chem. Phys. Lett., 2000, 342,58.

371. L. I. Liu, N. N. Barashikov, C. P. Pulsule, S. Gangopadhyay and W. L. Borst, J.Appl. Phys., 2000, 88, 4860.

372. J. W. Yu, J. K. Kim, H. N. Cho, D. Y. Kim, C.Y. Kim, N. W. Song and D. Kim,Macromolecules, 2000, 33, 5443.

373. M. W. McCutcheon, J. F. Young, A. G. Pattantyus-Abraham and M. O. Wolf, J.Appl. Phys., 2001, 89, 4376.

374. M. Tsushima, N. Ikeda, A. Yoshimura, K. Nozaki and T. Ohno,Coord.Chem.Rev.,2000, 208, 299.

375. M. A. Rawashdeh-Omary, C. L. Larochelle and H. Patterson, Inorg. Chem., 2000,39, 4527.

376. M. D. Ward, Int. J. Photoenergy, 1999, 1, 121.377. A. Harriman, A. Khatyr, R. Ziessel and A. C. Benniston, Angew. Chem., Int. Ed.,

2000, 39, 4287.378. A. Juris, L. Prodi, A. Harriman, R. Ziessel, M. Hissler, A. El-ghayoury, F. Wu, E. C.

Riesgo and R. P. Thummel, Inorg. Chem., 2000, 39, 3590.379. M. Ravikanth, N. Agarewal and D. Kumaresan, Chem. Lett., 2000, 836.380. R. K. Lummi, A. Ambroise, T. Balasubramanian, R. W. Wagner, D. F. Bocian, D.

Holten and J. S. Lindsey, J. Am. Chem. Soc., 2000, 122, 7579.381. S. Encinas, F. Barigelletti, A. M. Barthram, M. D. Ward and S. Campagna, Chem.

Commun., 2001, 277.382. R. P. Evstigneeva, V. Z. Paschenko, V. N. Luzgina, E. A. Larkina, A. A. Grihkov, V.

B. Tusov and V. V. Gorokhov, Dokl. Akad.Nauk, 1999, 369, 57.383. M. A. Miller, R. K. Lummi, S. Prathipan, D. Holten and J. S. Lindsey, J. Org.

Chem., 2000, 65, 6634.384. C. Serpa and L. G. Arnaut, J. Phys. Chem. A, 2000, 104, 11075.385. K. Kokobo, T. Masaki and T. Oshima, Org. Lett., 2000, 2, 1979.386. S. Iwai, S. Murata and M. Tachiya, Springer Ser. Chem. Phys., 2001, 66, 488.387. X. Allonas, P. Jacques, A. Accary, M. Kessler and F. Heisel, J. Fluoresc., 2000, 10,

237.388. W. Pishel and W. M. Nau, J. Phys. Org. Chem., 2000, 13, 640.389. L. Boilet, G. Burdzinski, G. Buntinx, C. Lefemeux and O. Poizat, J. Phys. Chem. A,

2001, 104, 10455.390. B. Akhremitchev, C. Wang and G. C. Walker, Laser Chem., 1999, 19, 408.391. S. Nad and H. Pal, J. Photochem. Photobiol. A, 2000, 134, 9.

Photochemistry42

392. T. N. Inada, K. Kikuchi, Y. Takahashi, H. Ikeda and T. Miyashi, J. Photochem.Photobiol. A, 2000, 137, 93.

393. J. Gemer, K. Hildenbrand, S. Naumov and D. Eckert, Phys. Chem. Chem. Phys.,2000, 2, 4199.

394. A. J. Myles and N. R. Branda, Tetrahedron Lett., 2000, 41, 3785.395. S. Dileesch and K. R. Gepidas, Chem. Phys. Lett., 2000, 330, 397.396. T. Fournier, G. D. Scholes, I. R. Gould, S. M. Tavender, D. Phillips and A. W.

Parker, Laser Chem., 1999, 19, 397.397. A. T. Yeh, C. V. Shank and J. K. McCusker, Science, 2000, 289, 835.398. A. G. Griesbeck, M. S. Gudipati, J. Hirt, J. Lex, M. Oelgemoeller, H. Schmickler

and F. Schouren, J. Org. Chem., 2000, 65, 7151.399. E. Shimada, M. Sugano, M. Iwahashi, Y. Mori, Y. Sakaguchi and H. Hayashi, J.

Phys. Chem. A, 2001, 105, 2987.400. F. D. Lewis, L. S. Li, T. L. Kurth and R. S. Kalgutkar, J. Am.Chem. Soc., 2000, 122,

8573.401. T. Osakai and K. Muto, J. Electroanal. Chem., 2001, 499, 95.402. C. Costentin, M. Robert and J.-M. Saveant, J. Phys. Chem. A, 2000, 104, 7492.403. H. L. Tavernier, M. M. Kalashnikov and M. D. Fayer, J. Chem. Phys., 2000, 113,

10191.404. P. O. J. Scherer, J. Phys. Chem. A, 2000, 104, 6301.405. J. Zhou, B. R. Findley, A. Teslja, C. L. Braun and N. Sutin, J. Phys. Chem. A, 2000,

104, 11512.406. A. L. Burnshtein, E. Krissinel and U. E. Steiner, Phys. Chem. Chem. Phys., 2001, 3,

198.407. G. Angulo, G. Grampp, S. Landgraf and J. Sobek, J. Inf. Rec., 2000, 25, 381.408. A. J. Myles and N. E. Branda, J. Am. Chem. Soc., 2001, 123, 177.409. M. A. Smitha, E. Prasad and K. R. Gopindas, J. Am. Chem. Soc., 2001, 123, 1159.410. W. Jarzeba, S. Pommeret and J.-C. Mialocq, Chem. Phys. Lett., 2000, 333, 419.411. G. Tamulaitis, V. Gutbinas, A. Undzenas and I. Valkunas, Environ. Chem. Phys.,

1999, 21, 89.412. G. Zerza, A. Gravino, H. Neugebauer, N. S. Saricifici, R. Gomez, J. L. Segura, N.

Martin, M. Svensson and M. R. Andersson, J. Phys. Chem. A, 2001, 105, 4172.413. D. Moses, A. Dogario and A. J. Heger, Synth.Met., 2001, 116, 19.414. A. C. Benniston, S. Gardner, L. J. Farrugia and A. Harriman, J. Chem.Res. Synop.,

2000, 360.415. M. Linke, J.-C. Chambron, V. Heitz, J.-P. Sauvage, E. Encinas, F. Barigelletti and

L. Flamigni, J. Am. Chem. Soc., 2000, 122, 11834.416. S. Fukuzumi, H. Imahori, H. Yamada,M. E. El-Khouly, M. Fijisuka, O. Ito and D.

M. Guldi, J. Am. Chem. Soc., 2001, 123, 2571.417. S. A. do Monte, Chem. Phys. Lett., 2001, 338, 462.418. S. Leroy, T. Soujanya and F. Fages, Tetrahedron Lett., 2001, 42, 1665.419. H. Shiratori, T. Ohno, K. Nozaki, I. Yamazaki, Y. Nishimura and A. Osuka, J.Org.

Chem., 2000, 65, 8747.420. M. Schreiber, D. Kilm and U. Kleinekathofer, Los Alamos Natl. Lab., Prep. Arch.

Phys., 2000, 1014.421. M. A. El-Kemary, J. Photochem. Photobiol. A, 2000, 137, 9.422. Y. Shen, K. A.Walters, K. Abboud andK. S. Schanze, Inorg.Chim.Acta, 2000, 300,

414.423. P. Le Thao, J. E. Rogers and L. A. Kelly, J. Phys. Chem. A, 2000, 104, 6778.424. Y. Mori, Y. Sakaguchi and H. Hayashi, Bull. Chem. Soc. Jpn., 2001, 74, 293.


425. N. R. Lokan, M. N. Paddon-Row,M. Koeberg and J. W. Verhoeven, J. Am. Chem.Soc., 2000, 122, 5075.

426. F. J. Hoogesteger, C. A. Van Walree, L. W. Jenneskens, M. R. Roest, J. W.Verhoeven, W. Schuddeboom, J. J. Piet and J. M. Warman,Chem.: Eur. J., 2000, 6,2948.

427. K. Kils, J. Kajanus, A. N. Macpherson, J. Martensson and B. Albinsson, J. Am.Chem. Soc., 2001, 123, 3069.

428. L. Flamigni, I. M. Dixon, J.-P. Collin and J.-P. Sauvage, Chem. Commun., 2000,2479.

429. M. Seischab, T. Lodenkemper, A. Stockmann, S. Schneider, M. Koeberg, M. R.Roest, J. W. Verhoeven, J. M. Lawson andM. N. Paddon-Row,Phys.Chem.Chem.Phys., 2000, 2, 1889.

430. G. P.Wiederrecht,W. A. Svec,M. R.Wasielewski, T. Galili and H. Levanon, J.Am.Chem. Soc., 2000, 122, 8715.

431. S. Techert, S. Schmatz, A. Wissner and B. Staerk, J. Phys. Chem. A, 2000, 104,5700.

432. S. E. Miller, A. S. Lukas, E. Marsh, P. Bushard and M. R. Wasielewski, J. Am.Chem. Soc., 2000, 122, 7802.

433. M. Sykora, K. A. Maxwell, J. M. DeSimonne and T. J. Meyer,Proc.Natl.Acad. Sci.USA, 2000, 97, 7687.

434. K. E. Beg, A. Tran, M. E. Raymond, M. Abrahamsson, J. Wolny, S. Redon, M.Andersson, L. Sun, S. Stenbjorn, L. Hammarstrom, H. Toftlund and B. Akermark,Eur. J. Inorg. Chem., 2001, 1019.

435. A. El-ghayoury, A. Harriman and R. Ziessel, J. Phys. Chem. A, 2000, 104, 7906.436. L. S. Kelso, T. A. Smith, A. C. Schultz, P. C. Junk, R. N. Warrener, K. P. Ghiggino

and F. R. Keene, J. Chem. Soc., Dalton Trans., 2000, 2599.437. L. Sun, L. Hammarstrom, B. Akermark and S. Styring, Trends Inorg. Chem., 1999,

6, 151.438. S. Fraysse, C. Coudret and J.-P. Launay, Eur. J. Inorg. Chem., 2000, 1581.439. R. T. Hayes, M. R. Wasielewski and D. Gosztola, J. Am. Chem. Soc., 2000, 122,

5563.440. S. D. O. Dantas, F. M. V. B. Barone, S. F. Braga and D. S. Galvao, Synth. Met.,

2001, 116, 275.441. I. B. Martini, B. Ma, T. De Ros, R. Helgeson, F. Wudl and B. J. Schwartz, Proc. —

Electrochem. Soc., 2000, 9 (Fullerenes: Functionalised Fullerenes), 135.442. D. M. Guldi and P. V. Kamat, Fullerenes: Chem. Phys. Technol., 2000, 225.443. J. H. Rice, R. Aures, J.-P. Galaup and S. Leach, Chem. Phys., 2001, 263, 401.444. S. M. Bachilo, A. F. Benedetto and R. B. Weisman, Proc. — Electrochem. Soc., 2000,

8 (Fullerenes: Electrochemistry and Photochemistry), 208.445. S. M. Bachilo, A. F. Benedetto, R. B. Weisman, J. R. Nossal and W. E. Billups, J.

Phys. Chem. A, 2000, 104, 11265.446. M. Fujitsuka,H. Kassai, A.Masuhara, S. Okada, E. Oikawa,H. Nakashima,O. Ito

and A. Yase, J. Photochem. Photobiol. A, 2000, 133, 45.447. L. Juha, B. Ehrenberg, S. Couris, E. Koudoumas, S. Leach, V. Hamplova, Z.

Pokorea, A.Mullerova and P. Kubat,Proc. — Electrochem. Soc., 2000, 8 (Fullerenes:Electrochemistry and Photochemistry), 233.

448. R. Stackow, G. Schick, T. Jarrosson, Y. Rubin and C. S. Foote, J. Phys. Chem. B,2000, 104, 7914.

449. L. Juha, B. Ehrenberg, S. Couris, E. Koudoumas, S. Leach, V. Hamplova, Z.Pokorea, A. Mullerova and P. Kubat, Chem. Phys. Lett., 2001, 335, 539.

Photochemistry44

450. M. Fujitsuka, H. Takahashi, T. Kudo, K. Tohji, A. Kasuya and O. Ito, J. Phys.Chem. A, 2001, 105, 675.

451. A. Sienkiewicz, S. Garaj, E. Bialkowska-Jaworska and L. Forro, AIP Conf. Proc.,2000, 544, 69.

452. F. Prat, C. Marti, S. Nobell, X. Zhang, C. S. Foote, R. Gonzalez Moreno, J. L.Bourdelande and J. Font, Phys. Chem. Chem. Phys., 2001, 3, 1638.

453. L. Juha, M. Farnikova, V. Hamplova, J. Kodymova, A. Mullerova, J. Krasa, L.Laska, O. Spalek, P. Kubat, L. Stibor, E. Koudoumas and S. Couris, Fullerene Sci.Technol., 2000, 8, 289.

454. J. H. Rice, J.-P. Galaup, N. K. Wachter, P. K. Birkett and R. Taylor, Chem. Phys.Lett., 2001, 335, 553.

455. R. V. Bensasson, M. Schwell, M. Fanti, N. K. Wachter, J. O. Lopez, J.-M. Janot, P.R. Birkett, E. J. Land, S. Leach, P. Seta, R. Taylor and F. Zerbetto, ChemPhys-Chem., 2001, 2, 109.

456. S. M. Bachilo, A. F. Benedetto and R. B. Weisman, Proc. — Electrochem. Soc., 2000,8 (Fullerenes: Electrochemistry and Photochemistry), 281.

457. G. Schick,M. Levitus, L. Kvetko, B. A. Johnson, I. Lamparth, R. Lunkwitz, B. Ma,S. I. Khan,M. A. Garcia-Garibay and Y. Rubin, J.Am.Chem. Soc., 1999, 121, 3246.

458. I. Texier, A. Fedorov, M. N. Berberan-Santos, R. V. Bensasson, H. Schonbergen,M. Brettreich, A. Hirsch, C. Crowley and A. Russat,Proc. — Electrochem. Soc., 2000,8 (Fullerenes: Electrochemistry and Photochemistry), 223.

459. B. Nuber, A. Khong, S. R. Wilson and D. I. Schuster, Proc. — Electrochem. Soc.,2000, 9 (Fullerenes: Functionalised Fullerenes), 161.

460. M. Lumrani, R. Hamasaki, Y. Yamamoto, M. Mitsuishi and T. Miyashita, Chem.Commun., 2000, 1595.

461. Z. Ga, Y. Li, Z. Shi, F. Bai and D. Zhu, J. Phys. Chem. Solids, 2000, 61, 1075.462. J.-F. Eckert, N. Armaroli, F. Barigelletti, P. Ceroni, J.-F. Nicoud and J.-F. Nieren-

garten, Proc. — Electrochem. Soc., 2000, 8 (Fullerenes: Electrochemistry and Photo-chemistry), 256.

463. M. A. Hernandez, N. Martin, L. Sanchez and D. M. Guldi, J. Organomet. Chem.,2000, 599, 2.

464. S. Luzzati, M. Panigoni and M. Catellani, Synth.Met., 2001, 116, 171.465. K. Matsumoto, M. Fujitsuka, T. Sato, S. Onodera and O. Ito, J. Phys. Chem. B,

2000, 104, 11632.466. A. Cravino, G. Zerza, H. Neugebauer, N. S. Saricifitci, M. Maggini, S. Bucella, M.

Svensson and M. K. Andersson, Chem. Commun., 2000, 2487.467. L. Pasimeni, M. Ruzzi, M. Prato, T. Da Ros, G. Barbarelli and M. Zambianchi,

Chem. Phys., 2001, 263, 89.468. M. Fujitsuka, K. Mitsumoto, O. Ito, T. Yamashiro, Y. Asu and T. Otsubo, Res.

Chem. Intermed., 2001, 27, 73.469. P. A. Van Hal, J. Knol and B. M. W. Langeveld-Voss, J. Phys. Chem. A, 2000, 104,

5974.470. P. A. Van Hal, E. H. A. Beckers, E. Peeters, J. J. Apperloo and R. A. J. Janssen,

Chem. Phys. Lett., 2000, 328, 403.471. E. Peeters, P. A. Van Hal, J. Knol, C. J. Brabec, N. S. Sariciftci, J. C. Hummelen and

R. A. J. Janssen, J. Phys. Chem. B, 2000, 104, 10174.472. R. M. Metzger, Proc. — Electrochem. Soc., 2000, 8 (Fullerenes: Electrochemistry and

Photochemistry), 198.473. T. W. Hamann, A. P. Bussandri, H. VanWilligen, S. Najab and J. C. Warner, Proc.

— Electrochem. Soc., 2000, 8 (Fullerenes: Electrochemistry and Photochemistry), 289.


474. D. M. Martino and H. Van Willigen, J. Phys. Chem. A, 2000, 104, 10701.475. O. Ito, T. Konishi and M. Fujitsuka, Proc. — Electrochem. Soc., 2000, 8 (Fullerenes:

Electrochemistry and Photochemistry), 140..476. H. Imahori, S. Fukuzumi, H. Yamada, H. Norieda, Y. Sakata, Y. Nishimura, I.

Yamazaki, M. Fujitsuka and O. Ito, Proc. — Electrochem. Soc., 2000, 8 (Fullerenes:Electrochemistry and Photochemistry), 79.

477. Q. J. Li, Q. J. Gong, L. M. Du and W. J. Jin, Spectrochim. Acta, Part A, 2001, 57,17.

478. J. Sun, Y. Liu, D. Chen and Q. Zhang, J. Phys. Chem. Solids, 2000, 61, 1149.479. S. Komamine,M. Fujitsuka, O. Ito, K. Moriwaki, T. Miyata and T. Ohno, J. Phys.

Chem. A, 2000, 104, 11497.480. N. Martin, L. Sanchez, B. Illeescas, S. Gonzalez, M. Angeles Herranz and D. M.

Guldi, Carbon, 2000, 38, 1577.481. V. Brezova, D. Dvoranova, P. Rapta and A. Stasko, Spectrochim. Acta, Part A,

2000, 56, 2729.482. T. Konishi, M. Fujitsuka, O. Ito, Y. Toba and Y. Usui, Bull. Chem. Soc. Jpn., 2001,

74, 39.483. A. Masuhara, M. Fujitsuka and O. Ito, Bull. Chem. Soc. Jpn., 2000, 73, 2199.484. B. Komamine, M. Fujitsuka, O. Ito and A. Itaya, J. Photochem. Photobiol.A, 2000,

135, 111.485. V. Brezova, M. Gembicka and A. Stasko, Fullerene Sci. Technol., 2000, 8, 225.486. H. Imahori, K. Tamaki, H. Yamada, K. Yamada, Y. Sakata, Y. Nishimura, I.

Yamazaki, M. Fujitsuka and O. Ito, Carbon, 2000, 38, 1599.487. J.-F. Nierengarten, J.-F. Eckert, D. Felder, J.-F. Nicoud, N. Armaroli, G. Marconi,

V. Vicinelli, C. Boudon, J.-P. Gisselbrecht and M. Gross, Carbon, 2000, 38, 1587.488. B. Jing, D. Zhang and D. Zhu, Tetrahedron Lett., 2000, 41, 8559.489. D. M. Guldi, M. Maggini, N. Martin and M. Prato, Carbon, 2000, 38, 1615.490. M. Diekers, A. Hirsch, C. Luo, D. M. Guldi, K. Bauer and U. Nickel, Org. Lett.,

2000, 2, 2741.491. G. Torres-Garcia, D. M. Guldi and J. Mattay, J. Inf. Rec., 2000, 25, 273.492. I. B. Martini, B. Ma, T. Da Ros, R. Helgeson, F. Wudl and B. J. Schwartz, Chem.

Phys. Lett., 2000, 327, 253.493. S. Nath, D. K. Palit and A. V. Sapre, Chem. Phys. Lett., 2000, 330, 255.494. O. Ito, M. Yamazaki and M. Fujitsuka, Proc. — Electrochem. Soc., 2000, 8

(Fullerenes: Electrochemistry and Photochemistry), 306.495. D. I. Schuster, Carbon, 2000, 38, 1607.496. H. Imahori, S. Fukuzumi, K. Tamaki, K. Yamada and Y. Sakata, Proc. — Elec-

trochem. Soc., 2000, 9 (Fullerenes: Functionalised Fullerenes), 60.497. O.Kutski,M.Wedel, F. P.Montforte, S. Smirnov, S. Cosnier andA.Walter,Proc. —

Electrochem. Soc., 2000, 8 (Fullerenes: Electrochemistry and Photochemistry), 172.498. N. Armaroli, G. Marconi, L. Eschegoyen, J.-P. Bourgeois and F. Diederich, Proc. —

Electrochem. Soc., 2000, 9 (Fullerenes: Functionalised Fullerenes), 92.499. T. DaRos,M. Prato, D.M.Guldi,M. Rizzi and L. Pasimeni,Chem.:Eur. J., 2001, 7,

816.500. S. MacMahon, S. R. Wilson and D. I. Schuster, Proc. — Electrochem. Soc., 2000, 8

(Fullerenes: Electrochemistry and Photochemistry), 155.501. F. P. Montforte and O. Kutski, Angew. Chem., Int. Ed., 2000, 39, 599.502. N. V. Tkachenko, A. Y. Tauber, V. Vehmanen, A. A. Alekseev, P. H. Hynninen and

H. Lemmetyinen, Proc. — Electrochem. Soc., 2000, 8 (Fullerenes: Electrochemistryand Photochemistry), 161.

Photochemistry46

503. A. Ikeda, M. Kawaguchi, Y. Suzuki, T. Hatano, M. Numato, S. Shinkai, A. OhtaandM. Aratono, J. Inclusion Phenom.Macrocycl.Chem., 2000, 38, 163.

504. N. Armaroli, G. Marconi, L. Eschegoyen, J.-P. Bourgeois and F. Diederich,Chem.:Eur. J., 2000, 6, 1629.

505. H. Imahori, M. E. El-Khouly, M. Fujitsuka, O. Ito, Y. Sakata and S. Fukuzumi, J.Phys. Chem. A, 2001, 105, 325.

506. H. Imahori, K. Tamaki, D.M.Guldi, C. Luo,M. Fujitsuka, O. Ito, Y. Sakata and S.Fukuzumi, J. Am. Chem. Soc., 2001, 123, 2607.

507. J. L. Bahr, D. Kuciauskas, P. A. Liddel, A. L. Moore, T. A. Moore and D. Gust,Photochem. Photobiol., 2000, 72, 598.

508. G. Deviprasad, M. E. Zandler and F. D’Souza, Proc. — Electrochem. Soc., 2000, 8(Fullerenes: Electrochemistry and Photochemistry), 182.

509. K. Noworyta, E. P. Krinichnaya, W. Kutner, P. M. Smith, G. Deviprasad and F.D’Souza,Proc. — Electrochem. Soc., 2000, 8 (Fullerenes:Electrochemistry and Photo-chemistry), 54.

510. D.M. Guldi, C. Luo,M.Maggini,M. Enzo, S.Mondini, N. A. Kotov andM. Prato,Proc. — Electrochem. Soc., 2000, 8 (Fullerenes:Electrochemistry and Photochemistry),202.

511. A. M. de la Pena, M. C. Mahedero and A. B. Sanchez, Analusis, 2000, 28, 670.512. M. E.McCarroll, F. H. Billiot and I.M.Warner, J.Am.Chem. Soc., 2001, 123, 8173.513. W. J. Joo, H. D. Shin, C. H. Oh, S. H. Song, P. S. Kim, B. S. Ko and Y. K. Han, J.

Chem. Phys., 2000, 113, 8848.514. R. Pramanik, P. Jumar Das and S. Bagchi, Phys. Chem. Chem. Phys., 2000, 2, 4307.515. M. M. da Garca, Adv. Collid. Interface Sci., 2001, 89, 1.516. K. A. Kneas, J. N. Demas, B. A. DeGraff and A. Periasamy, Microsc. Microanal.,

2000, 6, 551.517. O. Pekcan, D. Kaya and M. Erdogan, J. Appl. Polym. Sci., 2001, 80, 1907.518. C. R. Hidrovo and D. P. Hart,Meas. Sci. Technol., 2001, 12, 467.519. B. Fong, W. Stryjewski and P. S. Russo, J. Collid. Interface Sci., 2001, 239, 374,520. H. J. Egelhaaf, L. Luer, A. Tompert, P. Bauerle, K. Mullen and D. Oelkrug, Synth.

Met., 2000, 155, 63.521. V. V. Apanasovich, E. G. Novikov and N. N. Yatskov, J. Appl. Spectrosc., 2000, 67,

842.522. R. Argaman, T. Molotsky and D. Huppert, J. Phys. Chem. A, 2000, 104, 7934.523. D. T. Cramb and S. C. Beck, J. Photochem. Photobiol. A, 2000, 134, 87.524. V. Capek, Czeck J. Phys., 2001, 51, 513.525. M. Wen and A. V. McCormick,Macromolecules, 2000, 33, 9247.526. A. J. Garcia-Adeva and D. L. Huber, J. Lumin., 2000, 92, 65.527. I. R. Lee, W. K. Chen, Y. C. Chung and F. Y. Cheng, J. Phys. Chem. A, 2000, 104,

10595.528. T. Palszegi, V. Szoca, M. Breza and V. Lukes,NATO Sci. Ser., 2000, 79, 139.529. M. Corboz, I. Alxneit, G. Stoll and H. R. Tschudi, J. Phys. Chem. B, 2000, 104,

10569.530. D. C. Lamb, A. Schenk, C. Rocker and G. U. Nienhaus, J. Phys. Org. Chem., 2000,

13, 654.531. T. Heyduk and E. Heyduk, Anal. Biochem., 2001, 289, 60.532. W. P. Partridge and N. M. Laurendeau, Appl. Phys. B: Laser Opt., 2000, 71, 237.533. M. J. Pelletier and R. Altkorn, Appl. Spectrosc., 2000, 54, 1837.534. H. Malm, G. Sparr, J. Holt and C. F. Kaminski, J. Opt. Soc. Am. A, 2000, 17, 2148.535. S. A. Bagnich and A. V. Ronash, Chem. Phys., 2001, 263, 101.


536. P. Evers, J. Giraud-Girard, S. Grimme, J. Manz, C.Monte, M. Oppel, W. Rettig, P.Saalfrank and P. Zimmermann, J. Phys. Chem. A, 2001, 105, 2911.

537. S. Frank, A. Dinklage and C. Wilks, Rev. Sci. Instrum., 2001, 72, 2048.538. P. Vallotton and H. Vogel, J. Fluoresc., 2000, 10, 325.539. T. A. Smith, D. J. Haines and K. P. Ghiggino, J. Fluoresc., 2000, 10, 865.540. L. Catani, C. Gellini, L. Moroni and P. R. Salvi, J. Phys. Chem. A, 2000, 104, 6566.541. G. Chirico, F. Olivini and S. Beretta, Appl. Spectrosc., 2000, 54, 1084.542. A. F. Ruckstuhl, M. F. Jacobson, R. W. Field and J. A. Dodd, J. Quant. Spectrosc.

Radiat. Transfer, 2001, 68, 179.543. E. Novikon and N. Boens, J. Chem. Phys., 2001, 114, 1745.544. M. Bischoff, G. Stobrawa and S. Rentsch, Laser Chem., 2000, 18, 203.545. K. Starchev, J. Ricka and J. Buffle, J. Collid. Interface Sci., 2000, 233, 50.546. X. Lin and T. Song, Proc. SPIE — Int. Soc. Opt. Eng., 2000, 4221 (Optical Measure-

ment and Nondestructive Testing Techniques and Applications), 198.547. R. J. Sension, A. G. Cole, N. A. Anderson and J. J. Shiang, Springer Ser. Chem.

Phys., 2001, 66, 648.548. J. J. Turner, M.W. George, I. P. Clark and I. G. Virrels, Laser Chem., 1999, 19, 246.549. E. Vauthey, EPA Newsletter, 2000, 70, 30.550. N. J. Turro, M. H. Kleinman and E. Karatekin, Angew. Chem., Int. Ed., 2000, 39,

4437.551. S. Kinoshita, H. Ozawa, Y. Manematsu, I. Tanaka, N. Sugimoto and S. Fujiwara,

Rev. Sci. Instrum., 2000, 71, 3317.552. J. Takeda, K. Nakajima, S. Kirita, S. Tomimoto, S. Saito and T. Suemoto, Phys.

Rev. B: Condens.Matter Mater. Phys., 2000, 62, 10085.553. H. Kano and T. Kobayashi, J. Chin. Chem. Soc. (Taipei), 2000, 47, 859.554. T. Nagahara, K. Kanematsu and T. Okeda, Springer Ser. Chem. Phys., 2001, 66,

192.555. H. Murakami, J.Mol. Liq., 2000, 89, 33.556. M. Misawa and T. Kobayashi, J. Chem. Phys., 2000, 113, 7546.557. H. Yang, P. T. Snee, K. T. Kotz, C. K. Payne and C. B. Harris, J. Am. Chem. Soc.,

2001, 123, 4204.558. M. Wermuth and H. U. Gudel, Chem. Phys. Lett., 2000, 323, 514.559. N. Kurokawa, H. Yoshikawa, H. Masuhara, N. Hirota and K. Hyodo, J.Microsc.,

2001, 202, 420.560. H. F. Hamann,M. Kuno, A. Gallagher and D. J. Nesbitt, J.Chem.Phys., 2001, 114,

8596.561. N. M. Haralampus-Grynaviski, M. J. Stimson and J. D. Simon, Appl. Spectrosc.,

2000, 54, 1727.562. J. M. Smith, P. A. Hiskett and G. S. Buller, Opt. Lett., 2001, 26, 731.563. J. M. Smith, P. A. Hiskett, L. Gontijo, L. Purves and G. S. Buller,Rev. Sci. Instrum.,

2001, 72, 2325.564. M. O. Cambaliza and C. Saloma, Opt. Commun., 2000, 184, 25.565. J. Widengren and C. A. M. Seidel, Phys. Chem. Chem. Phys., 2000, 2, 3435.566. F. Delie, R. Gurey and A. Zimmer, Biol. Chem., 2001, 382, 487.567. Y. Iwaki and N. Ohta, Chem. Lett., 2000, 894.568. M. Rutloh and J. Stumpe, J. Inf. Rec., 2000, 25, 39.569. M. Kemerink, J. W. Gerritsen, J. G. H. Hermsen, P. M. Koenraad, H. van Kempen

and J. H. Wolter, Rev. Sci. Instrum., 2001, 72, 132.570. H. Hayashi, Y. Sakaguchi, M. Wakasa, Y. Mori and K. Nishizawa, Appl. Magn.

Reson., 2000, 18, 307.

Photochemistry48

571. T. C. Yang, D. J. Sloop, S. I. Weissman and T. S. Lin, Chem. Phys. Lett., 2000, 331,489.

572. A. Weichert, C. Riehn and B. Brutschy, J. Chem. Phys., 2000, 113, 7830.573. P. B. Conibear and C. R. Bagshaw, J.Microsc., 2000, 200, 218.574. S. De Feyter, J. Hofkens,M. Van der Auweraer, R. J. M.Nolte, K.Mullen and F. C.

De Schryver, Chem. Commun., 2001, 585.575. M. Towrie, G. Gaborel, P. Matousek, A. W. Parker, W. Shaikh and R. H. Bisby,

Laser Chem., 1999, 19, 153.576. K. Takenshita, N. Hirota and M. Terizima, J. Photochem. Photobiol. A, 2000, 134,

103.577. X. Ho and T. G. Spiro, Laser Chem., 1999, 19, 141.


Part II

Organic Aspects of Photochemistry

1Photolysis of Carbonyl Compounds

BYWILLIAMM. HORSPOOL

Several reviews have been published during the past year that are pertinent tothis section. Among these is a review highlighting the photochemistry in mixedcrystals, co-crystals and the solid state of mixtures.1 Others have detailed someaspects of bimolecular reactivity in single crystals.2

There is growing interest in photochemistry carried out under the constraintsof the crystalline phase or in zeolites. Ramamurthy3,4 is active in this area and hehas published extensive reviews of photochemistry carried out under bothconditions.5 Yamashita and Anpo6 have discussed pore effects in ZSM-5 zeolitesin relation to the photochemical reactions of pentan-2-one under such con-straints. Others have reported both theoretical and experimental studies of thereactivity of the same ketone in zeolites. 7 The ratio of products (Norrish TypeI/II) is dependent to a large extent upon the cation within the cage.

Reviews have been published on photochemical processes controlled byelectron-transfer processes8 and asymmetric photochemical reactions in sol-ution.9 A short review has described the n�*-excited state reactivity of ketones.10

Specific studies on the behaviour of ketones, such as the detailed report ofphotophysical properties of p-aminobenzophenone, are also worthy of men-tion.11 The irradiation of acetophenone in aerated solutions using wavelengths�200 nm is also of interest and results in the formation of 2-hydroxy- and3-hydroxy-acetophenone as the principal products.12 Asymmetric recognitionhas been demonstrated using chiral fluorenone derivatives such as 1[(1S,2R,5S)-(�)-menthyloxycarbonyloxy]fluoren-9-one.13 A study of the photophysical be-haviour of the sunscreenmenthyl anthranilate in a variety of solvent systems hasbeen reported.14 While the triplet state is readily quenched by oxygen it can beobserved in low-temperature glasses.

1 Norrish Type I Reactions

Several studies dealing with the photochemistry of acetone under a variety ofconditions have been reported. Thus, irradiation of the ketone in air affordsacetyl radicals by a conventional Norrish Type I process.15 The influences ofpressure and of wavelength on the efficiency of the reaction were determined.Acetyl radical and methyl radicals are also formed on infrared multiphoton


53

irradiation of acetone.16 The fragments generated by the irradiative decomposi-tion of acetone have been studied using time-of-flight mass spectrometry17 andcomputative procedures such as CASSCFmethods have been used to probe thephotodissociationof acetone.18 A study of the photochemical (at 248 and 308 nm)behaviour of acetone in the presence and absence of water has been carried out.19

The photochemical reaction of acetone and HBr has been investigated.20 Excita-tion at 266 or 309 nm results in the reaction of HBr/acetone complexes.

Other simple carbonyl compounds such as CO(CN)2 also undergo NorrishType I processes on irradiation at 193 nm.21 This treatment has shown thesimilarity of behaviour to acetone and two different CN fragments are produced.One of these is formed by the conventional �-fission process while the otherarises by cleavage of the resultant COCN radical.The photochemistry and the photophysics of the arylpropanones (1) have been

investigated.22 These compounds are models for the photoinitiation of free rad-ical polymerisation. �-Cleavage of the compounds (1) is favoured with p-fluoroand p-chloro substituents where the n�* lowest triplet state is active. The charac-ter of the lowest excited state is changed with p-dimethylamino and p-thio ethersubstituents. The spectra of the persistent radicals formed on irradiation of aseries of 4,4�-dialkylsubstituted benzophenones in MFI zeolites have been re-corded.23 Further studies of the photochemical behaviour of dibenzyl ketonederivatives in MFI zeolites have been carried out.24 A review has highlighted theprocesses involved in electron spin polarisation in supramolecular systems suchas zeolites.25 Others have also reported on phenacetyl radicals that are formed byirradiation of dibenzylketones.26The decarbonylation of the radicals was studiedand the influence of the p-substituents (MeO, Me, Cl, CF3) was assessed.Cyclobutanones also undergo Norrish Type I processes and calculations

relating to the photochemical activity of this cyclic ketone have been carriedout.27 A study of the cis,trans-isomerism of some 2-azetidinones has been re-ported.28 The products obtained from the process are dependent both on thesubstitution on the nitrogen atom and the ability of substituents at C-3 and C-4to stabilise radical centres.

Norrish Type I fission occurs on the irradiation of the �-alkylphenylindanones(2).29 The final products from this reaction mode have been identified as o-formylstilbenes as a result of disproportionation within the 1,5-biradical. Photo-dissociation of cyclopentanone and cyclohexanonehas been studied using irradi-ation at 800 nm with a pulsed-laser system.30

Photochemistry54

2 Norrish Type II Reactions

2.1 1,5-Hydrogen Transfer. — The Norrish Type II photoreactivity of alkylaryl ketones on silica gel surfaces and in solution has been investigated.31 Theauthors report that the amount of acetophenone produced on irradiation ofvalerophenone is dependent upon the surface loading.32 The yield increaseslinearly up to a maximum loading of 60%. Valerophenone is photochemicallyactive to some extent in frozen solvents such as benzene, cyclohexane, t-butanol,hexadecane and water. This activity is observed even although there is restrictedC—Cbond rotation. It appears that a fraction of the valerophenonemolecules areoriented so that a 1,5-hydrogen abstraction reaction can occur even in thisconstrained environment. There is also conformational restriction ofbutyrophenone and valerophenone �-cyclodextrin complexes and as a result thephotochemistry observed is different from that in the solution phase.33 TheNorrish Type II behaviour of the aryl ketone (3) in a monolayer on gold has beenstudied for the first time.34 The photo-deconjugation of (4) to give (5) occurs on254 nm irradiation in methylene chloride at �10 oC and this step, a NorrishType II process, has been used as part of a synthesis of (R)-sesquilavandulol.35

The irradiation of the ketone (6) at ��300 nm in methylene chloride providesan efficient method for the synthesis of the cyclopropyl ketone (7). The processinvolved is a standard Norrish Type II hydrogen abstraction with the formationof a 1,4-biradical (8). This subsequently eliminates the leaving group, OMs, toreform the carbonyl group and afford a 1,3-biradical which cyclises to give (7).The scope of the reaction was investigated using the derivatives (9). As can beseen in the results, affording (10), (11) and (12), there is a preference for cyclisationwithin the 1,3-biradical to yield the trans-cyclopropane (10) but the cis-cyclo-propane (11) and the alkene (12) can also be formed. The reaction can also beused for the synthesis of bicyclic molecules such as (13) obtained by irradiation of(14).36

The asymmetric induction encountered in the formation of the cyclobutanolresulting from the irradiation of the ketone (15a) with different chiral auxiliaries

II/1: Photolysis of Carbonyl Compounds 55

has been evaluated.37 The photoreaction of (15a) yields the corresponding cyclo-butanol with only 14% de in solution. A more dramatic effect is observed in thecrystalline phase when a de of 96% is obtained. The results are less encouragingwith (15b) where only 18% de is obtained in the crystal and 26% de in solution.Ketone (16) is converted photochemically into the three products (17, 47%), (18,47%) and (19, 6%) on irradiation in acetonitrile.38 The reaction pathway changesdramatically in single crystals of (16) irradiated through Pyrex at �20 °C when(20) is formed exclusively. The outcome of the reaction in whatever medium isused is controlled by the ability of the biradicals to cyclise. The authors suggestthat the biradical formed by abstraction of the hydrogen at C-10 in (16) is slow tocyclise in solution but becomes the dominant process in the crystal.Decomposition of �-keto esters of primary alcohols occurs by irradiation at

350 nm from the triplet state.39 The predominant reaction encountered is �-hydrogen abstraction and fragmentation of the resultant biradical. �-Hydrogenabstraction is also the outcome of irradiation of �-benzoylpropionic acid deriva-tives.40

Pincock and his co-workers41 have studied the photochemical reactivity oftrans-2-phenylcyclohexyl 4-cyanobenzoate (21). Irradiation brings about cleav-age to give 1-phenylcyclohexene and 4-cyanobenzoic acid. A Norrish Type IIprocess is thought to be involved from the usually inefficient ��* excited state ofthe ester moiety. Interestingly the naphthyl benzoates (22) do not undergo thisreaction and instead afford products of intramolecular cycloaddition.42 1,5-Hydrogen transfer reactions are also brought about on irradiation of the (S)-ketone (23).43 This process yields the 1,4-biradical which cyclises to give theazetidinols (24). The reaction was developed further and used the photocyclisa-tion of (S)-3,4-diacetoxy-C6H3COCH2N(COCH3)Me (from adrenaline) as a syn-

Photochemistry56

thetic path to 3-hydroxy-3-azetidinecarboxylic acid. Nishino et al.44 have exam-ined the pH-dependent photochemistry of amino acids such as leucine (25) usingcircularly polarised light. Under these conditions racemic leucine undergoesenantiomeric enrichment to afford (26, 1.3% ee). The photochemical reactivity ofmusk ketone (27) in cyclohexane and methanol has been studied.45

The reaction dynamics for the triplet-state-induced hydrogen transfer in 2-methylbenzophenone have been measured.46 The photochemical process in suchsystems results in the formation of enols by 1,5-hydrogen transfer. The photo-chromism exhibited by (28) in the solid state has been studied in detail, andapparently the process is the result of an intramolecular hydrogen abstraction toafford the enol (29).47

The photochemically induced hydrogen transfer reactivity in the salicylatederivatives (30) has been reported,48 as has the photoinduced proton transferwithin 3-hydroxy-2-naphthoic acid (31).49 In the latter case a large Stokes-shifted


emission is observed which is dependent upon pH, solvent, temperature andexcitation wavelength. The large Stokes shift is the result of intramolecularhydrogen transfer. A detailed study of the photoinduced proton transfer withinthe acetonaphthol (32) has been carried out in order to investigate the internaltwisting processes within the molecule.50 Photoenolisation of the hydroxyquino-line derivative (33) occurs on irradaition.51

2.2 Other Hydrogen Transfers. — The photochemical rearrangements encoun-tered in the unsaturated ketones (34) have been examined.52 The reactions in-volve either hydrogen abstraction by the excited carbonyl group from the�-position, which in this instance is situated between the two vinyl substituents,or a di-�-methane process. This latter reaction affords the cyclopropane prod-ucts (35). The free radical path involving the intermediate (36) formed by hydro-gen abstraction has two possible reaction paths. The usualmode is bonding at ‘a’in the biradical intermediate (36) which affords the cyclopropyl ketone (37) thatrings opens to afford the furan derivatives (38). Alternatively, within this vi-nylogous system, bonding can occur at ‘b’ or ‘c’ to yield the cyclopentenes (39)and (40). The reaction outcome as may be expected, is to some extent dependentupon the substitution on the starting material and the influence these substitu-ents have upon the stability of the biradical intermediates.The influence of environment on the photochemical cyclisation of the

acetophenones (41) into the indanols (42), brought about by a 1,6-hydrogentransfer, has been assessed.53 This detailed investigation has shown that there is acorrelation between the reactivity and the crystal structure. A �-hydrogen ab-straction is also involved in the conversion of the derivatives (43) into thebenzofurans (44).54This cyclisation mode has been used as a path to the synthesis

Photochemistry58

of coumestrol. The photochemical cyclisation of suitably ortho-substituted aryl-ketones has been reviewed.55 These reactions arise from the n�* excited state anda 1,6-hydrogen transfer. The resultant 1,5-biradicals can readily cyclise to yieldbenzofuran derivatives. A study of the photochemical dynamics of the irradi-ation of (45a) and (45b) has been reported.56 The irradiation of (45a) affords onlya single product identified as (46), but the oxirane (45b), while following the samereaction path to yield (47), also undergoes ring-opening to yield (48). Theinfluence of the oxygen in the three-membered ring on the outcome of thereaction is discussed.


3 Oxetane Formation

Adam and co-workers57 have examined the photochemical addition of benzo-phenone to both cis- and trans-cyclooctene and have uncovered a remarkabletemperature effect on the formation of the oxetane products (49) and (50). Theresults show that the formation of the trans-oxetane (50) from the cis-cycloocteneis favoured at higher temperatures. Thus the ratio of (50):(49) changes from 98:2at �95 °C to 20:80 at 110 °C. Addition of benzophenone to trans-cyclooctenealso favours the formation of the trans-oxetane (50). There is also a temperatureeffect in this addition and at �80 °C the ratio is 35:65 (c:t). Even at 40 °C there isstill a slight preference for the trans product (ratio 49:51; c:t). At 110 °C thereaction favours the formation of the cis-oxetane (ratio 70:30; c:t). Among avariety of factors that control the outcome of this reaction the authors suggestthat conformational factors are important.

The diastereoselectivity of the photo-addition of aldehydes to the alkenes (51)has been demonstrated to be excited state dependent.58Thus, a low ds is obtainedin the product oxetanes (52) from the singlet state while a higher ds is returnedfrom the triplet excited states of the carbonyl compounds. The photochemicaladdition of benzophenone to 5-methyl-2-furylphenylmethanol yields twooxetane derivatives in a ratio of 1:1.59 The influence of substituents upon theoutcome of the Paterno-Buchi cycloadditions between the furans (53) and thealdehydes and ketones (54) has been assessed.60 These high-yielding additionsaffording the oxetanes (55) and (56) are brought about in degassed acetonitrileusing wavelengths �290 nm. The path followed within the system is to a largeextent dependent upon both the type of carbonyl function and the substituentson the furan. The multiplicity of the carbonyl excited state is also important. Thealdehydes, for example, add quite randomly independent of the excited statemultiplicity. The ketones (54d, e), on the other hand, react from the triplet stategiving regioselective formation of the oxetanes (56). Acetone, which apparentlyreacts from its singlet state, is once more stereo-random in the addition mode.Further studies by Bach and his co-workers61 have given details of the

Paterno-Buchi addition of benzaldehyde to alkenes such as (57). The addition of

Photochemistry60

the aldehyde takes place in a syn-manner and gives products where the groupsare cis to each other. This specific addition mode has been made use of in asynthetic approach to preussin (58). Bach62 has reviewed this class of photo-chemical addition aldehydes to N-acyl enamines. Unstable oxetanes are ob-tained on the irradiation of benzil derivatives in the presence of (S)-2-(2-methoxymethylpiperidinyl)propenenitrile.63

4 Miscellaneous Reactions

4.1 Decarbonylation and Decarboxylation. — Laser irradiation at 370 nm hasbeen used to detect formaldehyde in the primary flame front of a Bunsen flame.64

The photochemical dynamics for the fragmentation of methanal has beenstudied theoretically.65

Morokuma and his co-workers66 have suggested that the photodissociation ofketene in its T1 excited state is highly non-statistical. Irradiation of ketene at 193nm has shown that there are four different decomposition paths.67 Two of theseafford CO and either triplet or singlet methylene. The spectrum of singletmethylene generated by the photochemical decomposition of ketene has beenrecorded.68

The acetone-sensitised photochemical decarbonylation of cyclobutanones tocyclopropane derivatives has been described.69 Laser irradiation of the ketone(59) brings about decarbonylation and the formation of the biradical (60).70 Thissame radical can be produced by irradiation of the dichloro-compound (61). The


biradical (60) does not cleave to yield p-xylylene but either ring-closes to theparacyclophane (62) or dimerises to yield (63) in low yield. The dianhydride (64)undergoes interesting photochemistry when irradiated in a low temperaturematrix.71 Irradiation at 308 nm affords the naphthyne monoanhydride (65) andprolonged irradiation at this wavelength converts (64) into the anhydride (66).Irradiation of naphthyne anhydride (65) at 248 nm brings about the seconddecomposition step and the formation of the naphth-1,5-dyne (67). This inter-mediate undergoes ring opening to yield the polyyne (68).

Both experimental and theoretical methods have been used to explore thephotodissociation of formic acid.72 A comparison of the decomposition of aceticacid and benzamide on different types of TiO2 catalysts has been reported.73

Apparently the specific area of the catalyst does not affect the decomposition ofbenzamide. The decomposition of butanoic acid on a TiO2 catalyst, giving aceticand succinic acids, has also been examined and the influence of changes in pHhave been quantified.74 Acrylic acid undergoes photochemical dissociation fromseveral excited states.75 Thus the loss of a hydroxy radical occurs on the T2—S1

interface while formation of a vinyl radical arises on the T1 surface. Aliphaticamino acids undergo rapid decarboxylation when irradiated in the presence of4-carboxybenzophenone.76 Under these conditions the triplet state of the benzo-phenone is the active species. The photophysical properties of phenylalaninehave been studied.77 The decomposition of phenylglycine has been investigatedunder pyrene sensitisation.78 The reaction can be accelerated by the addition ofdiethyl isophthalate or terephthalonitrile as electron-accepting sensitisers.Photo-oxidative decarboxylation of amino acids in mesoporous silica has beeninvestigated with the protected amino acids (69).79 Irradiation of such com-pounds with a 400 W lamp for 36 hours in hexane as the solvent provided theimides (70).

Photochemistry62

The photochemical reactivity of aryl-substituted acetic acids in acetonitrilewith HgF2 has been described and the corresponding benzyl radicals that areformed dimerise to afford 1,2-diarylethanes.80 The photochemical decompositionof 4-chlorophenoxy- and 2,4-dichlorophenoxyacetic acid has been studied in airsaturated mixtures and in the presence of traces Fe3�.81 Irradiation in the245—250 nm range of the acids (71—73) in water/acetonitrile mixtures set at pH 7controlled by the addition of sodium hydroxide brings about efficient decar-boxylation.82 Dark controls demonstrate that the reactions are truly photo-chemical. The decarboxylation occurs with high quantum yields (71, ��0.66; 72,��0.62; 73, ��0.22). The reactions are thought to arise from the excited singletstate and result in the formation of the corresponding anion following decar-boxylation. The leaving group need not be carbon dioxide, a fact demonstratedusing the alcohol (74) when a 70% yield of 3-methylbenzophenone is obtained,formally a loss of formaldehyde. Photodecarboxylation of the anion of keto-profen has been studied by laser-induced optoacoustic spectroscopy.83 There is amarked enhancement of decarboxylationwhen phenyl and 1-naphthyl esters areirradiated in polyethylene films at sub-ambient temperatures.84 The photochemi-cal reactivity of the naphthyl esters (75) in stretched and unstretched polymerfilms has been studied.85 Decarboxylation of (76) results on irradiation at 254 nmin acetonitrile solution and this yields cyclohexylmesitylene (77).86 When theirradiation is repeated in solutions containing a trace of acid and ethanol thereaction follows a different path and yields ethyl cyclohexanecarboxylate and the2,4,6-trimethylphenol.The decarboxylation of (78) to afford (79) can be carried out efficiently by

irradiation in benzene in the presence of ButSH/quinoline to give (78), necrodol,in 81% yield.87 The photochemical decarboxylation of chromone-2-carboxylicacid in ethanol affords 4-hydroxycoumarin and 2-(1�-hydroxyethyl)chromone.88

The photochemical equilibria exhibited by anthracene-9-carboxylic acid in avariety of media have been investigated.89 A laser flash study of the activity of thefluoroquinolone antibiotic flumequine has been reported.90 A detailed study ofthe photofragmentation undergone by other fluoroquinolone antibiotics hasbeen carried out.91 Medium effects were also investigated.92 The results of a studyof the photochemical reactions undergone by some furocoumarins have beenpublished.93


The Barton ester (80) cleaves on laser irradiation at 355 nm and the resultantradical (81) undergoes bond fission with the formation of the radical cation (82).94

Other studies have focused on the Barton esters (83) which on irradiation yieldthe radicals (84).95 Irradiation of Barton ester (85) provides a good route to theradical (86) within which the rate of ring opening of the cyclobutane ring wasstudied.96 Irradiation of Barton ester (87) in acetonitrile or a sodium phosphatebuffer at pH 7.4 leads to O—C bond fission and the production of the ubiquinolradical (88).97

Use of the Barton ester (89) has been made in new photochemistry of the alkylboronic esters (90).98 Irradiation of (89) with a 300 W halogen lamp in thepresence of (90) affords the mixture of adducts (91) and (92) in a ratio of 6:1.Several boronic esters were examined and the best yields (68%) were obtainedwith the catechol derivative of (90). The study also included reactions of (93) with

Photochemistry64

the Barton ester and a variety of alkenes (94). This reaction providedmoderate toexcellent yields of the adducts (95) as a mixture of trans and cis in ratios greaterthan 80:20. Reactions were also carried out with indene derivatives of (93).

The radical (96) can be formed by the irradiation of (97) in acetonitrile.99

Cleavage of the O—N bond is solvent dependent and is not as efficient whennon-polar solvents are used. The products formed from the reaction were identi-fied as the dimer (98) and anthracene-9-carboxylic acid. Anthracene-9-carboxyradical is also formed by irradiation at 308 nm of (99).100 The polymer supportedthiazole thione (100) has been developed as a means of producing free alkoxyradicals.101 Irradiation liberates the R radical from the substrate.


4.2 Reactions of Miscellaneous Haloketones and Acid Chlorides. — The photo-chemical reactivity of a series of 2-substituted N-(2-halogenoalkanoyl) anilinesand cyclic amines has been reported.102 Fission of a C—C bond occurs onirradiation of the iodocycloalkanones (101). This is an extension of earlierwork103 and the present report details the bond fission processes in alcohol (R3

OH) solution.104 The principal products are the esters (102) that are formed inyields of 65—88%. The authors suggest that the photochemical reaction broughtabout by initial C—I bond fission using wavelengths �300 nm involves anelectron transfer with the resultant formation of the ions (103), for example. Thereactions are carried out in a trace of water and it is at this stage that water addsto the cation to afford the 2-hydroxycyclohexanone. Although there is noexperimental support for the next step of the sequence the authors104 propose theformation of the alkoxy radical (104) which then undergoes the necessary C—Cbond fission that ultimately yields the products.

4.3 Other Processes. — The fragment HCO is formed on irradiation at 193 nmof propenal.105 The photochemical reaction between the dianions of phenylaceticacid (105) and aryl halides has been studied.106 The reaction is dependent on thenature of the counterion and with K� only the biphenylacetic acid (106) isformed. Mixtures of (106) and (107) are obtained using the Na� salt while withLi� only �-arylation is observed affording (107). A study of the alkylation ofglycine derivatives (108) has been reported.107 The process involves the irradi-

Photochemistry66

ation of the glycine in solution containing di-t-butyl peroxide, benzophenoneand toluene. Several products are formed as shown in the Scheme. The condi-tions for the formation of the principal product (109) have been optimised.Irradiation of mixtures of the pyran (110) with a variety of ketones has beenreported.108 The excited-state ketones abstract hydrogen from the 4-position ofthe pyran and combination between the resultant radicals affords the substitutedderivatives (111).A new photolabile linker (112) has been described which on irradiation at 350

nm in THF with tributyltin hydride results in liberation of the indole in 55%


yield.109 The Norrish Type I cleavage in (113) affords a radical that allows for therelease of the immobilised alcohols.110 A copolymer containing the t-butyl-4-vinylphenyl carbonate (114) moiety undergoes photochemical decompositionand this has been used as a means of producing a photopattern.111 A newphotoremovable protecting group containing a 2,5-dimethylphenacyl chromo-phore112 and a photolabile linker based on 3�-methoxybenzoin have been

Photochemistry68

described.113 Further developments in the study of photoremovable protectinggroups have extended the range of absorption of such species.114

A detailed investigation of photoremovable protecting groups based on (115)and (116) has been carried out.115 The reactions involve single electron transferwith the generation of zwitterionic biradicals such as (117) formed from theirradiation of (115). The collapse of the intermediate (117) liberates acetic acid.Peptide synthesis based on t-Boc chemistry has been described.116

5 References

1. Y. Ito, Mol. Supramol. Photochem., 1999, 3(Organic Molecular Photochemistry), 1(Chem. Abstr., 2000, 133, 163775).

2. K. Venkatesan,Mol. Solid State, 1999, 3, 89 (Chem. Abstr., 2000, 133, 127499).3. V. Ramamurthy, R. J. Robbin, K. J. Thomas and P. H. Lakshminarasimhan,Mol.

Solid State, 1999, 2, 63 (Chem. Abstr., 2000, 132, 307878).4. V. Ramamurthy, J. Photochem. Photobiol.,C, 2000, 1, 145 (Chem. Abstr., 2001, 134,

245079).5. A. Joy and V. Ramamurthy, Chem.-Eur. J., 2000, 6, 1287.6. H. Yamashita andM. Anpo,Photofunct.Zeolites, 2000, 99 (Chem.Abstr., 2001, 134,

34935).


7. H. Yamashita, M. Nishimura, H. Bessho, S. Takada, T. Nakajima, M. Hada, H.Nakatsuji and M. Anpo, Res. Chem. Intermed., 2001, 27, 89 (Chem. Abstr., 2001,309583).

8. A. Albini,Chem. BeginningThirdMillennium,Proc.Ger.-Ital.Meet. 1999, 83 (Chem.Abstr., 2000, 133, 281321).

9. S. R. L. Everitt and Y. Inoue,Mol. Supramol. Photochem., 1999, 3(Organic Molecu-lar Photochemistry), 71 (Chem. Abstr., 2000, 133, 163776).

10. W. M. Nau, EPA Newsl., 2000, 70, 6 (Chem. Abstr., 2001, 134, 287681).11. A. K. Singh, A. C. Bhasikuttan, D. K. Palit and J. P. Mittal, J. Phys. Chem.A, 2000,

104, 7002.12. Y.-M. Xu,Huaxue Xuebao, 2000, 58, 572 (Chem. Abstr., 2000, 388393).13. Y. Aikawa, T. Shimada, H. Tachibana and H. Inoue, J. Photosci., 1999, 6, 165

(Chem. Abstr., 2000, 133, 266453).14. A. Beeby and A. E. Jones, Photochem. Photobiol., 2000, 72, 10.15. M. Emrich and P. Warneck, J. Phys. Chem. A, 2000, 104, 9436.16. C. L. Berrie, C. A. Longfellow, A. G. Suits andY. T. Lee, J.Phys.Chem.A, 2001, 105,

2557.17. I. H. Suzuki and N. Saito, Chem. Phys., 2000, 253, 351.18. D. Liu, W.-H. Fang and X.-Y. Fu, Chem. Phys. Lett., 2000, 325, 86.19. S. Aloisio and J. S. Francisco,Chem. Phys. Lett., 2000, 329, 179 (Chem.Abstr., 2000,

751354).20. P. R. McCurdy, E. R. Vorpagel and W. P. Hess, J. Chem. Phys., 2001, 114, 169

(Chem. Abstr., 2001, 623).21. Q. Li, R. T. Carter and J. R. Huber,Chem. Phys. Lett., 2000, 323, 105 (Chem. Abstr.,

2000, 402726).22. S. Jockusch, M. S. Landis, B. Freiermuth and N. J. Turro, Macromolecules, 2001,

34, 1619 (Chem. Abstr., 2001, 134, 318508).23. N. J. Turro, X.-G. Lei, S. F. Niu, Z. Liu, S. Jockusch andM. F. Ottaviana,Org.Lett.,

2000, 2, 3991.24. N. T. Turro, X.-G. Lei, W. Li, Z. Liu, A. McDermott, M. F. Ottaviani and L.

Abrams, J. Am. Chem. Soc., 2000, 122, 11649.25. N. J. Turro, M. H. Kleinman and E. Karatekin, Angew. Chem. Int. Ed. Engl., 2000,

39, 4436.26. X. Zhang and W. M. Nau, J. Phys. Org. Chem., 2000, 13, 634 (Chem. Abstr., 2001,

134, 71284).27. D. Liu,W. Fang andX. Fu, Wuli HuaxueXuebao, 2000, 16, 961 (Chem.Abstr., 2000,

864708).28. R. Alcazar, P. Ramirez, R. Vicente, M. J. Mancheno, M. A. Sierra and M. Gomez-

Gallego,Heterocycles, 2001, 55 511 (Chem. Abstr., 2001, 211953).29. S. Y. Jeong and B. S. Park, J. Photosci., 2000, 7, 35 (Chem. Abstr., 2000, 799691).30. C. Y. Wu, Y. J. Ziong, J. X. Wang and F. A. Kong, Chin. Chem. Lett., 2000, 11, 545

(Chem. Abstr., 2000, 512993).31. T. Hasegawa, M. Kajiyama and Y. Yamazaki, J. Phys. Org. Chem., 2000, 13, 437

(Chem. Abstr., 2000, 587457).32. P. Klan, J. Janosek and Z. Kriz, J. Photochem. Photobiol. A: Chem., 2000, 134,

37.33. T. J. Brett and J. J. Stezowski, Chem. Commun., 2000, 857.34. A. J. Kell, D. L. B. Stringle and M. S. Workentin, Org. Lett., 2000, 2, 3381.35. S. Faure, J. D. Connolly, C. O. Fakunle and O. Piva, Tetrahedron, 2000, 56, 9647.36. P. Wessig and O. Muhling, Angew. Chem. Int. Ed. Engl., 2001, 40, 1064.

Photochemistry70

37. E. Cheung, M. R. Netherton, J. R. Scheffer, J. Trotter and A. Zenova, TetrahedronLett., 2000, 41, 9673.

38. E. Cheung, T. Kang, J. R. Scheffer and J. Trotter, Chem. Commun., 2000, 2309.39. S. Rochat, J. Y. de Saint Laumer and A. Herrmann, Helv. Chim. Acta, 2000, 83,

1645.40. P. Wessig, U. Lindemann and J. Schwarz, J. Inf. Rec., 2000, 25, 65 (Chem. Abstr.,

2001, 30190; also Chem. Abstr., 2001, 134, 237034).41. J. A. Pincock, S. Rifai and R. Stefanova, Can. J. Chem., 2001, 79, 63.42. K. Morley and J. A. Pincock, J. Org. Chem., 2001, 66, 2995.43. P. Wessig, U. Lindemann and O. Surygina, J. Inf.Rec., 2000, 25, 245 (Chem.Abstr.,

2001, 30214; also Chem. Abstr., 2001, 134, 252211).44. H. Nishino, A. Kosaka, G. A. Hembury, H. Shitomi, H. Onuki and Y. Inoue, Org.

Lett., 2001, 3, 921.45. X. Zhao and W. Schwack, Toxicol. Environ. Chem., 2000, 74, 217 (Chem. Abstr.,

2000, 579279; Chem. Abstr., 2000, 133, 303332).46. T. Suzuki, T. Omori and T. Ichimura, J. Phys. Chem. A, 2000, 104, 11671.47. T. K. Sarkar, S. K. Ghosh, J. N. Moorthy, J.-M. Fang, S. K. Nandy, N.

Sathyamurthy and D. Chakraborty, Tetrahedron Lett., 2000, 41, 6909.48. H. C. Ludemann, F. Hillenkamp and R. W. Redmond, J. Phys. Chem.A, 2000, 104,

3884.49. H. Mishra, H. C. Joshi, H. B. Tripathi, S. Maheshwary, N. Sathyamurthy, M.

Panda and J. Chandrasekhar, J. Photochem. Photobiol. A- Chem., 2001, 139, 23.50. J. A. Organero, M. Moreno, L. Santos, J. M. Lluch and A. Douhal, J. Phys. Chem.

A, 2000, 104, 8424.51. J. D. Geerlings, C. A. G. O. Varma and M. C. van Hemert, J. Phys. Chem. A, 2000,

104, 7409.52. K. Mikami and Y. Okubo, Synlett, 2000, 1135.53. E. Cheung, K. Rademacher, J. R. Scheffer and J. Trotter, Tetrahedron, 2000, 56,

6739.54. G. A. Kraus and N. Zhang, J. Org. Chem., 2000, 65, 5644.55. T. Horaguchi, Trends Heterocycl. Chem., 1999, 6, 1 (Chem. Abstr., 2001, 134,

207657).56. H. Kim, T. G. Kim, J. Hahn, D. J. Jang, D.-J. Chang and B. S. Park, J. Phys. Chem.

A, 2001, 105, 3555.57. W. Adam, V. R. Stegmann and S. Weinkotz, J. Am. Chem. Soc., 2001, 123, 2452.58. A. G. Griesbeck, M. Fiege, S. Bondock and M. S. Gudipati, Org. Lett., 2000, 2,

3623.59. M. D’Auria and R. Racioppi, ARKIVOC, 2000, 1, 145 (Chem. Abstr., 2001, 134,

49085).60. M. Abe, E. Torii and M. Nojima, J. Org. Chem., 2000, 65, 3426.61. T. Bach, H. Brummerhop and K. Harms, Chem.-Eur. J., 2000, 6, 3838.62. T. Bach, Synlett, 2000, 1699.63. C. VanWolven,D. Dopp andM.A. Fischer, J. Inf.Rec., 2000, 25, 209 (Chem.Abstr.,

2001, 134, 259105).64. R. J. H. Klein-Douwel, J. Jorge, G. P. Smith and D. R. Crosley,Appl.Opt., 2000, 39,

3712 (Chem. Abstr., 2000, 572730).65. X. Li, J. M. Millam and H. B. Schlegel, J. Chem. Phys., 2000, 113, 10062.66. A. L. Kaledin, J. Seong and K. Morokuma, J. Phys. Chem. A, 2001, 105, 2731.67. G. P. Glass, S. S. Kumaran and J. V. Michael, J. Phys. Chem. A, 2000, 104, 8360.68. M. L. Costen, H. Katayanagi and G. E. Hall, J. Phys. Chem. A, 2000, 104, 10247.


69. J. Ramnauth and E. Lee-Ruff, Can. J. Chem., 2001, 79, 114.70. M. A. Miranda, E. Font-Sanchis, J. Perez-Prieto and J. C. Scaiano, J. Org. Chem.,

2001, 66, 2717.71. T. Sato, H. Niino and A. Yabe, Chem. Commun., 2000, 1205.72. H. Su, Y. He, F. Kong, W. Fang and R. Liu, J. Chem. Phys., 2000, 113, 1891.73. O. Heintz, D. Robert and J. V.Weber, J.Photochem.Photobiol.A:Chem., 2000, 135,

77.74. C. Guillard, J. Photochem. Photobiol. A: Chem., 2000, 135, 65.75. W. H. Fang and R. Z. Liu, J. Am. Chem. Soc., 2000, 122, 10886.76. G. L. Hug, M. Bonifacic, K.-D. Asmus and D. A. Armstrong, J. Phys. Chem. B,

2000, 104, 6674.77. A. Rzeska, J. Malicka, K. Stachowiak, A. Szymanska, L. Lankiewicz andW.Wiczk,

J. Photochem. Photobiol. A- Chem., 2001, 140, 21.78. S. Ikeda, S. Murata, K. Ishii and H. Hamaguchi, Bull. Chem. Soc. Jpn., 2000, 73,

2783.79. A. Itoh, T. Kodama, S. Inagaki and Y. Masaki, Chem. Lett., 2000, 542.80. M. H. Habibi and S. Farhadi, Asian Chem. Lett., 1998, 2, 111 (Chem. Abstr., 2001,

134, 115697).81. S. Klementova and J. Matouskova, Res. J. Chem. Environ., 2000, 4, 25 (Chem.

Abstr., 2001, 1556).82. M. S. Xu and P. Wan, Chem. Commun., 2000, 2147.83. C. D. Borsarelli, S. E. Braslavsky, S. Sortino, G.Marconi and S. Monti, Photochem.

Photobiol., 2000, 72, 163.84. W.Q. Gu, D. J. Abdallah and R. G.Weiss, J.Photochem.Photobiol.A-Chem., 2001,

139, 79.85. W. Q. Gu and R. G. Weiss, Tetrahedron, 2000, 56, 6913.86. T. Mori, T. Wada and Y. Inoue, Org. Lett., 2000, 2, 3401.87. S. Samajadar, A. Ghatak, S. Banerjee and S. Ghosh, Tetrahedron, 2001, 57, 2011.88. H. Kawata, T. Kumagai, T. Morita and S. Niizuma, J. Photochem. Photobiol. A:

Chem., 2001, 138, 281.89. M. S. A. Abdel-Mottaleb, H. R. Galal, A. F. M. Dessouky, M. El-Naggar, D.

Mekkawi, S. S. Ali and G. M. Attya, Int. J. Photoenergy, 2000, 2, 47 (Chem. Abstr.,2000, 809159).

90. M. Bazin, F. Bosca, M. L. Marin, M. A. Miranda, L. K. Patterson and R. Santus,Photochem. Photobiol., 2000, 72, 451.

91. E. Fasani, A. Albini, M.Mella, M. Rampi and F. B. Negra, J. Photoenergy, 1999, 1,7 (Chem. Abstr., 2000, 629163).

92. Z. Liu, Z. Huang and R. Cai, Spectrochim. Acta, Part A, 2000, 56, 1787 (Chem.Abstr., 2000, 133, 157079).

93. F. Bordin, J. Photoenergy, 1999, 1, 1 (Chem. Abstr., 2000, 629162).94. M.Newcomb,N.Miranda, X. H. Huang andD. Crich, J.Am.Chem. Soc., 2000, 122,

6128.95. B. C. Bales, J. H. Horner, X. H. Huang, M. Newcomb, D. Crich and M. M.

Greenberg, J. Am. Chem. Soc., 2001, 123, 3623.96. S. Y. Choi, J. H. Horner and M. Newcomb, J. Org. Chem., 2000, 65, 4447.97. B. E. Schultz, K. C. Hansen, C. C. Lin and S. I. Chan, J.Org.Chem., 2000, 65, 3244.98. C. Cadot, J. Cossy and P. I. Dalko, Chem. Commun., 2000, 1017.99. Y. Saitoh, K. Segawa, H. Itoh and H. Sakuragi, Tetrahedron Lett., 2000, 41, 8353.100. Y. Saitoh, M. Kaneko, K. Segawa, H. Itoh and H. Sakuragi, Chem. Lett., 2001, 82.101. L. De Luca, G. Giacomelli, G. Porcu and M. Taddei, Org. Lett., 2001, 3, 855.

Photochemistry72

102. T. Nishio, H. Asai and T. Miyazaki,Helv. Chim. Acta, 2000, 83, 1475.103. S. J. Ji, E. Takahashi, T. T. Takahashi and C. A. Horiuchi, Tetrahedron Lett., 1999,

40, 9263104. S. J. Ji and C. A. Horiuchi, Bull. Chem. Soc. Jpn., 2000, 73, 1645.105. Y.-T. Kao, W.-C. Chen, C.-H. Yu and I-C. Chen, J. Chem. Phys., 2001, 114, 8964.106. G. C. Nwokogu, J. W.Wong, T. D. Greenwood and J. F. Wolfe, Org. Lett., 2000, 2,

2643.107. H. S. Knowles, K. Hunt and A. F. Parsons, Tetrahedron Lett., 2000, 41, 7121.108. D. Saleur, J. P. Bouillon, C. Portella and N. Hoffmann,Tetrahedron Lett., 2000, 41,

5199.109. J. R. Horton, L. M. Stamp and A. Routledge, Tetrahedron Lett., 2000, 41, 9181.110. R. Glatthar and B., Org. Lett., 2000, 2, 2315.111. T. S. Li, M. Mitsuishi and T. Miyashita, Chem. Lett., 2000, 608.112. P. Klan, M. Zabadal and D. Heger, Org. Lett., 2000, 2, 1569.113. E. R. Felder, P. Petriella and P. Schneider, Proc. ECSOC—1: First Int. Electron.

Conf. Synth. Org. Chem., 1997—1998, 563 (Chem. Abstr., 2001, 134, 193007).114. P. G. Conrad, R. S. Givens, J. F.W.Weber andK.Kandler,Org.Lett., 2000, 2, 1545.115. K. Lee and D. E. Falvey, J. Am. Chem. Soc., 2000, 122, 9361.116. J. P. Pellois,W.Wang andX. Gao, J.Comb.Chem., 2000, 2, 355 (Chem.Abstr., 2000,

133, 150874).


2Enone Cycloadditions and Rearrangements:Photoreactions of Dienones and Quinones


1 Cycloaddition Reactions

1.1 Intermolecular Cycloaddition. — 1.1.1 Open-chain Systems. The results ofdetailed calculations on the photochemical addition of alkenes to �,�-un-saturated enones such as acrolein have been published.1 Mixtures of (2��2�)-photodimers are formed on irradiation of the furan derivatives (1). Similarbehaviour is reported for the corresponding thiophene derivatives.2

Panja et al. have reported details of a study into the charge transfer exhibitedby 4-N,N-dimethylaminocinnamaldehyde encapsulated in �-cyclodextrin.3 Afurther study of this system has examined the photodynamics of 4-N,N-dimethylaminocinnamaldehyde and the authors have suggested that the anom-alous fluorescence in polar aprotic solvents can be attributable to a twistedintramolecular charge transfer.4 The crystal structures of the trans-cinnamides(2) have been determined and irradiation of the crystals results in (2��2�)-photodimerisation without destruction of the crystalline form.5 A study of thedimerisation of derivatised cinnamates (3) has been reported and interestingly,while cinnamate esters have often been shown to be reluctant to dimerise unlikefree cinnamic acid, in the present investigation intermolecular complexation andirradiation of (3) affords the three cyclobutane derivatives (4—6).6 Similar quan-tum yields are observed when (3) is complexed with 0.5 mole of (7), but the majorchange occurs when (8) is used as the complexing agent, when better quantumyields for the dimerisation were observed. The cinnamides (9) also undergo(2��2�)-cycloaddition to afford the dimers (10) and (11) in variable yields withcinnamide (9a) itself giving only 18%of the dimer.7Control over the dimerisationof these cinnamides (9) can be exercised using hydrogen bonding within co-


74

crystals prepared using a variety of diacids such as (12). Some of these results areshown in Scheme 1. Photodimerisation of a series of phenyl-substituted cinna-mates has been reported.8 The (2��2�)-photodimerisation of cinnamic acid andsome of its derivatives has been studied using Raman spectroscopy,9 and amolecular dynamic study of the dimerisation of 3- and 4-cyanocinnamic acids ina microcrystalline environment has been carried out.10

1.1.2 Additions to Cyclopentenones and Related Systems. Chow et al. have de-scribed further studies on the photoaddition of dibenzoylmethanatoboron di-fluoride which arises from its singlet-excited state to enones such as cyclo-

II/2: Enone Cycloadditions and Rearrangements 75

pentenones.11 The cycloaddition of alkynes to the bis-enone (13) results in theformation of the adducts (14) which are themselves photochemically reactive andundergo ring opening to (15).12 Pete and co-workers13 have reported the results ofa study involving the sensitised (4,4�-dimethoxybenzophenone) cycloadditionreactions of the enone (16) to suitably substituted amine derivatives such as (17).13

The results obtained are described by the authors as tandem addition reactionsthat are both efficient and diastereoselective. A typical example is the additionillustrated in Scheme 2 for the amine (17) that affords the four products. Thereactionwas extended to use the aminoalkyne (18) which yields the two products(19) and (20) in 32 and 29%yields, respectively. A newmethod for the synthesis ofchiral cycloaminobutyrolactones has been devised based on the photochemicaladdition of cyclic amines to 5-(R)-(1)-menthyloxy-2(5H)-furanone.14 The addi-tions are both regio- and stereoselective. The enone (16) also undergoes efficientaddition of amines such as (21) to afford a diastereoisomeric mixture of (22).15,16

The reactions are carried out in acetonitrile and use excited aromatic ketones asthe means of generating free radicals. The best results are obtained using xan-thone or dimethoxybenzophenone.

Photochemistry76

(2��2�)-Photocycloaddition has been used in a route to the synthesis ofbyssochlamic acid (23).17The reaction involves the synthesis of (24) by cycloaddi-tion of pent-1-ene to the anhydride (25). This product is subsequently trans-formed into the bis-anhydride (26) which on irradiation affords the two adducts(27) and (28). These adducts then undergo thermal ring-opening and furtherchemical transformation ultimately affords the desired product (23).

1.1.3 Additions to Cyclohexenones and Related Systems. Several sets of dia-stereoisomeric adducts are formed on the photochemical addition of 3-methyl-cyclohex-2-en-1-one to C70 fullerene.18 On irradiation (��340 nm) in benzenesolution, the new enones (29) undergo addition to eneynes or alkenes.19 For


2-methylbut-1-en-3-yne, the products are the cycloadducts (30) and (31). Itshould be noted that the addition reactions take place exclusively to the alkynemoiety of the ene—yne system. This cycloaddition also occurs with 2,3-dimethyl-but-2-ene when the principal products are the (2��2�) cycloadducts (32) and theisochromenes (33). Cholest-4-ene-3-one does not dimerise when irradiated insolution but in the solid state photodimerisation occurs to yield (34) and (35).20

The iodonium ylide (36) undergoes photochemically induced addition toalkenes such as (37) to give (38) in high yield.21 Bach andBergmann have reportedthe efficient cyclisations encountered between the enone (39) and the alkenes(40).22 These photoreactions are carried out in the presence of the templatemolecule (41) to which the enone binds: this ensures that the cycloadditions takeplace with high diastereoselectivity as illustrated in (42). The diastereoselectivityobserved is in the range of 81—92% when the reactions are carried out at lowtemperature (�60 °C). Brett and co-workers have determined the packing of thetwo coumarins (43) in �-cyclodextrin.23,24 Irradiation of these complexes led tothe antihead-to-tail dimers (44) reflecting the orientation of the coumarinswithin the complexes. The photophysical properties of the coumarin (45) havealso been investigated,25 and the influence of substituents on the spectra of thecoumarins (46) and (47) contained in �-cyclodextrin has been assessed.26 Thedynamics for the complexation of flavone and chromone in their triplet states

Photochemistry78

within �-cyclodextrin has been studied,27 and a series of photolabile protectinggroups has been described in a recent patent application.28One example of thislatter process is the enone (48) which on irradiation at 365 nm at pH 7.2undergoes facile cleavage to yield glutamate in 98.7%.

Irradiation at 350 nm in acetonitrile of the isocoumarin derivative (49) resultsin the formation of the dimer (50) in high yield.29The isocoumarin also undergoesaddition to alkenes such as tetrachloroethene with wavelengths �390 nm toafford cyclobutanes. Prolonged irradiation gives a mixture of bis adducts. Enan-


tioselective (2��2�)-photo-cycloadditions have been described for the enones(51), (52) and (53).30 Irradiation of (51) as an inclusion complex with (54) results inthe formation of the dimer (55a) with high enantioselectivity. An analogousreaction of (52) using (54b) as the host gives the dimer (55b) with 100% ee.Irradiation of cyclohexenone (53) in the inclusion complex, formed with (56) gavethe dimer (57) with an ee of 58%. Benzopyran-1-one (58) undergoes slow decom-position when irradiated in the solid state which is in contrast to the outcomewith the thio-analogues (59).31Here irradiation of (59a) affords only the cis-head-to-head dimer (60) and the reaction appears to be substituent dependent. Irradi-ation of (59b) in the crystalline state affords a 4:5 mixture of the dimers (60,R�CF3) and (61).

The photochemical cycloaddition reactions of 2H-1-benzopyran-3-carbo-nitrile and 2H-benzothiopyran-3-carbonitrile with 2,3-dimethylbut-2-ene and 2-methylbut-1-en-3-yne have been reported.32 2-Aminopropenenitriles undergo(2��2�)-photocycloaddition to 3-(2-benzothiazolyl)coumarin,33 and a reviewhas highlighted some of the photochemical reactions of N-heterocyclic com-pounds in the solid state.34 The influence of solvent on the S1 and T1 states ofMichler’s ketone has been investigated.35

1.2 Intramolecular Additions. — Irradiation (sensitised by ketocoumarins) ofthin films of liquid crystalline poly(aryl cinnamate) results in photochemicalcrosslinking.36 The results suggest that the cinnamate ethene bond becomes

Photochemistry80

saturated with the most likely cause of this being photochemical (2��2�)-cycloaddition. Irradiation of percinnamate-modified �-cyclodextrin induces(2��2�)-cycloaddition forming a closed cage.37When the irradiation is carriedout with the modified cyclodextrin encapsulating the pheromone (62) the poresin the resultant cage are sufficiently small to retain the pheromone. The intra-molecular (2��2�)-cycloaddition reaction of (63) has been studied,38 and poly-mers containing p-phenylenediacryloyl chromophores are photochemically re-active and undergo [2�2]-photocycloaddition in solution or in melts.39 Otherphotochemical processes such as the photo-Fries reaction also occur.

1.2.1 Intramolecular Additions to Cyclopentenones. The cycloaddition of aminosubstituted enones (64, n�1 and 2) with cyclopentene yields three products (65),(66) or (67) in ratios dependent upon the substitution pattern of the amino sidechain.40 Only (65) is a cycloaddition product and (66) and (67) result fromintramolecular hydrogen abstraction processes. The enone (68) is also prone torearrange photochemically to give (69, 50%) and (70, 17%) again via hydrogenabstraction paths. Cycloaddition does occur intramolecularly with the deriva-tives (71) to give (72) in moderate to good yields. The photochemical intra-molecular cycloadditions within the enones (73—75) have been used as thesynthetic approach to key intermediates in the synthesis of antagonist ginkolideB.41 Several examples of this cycloaddition and the specificity occurring withinthe reaction were reported as illustrated in Scheme 3.

1.2.2 Additions to Cyclohexenones and Related Systems.The photochemical (irra-diation at 366 nm) intramolecular cyclisations encountered with the enonederivatives (76) in methylene chloride have been reported.42 The reaction makesuse of a chiral side chain to give the adducts (77) and (78) which can be elaboratedinto the two natural products italicene (79) and isoitalicene (80).


Mariano and co-workers43 have described the intramolecular cycloadditionreactions of the perchlorate eniminium salts (81). The cycloadditions generallyoccur with the retention of the geometry of the starting ethene component(Scheme 4). Irradiation of the prochiral quinolone (82) results in the formation ofthe diastereoisomeric products (83) and (84).44 A study of how this intramolecularphotocycloaddition was affected by chiral substrates was carried out using theimides (85), (86) and (87). The cycloadditions encountered in the presence of theimides take place usually in high yield when (86) and (87) are used. The reactionsare also temperature dependent with the best enantiomeric excesses being ob-tained at �60 °C. The scope of the intramolecular (2��2�)-photoadditionswithin the derivatives of dioxenones has been assessed.45,46 The irradiation at 300nm of (88) in acetonitrile/acetone (9:1) affords the cycloadduct (89) as a 1:1mixture of diastereoisomers which can be converted into compound (90) in twosteps in a yield of 52%. Stereoelectronic effects are thought to control theoutcome of the efficient photocyclisation (300 nm) of (91) to yield the bi-cyclo[2.2.0]hexane (92). Further evidence for the stereoelectronic control of thecyclisationwas demonstrated by the cyclisation of (93) into (94) while (95) affords(96). The reaction seems to be quite robust and several derivatives were reported.

Photochemistry82

Compound (97) is reported to behave as a photo-activated molecular switch.Thus irradiation at 350 nm induces (2��2�)-cycloaddition between thecoumarin moieties, and the cyclobutane ring is cleaved to reform the open chainsystem with 254 nm radiation.47


2 Rearrangement Reactions

2.1 �,�-Unsaturated Systems. — 2.1.1 Isomerisation. The polarised excitedstate of �-allenic ketones can be populated by n�* excitation of the carbonylfunction and facile addition of methanol then results in the formation of esters.48

A detailed study of the isomerisation in the unsaturated esters and aldehydes (98)and (99) has been published.49 trans—cis-Isomerisation is also observed with thesubstituted naphthylacrylates (100).50 In this case, direct irradiation gives photo-stationary state compositions enriched in the Z-isomers (80%) while the reverseoccurs when the isomerisation is brought about under sensitised conditions.Photoisomerisation of p-coumaric acid in water takes place with a quantumyield of 0.46 and the results suggest that hydrogen bonding occurs between theacid and water.51 An ab initio study of the potential surfaces for twisting in the

Photochemistry84

anionic form of coumaric acid has been reported,52 and the photochemicalisomerisation of trans-urocanic acid (101) to the cis-isomer is most efficient when(101) is irradiated into the tail of its absorption profile.53 No isomerisation isobserved when the molecule is irradiated in the 260—285 nm region where itabsorbs most strongly. Molecular dynamics calculations have been carried outon the crystalline enone (102),54 and the E,Z-isomerisation of the ketoacids (103,104) has been investigated.55

The isomerisation of the flavanones (105) is dependent on the substitutionpattern.56 The labelled probe (106) for binding specifically to tentoxin bindingsites has been synthesised and is reactive on irradiation at 366 nm in methanolsolutions.57 The behaviour of all-trans-retinal with both hydrogen and electron


donors has been reported.58 A study of all-trans-retinal has examined ultrafastelectronic relaxation.59 A patent application has been made covering somereversibly photoisomerisable cycloalkenones such as (Z)-cycloocten-4-one.60

Paquette and his co-workers61 have used photochemical isomerisation of anethene bond as a step in a synthesis of scerophytin A and B.

Irradiation of the chalcone derivative (107) shows that only cis—trans-isomerisation occurs,62 and the photoreactions of the chalcone (108) in bothneutral and acidic solution have been investigated.63 Chalcone (109) exhibitsphotochromism when irradiated in toluene solution,64 and the wavelength de-pendent photochemistry of some chalcone derivatives using a variety ofwavelengths (313, 334, 366 and 406 nm) has been described.65 The photo-chromism of some derivatives of 6-X-4H-3(bicyclo[2.2.1]-5-heptene-2,3-dicar-boximidomethyl)-4-chromones (X�Me, Cl or NO2) has been studied66 as havethe photochromic properties of some novel anellated chromenes.67The substitu-tion pattern around these latter molecules has provided more stable colouredforms. A detailed examination of the hydrogen bonding dynamics between thecoumarin (110) and a variety of solvents has been reported,68 and photophysicaldata have been collected for a series of thio- and seleno-psoralens.69

2.1.2 Hydrogen Abstraction Reactions. Irradiation of the ascorbic acid derivative(111) in the presence of quinones results in its oxidation to the triketone (112)with concomitant reduction of the quinone.70 Several benzoquinones and naph-thoquinones were examined in this process and the yields of the corresponding

Photochemistry86

hydroquinones are usually high. No evidence for the formation of cycloadducts,such as oxetanes, was obtained.

2.1.3 Rearrangement Reactions. A detailed report has been published dealingwith the photochemical conversion of the N-acetyl �-dehydrophenylalanine(113) into the cis,trans-mixture of the azetine (114, 42% total) and the isoquino-line (115, 24%).71 Irradiation of the dienamides (116) in a mixed solvent (ben-zene/toluene/methanol) in the presence of sodium tetrahydroborate results inefficient cyclisation to yield (117) which is considered to be a convenient inter-mediate in the synthesis of (S)-(�)-pipecoline.72 A further study on the photo-chemical reactivity of o-acylstyrenes (e.g. 118) has been reported.73 In this studythe work of Kessar74 was reinvestigated and shown to be repeatable. With thederivatives (119) the cycloadditions afford the oxabicyclo[3.2.1]octanes (120)and (121). The authors73 argue that a ketene cannot be involved in these examplesand that the key intermediate is (122) which undergoes addition to the vinylgroup of (119) to afford the final products. The enone (123) has been incorporatedinto inclusion complexes with a variety of guest compounds such as benzenederivatives, chlorinated hydrocarbons and ketones, and irradiation of thesecrystalline complexes induces a reversible colour change even though the enone(123) is itself colourless.75

SET reactions can be used in the oxidation of siloxycyclopropanes. Thistreatment brings about fragmentation with the formation of �-keto radicals.76 Afurther communication has given an account of the SET processes betweentriethylamine and �-cyclopropylketones which induces ring opening to give ahomoallyl radical that cyclises with the pendant side chains.77


2.2 �,�-Unsaturated Systems. — 2.2.1 The Oxa Di-�-methane Reaction and Re-lated Processes. Brief irradiation at 300 nm through a Pyrex filter in acetonitrilesolution brings about the facile conversion of the bridged diketones (124) into theoctenediones (125).78 These rearrangements are typical examples of 1,3-acyl mi-grations occurring within a �,�-unsaturated enone. The oxa-di-�-methane reac-tivity of the enones (126) has been studied, and acetone-sensitised irradiationbrings about conversion to the tetracyclic compounds (127) which have beenused in the synthesis of naturally occurring compounds such as coriolin (128).79

The photochemical cyclisation of 11-methyl-3-oxa-tricyclo[5.2.2.01,5]unde-cenones has been investigated,80 and sensitised irradiation of the enone (129) inhexane solution affords only the 1,3-acyl migrated product (130) but in methanolboth (130) and (131) are formed in a ratio of 78:22.81 The 1,3-migration product(130) arises from the n�* state while the oxa-di-�-methane product (131) arisesfrom the ��* state. A dramatic change is observed when the reactions are carriedout in zeolite cages and the ��* state product (131) becomes predominant. Thischange is a result of a lowering of the energy of the ��* state by co-ordinationwith Li�. A similar observation is made with the enone (132) as shown in Scheme5 where the di-�-methane rearrangement products (133) and (134) are formed.Zimmerman and co-workers have studied the photochemical rearrangement of(135) in a variety of crystalline media.82 The outcome of the rearrangement isdependent upon the host molecule and with (136) as the host rearrangement

Photochemistry88

takes place to afford products where the phenyl group has migrated, but withhosts (137) and (138) exclusive cyanophenyl migration occurs. A study of theinfluence of chiral auxiliaries on the outcome of photochemical processes in theconstrained environment of zeolites has been reported.83For example, the enone(139) rearranges to the products (140) and (141) with des of 81% when KYfaujasite is used. The influence of the cation was also examined.

2.2.2 Other Rearrangements. Paquette and co-workers84 have published a fullreport on the new photochemical reactivity of cyclopentenones reported earlierin note form.85 This novel process was uncovered during a study of the photo-chemical isomerisation of (142) which on irradiation in dioxane affords the twoproducts (143) and (144) in 68%and 6%, respectively. In a less polar solvent suchas benzene the isomerisation gives the same products but in the remarkablydifferent yields of 7 and 52% respectively. The reaction is more complex when(142) has a deprotected alcohol function and this complexity is a result of theadditional reactivity of the second hydroxy group. The mechanism by which thisrearrangement occurs was probed using compound (145). Here an analogous


rearrangement to that encountered with (142) was observed. The isomeric enone(146) behaves somewhat differently yielding two products identified as (147) and(148). The authors84,85 suggest that the reaction involves cyclisation to the biradi-cal (149) which rearranges to the ketene (150) and this is the intermediate for theproducts.Chang and Park86 report that the irradiation of the bicyclohexenones (151) at

365 nm converts them efficiently (high chemical and quantum yields) into thenaphthols (152). The reaction arises from the triplet state and both sensitisationand quenching experiments have been used to substantiate this claim. The ketene(153) is considered to be the intermediate but attempts to trap this were unsuc-cessful.

Photochemistry90

3 Photoreactions of Thymines and Related Compounds

3.1 Photoreactions of Pyridones. — The chiral host (154) has been employed inthe reactions of the pyridones shown in Scheme 6.87 Thus, irradiation affords theDewar pyridones when ether derivatives are used. With pyridones (X�H) highenantioselective addition to cyclopentadiene affords the derivative (155). Gauvryand Huet88 have used the method originally described by Dilling89 for thesynthesis of (156) from 2-hydroxypyridine (157) and have established that thereaction needs to be carried out in dilute solution (10�3 M) and with longirradiation periods to ensure a high yield of product. The photochemical cyclisa-tion of (158) to afford (159) has been reported previously and this has now beenused as a key intermediate in the synthesis of taxol.90 Tautomerism results onirradiation of 1,3,6,8,10-pentamethyl- and 1,3,5,7,9-pentamethylcycloocta-pyrimidine-2,4-diones.91

3.2 Photoreactions of Thymines etc. — Uracil and cytosine undergo photooxi-dation on irradiation in the presence of peroxydiphosphate.92 Titanium dioxide


mediated oxidation of uracil, thymine and 6-methyluracil is retarded by thepresence of Cu2�,93 and uracil undergoes photochemical addition when irra-diated in phosphate buffered saline to give 6-phosphoryloxyuracil.94

Irradiation of 6-chloro-1,3-dimethyluracil in TFA at low temperatures and inthe presence of mesitylene affords 1,3,5,7,9-pentamethylcyclooctapyrimidine-2,4-dione which is also photochemically reactive.95 Irradiation of 6-chloro-1,3-dimethyluracil in mesitylene with added TFA for one hour affords a 1,3,6,8,10-pentamethylcyclooctapyrimidine derivative as well as diazapentacyclo-[6.4.0.01,3.02,5.04,8]dodecane.96

The cyclobutane dimer formed from 1,3-dimethyluracil undergoes photo-chemical cleavage to the monomer when irradiated in the presence of (1,10-phenanthroline)tricarbonylrhenium() chloride as the sensitiser.97 Changes in themass spectral intensity shown after multiphoton ionisation of thymine and uracilclusters have been interpreted as evidence for photodimerisation.98 1-Alkyl-thymine dimerisation has been studied in the crystalline phase and the length ofthe chain is found to affect the crystal structure and the dimerisation process.99

Thus, 1-pentyl, 1-nonyl and 1-decylthymines give a trans,syn-photodimer while1-octylthymine affords a trans,anti-dimer. The photocrosslinking of PVA con-taining uracil and thymine units results from (2��2�)-cycloadditionbetween the

Photochemistry92

uracil and thymine groups and this has been discussed in a short review.100 Astudy of the photochemical reactivity of thymine in solid layers on a quartzsurface using ��280 nm has revealed that dimerisation occurs in the crystallinephase of the layers.101 The outcome of the irradiation of polymer films containingthymine derivatives with long alkyl chains has been reported.102 The thin poly-mer films were irradiated at 280 nm and dimerisation of the thymine units wasobserved in a rate of dimerisation which was directly related to the length of thealkyl chains (i.e. increasing length required longer irradiation times). Annealingthe films diminished the photodimerisation and this was thought to be due to theproduction of inactive micro crystals.The oxetanes (160) are formed by the addition of aryl ketones or aldehydes to

thymine. A laser flash study of their decomposition has shown that they decom-pose adiabatically to yield ground-state thymine and triplet-state ketone oraldehyde. Results of this type are considered to have implications in the generalarea of DNA photo-damage and photo-enzymatic repair.103 Radical ion inter-mediates have been demonstrated to be involved in the sensitised repair ofthymine oxetane.104 The cyanobenzophenone derivative (161) undergoes photo-induced SET reactions in duplex DNA systems.105 The template-directed addi-tion reactions between (162) and the vinyldeoxyuridine (163) have been inves-tigated using 366 nm radiation which gives the cycloadduct (164).106,107 A study ofthe formation of cyclobutane dimers on irradiation of skin cells has been re-ported.108 A detailed investigation of the photosensitised bond fission processesencountered in the isomeric dihydrothymine dimers (165) and (167) in aqueoussolution has been described.109 The influence of conformational effects on thephotophysical characteristics of some C5—C5� dihydrothymine dimers has beenassessed.110

The photochemical isomerisation of the oxime derivative of cytosine has beenobserved.111 Photo-decomposition of (168) has been used as a route to thecorresponding thyminylmethyl radical (169) and, likewise, the ketone (170) af-fords the 2�-deoxyuridin-1�-yl radical (171) in a Norrish Type I process.112 Thet-butyl ketone (172, R�But) is inert to irradiation at 350 nm and 300 nm but thebenzyl ketone (172, R�PhCH2) is photochemically reactive and provides a routeto the radical (173) again by a Norrish Type I fission process.113


3.3 Miscellaneous Processes. — Good cross-linking ability has been shown for1,4-bis[n�-(8-psoralenoxyalkyl]piperazine.114 The photochemical activity ofsome psoralen derivatives linked to triplet helix forming oligonucleotides hasbeen examined.115 Laser photoionisation has been used to generate the radicalcations of a variety of psoralens such as the 8-methoxy derivative.116 The reac-tions encountered between these species and biological substrates such as nuc-leotides and amino acids have been studied and the results demonstrate thatelectron-transfer processes are important in the use of psoralens as photoac-tivated drugs. Studies have revealed that tiaprofenic acid sensitises cellular DNAto subsequent irradiation.117 A patent application has been lodged dealing withphotodeprotection of immobilised nucleoside derivatives and the method can beused in the production of DNA chips.118 Further details relating to the photoen-zymatic repair of the so-called (6—4)-photoproducts of DNA has examined the

Photochemistry94

involvement of oxetane and azetidine intermediates and the role by electron-transfer processes.119

The driving force dependence of photoinduced electron-transfer dynamics induplexDNA has been investigated for 16 synthetic DNA hairpins which have anacceptor chromophore serving as a linker between two complementaryoligonucleotide arms containing a single donor nucleobase located either adjac-ent to the linker or separated from the linker by two unreactive base pairs.120Therate constants for both charge separation and charge recombination processeshave been determined by means of subpicosecond time-resolved transient ab-sorption spectroscopy and the results analysed using quantummechanicalMar-cus theory. This analysis provides intimate details about electron-transfer pro-cesses in DNA including the distance dependence of the electronic couplingbetween the acceptor and nucleobase donor and the solvent and nuclear re-organisation energies. Electron-transfer processes within a series of syntheticDNA hairpins have been studied,121 and the results of a laser flash photolyticstudy of N-acetylhistidine with 2,2�-dipyridyl have been reported.122

4 Photochemistry of Dienones

4.1 Cross-conjugated Dienones. —Details of the photochemical rearrangementof the cyclohexadienones (174) into the bicyclopentenones (175) have beenreported.123 This work was the subject of some earlier publications by the sameauthors.124 The cyclohexadienones (176) aromatise on irradiation at 300 nm andthe resulting phenols (177) are all formed via an alkyl group migration from C-4to C-3 within the cyclohexadienone moiety.125

The santonin derivative (178a) undergoes photochemical conversion into theenone (179) on irradiation in acetic acid.126The product is typical for this type ofrearrangement of a cross-conjugated cyclohexadienone and is a key intermediatein an approach to the synthesis of 4�-hydroxy-8,12-guaianolides. Further usehas been made of the rearrangement of (178b) into (180) in the presence of aceticacid.127 The product (180) of this photochemical reaction has been used in thestereoselective synthesis of 7,11-guaien-8,12-olides. Pedro and co-workers128

have made use of the photo-rearrangement of the dienone (181) under acidicconditions to yield (182) which is a key intermediate in a synthetic approach tooxaguaianolides.


The photochromism exhibited by pyrimidinespirocyclohexadienones hasbeen reviewed.129

4.2 Linearly Conjugated Dienones. — The cyclohexadienone (183) undergoesring opening on irradiation in H2O/THF or MeOH/THF to give the expectedketene (184) which can be trapped by water or methanol and is also photochemi-cally labile undergoing cyclisation to afford the biradical (185).130 This represen-tation is preferred to the alternative, a highly strained allene. 1,3-Silyl migrationoccurs in (185) to give the final products (186). When irradiation is carried out indi-isopropylamine/THF the product isolated is (187) where a second addition ofamine has occurred. Irradiation of cyclohexa-2,4-diene-1-ones is well known tobring about ring opening with the formation of a ketene, and when the reaction iscarried out in the presence of diamines bis-amides are formed.131 Ring-openedamides have been synthesised following the irradiation of some cyclohexa-2,4-dienone derivatives in the presence of amines.132 An argument has been presented

Photochemistry96

that casts doubt on the involvement of the colchicine triplet state in its isomerisminto �- and �-lumicolchicine.133

The cycloadditions undergone by the pyrones (188) with maleimide in thecrystalline phase afford the adducts (189).134

Irradiation of the tropolone ethers (190) results in conversion to the isomer(191) which on prolonged irradiation is converted into (192) by a process thatwas reported many years ago. The rearrangement of these systems has beenstudied in the confines of cyclodextrins to examine the possibility of enantioselec-tive cyclisations and modest ee percentages were obtained as shown in Scheme7.135

5 1,2-, 1,3- and 1,4-Diketones

5.1 Reactions of 1,2-Diketones and Other 1,2-Dicarbonyl Compounds. — Thephotofragmentation of glyoxal involves the singlet-excited state and decay fromthis to the ground state is accompanied by fission into hydrogen and CO.136 Anab initio study on the unimolecular dissociation of glyoxal has been carriedout.137,138

A further patent dealing with the chlorocarbonylation using oxalyl chloride of1,4-dinitrocubane has been filed.139 A study of the irradiation of a series of


1,2-diketones in an outdoor reaction chamber has been reported,140 and photo-lysis frequencies for some dicarbonyl compounds (biacetyl, methyl glyoxal andglyoxal) in the atmosphere have been determined.141 The photodissociation ofmethylglyoxal in the range 290—440 nm has been studied,142 and the excitationspectra of biacetyl have been recorded.143

Further interest has been shown in the control that compounds such as (193)can exercise on photochemical cyclisations in solid-state crystals.144 In thisexample the hydrogen abstraction process within the amide (194) to afford (195)and (196) has been studied. The outcome is different dependent upon the inclu-sion compound used. Thus with (193, n�1) the product formed is (�)-(195) in21% yield and with an ee of 99%. When (193, n�2) is used the product is(�)-(196) obtained in 48% with an ee of 98%.

The photochemical disappearance of 4,4�-dihalosubstituted benzils is en-hanced when ultrasound irradiation is used.145 2-Oxabicyclo[3.2.0]heptane-2,3-dione derivatives are formed on irradiation of 5-phenylfuran-2,3-dione in thepresence of styrene.146 1-Phenylpropane-1,2-dione and butane-2,3-dione havebeen used as sensitisers using visible light for polymerising dental resins.147 Thephotodecomposition of derivatives of 1-phenyl-3-sulfonyloxypropane-1,2-diones has been reported.148

A complex mixture of products is formed on irradiation of indane-1,2,3-trionein methylene chloride solution with 2,3-dimethylbut-2-ene as the addend withhydrogen abstraction, oxetane and dioxene formation being among the reactionmodes observed.149 The irradiation of N-acetylisatin (197) with phenylacetylene,for example, affords the 2:1 cycloadduct (198). Other acetylenes also undergo thisaddition reaction.150 The isatin derivative (197) also undergoes oxetane forma-tion when it is irradiated in the presence of alkenes. For example, the addition ofthe styrene derivatives (199) yields the oxetanes (200).151 The triones (201) arephotochemically reactive when irradiated in the presence of the alkynes (202).152

With diphenylacetylene the polycyclic dione (203, X�H) is obtained as theprincipal product with the minor product (204) resulting from ring opening of anoxetene. The major product from the photoreaction arises by dehydrogenativecyclisation.

5.2 Reactions of 1,3-Diketones. — Irradiation (��* excitation) in a supersonicjet of 1,1,1,5,5,5-hexafluoropentane-2,4-dione in its enol form brings aboutC—OH bond fission and the formation of hydroxy radicals.153 The solid-statephotochemical reactivity of dialkyl 1,3-acetonedicarboxylates (205) has beenexamined and decarbonylation and rebonding between the resultant radical pair

Photochemistry98

to give dialkyl succinates (206) has been described.154 A study of the formation ofthe radicals (207) using laser flash or pulse radiolysis has been reported.155 Theradical (207) is formed initially but is rapidly transformed into the phenoxylradical, and the importance of such species in cancer chemoprevention wasdiscussed. The influence of solvent on the photophysical properties of the nat-urally occurring dione (207a) has been assessed.156

A photophysical study of the excitation of 4-cyclopentene-1,3-dione has beencarried out.157 A review of the photochemical behaviour of compounds such asthe Meldrum’s acid derivative (208) has been published.158 Photochemical reac-tivity of vinyl or allenyl methane derivatives such as methylene Meldrum’s acidhas been reviewed.159 Both (2��2�) and (4��2�)-photocycloadditions occur onirradiation of substituted 1-acetonaphthones and 2-morpholinoacrylonitrile.160


5.3 Reactions of 1,4-Diketones. — Pyrex-filtered irradiation of powderedsamples of benzoylbenzamides (209) results in their transformation into asym-metric phthalimides (210).161 Several mechanistic paths were considered for thisprocess but the results indicate that the preferred route involves a radical pairthought to be (211), and cyclisation within this species and rebonding to give thefinal products. The irradiation of the diketones (212) as suspensions in waterusing Pyrex-filtered light has been examined.162The product from the irradiationof (212a) is the thermally unstable ketene (213b) that is formed by phenylmigrationwithin the cis-diketonemoiety. The stability of the ketene produced bythis rearrangement can be enhanced by a methyl group at the bridgehead as in(212b) and this then yields the ketene (213b) which is thermally stable to around40 °C but at which point readily adds methanol to give the ester (214). Themigration of the phenyl group always occurs in these solid-state reactions fromthe more crowded benzoyl group. This tendency was also demonstrated in theketones (212c) and (212d). The yields of the ketenes obtained are in the 25—40%range.

The homoquinones (215) undergo addition reactions with ethyl vinyl etherfrom irradiation with wavelengths�300 nm in benzene solution under an argonatmosphere.163The reactions exhibit some substitution dependence and additionof the vinyl ether to the homoquinone derivatives (215a—e) yields conventional(2��2�)-cycloadducts identified as (216) in good to excellent yields. Only withthe dibromo derivative (215f) does a different reaction occur and this yields theadduct (217, 57%). All of the processes are thought to involve a biradical

Photochemistry100

presumed to be (218) and C—C bond formation will afford the cyclobutanes. Theauthors suggest that the homoquinone (215f) reacts via the cation (219) whichcyclises by C—O bond formation. A similar series of products is formed using thepositional isomers (220) from which (221) and (222) are formed. Exclusiveoxetane formation occurs on irradiation of 2,6,6-trimethylcyclohex-2-en-1,4-dione in the presence of alkenes.164

Maleimide is reported to exhibit rapid tautomerism in the triplet-excited state.This apparently has prevented the authors165 from measuring the triplet-statequantum yield.N-Alkylation, however, prevents this tautomerism and the quan-tum yield for triplet-excited state formation has been measured as 0.03 for theN-methyl, 0.07 for theN-ethyl and 0.05 for theN-propyl derivatives. Irradiationof the �-hexopyranosyl imide (223) in acetonitrile for 2.5 h brings about itsconversion to the lactam (224).166 The reaction is quite selective and involves ahydrogen abstraction process to give the 1,4-biradical (225) which is the key tothe transformation: cyclisation and rearrangement eventually affords (224) in69% yield. The �-isomer of (223) is also photochemically reactive. The hydrogenabstraction path and cyclisation selectively affords the final product (226, 83%).


Manno derivatives (e.g. 227) were also examined and in this instance twoproducts (228, 20%) and (229, 62%) were obtained. A low regioselectivity isobserved in the photochemical addition of (230) to alkyl-substituted naphtha-lenes and the principal products are the adducts (231).167

The photochemical properties of some derivatives of p-phenylenediacrylicacids have been studied.168 A detailed examination of the photoconversion of amixture of stereoisomers of (232) into the carboxylic acid (233) has been re-ported.169

5.3.1 Phthalimides and Related Compounds. The Pyrex-filtered irradiation of(234) in acetone/acetonitrile has provided a route to the cyclobutane derivatives(235).170 The outcome of the reactions is variable and with (234, R�Me) theproduct (235, R�Me) is obtained in 65% yield while only 8% of (235,R,R�[CH2]4) is obtained from (234, R�[CH2]4). A series of intramolecularcycloaddition reactions of the maleimide derivatives (236) and (237) have beendescribed.171 Products (238) and (239) were obtained in moderate to excellentyields. Such formation follows the normal (2��2�)-addition mode to themaleimide C——N group in (240) and ring opening of the resultant adduct affordsthe final products. The addition via (240) explains the observed regio- andstereo-chemistries.

Photochemistry102

Further examples of the acetone-sensitised reactivity ofN-methylphthalimidewith �-ketocarboxylates (241) have been published and a variety of products arereported as shown in Scheme 8.172 Griesbeck and his co-workers173 have alsodescribed intramolecular examples of the utility of the decarboxylative cyclisa-tions. They have shown that subtle changes in the structure can influence theresults greatly. Thus, the derivative (242) does not cyclise but merely decar-boxylates. However, the derivatives (243) are synthetically useful and irradiationaffords the products (244). More complex structures can be synthesised such as(245) from the irradiation of (246). These cyclisations afford products with 86 and79% ee. Other cyclisations affording (247) have also been described. A furtherexample of decarboxylative cyclisation occurs on irradiation of (248) inacetone/water to give (249).174 Associated with other work on such systems,Griesbeck and co-workers175 have examined the influence of deactivation pro-cesses such as hydrogen bonding upon the photodecarboxylation of �-phthalimido potassium carboxylates. The same workers have also published areview dealing with photocyclisations of this type and others that occurstereoselectively.176

The macrocyclic cyclisations of a series of phthalimide derivatives (250) has

Photochemistry104

been studied.177 Irradiation of (250, n�2 or 3) in acetone results in the quantitat-ive formation of the derivatives (251). Irradiation of (250) in acetonitrile results inloss of the side chain while the derivatives (250, n�5 or 10) behave in the samemanner when irradiated in acetone. The influence of side chain substitution wasalso investigated and (252) is converted into (253) in 61% yield on irradiation inacetone. Other researchers have described interesting additions of 2-phenyl-propene to the phthalimide derivative (254) which give the cyclised product (255)in good yield as a mixture of isomers.178 The reaction was extended to thesynthesis of large ring compounds such as (256). Again the reaction involves asuitably substituted phthalimide and the propene and results in the formation ofthe two isomers (256) in 16 and 14%. Earlier studies by Mariano and hisco-workers demonstrated that efficient cyclisation of (257) could be carried out.The formation of the spiro product (258) is the result of a SET process. Suchcyclisations have been extended to the phthalimide derivatives (259) and (260).179


The products (261) formed from (259) are obtained in good yield. Larger ringcompounds can also be synthesised. Thus, irradiation of (260) affords the prod-ucts (262, n�1) and (262, n�2) in 80% and 72%, respectively. The photochemi-cal ring expansion of cycloalkanones has provided a route to allylicN-phenylim-ides.180

Electron transfer within the naphthalimide derivatives (263) has beenstudied.181 The fluorescent behaviour and the pH dependence have been evalu-ated for a series of tetracarboxydiimides.182 The addition reactions encounteredwith the carboxamide (264) have been reported.183 A study of the photophysics ofN,N-ditridecyl-3,4:9,10-perylenetetracarboxylic diimide has been reported.184

5.3.2 Fulgides and Fulgimides. Considerable improvement on the reversibility inphotochromism of fulgides has been reported from studies in films,185 andprogress continues to be shown in the development of new photochromicsystems. Thus, the photochromic fulgides (265, 266) have been synthesised andpatented.186 The effect of pressure on the photochromicity of the furyl fulgide�2-[1-(2,5-dimethyl-3-furyl)-2-methylpropylidene]-3-isopropylidenesuccinic an-hydride� has been evaluated.187 Others have also investigated the photo-chromism of some anhydrides and fulgides.188 Ab initio calculations have beencarried out on some thienylfulgides,189 and the photochromic properties ofbenzofurylfulgides condensed with binaphthol have been investigated.190 Detailsof the synthesis and the photochromic properties of the fulgides (267, 268) havebeen reported.191 Cyclisation in toluene solution by irradiation at 366 nm of thethiofulgides (269) affords the thermally stable photochromes (270).192 The

Photochemistry106

heliochromism of some benzothienylfulgides193 and other photochromic fulgideshas been reported.194 The fatigue resistance of some fulgides, in so-called nakedspin-coated polymer, can be increased by careful exclusion of air.195 A convenientsynthetic approach to some photochromic fulgides has been described usingcarbonylation of but-2-yne-1,4-diols.196 Yokoyama197 has reviewed some of thephotochemistry undergone by fulgides and this article in particular has focusedupon the use of such molecules for photochemical switches. A review of thephotochromism exhibited by fulgides has been published.198 Calculations havebeen carried out to assess modelling for the design of new photochromic sys-tems.199

The photochromic properties of some novel indol-2-ylfulgimides have beenstudied.200 Irradiation of (271) at 366 nm brings about cyclisation to yield thestable ‘photochromes’ (272).201


6 Quinones

6.1 o-Quinones. — A study of the photoreduction of benzoquinones by N,N-dimethylaniline derivatives has been reported.202 The irradiations were carriedout in the 400 nm region (�,�*excitation) and irradiation at 600 nm brings aboutan n�* excitation. The authors suggest that a reversible triplet exciplex isinvolved in the photoreductions. The biradicals produced on irradiation ofquinones with norbornadiene or quadricyclane have been studied by CIDNP.203

Photochemical allylation of 1,2-naphthoquinones has been reported. Thereaction involves irradiation of the quinones with allylsilanes and a tripletexciplex is implicated. This reaction produces a [3�2]-cycloadduct that isconverted into the final product (Scheme 9).204 Irradiation at 450 nm of a series ofphenanthraquinonederivatives in the presence of alkenes yields dioxenes usuallywith reasonable stereochemical integrity.205 The reactions are efficient andphenanthraquinone itself undergoes addition with unit quantum efficiency. Stu-dies of the factors that control photoinduced electron transfer within a por-phyrin—phenoxynaphthacenequinone photochromic system have been evalu-ated.206

6.2 p-Quinones. — The addition of benzaldehyde to benzoquinone can be car-ried out efficiently by irradiation in benzene in the presence of benzophenone. Arecent study has demonstrated that the process is more efficient in supercriticalcarbon dioxide and under these conditions, as shown in Scheme 10, yields as highas 81% can be achieved.207 Electron transfer from 1,3,5-trimethoxybenzene to aseries of quinones (benzoquinone, 2-methylnaphthoquinoneand anthraquinone)has been reported.208 The low-lying electronic states of p-benzoquinone radicalanion have been studied from a theoretical standpoint.209 Both laser flash photo-lysis and continuous irradiation have been used to establish the mechanismwhereby 3-arylbenzoquinones undergo cyclisation to yield 2-hydroxybenzo-furan derivatives. The triplet n�* excited state of the quinone is involved.210

A series of products is formed when halogenated 1,4-benzoquinones (e.g. p-chloranil) are irradiated in the presence of 2,3-dimethylbut-2-ene or 3,4-dimethylpent-2-ene.211 The products were identified as monoallyl ethers (273)and (274) of the corresponding hydroquinones. Calculations have been used to

Photochemistry108

optimise the structures of 2,3-dicyano-5,6-dichloro-p-benzoquinone and its rad-ical anion.212

Both hydrogen abstraction and electron transfer reaction paths have beenreported in a study of the laser irradiation at 248 nm of 1,2- and 1,4-naph-thoquinones.213 The topochemical photo-polymerisation of the bisquinone de-rivatives (275) has been studied.214

The ��* triplet excited state of 1,4-anthraquinone has been examined usingflash and steady-state photolysis.215 Dimerisation and hydrogen abstraction re-actions were reported and no (2��2�)-cycloadducts were detected when thequinone was irradiated in the presence of alkenes. The photochemical one-electron reduction involving radical ions of 1,4-dihydroxyanthraquinone hasbeen studied in the presence of 1-benzyl-1,4-dihydronicotinamide and 5,5-dimethyl-1-pyrroline N-oxide.216 1-Hydroxyanthraquinone (276a) undergoes


photochemical amination on irradiation in the presence of n-butylamine to givethe two products (276b) and (276c) in a ratio that is dependent on the reactionconditions.217 In acetonitrile under an atmosphere of air the ratio of (276b):(276c)is 5:1. This changes to 0.3:1 when the reaction is run under nitrogen. Interestinglythe corresponding 1-aminoanthraquinone does not undergo amination. Thequinones (277) also undergo amination with the same amine to yield the 4-butylaminoquinone (277, R�NHBun). Rapid proton transfer within the quinone(278) is the result of formation of the lowest excited singlet state.218 A series ofoligomers based on the system shown in (279) has examined one-electron trans-fer to the anthraquinone moiety.219 The possibility that one-electron transferoccurred from thymine dimers to anthraquinone resulting in the repair of theDNA was investigated. The results showed that there was little or no repair atsuch sites. A review has highlighted the photo- and radiation chemistry ofquinones that are of value in chemotherapy.220

A stable radical ion pair is formed when 3,4-di-O-benzylhypericin is irradiatedin the presence of bis-1,8-N,N-dimethylaminonaphthalene.221 The photochemi-cal rearrangement of 3-O-benzylhypericin has been described,222 and a synthesisof racemic methylenomycins A and B has been reported making use of thephotochemical rearrangement of quinones as the key step.223 A review of thegeneral area of photochromism in quinones has been published.224

7 References

1. S. Wilsey, L. Gonzalez, M. A. Robb and K. N. Houk, J. Am. Chem. Soc., 2000, 122,5866.

Photochemistry110

2. M. D’Auria, L. Emanuele, G. Mauriello and R. Racioppi, J. Photochem. Photobiol.A: Chem., 2000, 134, 147.

3. S. Panja, P. R. Bangal and S. Chakravorti,Chem. Phys. Lett., 2000, 329, 377 (Chem.Abstr., 2001, 134, 85910).

4. P. R. Bangal, S. Panja and S. Chakravorti, J.Photochem.Photobiol.A:Chem., 2001,139, 5.

5. H. Hosomi, Y. Ito and S. Ohba, Acta Crystallogr., Sect. B: Struct. Sci., 2000, B56,682 (Chem. Abstr., 2000, 578897).

6. D.M. Bassani, V. Darcos, S. Mahony and J. P. Desvergne, J.Am.Chem. Soc., 2000,122, 8795.

7. Y. Ito, H. Hosomi and S. Ohba, Tetrahedron, 2000, 56, 6833.8. S. Perny, P. Le Barny, J. Delaire, T. Buffeteau and C. Sourisseau, Liq. Cryst., 2000,

27, 341 (Chem. Abstr., 2000, 133, 127829).9. S. D. M. Allen, M. J. Almond, J.-L. Brunel, A. Gilbert, P. Hollins and J. Mascetti,

Spectrochim. Acta, Part A, 2000, 56, 2423 (Chem. Abstr., 2000, 679749).10. J. A. R. P. Sarma, B. Chaudhuri and G. R. Desiraji, Indian J. Chem., Sect. A: Inorg.,

Bio-inorg., Phys., Theor. Anal. Chem., 2000, 39A, 253 (Chem. Abstr., 2000, 358537).11. Y. L. Chow, S. S.Wang, H. Huang and J.-Q. He,Res.Chem. Intermed., 2000, 26, 643

(Chem. Abstr., 2001, 343729).12. H. Kawai, T. Suzuki, M. Ohkita and T. Tsuji, Chem.-Eur. J., 2000, 6, 4177.13. S. Bertrand, N. Hoffmann, S. Humbel and J. P. Pete, J. Org. Chem., 2000, 65, 8690.14. Z.-Y.Wang, T.-Y. Jian andQ.-H. Chen,Chin. J.Chem., 2001, 19, 177 (Chem.Abstr.,

2001, 126684).15. S. Bertrand, N. Hoffmann and J.-P. Pete, Eur. J. Org. Chem., 2000, 2227.16. S. Bertrand, N. Hoffmann and J.-P. Pete, J. Inf. Rec., 2000, 25, 215 (Chem. Abstr.,

2001, 134, 259106).17. J. D. White, J. Kim and N. E. Drapela, J. Am. Chem. Soc., 2000, 122, 8665.18. J. Rosenthal, A. Khong, S. R. Wilson and D. I. Schuster, Proc.- Electrochem. Soc.,

2000, 216 (Chem. Abstr., 2001, 88102).19. L. O. Ferrer and P. Margaretha, Chem. Commun., 2001, 481.20. M. Dellagreca, P. Monaco, L. Previtera, A. Zarrelli, A. Fiorentino, F. Giordano

and C. A. Mattia, J. Org. Chem., 2001, 66, 2057.21. E. P. Gogonas and L. P. Hadjiarapoglou, Tetrahedron Lett., 2000, 41, 9299.22. T. Bach and H. Bergmann, J. Am. Chem. Soc., 2000, 122, 11525.23. T. J. Brett, J. M. Alexander and J. J. Stezowski, J. Chem. Soc., PerkinTrans. 2, 2000,

1095.24. T. J. Brett, J. M. Alexander and J. J. Stezowski, J. Chem. Soc., PerkinTrans. 2, 2000,

1105.25. S. Nad and H. Pal, J. Phys. Chem. A, 2001, 105, 1097.26. Z. Dai and S. Wu, Ganguang Kexue Yu Guang Huaxue, 2000, 18, 67 (Chem. Abstr.,

2000, 132, 308223).27. M. Christoff, L. T. Okano and C. Bohne, J. Photochem. Photobiol. A: Chem., 2000,

134, 169.28. R. Y. Tsien and T. Furuta, PCT Int. Appl. WO 00 31,588 (Chem. Abstr., 2000, 133,

17381).29. M. A. Kinder and P. Margaretha, Org. Lett., 2000, 2, 4253.30. K. Tanaka, E. Mochizuki, N. Yasui, Y. Kai, I. Miyahara, K. Hirotsu and F. Toda,

Tetrahedron, 2000, 56, 6853.31. M. A. Kinder, J. Kopf and P. Margaretha, Tetrahedron, 2000, 56, 6763.32. D. Schwebel and P. Margaretha,Helv. Chim. Acta, 2000, 83, 1168.


33. S. Neubauer, A. Blecking, D. Dopp andG. Henkel, J. Inf.Rec., 2000, 25, 195 (Chem.Abstr., 2001, 134, 245114).

34. Y. Wang, J. Meng and T. Matsuura, Trends Heterocycl. Chem., 1999, 6, 21 (Chem.Abstr., 2001, 134, 207734).

35. A. K. Singh, D. K. Palit and J. P. Mittal,Res.Chem. Intermed., 2001, 27, 125 (Chem.Abstr., 2001, 309587).

36. D. Creed, C. E. Hoyle, L. Jin, A. M. Peeler, P. Subramanian and V. Krishnan, J.Polym. Sci., Part A: Polym. Chem., 2001, 39, 134 (Chem. Abstr., 2001, 134, 208445).

37. R. Arad-Yellin, G. Tsoucaris and B. S. Green, Tetrahedron Lett., 2001, 42, 1335.38. H. Maeda, A. Sugimoto and K. Mizuno, Org. Lett., 2000, 2, 3305.39. M. Onciu, C. I. Constantin and E. Rusu, Roum. Chem. Q. Rev., 2000, 7, 13 (Chem.

Abstr., 2001, 230927).40. C. Meyer, O. Piva and J.-P. Pete, Tetrahedron, 2000, 56, 4479.41. M. T. Crimmins, J.M. Pace, P. G. Nantermet, A. S. Kim-Meade, J. B. Thomas, S. H.

Watterson and A. S. Wagman, J. Am. Chem. Soc., 2000, 122, 8453.42. S. Faure and O. Piva, Tetrahedron Lett., 2001, 42, 255.43. X. L. Kai, V. Chang, C. F. Chen, H. J. Kim and P. S. Mariano, Tetrahedron Lett.,

2000, 41, 9445.44. T. Bach, H. Bergmann and K. Harms, Angew. Chem. Int. Ed. Engl., 2000, 39, 2302.45. R. H. Blaauw, J. F. Briere, R. de Jong, J. C. J. Benningshof, A. E. van Ginkel, F. P. J.

T. Rutjes, J. Fraanje, K. Goublitz, H. Schenk and H. Hiemstra, Chem. Commun.,2000, 1463.

46. R. H. Blaauw, J. F. Briere, R. De Jong, J. C. J. Benningshof, A. E. van Ginkel, J.Fraanje, K. Goubitz, H. Schenk, F. P. J. T. Rutjes and H. Hiemstra, J. Org. Chem.,2001, 66, 233.

47. M. M. Birau and Z. Y. Wang, Tetrahedron Lett., 2000, 41, 4025.48. K. Kumar, S. Kaur and M. P. S. Ishar, Indian J. Chem., Sect. B: Org. Chem. Incl.

Med. Chem., 2000, 39B, 643 (Chem. Abstr., 2001, 76689).49. E. Garcia-Exposito, R. Gonzalez-Moreno, M. Martin-Vila, E. Muray, J. Rife, J. L.

Bourdelande, V. Branchadell and R. M. Ortuno, J. Org. Chem., 2000, 65, 6958.50. K. M. Bushan, G. V. Rao, T. Soujanya, V. J. Rao, S. Saha, and A. Samanta, J. Org.

Chem., 2001, 66, 68151. K. Takeshita, N. Hirota andM. Terazima, J.Photochem.Photobiol.A:Chem., 2000,

134, 103.52. A. Yamada, S. Yamamoto, T. Yamato and T. Kakitani, THEOCHEM, 2001, 536,

195 (Chem. Abstr., 2001, 134, 310769).53. W. L. Ryan and D. H. Levy, J. Am. Chem. Soc., 2001, 123, 961.54. K. Honda, F. Nakanishi, S. Lee, M. Mikami, S. Tsuzuki, T. Yamamoto and N.

Feeder,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2001, 356, 413 (Chem. Abstr.,2001, 297298).

55. S. Ghelli, M. P. Costi, L. Toma, D. Barlocco and G. Ponterini, Tetrahedron, 2000,56, 7561.

56. S. A. Ansari, K. G. Marathe and M. J. Pujari, J. Indian Counc. Chem., 2000, 17, 7(Chem. Abstr., 2001, 134, 252167).

57. J.-M.Gomis, J. Santolini, F. Cavelier, J. Verducci, E. Pinet, F. Andre and J.-P. Noel,J. Labelled Compd. Radiopharm., 2000, 43, 323 (Chem. Abstr., 2000, 133, 30931).

58. W. S. Harper and E. R. Gaillard, Photochem. Photobiol., 2001, 73, 71.59. S. Yamaguchi and H. Hamaguchi, J. Phys. Chem. A, 2000, 104, 4272.60. K. Fukui, Y. Naito and Y. Inoue, Jpn.KokaiTokkyo Koho JP 2000, 281,615 (Chem.

Abstr., 2000, 133, 266534).

Photochemistry112

61. F. Gallou, D. W. C. MacMillan, L. E. Overman, L. A. Paquette, L. D. Penningtonand J. Yang, Org. Lett., 2001, 3, 135.

62. Y. Norikane, H. Itoh and T. Arai, Chem. Lett., 2000, 1094.63. R. Matsushima and T. Murakami, Bull. Chem. Soc. Jpn., 2000, 73, 2215.64. K. Tokumura, N. Taniguchi, T. Kimura and R. Matsushima, Chem. Lett., 2001,

126.65. V. V. Kudryavtsev, N. I. Rtishchev, G. I. Nosova, N. A. Solovskaya, V. A.

Luk’yashina and A. V. Dobrodunov, Russ. J. Gen. Chem., 2000, 70, 1272 (Chem.Abstr., 2001, 146199).

66. A. Gaplovsky, J. Donovalova, M. Lacova, R. Mracnova and H. M. El-Shaaer, J.Photochem. Photobiol. A: Chem., 2000, 136, 61.

67. P. J. Coelho, L. M. Carvalho. J. C. Silva, A. M. F. Oliveira-Campos, A. Samat andR. Guglielmetti,Helv. Chim. Acta, 2001, 84, 117.

68. E. T. J. Nibbering, F. Tschirschwitz, C. Chudoba andT. Elsaesser, J.Phys.Chem.A,2000, 104, 4236.

69. G.G. Aloisi, F. Elisei, S.Moro, G.Miolo andF. Dall’Acqua,Photochem.Photobiol.,2000, 71, 506.

70. M. Kulkarni and S. D. Kate, J. Chem. Soc., Perkin Trans. 1, 2000, 4242.71. H. Hoshina, K. Kubo, A. Morita and T. Sakurai, Tetrahedron, 2000, 56, 2941.72. F. Bois, D. Gardette and J. C. Gramain, Tetrahedron Lett., 2000, 41, 8769.73. K. Oda, R. Nakagami, N. Nishizono and M. Machida, Chem. Lett., 2000, 1386.74. S. Kessar, Chem. Commun., 1993, 182875. K. Tanaka, T. Watanabe and F. Toda, Chem. Commun., 2000, 1361.76. H. Rinderhagen, J. Grota and J. Mattay, J. Inf. Rec., 2000, 25, 229 (Chem. Abstr.,

2001, 134, 245116).77. P. Schmoldt and J. Mattay, J. Inf. Rec., 2000, 25, 239 (Chem. Abstr., 2001, 134,

245117).78. V. Nair, D. Maliakal, G. Anilkumar and N. P. Rath, Synlett, 2000, 1139.79. V. Singh, B. Samanta and V. V. Kane, Tetrahedron, 2000, 56, 7785.80. V. Singh and S. Q. Alam, Bioorg. Med. Chem. Lett., 2000, 10, 2517 (Chem. Abstr.,

2000, 844926).81. S. Uppili, S. Takagi, R. B. Sunoj, P. Lakshminarasimhan, J. Chandrasekhar and V.

Ramamurthy, Tetrahedron Lett., 2001, 42, 2079.82. H. E. Zimmerman, I. V. Alabugin and V. N. Smolenskaya, Tetrahedron, 2000, 56,

6821.83. S. Jayaraman, S. Uppili, A. Natarajan, A. Joy, K. C.W. Chong,M. R. Netherton, A.

Zenova, J. R. Scheffer and V. Ramamurthy, Tetrahedron Lett., 2000, 41, 8231.84. L. A. Paquette, F. Gallou, Z. Zhao, D. G. Young, J. Liu, J. Yang andD. Friedrich, J.

Am. Chem. Soc., 2000, 122, 9610.85. L. A. Paquette, Z. Zhao, F. Gallou and J. Liu, J. Am. Chem. Soc., 2000, 122, 1540.86. D. J. Chang and B. S. Park, Tetrahedron Lett., 2001, 42, 711.87. T. Bach, H. Bergmann and K. Harms, Org. Lett., 2001, 3, 601.88. N. Gauvry and F. Huet, J. Org. Chem., 2001, 66, 583.89. W. L. Dilling, Org. Photochem. Synth., 1976, 2, 5.90. Y. G. Lee, K. F. McGee, J. H. Chen, D. Rucando and S. M. Sieburth, J.Org.Chem.,

2000, 65, 6676.91. K. Ohkura, K. Nishijima, S. Uchiyama, A. Sakushima and K.-I. Seki,Heterocycles,

2001, 54, 65 (Chem. Abstr., 2001, 77723).92. M. R. Kumar, M. T. Rao and M. Adinarayana, Indian J. Biochem. Biophys., 2000,

37, 13 (Chem. Abstr., 2000, 133, 135157).


93. M. R. Dhananjeyan, V. Kandavelu and R. Renganathan, J. Mol. Catal. A: Chem.,2000, 158, 577 (Chem. Abstr., 2000, 133, 296112).

94. F. Lin, Chin. Chem. Lett., 2000, 11, 679 (Chem. Abstr., 2000, 133, 281843).95. K. Ohkura, K.-I. Nishijima, A. Sakushima and K.-I. Seki, Heterocycles, 2000, 53,

1247.96. K. Ohkura, K. Nishijima and K. Seki, Chem. Pharm. Bull., 2001, 49, 384 (Chem.

Abstr., 2001, 252577).97. H. Kunkely and A. Vogler, Inorg.Chem.Commun., 2000, 3, 188 (Chem.Abstr., 2000,

132, 341049).98. N. J. Kim, H. Kang, G. Jeong, Y. S. Kim, K. T. Lee and S. K. Kim, Proc.Nat.Acad.

Sci.USA, 2001, 98, 4841 (Chem. Abstr., 2001, 327363).99. Y. Inaki, E. Mochizuki, N. Yasui, M. Miyata and K. Mikiji, J. Photopolym. Sci.

Technol., 2000, 13 177 (Chem. Abstr., 2000, 579487).100. Y. Inagi and H. Hiratsuka,Kobunshi Kako, 2000, 49, 393 (Chem. Abstr., 2001, 134,

139054).101. V. M. Malkin and V. L. Rapoport, Vestn. S.-Peterb.Univ., Ser. 4: Fiz.Khim., 1999,

108 (Chem. Abstr., 2000, 386953).102. E. Mochizuki, N. Tohnai, Y. Wang, T. Saito, Y. Inaki, M. Miyata, N. Yasui and Y.

Kai, Polym. J. (Tokyo), 2000, 32, 492.103. A. Joseph and D. E. Falvey, J. Am. Chem. Soc., 2001, 123, 3145.104. A. Joseph, G. Prakash and D. E. Falvey, J. Am. Chem. Soc., 2000, 122, 11219.105. K. Nakatani, C. Dohno and I. Saito, Tetrahedron Lett., 2000, 41, 10041.106. K. Fujimoto, S. Matsuda, N. Takahashi and I. Saito, J. Am. Chem. Soc., 2000, 122,

5646.107. K. Fujimoto, N. Ogawa, M. Hayashi, S. Matsuda and I. Saito, Tetrahedron Lett.,

2000, 41, 9437.108. S. K. Katiyar, M. S. Matsui and H.Mukhtar, Photochem.Photobiol., 2000, 72, 788.109. H. Shinohara, H. Hatta, S. Fujita and S. Nishimoto, J. Phys. Chem. A, 2000, 104,

2886.110. T. Ito, H. Shinohara and S. Nishimoto, Photochem. Photobiol., 2000, 72, 719.111. T. Stepanenko, L. Lapinski, A. L. Sobelewski, M. J. Nowak and B. Kierdaszuk, J.

Phys. Chem. A, 2000, 104, 9459.112. C. Chatgilialoglu, C. Ferreri, R. Bazzanini, M. Guerra, S. Y. Choi, C. J. Emanuel, J.

H. Horner and M. Newcomb, J. Am. Chem. Soc., 2000, 122, 9525.113 A. S. Anderson, J. T. Hwang and M. M. Greenberg, J. Org. Chem., 2000, 65, 4648.114. S. K. Kim, H. O. Park and S. C. Shim, Photochem. Photobiol., 2000, 72, 472.115. D. H. Oh and P. C. Hanawalt, Photochem. Photobiol., 2000, 72, 298.116. P. D. Wood, A. Mnyusiwalla, L. Chen and L. J. Johnston, Photochem. Photobiol.,

2000, 72, 155.117. C. Agapakis-Causse, F. Bosca, J. V. Castell, D. Hernandez, M. L. Marin andM. A.

Miranda, Photochem. Photobiol., 2000, 71, 499.118. K.-P. Stengele and H. Giegrich, PCT Appl. WO 2000053309 (Chem. Abstr., 2000,

645917).119. Y. S. Wang, P. P. Gaspar and J. S. Taylor, J. Am. Chem. Soc., 2000, 122, 5510.120. F. D. Lewis, R. S. Kalgutkar, Y. S. Wu, X. Y. Liu, J. Q. Lu, R. T. Hayes, S. E. Miller

and M. R. Wasielewski, J. Am. Chem. Soc., 2000, 122, 12346.121. M. R. Wasielewski, J. Am. Chem. Soc., 2000, 122, 12346.122. Y. P. Tsentalovich, O. B. Morozova, A. V. Yurkovskaya, P. J. Hore and R. Z.

Sagdeev, J. Phys. Chem. A, 2000, 104, 6912.123. A. G. Schultz and L. O. Lockwood, J. Org. Chem., 2000, 65, 6354.

Photochemistry114

124. A. G. Schultz and E. G. Antoulinakis, J. Org. Chem., 1996, 61, 4555.125. Z. H. Guo and A. G. Schultz, Org. Lett., 2001, 3, 1177.126. G. Blay, V. Bargues, L. Cardona, A. M. Collado, B. Garcia, M. C. Munoz and J. R.

Pedro, J. Org. Chem., 2000, 65, 2138.127. G. Blay, V. Bargues, L. Cardona, B. Garcia and J. R. Pedro, J.Org.Chem., 2000, 65,

6703.128. G. Blay, L. Cardona, B. Garcia, L. Lahoz, B. Monje and J. R. Pedro, Tetrahedron,

2000, 56, 6331.129. V. I. Minkin, V. N. Komissarov and V. A. Kharlanov, Org. Photochromic Ther-

mochromic Compd., 1999, 315 (Chem. Abstr., 2000, 132, 321811).130. M. Fernandez-Zertuche, R. Hernandez-Lamoneda and A. Ramirez-Solis, J. Org.

Chem., 2000, 65, 5207.131. Y.M. Kim, S. J. Song, T.W. Kwon and S. K. Chung,Molecules, 2000, 5, 961 (Chem.

Abstr., 2000, 577175).132. T. W. Kwon, Y. M. Kim, S. J. Song, Y. U. Kwon and S. K. Chung, Bioorg. Med.

Chem. Lett., 2000, 10, 1551 (Chem. Abstr., 2000, 133, 252101).133. A. L. P. Nery, F. H. Quina, P. F. Moreira, C. E. R. Medeiros, W. J. Baader, K.

Shimizu, L. H. Catalani and E. J. H. Bechara, Photochem.Photobiol., 2001, 73, 213.134. T. Obata, T. Shimo,M. Yasutake, T. Shinmyozu,M. Kawaminami, R. Yoshida and

K. Somekawa, Tetrahedron, 2001, 57, 1531.135. S. Koondanjeri, A. Joy and V. Ramamurthy, Tetrahedron, 2000, 56, 7003.136. X. Li, J. M.Millam and H. B. Schlegel, J.Chem.Phys., 2001, 114, 114 (Chem.Abstr.,

2001, 603 or 346343).137. D. M. Koch, N. H. Khieu and G. H. Peslherbe, J. Phys. Chem. A, 2001, 105, 3598.138. X. Li and H. B. Schlegel, J. Chem. Phys., 2001, 114, 8 (Chem. Abstr., 2001, 603).139. A. Bashir-Hashemi, U.S. US 6,222,068 (Chem. Abstr., 2001, 134, 295568).140. B. Klotz, F. Graedler, S. Sorensen, I. Barnes and K.-H. Becker, Ber.- Bergische

Univ., Gesamthochsch. Wuppertal, Fachbereich 9, Phys. Chem., 2000, 25 (Chem.Abstr., 2001, 134, 78517).

141. B. Klotz, F. Graedler, S. Sorensen, I. Barnes and K.-H. Becker, Int. J.Chem.Kinet.,2001, 33, 9 (Chem. Abstr., 2001, 22115).

142. Y. Q. Chen, W. J. Wang and L. Zhu, J. Phys. Chem. A, 2000, 104, 11126.143. L.-S. Pei, Y. Chen, J. Jin, Y.-D. Gao, J.-H. Dai and C.-X. Chen, Gaodeng Xuexiao

Huaxue Xuebao, 2000, 21, 1093 (Chem. Abstr., 2000, 576107).144. S. Ohba, H. Hosomi, K. Tanaka, H. Miyamoto and F. Toda, Bull. Chem. Soc. Jpn.,

2000, 73, 2075.145. H. Sohyima, T. Kimura, M. Fujita and T. Ando, Ultrason. Sonochem., 2000, 8, 7

(Chem. Abstr., 2000, 873131).146. Y. Horiguchi, T. Saitoh, N. Koseki, H. Suzuki, J. Toda and T. Sano, Heterocycles,

2000, 53, 1329.147. G. J. Sun andK.H. Chae,Polymer, 2000, 41, 6205 (Chem.Abstr., 2000, 133, 140160).148. H. J. Hageman and P. Oosterhoff,Macromol. Chem. Phys., 2000, 201, 1687 (Chem.

Abstr., 2000, 740723).149. M. T. Silva, R. Braz-Filho and J. C. Netto-Ferreira, J. Braz. Chem. Soc., 2000, 11,

479 (Chem. Abstr., 2001, 134, 139092).150. J. Xue, Y. Zhang, X. L. Wang, H.-K. Fun and J.-H. Xu, Org. Lett., 2000, 2, 2583.151. J. Xue, Y. Zhang, T. Wu, H.-K. Fun and J.-H. Xu, J. Chem. Soc., Perkin Trans. 1,

2001, 183.152. Y. Zhang, S. P. Qian, H. K. Fun and J. H. Xu, Tetrahedron Lett., 2000, 41, 8141.153. M. C. Yoon, Y. S. Choi and S. K. Kim, J. Phys. Chem. A, 2000, 104, 4352.


154. Z. Yang and M. A. Garcia-Garibay, Org. Lett., 2000, 2, 1963.155. S. V. Jovanovic, C. W. Boone, S. Steenken, M. Trinoga and R. B. Kaskey, J. Am.

Chem. Soc., 2001, 123, 3064.156. S. M. Khopde, K. Priyadarsini, D. K. Palit and T. Mukherjee, Photochem. Photo-

biol., 2000, 72, 625.157. R. A. Back and R. D. Gordon, J.Mol. Spectrosc., 2000, 204, 85 (Chem.Abstr., 2001,

134, 107383).158. T. Tsuno andK. Sugiyama,Recent Res.Dev.Org.Chem., 1999, 3, 435 (Chem.Abstr.,

2000, 899166).159. T. Tsuno and K. Sugiyama,Recent Res.Dev.Org.Chem., 1999, 3 (Pt. 2), 435 (Chem.

Abstr., 2001, 134, 245077).160. H. R. Memarian, M. Nasr-Esfhani and D. Dopp, New J. Chem., 2001, 25, 476

(Chem. Abstr., 2001, 160858).161. M. Sakamoto, N. Sekine, H. Miyoshi, T. Mino and F. Fujita, J. Am. Chem. Soc.,

2000, 122, 10210.162. M. Chanda, D. Maji and S. Lahiri, Chem. Commun., 2001, 543.163. K. Kokubo, Y. Nakajima, K. Iijima, H. Yamaguchi, T. Kawamoto and T. Oshima,

J. Org. Chem., 2000, 65, 3371.164. L. H. Catalani, D. De B. Rezende and I. P. De Arruda Campos, J. Chem. Res.,

Synop., 2000, 111.165. J. von Sonntag and W. Knolle, J. Photochem. Photobiol. A: Chem., 2000, 136, 133.166. S. Thiering, C. E. Sowa and J. Thiem, J. Chem. Soc., Perkin Trans. 1, 2001, 801.167. G. W. Breton and K. A. Newton, J. Org. Chem., 2000, 65, 2863.168. F. Nakanishi and J. Nagasawa, Busshitsu Kogaku Kogyo Gijutsu Kenkyusho

Hokoku, 2000, 8, 89 (Chem. Abstr., 2001, 134, 163342).169. B. Ohtani, S. Kusakabe, K. Okada, S. Tsuru, S. Nishimoto, Y. Amino, K. Izawa, Y.

Nakato, M. Matsumura, Y. Nakaoka and Y. Nosaka, J. Chem. Soc., Perkin Trans.2, 2001, 201.

170. D. Laurenti, C. Santelli-Ouvier, G. Pepe and M. Santelli, J. Org. Chem., 2000, 65,6418.

171. K. I. Booker-Milburn, C. E. Anson, C. Clissold, N. J. Costin, R. F. Dainty, M.Murray, D. Patel and A. Sharpe, Eur. J. Org. Chem., 2001, 1473.

172. A. G. Griesbeck, M. Oelgemoller and J. Lex, Synlett, 2000, 1455.173. A. G. Griesbeck,W. Kramer and J. Lex,Angew.Chem. Int.Ed. Engl., 2001, 40, 577.174. A. G. Griesbeck, W. Kramer, A. Bartoschek and H. Schmickler,Org. Lett., 2001, 3,

537.175. A. Bartoschek, A. G. Griesbeck and M. Oelgemoller, J. Inf. Rec., 2000, 25, 119

(Chem. Abstr., 2001, 134, 251937).176. A. G. Griesbeck and M. Fiege,Mol. Supramol. Photochem., 2000, 6, 33.177. A. G. Griesbeck, M. Oelgemoller and J. Lex, J. Org. Chem., 2000, 65, 9028.178. L. Zhu, H. K. Fun and J. H. Xu, Tetrahedron Lett., 2000, 41, 8553.179. U. C. Yoon, S. W. Oh, J. H. Lee, J. H. Park, K. T. Kang and P. S. Mariano, J. Org.

Chem., 2001, 66, 939.180. J. A. Heerklotz, C. C. Fu, A. Linden andM.Hesse,Helv.Chim.Acta, 2000, 83, 1809.181. T. P. Le, J. E. Rogers and L. A. Kelly, J. Phys. Chem. A, 2000, 104, 6778.182. S. Schieffer and A. G. Griesbeck, J. Inf. Rec., 2000, 25, 331 (Chem. Abstr., 2001,

74832).183. S. Kohmoto, T. Kobayashi, J. Minami, X. Ying, K. Yamaguchi, T. Karatsu, A.

Kitamura, K. Kishikawa and A. Yamamoto, J. Org. Chem., 2001, 66, 66.184. S. A. El-Daly and T. A. Fayed, J. Photochem. Photobiol. A: Chem., 2000, 137, 15.

Photochemistry116

185. R. Matsushima, T. Hayashi and M. Nishiyama,Mol. Cryst. Liq. Cryst. Sci. Tech-nol., Sect. A, 2000, 344, 241 (Chem. Abstr., 2000, 764127).

186. M. Fan, W. Zhao, X. Han and Y. Ming, Faming Zhuanli Shenqing GongkaiShuomingshuCN, 1,213,686 (Chem. Abstr., 2000, 132, 315895).

187. T. Sekiya, T. Fujita, S. Ohta and S. Kurita, Phys. Status Solidi B, 2001, 223, 355(Chem. Abstr., 2001, 88578).

188. S. S. Deshmukh and S. Banerjee, Asian J. Chem., 2001, 13, 481 (Chem. Abstr., 2001,273173).

189. Y. Yoshioka, M. Usami and K. Yamaguchi, Mol. Cryst. Liq. Cryst. Sci. Technol.,Sect. A, 2000, 345, 81 (Chem. Abstr., 2000, 764157).

190. Y. Yokoyama, Y. Kurosaki, T. Sagisaka and H. Azami,Mol. Cryst. Liq. Cryst. Sci.Technol., Sect. A, 2000, 344, 223 (Chem. Abstr., 2000, 764124).

191. A. M. A. Asiri, A. Cleeves and H. G. Heller, J. Chem. Soc., Perkin Trans. 1, 2000,2741.

192. M. Badland, A. Cleeves, H. G. Heller, D. S. Hughes and M. B. Hursthouse, Chem.Commun., 2000, 1567.

193. Y. Yokoyama, N. Nakata, K. Sugama and Y. Yokoyama, Mol. Cryst. Liq. Cryst.Sci. Technol., Sect. A, 2000, 344, 253 (Chem. Abstr., 2000, 764129).

194. Z. Sun, R. S. Hosmane and M. Tadros, J.Heterocycl. Chem., 2000, 37, 1439 (Chem.Abstr., 2001, 88174).

195. R. Matsushima, M. Nishiyama and M. Doi, J. Photochem. Photobiol. A: Chem.,2001, 139, 63.

196. J. Kiji, T. Okano, A. Takemoto, S.-Y. Mio, T. Konishi, S. Yuuichi, T. Sagisaka andY. Yokoyama,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 344, 235 (Chem.Abstr., 2000, 764126).

197. Y. Yokoyama, Chem. Rev., 2000, 100, 1717.198. M.-G. Fan, L. Yu and W. Zhao, Org. Photochromic Thermochromic Compd., 1999,

141 (Chem. Abstr., 2000, 132, 321766).199. M. A. Robb, M. J. Bearpark, P. Celani, F. Bernardi and M. Olivucci, Mol. Cryst.

Liq. Cryst. Sci. Technol., Sect. A, 2000, 344, 31 (Chem. Abstr., 2000, 764095).200. Y. Liang, A. S. Dvornikov and P. M. Rentzepis, J. Mater. Chem., 2000, 10, 2477

(Chem. Abstr., 2000, 756303).201. H. G. Heller, D. S. Hughes, M. B. Hursthouse and N. G. Rowles, Chem. Commun.,

2000, 1397.202. S. A. Chesnokov, V. K. Cherkasov, Yu. V. Chechet, N. I. Nevodchikov, G. A.

Abakumov andO. N.Mamyesheva,Russ.Chem.Bull., 2000, 49, 1506 (Chem.Abstr.,2000, 879294).

203. M. Goez and I. Frisch, J. Inf. Rec., 2000, 25, 287 (Chem. Abstr., 2001, 134, 302899).204. A. Takuwa, T. Sasaki, H. Iwamoto and Y. Nishigaichi, Synthesis, 2001, 63 (Chem.

Abstr., 2001, 48302).205. J. H. Ho, T. I. Ho, T. H. Chen and Y. L. Chow, J. Photochem. Photobiol. A: Chem.,

2001, 138, 111.206. A. J. Myles and N. R. Branda, J. Am. Chem. Soc., 2001, 123, 177.207. R. Pacut, M. L. Grimm, G. A. Kraus and J. M. Tanko, Tetrahedron Lett., 2001, 42,

1415.208. C. Serpa and L. G. Arnaut, J. Phys. Chem. A, 2000, 104, 11075.209. R. Pou-Amerigo, L. Serrano-Andres,M. Merchan, E. Orti and N. Forsberg, J. Am.

Chem. Soc., 2000, 122, 6067.210. C. Belin, S. Bearnais-Barbry and R. Bonneau, J. Photochem. Photobiol. A: Chem.,

2001, 139, 111.


211. K. Kokubo, T. Masaki and T. Oshima, Org. Lett., 2000, 2, 1979.212. S. H. Ma, X. D. Zhang, H. Xu, L. L. Shen, X. K. Zhang and Q. Y. Zhang, J.

Photochem. Photobiol. A: Chem., 2001, 139, 97.213. J. Chen, G. Chu, X. Xu, Z. Zhang and S. Yao, Huaxue Wuli Xuebao, 2000, 13, 145

(Chem. Abstr., 2000, 329922).214. H. Irngartinger and M. Skipinski, Tetrahedron, 2000, 56, 6781.215. T. Yoshihara, M. Yamaji, T. Itoh, J. Nishimura, H. Shizuka and S. Tobita, J.

Photochem. Photobiol. A: Chem., 2001, 140, 7.216. Z. C. Xu, J. Y. An, Y. Z. Hu and F. Tian, Chin. Chem. Lett., 2000, 11, 479 (Chem.

Abstr., 2000, 133, 134941).217. M. Tajima, K. Kato, K. Matsunaga and H. Inoue, J. Photochem. Photobiol. A:

Chem., 2001, 140, 127.218. T. Nakayama, R. Yamauchi, H. Shin and K. Hamanoue, J. Phys. Chem. A, 2000,

104, 9698.219. A. K. Dotse, E. K. Boone and G. B. Schuster, J. Am. Chem. Soc., 2000, 122, 6825.220. T.Mukherjee,Proc. IndianNatl. Sci.Acad.,Part A, 2000, 6, 239 (Chem.Abstr., 2001,

134, 29011).221. T. G. Dax and H. Falk, Monatsh. Chem., 2000, 131, 1217 (Chem. Abstr., 2001,

11310).222. T. G. Dax, E. I. Kapinus and H. Falk,Helv. Chim. Acta, 2000, 83, 1744.223. F.-T. Hong, K.-S. Lee and C.-C. Liao, J. Chin. Chem. Soc. (Taipei), 2000, 47, 77

(Chem. Abstr., 2000, 132, 308163).224. V. A. Barachevsky, Org. Photochromic Thermochromic Compd., 1999, 267 (Chem.

Abstr., 2000, 132, 293511).

Photochemistry118

3Photochemistry of Alkenes, Alkynes andRelated Compounds


1 Reactions of Alkenes

1.1 cis,trans-Isomerisation. — A review has detailed recent work carried out onphotochemical cis,trans processes in the singlet state.1 A photochemical step hasbeen utilised in the synthesis of irones. One of the key steps was the photochemi-cal isomerisation of the �-double bond.2 The enantiodifferentiating photochem-istry of cyclooctene has been described using the nucleoside (1) as the chiralsensitiser.3 Benzoate substituted cyclodextrins have also been used to photo-isomerise Z-cyclooctene.4 The yields obtained are better than those found usingalkyl benzoates as the sensitisers. Irradiation of trans-�-methyl-�-nitrostyrene inacetonitrile brings about isomerisation to the corresponding cis-isomer with aquantum yield of 0.8.5 The photochemical isomerisation of the derivative (2) into(3) is a key step in the synthesis of locked side chain analogues of calcitriol.6 Thespectral properties of some 6-styryl-2,4-disubstituted pyrylium salts have beenmeasured.7 The trans,cis-isomerism within the naphthalenophane (4) has beenstudied.8 A detailed account of photochemical reactions of alcohol protectinggroups (5) has been presented.9 The deprotection of the alcohol is dependent on aprimary trans,cis-isomerisation path on irradiation at 254 nm which is followedby a photochemical 1,5-hydrogen migration to give intermediate (6) and then bya 1,5-silicon migration to yield (7). Collapse of this intermediate affords the freealcohol. Some of the classes of alcohol and the percentage yields are shown.

1.1.1 Stilbenes and Related Compounds. Long-wavelength trans,cis photochemis-try of stilbene and some derivatives has been described.10 The cooling kinetics of


119

photoexcited trans-stilbene have been studied using time-resolved Raman spec-troscopy.11 A resonance Raman spectrum has been observed following irradi-ation of cis-stilbene at 267 nm.12 Irradiation of trans-stilbene at a silica gel/airinterface affords considerable amounts of two dimers.13 Some isomerisation tothe cis-stilbene also takes place as well as oxidation to give benzaldehyde.The isomerism kinetics of the stilbene (8) have been measured.14 Stilbenes are

well known to undergo photochemical cyclisation to phenanthrene derivativeson irradiation. A recent study of this cyclisation reaction has examined thepotential for the synthesis of ketones following the cyclisation.15 Many exampleswere reported but the irradiation of (9) in acetonitrile with 0.5MHCl to yield theexpected intermediate (10) is typical. 1,9-Hydrogen migration occurs in (10) toafford the enol ether (11) which on hydrolysis under the acid conditions isconverted into (12) in 96% yield. A further study of this reaction has revealedthat the products obtained from (9) in acetonitrile solution are dependent on theconcentration of acid used.16 Thus the enone (13) is formed with 5�10�3 M HClwhile (12) is formed, as reported originally, with 0.5 M HCl.An examination of the excited-state properties of the stilbene derivatives (14)

has sought further information on themeta-amino effect.17 A detailed study of thephotophysics of a series of 1,2-diarylethenes (15) has been carried out.18 Variouscomputative methods have been used to investigate the isomerisation of simplestilbene derivatives and the stilbene super molecule (16).19 The photophysicalproperties of several triazine/stilbene fluorescent brighteners have been studiedin aqueous and alcoholic solutions.20 The photoisomerism of 4,4�-bis(benz-oxazolyl)stilbene in a variety of solvents has been studied and the activationenergy for the trans-cis-isomerisation was measured.21 The photoisomerisationof 4,4�-diaminostilbene-2,2�-disulfonate at a variety of wavelengths has beenstudied and the reaction was shown to be pH dependent.22

Photochemistry120

A study of the cis,trans-photoisomerism of the suberanes (17—19) has exam-ined the suitability of such molecules as optical switches.23 Irradiation of somecis-stilbenomethanofullerenes converts them quantitatively into the correspond-ing trans-isomers.24 Reviews have detailed both one-way and two-way isomerisa-tion in a variety of stilbene derivatives25 as well as other aspects of the photo-

II/3: Photochemistry of Alkenes, Alkynes and Related Compounds 121

chemistry of stilbene.26 The conformational equilibrium of some derivatives of(E,E)-2,6-di(arylvinyl)pyridine has been investigated.27

TheZ,E-isomerism of (20) has been studied in detail.28 The photoluminescenceof E-1-(9-anthrylethenyl)-4-chloromethyl-2,5-dimethoxybenzene (21) has beeninvestigated,29 and the results of a study into the photoisomerisation of 1-(9-anthryl)-2-(N-quinolinyl)ethene derivatives have been published.30 The efficienttrans—cis-isomerisation of 1-(9-anthryl)-2-pyridylethane has been described,31

and the photophysical properties of 1-pyrazinyl-2-(3-quinolinyl)ethene havebeen measured.32 Experiments have shown that it is possible to control thealignment of polymethacrylates using the photochemically induced E,Z-isomer-ism of styrylpyridine side-chains.33 Anthracene has been shown to be the mostefficient catalyst to effect cis—trans-isomerisation in 1-(3,5-di-t-butylstyryl)pyrenewhich occurs with a quantum yield 11.5 times higher than for the uncatalysedprocess.34

1.1.2 The Dithienylethene System and Related Compounds. In recent years aconsiderable number of detailed studies have been reported into the photo-chromism of (22) and related systems both in solution and in constrainedenvironments. Irie35 has published a review detailing the photochromism of suchspecies in constrained environments. A further review has dealt with theirbehaviour in the crystalline phase36 and a general review has surveyed the recentadvances in the field.37 A new read-out systemhas been suggested as a method fordetermining degradation in optical memory systems using photochromicdiarylethenes.38 The photochromism of 1,2-bis(2,5-dimethyl-3-thienyl)per-fluorocyclopentene (22) and 1,2-bis(2-methyl-6-nitro-1-benzothiophen-3-yl) per-

Photochemistry122

fluorocyclopentene in the solid state has been studied.39 A further study hasdemonstrated that irradiation of the chiral cyclohexane (23) provides a largepitch change in the chiral nematic phase.40 The photochromism of the dithienylalkene (24) in clays has been studied,41,42 while the photochemical colourisationof (22) and some of its derivatives has been studied in polymer matrices.43 Theradiation sensitivity of such cyclopentene derivatives has also been examined.44

An X-ray crystallographic study of the photochromism exhibited by (22) in thecrystalline state has been carried out.45 The unsubstituted perfluorocyclopentenederivative (25) has also been shown to undergo the usual photochemical cyclisa-tion but degradation by dehydrogenation to afford (26) is a competing process.46

Interestingly compound (22) also undergoes photo-decomposition to give (27)which is thought to arise by S—C bond fission of the ring-closed form to yieldbiradicals such as (28).47 Rearrangement within (28) affords (27).

Many variations on the substituents surrounding the basic skeleton of (22)have been carried out over the years. Aryl substitution of the thiophene rings hasbeen applied and a pulse-laser study of (29) has been reported.48 The compoundsgenerally show photochromism, as do all the derivatives (30), when irradiated at366 nm, which induces their conversion to the blue cyclised form. Irradiation ofthe cyclised isomers at wavelengths �480 nm reverses the process in a ratedependent upon the substituents on the aromatic ring. The fastest reversal isachieved with the 4-tolyl substituent.49 Photochromism is exhibited on irradi-ation of crystals of 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopen-tene (31), and changes to the surface morphology of the crystal were observed


following the isomerisation.50 Other changes to the substitution around the rings,such as increasing the size of the substituents at the 2-position, do not appear toinfluence adversely the photochromicity of the systems. Thus (32) has beenshown to cyclise to the closed form even in the single-crystalline phase.51 Theinfluence of 2,2�-isopropyl substituents (e.g. 33) on the photoactivity of thephotochromic bisbenzothienylethenes has been quantified52,53 and refractive in-dex changes have been studied in photoisomerism of some diarylethene deriva-tives with 2,2�-t-butyl substituents.54 The effects of other substituents have alsobeen investigated as in the diastereoselective cyclisation of the photochromicdiarylethene (34).55,56 Other workers have described perfluorocyclopentene de-rivatives with an optically active group at the 2-position of the thiophene ring.57

The alkene (35) undergoes cyclisation to afford a blue compound on irradi-ation at ��366 nm.58 The reverse reaction occurs on irradiation at ��408 nm.Irradiation of amorphous films of the substance shows the same coloration andthe same wavelength dependence. Studies into the photochromic behaviour of(36) have revealed that the quantum yield of cyclisation is solvent dependent.59 Inthe crystalline phase the alkene (37) undergoes photochemical cyclisation onirradiation at 366 nm to give a blue form.60 Irradiation at longer wavelengths(578 nm) reforms the starting material. Photochromism is also observed whenthe alkene is complexed with Zn(hfac)2.2H2O. The dye (38) shows enhancedfluorescence with quantum yields of the emission rising to 0.83 from 0.001 whenthe thienyl unit specifically is irradiated at 313 nm which also brings about theusual ring closure of the alkene moiety.61

Photochemistry124

The alkene (39) undergoes ring closure on irradiation at 313 nm in solution.62

These compounds form extended aggregates in solution and provide a newself-assembly system for photochromic switches. The ring closure is photorever-sible and irradiation at ��520 nm reforms the starting material. A new series ofphotochromic compounds based on 1,2-bis(2-ethylthio-3-thienyl)perfluoro-cyclopentene has been synthesised and studied.63 Another example of the versa-tility of the dithienylethene photochromic system has been reported and thisinvolves the first example of incorporation of a porphorynic moiety.64 Thuscompound (40) undergoes ring closure on irradiation at 313 nm and ring openingof the closed form can be brought about using ��480 nm.Photoreversible photochromism of 1,2-bis(2-methyl-1-benzothiophen-3-

yl)perfluorocyclopentene derivatives (41)65 and of (42) and (43) in the amorphousstate has been observed.66 A full account of the photochromism exhibited by (44)has been published67 and a study of photoswitching within such molecules hasbeen described.68 The diarylethene (45) has been studied as a dopant in liquidcrystals and onUV-irradiation this causes a disruption of the cholesteric phase, aprocess which is reversed by irradiation with visible light.69

The aryl groups in such systems have also been substituted with aminofunctions as in (46) and the control on cyclisation of these alkenes that can beexercised by cyclodextrins has also been assessed.70 The study has also beenextended to examine the behaviour of the tetramethylammoniumsalt derivatives


Photochemistry126

(47).71 There are two arrangements possible for the triene, the one illustrated as(47), the antiparallel form, where cyclisation can occur and the one shownschematically as (48). This latter is referred to as the parallel arrangement andthis does not photocyclise. In �-cyclodextrin the amount of the antiparallel formis enhanced and the quantum yield for the formation of the cyclic form is alsoenhanced. In �-cyclodextrin, however, the reverse is true and the parallel form ispreferred leading to a reduction in the quantum yield for cyclisation. Somephotochromic compounds based on 1-(3-methylbenzo[b]thiophen-2-yl)-2-(2-methylindol-3-yl)cycloalkenes have been synthesised and, as these compoundshave absorption bands around the 440 nm range, they can be excited usingInGaN blue lasers.72

Other studies by Irie and his co-workers73 report three-dimensional erasableoptical recording using the photochromism of 1,2-bis(3-methyl-2-thienyl)per-fluorocyclopentene. Studies on the photochromic properties of diaryletheneswith terthiophene components have been reported,74 and the photocyclisation ofthe 1,2-dicyanodiarylethene (49) has been studied.75 The efficiency of the cyclisa-tion is wavelength dependent as shown by the quantum yield data for thereaction (�365�1.1, �405�0.32). The ring opening reaction is induced by irradi-ation at longer wavelength (�532�0.16). The behaviour of such systems in amor-phous films, cast polymer films and colloidal solutions has also been examined.76

Other workers have also reported photochromism in these molecules.77 A exam-ination of the photochromicity of compounds (50) and (51) has been reported.78

1.2 Miscellaneous Reactions. — Ab initio studies on the photodynamics ofethene have been reported.79 Pulsed laser photolysis has been used to measurethe absolute rate constant for the reaction of ethynyl radicals with ethyne.80

Irradiation of phenylacetylene in a molecular beam at 193 nm results in the


formation of ethyne and a C6H4 fragment. This fragment breaks down intohexa-1,3,5-triene.81 Complex hydrogen bonding has been detected in the crystalsof the diyne (52).82

1.2.1 Addition Reactions. A review has highlighted the applications of photo-induced alkylation of electrophilic alkenes.83 Further studies on the methoxycar-bonylation of alkenes have been reported.84 The addition products (53) and (54)and the reduction product (55) are formed when (56) is irradiated in the presenceof allyltrimethylsilane.85 The reaction is dependent on the present of an ‘additive’such as phenanthrene and the ratio of the products is dependent on the particu-lar additive used. Cyclic alkanes undergo abstraction of hydrogen to afford thecorresponding cycloalkyl radical when they are irradiated in the presence ofbenzophenone (or a polymer tethered derivative) as the hydrogen abstractingreagent.86 The resultant radicals add moderately efficiently to alkynes and se-lected results are shown in Scheme 1.

1.2.2 Electron-transfer Processes. Arnold and his co-workers87 have reported thephotochemical deconjugation of the arylcyclohexenes (57) to yield (58). Thereactions are brought about using single electron-transfer photochemistry. Cal-culations have been carried out to examine the electron-transfer behaviour of thetetracyanoethene/tetramethylethene system.88 A single electron-transfer reactionis involved in the conversion of (59) into (60).89 The reactions are carried outusingDCAas the electron-accepting sensitiser and the radical cation of the styrylmoiety cyclises to give the intermediate (61). A study of photochemically inducedintramolecular charge separation in the derivatives (62) and (63) has been carriedout.90

1.2.3 Other Processes. The photodissociation of several substituted alkenes hasbeen reported over the past year. Thus the fission processes encountered on the

Photochemistry128

irradiation at 193 nm of vinyl chloride have been investigated,91 and similarlythe photochemical dissociations of 1-chloro-1-fluoroethene92 and chlorotri-fluoroethene93 have been studied at the same wavelength. Several dissociationchannels were identified for the former compound, while three principal frag-mentation paths were detected for the latter molecule. Other workers have alsostudied the primary photofragmentation of 2-chloropropene induced by irradi-ation at 193 nm.94,95 Three processes were elucidated including two that involveC—Cl bond fission producing so called fast Cl and slowCl species. Elimination ofHCl is also a recognised decomposition pathway. A spectroscopic study of allylradicals generated by irradiation of either allyl iodide or hexa-1,5-diene has beenreported.96 Interestingly, the use of longer wavelength irradiation (254 nm) ofhalo compounds does not always bring about C—halogen bond rupture.97 Forexample, the irradiation of (64) in hexane with a low-pressure Hg lamp bringsabout complete conversion to the isomer (65).A photochemical desilylation of silyl enol ethers has been described.98

2 Reactions Involving Cyclopropane Rings

2.1 The Di-�-methane Rearrangement and Related Processes. — A re-investiga-tion of the photochemical behaviour of 1,3-diphenylpropene has shown thatirradiation in cyclohexane affords the products shown in Scheme 2.99 Thisoutcome is independent of wavelength and either 254 nm or 300 nm is effective,


but the former also induces isomerisation of the cis-cyclopropane to the trans-isomer (66). Product formation is solvent dependent and there is a markeddifference when acetonitrile is used. Thus irradiation of the 1,3-diphenylpropeneat 254 nm in acetonitrile affords the trans-isomer (66) as the major product (50%chemical yield), and the quantum yield for the di-�-methane rearrangement is anorder of magnitude greater than that observed in cyclohexane. The authorssuggest that the change in behaviour in changing from cyclohexane to aceto-nitrile is the result of excitation of the alkene to a higher singlet state. Directirradiation at ��300 nm of the trienes (67) results in efficient di-�-methanerearrangement to afford the homobarrelene derivatives (68).100 The barrellene(69) is also reactive in this mode and irradiation (Pyrex filter) in acetonitrilesolution for 20 min brings about the formation of the cyclooctatetraene (70,27%) and the semibullvalene derivative (71, trace).101 Irradiation of (69) intoluene gives the same products but the yield of (71) is enhanced to 43%. Theirradiation of the cyclooctatetraene derivative (70) in deuteriochloroform indu-ces ring closure in the octatetraene followed by bond fission to give (72) in 68%yield. The influence of substituents on the mode of cyclisation of the barrellenes(73) has been studied in detail.102 The derivatives (73a and b) cyclise by the3,11-bonding pathway to yield the semibullvalenes (74) quantitatively, whereasderivatives (73c and d) on irradiation exhibit both 3,11 and 2,12 bonding toafford mixtures of (74) and (75). Derivative (73e) exclusively follows the 2,12-

Photochemistry130

bonding path to give (75e). Interestingly, the dibenzodihydropentalenofurans(76) are photochemically reactive and irradiation converts them back into thedibenzosemibullvalene derivatives (77) by way of the triplet radicals (78) whichabsorb around 410 nm.103 Further studies on the photochemical rearrangementof bridgehead-substituted dibenzobarrelenes have been reported.104

A full account of the tri-�-methane photochemical reactions of, for example,(79) which results in the conversion to the two principal products (80) and (81)has been published.106, 106 The intermediate biradical (82) is the key to therearrangement.

Calculations regarding the photochemical cyclisation from the S1 state ofcyclo-octatetraene into semibullvalene have been reported107 and Wilsey108 hasexamined theoretically the rearrangement processes open to the non-conjugated


1,4-dienes. The various photochemical reactions of non-conjugated dienes havebeen reviewed.109

2.1.1 The Aza-di-�-methane Rearrangement and Related Processes. Furtherexamples of the aza-di-�-methane reaction within some pyrazino- andquinoxalino-fused naphthobarrelenes have been reported.110

2.2 Miscellaneous Reactions Involving Three-membered Ring Compounds. —The photoisomerism of the cyclopropane carboxylic esters (83) has been inves-tigated in a variety of organised media. The best results for the conversion to (84)were obtained by irradiation either in the pure crystalline state or in zeolites.111

Irradiation of cyclopropyl iodide affords allyl radicals following the fission of theC—I bond and ring opening of the cyclopropyl radical.112 The photochemicalreactivity of [1.1.1]-propellane with methylene has been described.113 �-Irradi-ation of (85) in a matrix at 77 K results in the conversion to the radical cation (86)which is photolabile and irradiation with visible light brings about its rearrange-ment to the phenalene radical cation.114 The tricyclic hydrocarbon (87) under-goes photochemical (254 nm) extrusion of dimethylcarbene and the formation ofindane.115 The nature of the solvent used influences the efficiency of the reactionand the best yields (15—20%) are obtained in cyclohexane. The cleavage reactionis less efficient in other solvents (benzene 13—15%, cyclohexylamine 6%, propan-2-ol 10% and isobutylene 7%).

A study of the influence of medium on the outcome of the irradiation of2-methylcyclopropene has been reported.116 In an argon matrix no reaction isobserved, but when the matrix is xenon or bromine-doped xenon irradiation at254 or 313 nm brings about ring opening and the formation of buta-1,3-dieneandmethylallene by way of carbenes. Cyclopropene has also been demonstratedto undergo ring opening to give propyne and allene. The photochemical reactiv-ity of the cyclopropenes (88) in both the singlet and the triplet excited states hasbeen examined.117 The cyclopropenes (89, 90) are photochemically reactive andirradiation at 254 nm brings about their conversion into the correspondingallenes (91, 92).118

Photochemistry132

The photochemical isomerisation of the vinylidenecyclopropanes (93) hasbeen studied in some detail.119 The outcome of the reaction, in terms of thephotostationary states attained, is dependent on the excited state involved. Onsensitisation a cis:trans ratio of 30:70 is achieved while direct irradiation gives a50:50 mixture. Only the 2-naphthyl derivative behaves differently from thisgeneral rule and both direct and sensitised irradiation give the same isomer ratio.In another study the cis—trans-isomerisation of (94) into (95) has been shown tobe brought about by a SET process using DCA as the sensitiser.120 Irradiationusing ��400 nm in aerated acetonitrile brings about the isomerisation with aquantum yield of 0.67. The isomerism involves the ring opening of the radicalcation of (94) into the open isomeric radical cation (96). When additives such asLiClO4 or Mg(ClO4)2 are added, the quantum yield rises and can be as high as13.7. The authors suggest that an electron-transfer chain process has to beinvolved. Irradiation of the tetramethyl substituted derivatives (97) in benzenebrings about the isomerisation into the butatrienes (98) by way of radicalcations.121 Mizuno and co-workers have shown that the vinylidenecyclo-propanes (99) undergo ring opening on irradiation to afford the biradicals(100) which can be trapped efficiently by suitably substituted alkenes such as(101).122 The products are the adducts (102) which are formed in moderate togood yields. The recent photochemistry of cyclopropanes, methylenecyclo-propanes and vinylidenecyclopropanes has been reviewed and a variety ofprocesses were discussed such as cis—trans isomerisation, polar additions andphoto-oxygenation.123

A description of the formation of a 1,3-dipole by irradiation of 2,3-diphenyl-2H-azirine and additions to the isomers of 3-(tosyloxymethylene)tetrahydro-furan-2-one has been published.124 Photoionisation of chloropropylene oxide hasbeen studied and the photoionisation efficiency spectra for the ions were re-corded.125 The photoionisation and photodissociation of epichlorohydrin havebeen studied.126 Phenanthrene type products are produced on irradiation ofcis-stilbene oxide (103) and the quantum yield for the consumption of startingmaterial is 1.1�10�2.127 Quantum chemical studies on 2-oxabicyclobutane havesought to explain its unusual chemical reactivity.128


Photochemistry134

3 Reactions of Dienes and Trienes

A short review has highlighted the photochemical reactivity of allenes.129 Irradi-ation (��300 nm, Xe-lamp, Pyrex filter) of allenes (104) in the presence of C10F21Ican be an efficient method for the formation of the adducts (105).130 The yieldsand the E/Z ratios are shown below the products (105). A study of the photo-chemical reaction of sensitisers such as (106) with allenes has been carried outand a typical result, a photo-NOCAS process, is shown in Scheme 3.131 Theselenium-substituted allenes are both thermally and photochemically reactiveand the products shown in Scheme 4.132

The photochemical isomerisation of germacrene D has been studied.133 Thedisrotatory ring opening of photochemically excited cyclobutene has beenstudied using ab initio molecular dynamics.134 Other studies have been carriedout using the ab initio multiple spawning (AIMS) method that permits thesolution of nuclear dynamics and electronic structure problems simultaneously.Application of this method to the ring opening of cyclobutene has shown that thedisrotatory motion is established within the first 50 fs following excitation.135

The triplet-state isomerisation of (107) involves allylmethylene intermedi-ates.136 The wavelength dependence for the isomerism exhibited by the dienes(108) has been established: the results are summarised in the Table.137 Theauthors suggest that these results implicate a twisted dipolar state depicted as(109). Patents have been filed for the synthesis of photochromic chromenederivatives.138—140


Table Isomerisation of diene (108)

Composition

Compound � (nm) Time (min) all-trans 4-cis

a �400 5 58 4210 20 8015 8 92

b �400 15 8 92c �400 15 9 91

�300 45 43 57

A theoretical study of the ring opening of cyclohexa-1,3-diene has been re-ported141 and its electrocyclic ring opening has been studied using ultrafastdiffraction imaging.142 The irradiation of the dihydropyridine derivatives (110)results in the formation of the 2-azabicyclo[2.2.0]hex-5-enes (111) in low tomoderate yields.143

The photophysical properties of the dienes (112) 1-(p-cyanophenyl)-4-phenyl-buta-1E,3E-diene, 1-(p-methoxyphenyl)-4-phenylbuta-1E,3E-diene and 1-(p-cy-anophenyl)-4-(p-methoxyphenyl)-1E,3E-dienehave been reported.144 The photo-isomerisation of 1-(n-pyridyl)-4-phenylbuta1,3-diene (n�2, 3, or 4) has beenstudied and shown to arise from the singlet manifold in low quantum yields.145

The photophysical properties of E,E-1-phenyl-4-(1�-pyrenyl)buta-1,3-diene havebeen described,146 and a theoretical study of the wave functions of buta-1,3-dienehas been carried out.147

Photochemically excited diacetylene is reactive with some arenes.148 Photoad-dition of the diyne (113) to dimethyl fumarate affords the three products shownin Scheme 5.149 A detailedmechanistic study of the process has provided evidencethat the cyclobutene (114) is the primary product and that further photochemicaladdition occurs to give the other two products.Computational studies have been carried out on the photochemical Bergman

cyclisation of enediynes such as (115).150 The photo-Bergman cyclisation of (116)affords (117) in moderate yields.151 Jones and co-workers152 have reported thephotochemical Bergman cyclisation of the diyne (118) which yields (119) in 44%yield.The carbodiimide derivatives (120) undergo inefficient reaction in sunlight.153

Photochemistry136

The reaction is muchmore rapid on irradiation using wavelengths�300 nm andon direct irradiation (120a—c) undergo cyclisation to give (121) in a processconsidered to involve the triplet state of the carbodiimide moiety and its cyclisa-tion to the biradical (122). The proof of the triplet nature of the reaction wasdemonstrated using sensitised irradiation at 254 nm in toluene or acetone whichinduces cyclisation of the derivatives (120d—g) in yields ranging from 66—96%.Acetophenone was shown to be the best of the triplet sensitisers studied andcyclisation also occurred using the derivative (123). The synthesis of a fullyreversible optical switch based on a tetraethynylethene-1,1�-binaphthalene has


been reported.154 Photochemically induced intramolecular cycloadditions within1-substituted-2-pentamethyldisilanylethynes (substituents are o-hydroxymethyl,acetoxymethyl or allyloxymethylphenyl) have been reported,155 and the photo-degradation of ethylnylestradiol has been studied using a variety of automatedtechniques.156 The photodissociation dynamics of propyne on irradiation at 157nm has been studied in detail and the process has been shown to involveelimination of hydrogen atoms from both the methyl group and the alkynemoiety.157 Photodissociation of propargyl bromide has been investigated.158

Photochemical SET triggered cyclisation of (124) affords (125) which can beconverted into racemic stypoldione (126).159 A review has highlighted the pericyc-lic reactions of conjugated dienes and trienes,160 and quantum yields for theisomerisation of all-trans-1,6-diphenylhexa-1,3,5-triene have been measured.161

The photophysics of the trienes (127) have been studied and their photo-isomerisation has been investigated and shown to be solvent polarity depend-ent.162 An examination of the S0 to S1 spectra of the tetraene (128) and thedependence upon laser power has been reported.163 A novel transient has beenobserved following subpicosecond time-resolved absorption spectroscopy ofall-trans-�-carotene.164 Liu and Hammond165 have reviewed the examples in theliterature of photochemical cis—trans-isomerisation with special attention beingpaid to medium effects and conformational changes. The photoisomerisation ofall-E,3S,5R,6R,3�R)-3,6,-epoxy-5,6-dihydro-�,�-carotene-5,3�-diol has been in-vestigated.166

Photochemistry138

3.1 VitaminD Analogues. — The results from the study of the UV irradiation ofpro-vitamin D3 (7-dehydrocholesterol) in human keratinocytes show that vit-amin D3 is produced.167 Calculations have been carried out to ascertain confor-mational abundances in a 3-desoxy-previtamin D model compound.168 A newlight source for the synthesis of vitamin D2 has been described and the besttransformations are achieved using a 283 nm UV source.169

4 (2��2�)-Intramolecular Additions

The hydrocarbon (129) has been synthesised in two steps from carvone.170

Nominally the product (129) can be obtained by a (2��2�)-cycloaddition inlimonene (130) and calculations have shown that the enthalpy to achieve thiscyclisation is 7.2 kcal mol�1, an endothermic reaction. Bach and co-workers171,172

have reviewed the synthetic potential of cyclisations of non-conjugated dienessuch as (131). Irradiationwith acetophenone as the sensitiser in acetone solutionsgives an 80% yield of (132) and (133) in a ratio of 66:33 respectively. Coppertriflate assisted cycloaddition of (134) gives the adduct (135) which is a usefulsource of the cyclopentenone (136) for conversion into the natural product�-necrodol.173 CuI-controlled (2��2�)-photoadditions of some tethered alkeneshave also been studied.174 Typically the irradiation of (137) affords a 1:1 mixtureof the adducts (138) and (139). A (2��2�)-intramolecular cycloaddition is en-countered in the photochemical transformations of 1,n-bis[trans-4-�2-(5-phenyl-1,3,4-oxadiazolyl)�ethenyl]alkanes where n�3, 4 or 6.175

Inoue and co-workers176 have described a method in a patent application forsynthesising optically active compounds using circularly polarised light. The


example cited involves irradiation of the racemic carboxylate (140) in acetonitrilewith r-circular polarised light at 290 nm which results in the selective excitationof (�)-(140) and its cyclisation into (�)-(141). Paramagnetic species are formedon irradiation of 7,7-dimethyl-1,4,5,6-tetraphenyl-2,3-benzo-7-silanorborna-diene.177

A detailed study of the synthesis of pagodanes by (2��2�)-photocycloaddi-tion has been published.178 Examples are the acetone-sensitised cycloaddition of(142) to afford (143) and (144). Phenanthrene anellated polycyclic hydrocarbonscan be obtained by irradiation of [n.2]metacyclophanes.179 Further studies onthe photochemical addition reactions encountered on the irradiation of thecyclophane (145) have been carried out.180

5 Dimerisation and Intermolecular Additions

The photochemical cycloaddition of the aryl alkene (146) to pyrene derivatives(147) yields the two 1:1 cycloadducts (148) and (149) and one 2:1 adduct (150).181

The involvement of singlet exciplexes in the cycloaddition of alkenes to 9-cyanophenanthrene has been investigated,182 and the photoaddition of ben-zofuran to the pyridine derivatives (151) occurs in benzene solution using excita-

Photochemistry140

tion at ��300 nm.183 The four products are illustrated in Scheme 6. The likelypath to these products involves (2��2�)-cycloaddition as the first step to yield(154) which on ring opening affords the aza-cyclooctatriene (155) and it is thisthat is transformed into the products (152) and (153). Dopp184 has reviewed thephotochemical addition reactions of captodative alkenes.

5.1 Dimerisation. — Heterocyclic substituted alkenes undergo photochemicaldimerisation through both the singlet and the triplet excited states and theadducts are formed with good regio- and stereo-selectivity.185 A review hashighlighted the solid-state photodimerisation of 1,4-dihydropyridines.186

The incorporation of the stilbene derivative (156) into a SAMon gold affords agold cluster that undergoes trans—cis-isomerisation on irradiation but no(2��2�)-photoaddition processes were detected.187 Irradiation at 313 nm offilms of liquid crystalline polymer containing the trans-4,4�-stilbene biscar-boxylate chromophoric systems leads to the disappearance of the stilbene systemwhich is attributed to the formation of (2��2�)-cycloaddition products.188 Thetrans—cis-isomerisation of 2-styrylpyridine in faujasite zeolites has been exam-ined and at low concentrations is the only photochemical reaction, but at higherloading levels (2��2�)-cycloaddition also takes place.189

6 Miscellaneous Reactions

6.1 Reactions Involving Cations and Radicals. — There are many reports deal-ing with the photochemical activity of alkyl halides using a variety of excitationwavelengths. Thus, photodissociation of methyl chloride, bromide and iodidecan be brought about by excitation at 121.6 nm.190 The photodissociation of


methyl iodide has been studied from a theoretical standpoint,191,192 and theangular distribution of photo fragments produced by irradiation of methyliodide at 304 nm has been studied.193

Chlorobromomethane undergoes photodissociation in the 193—242 nmrange194 and also by irradiation specifically at 254 nm.195 The irradiation ofdibromomethane is reported to yield detectable amounts of isodibromo-methane.196 The same authors have also examined the photoisomerisation ofbromoiodomethane.197 Further evidence for the formation of an isomer has beenobtained following the study of the photodissociation of chloroiodomethane198

and of diiodomethane.199,200 In the latter case, the species formed has beenidentified as isodiiodomethane (CH2-I-I).199,200 The authors suggest that thisspecies is probably involved in the cyclopropanation of alkenes.The primary photodissociation path for tribromomethane on irradiation at

193 nm is loss of a bromine atom.201 The photochemical reactivity between

Photochemistry142

tribromomethane and diphenylamine has been used to develop a new detectionmethod based on fluorimetry.202 The photodissociation of dichloro-fluoromethane has been studied,203 and irradiation at 193 nm of benzotrifluoridebrings about C—F fission as the primary process.204

The phototransformations undergone by some halomethanes (CCl3Br, CBr3F,CHCl2Br and CH2BrCl) under aerobic and anaerobic conditions have beeninvestigated.205 Irradiation at 185 and 254 nm of some chlorinated hydrocarbonshas been carried out in the absence of an oxidant.206 Evidence has been gatheredfrom the photodissociation (at 235 nm) of dichlorofluoromethane that a three-body decay path is operative.207 The photofragmentation of difluoro-diiodomethane at 193 nm has been reported,208 and irradiation of CF3I has beenstudied using the fourth harmonic of the YAG fundamental.209 A study of thephotochemical dissociation of CBrClF2 at 157.6 nm has shown that severalfragmentation paths occur with the formation of bromine and chlorine atoms aswell as CF2.210,211

The irradiation at 355 nm of ethyl bromide brings about the formation of thecorresponding cation and a study of the fragments produced in the decay of thisspecies has been made using TOF-MS.212 Perdeuterated ethyl iodide has beenphotolysed in solid parahydrogen at 4.4 K and the perdeuterated compoundsethylene, ethane and ethyl radicals were detected as was DI.213 Calculations havebeen carried out to ascertain the paths for the elimination of a hydrogen atomfrom excited ethyl radicals.214 The competition between ionic and radical paths inthe photochemical reactions encountered with the dihalo-1,2-diphenylethaneshas been studied.215 The photodissociation dynamics of 1-chloro-2-iodoethanehave been measured.216 The ethanes 1-chloro-1-fluoroethane,217 1,1-dichloro-1-fluoroethane218 and 1,1-dichloro-1-fluoroethane219 all undergo photodissoci-ation. The photochemical decomposition of several chlorinated hydrocarbonshas been investigated using 185 and 254 nm irradiation.220 The study was ofenvironmental interest since many of the chlorohydrocarbons (tetra-chloroethene, trichloroethene, 1,2-dichloroethene, chloroform and carbon tet-rachloride) are contaminants in ground water. Photodissociation dynamics havebeen established for a series of partially fluorinated alkyl iodides such asCF3CH2I,221 and fluorinated alkyl iodides are reported to undergo photodissoci-ation on irradiation at 266, 280 and 305 nm.222 The trifluoromethyl anion hasbeen obtained by electron bombardment of hexafluoroethane.223

The peracetylated pyranosyl bromo chlorides (157) are photochemically reac-tive in the presence of allyltributyltin and yield (158) and (159).224 The irradiationof (160, R�Br) in THF solution in the presence of tri-t-butyltin hydride results inthe formation of the corresponding radical from C—Br bond fission.225 Thisradical can add to acrylonitrile, for example, to give the adduct (161) which isaccompanied by the reduced compound (160, R�H).The cation (162) can be prepared by irradiation of the alcohol (163) at low

temperature in strong acid.226 The cation apparently undergoes a 1,2-hydrogenshift to afford (164) at ambient temperatures. The cations (165) can be formed byphotochemically induced heterolysis of the fluorenols (166) in zeolites.227 Otherworkers have demonstrated the formation of the cation (165, R�H) from


irradiation of fluorenol in both polar and non-polar solvents.228 Wan and co-workers have reviewed the photochemical reactivity of hydroxyaromatic com-pounds.229

6.2 Miscellaneous Rearrangements and Bond Fission Processes. — Methane isphotochemically decomposed into hydrogen, methylene and methyl radicalsunder 6.4 eV photon irradiation on a Cu(111) surface.230 Decomposition has alsobeen studied using 121.6 nm irradiation231 and a study of the photochemicaldecomposition of methane at 10.2 eV has been reported.232. The photofragmenta-tion of several straight chain alkanes such as propane, butane, pentane hexane,heptane, octane and decane by excitation at 157 nm has been reported and thework has been extended to examine the behaviour of some branched alkanes(2-methylpropane, 2-methylbutane and 2-methylpentane).233, 234

Laser irradiation of (167) in the cavities of NaY zeolites induces a single

Photochemistry144

electron transfer to yield the corresponding radical cation of (167) which thencleaves to give the cumyl cation and the cumyl radical.235 The involvement of anelectron-transfer process in this reaction is supported by the reactions of (167)carried out in the presence of electron donors such as p-chloranil when the samefission process occurs. The photochemical isomerisation of (168) into (169) hasbeen reported and the reactions of the triene (169) were investigated.236 A furtherreport by Albini and co-workers has focused attention on the SET induced ringopening of acetonides.137 Thus, the simplest acetonide (170) is irradiated in thepresence of TCNB and yields the acid (171). The TCNB undergoes alkylationwith the formation of the tricyanobenzene (172). This reaction type was extendedto include a study of (173) whereby (174) and (175) are formed in a 1:1 ratio andtotal yield of 43%. In more complex systems such as (176) intramoleculartrapping yields (177, 33%). Irradiation of (178) at 254 nm brings about theformation of o-quinone methide.238

A review has given details of the photochemical cleavage reactions involvingbenzyl—heteroatom single bonds.239 Benzyl radicals produced by irradiation ofbenzyl chloride in a glassy medium have been studied,240 and Leigh and Owenshave reported on the one- and two-photon photochemistry undergone by somebenzylsilacyclobutanes.241 The photochemical SRN1 reactivity of the iodopropane(179) with some anions (Scheme 7 ) has been studied in detail and photochemicalyields and chain propagation steps were quantified.242 An electron-transfermechanism is suggested to account for the reaction between 2-naphthoxide andhaloadamantanes,243 and a laser flash study has examined the formation of thealkoxides (180) from the corresponding alcohols.244 The photodissociation ofethoxy radicals has been investigated,245 and hydroxymethyl radicals undergophotochemical loss of hydrogen to yield methanal.246 Irradiation of acrylonitrileadsorbed on a copper surface brings about expulsion of cyanide anion.247


7 References

1. V. J. Rao, 1999,Mol. Supramol. Photochem., 3(Organic Molecular Photochemistry),169 (Chem. Abstr., 2000, 133, 163777).

2. G. Brenna, M. Delmonte, C. Fuganti and S. Serra,Helv. Chim. Acta, 2001, 84, 69.3. T. Wada, N. Sugahara, M. Kawano and Y. Inoue, Chem. Lett., 2000, 1174.4. Y. Inoue, T. Wada, N. Sugahara, K. Yamamoto, K. Kimura, L. H. Tong, X. M.

Gao, Z. J. Hou and Y. Liu, J. Org. Chem., 2000, 65, 8041.5. E. A. Lissi, E. Norambuena and C. Giannotti, Spectrosc. Lett., 2000, 33, 385 (Chem.

Abstr., 2000, 133, 142527).6. A. Fernandez-Gacio, C. Vitale and A. Mourino, J. Org. Chem., 2000, 65, 6978.7. P. Nikolov and S. Metzov, J. Photochem. Photobiol. A: Chem., 2000, 135, 13.8. R. Ballardini, V. Balzani, J. Becher, A. Di Fabio,M. T. Gandolfi, G.Mattersteig,M.

B. Nielsen, F. M. Raymo, S. J. Rowan, J. F. Stoddart, A. J. P. White and D. J.Williams, J. Org. Chem., 2000, 65, 4120.

9. M. C. Pirrung, L. Fallon, J. Zhu and Y. R. Lee, J. Am.Chem. Soc., 2001, 123, 3638.10. M. Seydack and J. Bendig, J. Fluoresc., 2000, 10, 291 (Chem.Abstr., 2000, 594793).11. K. Iwata and H.-O. Hamaguchi, Laser Chem., 1999, 19, 367 (Chem. Abstr., 2000,

763994).12. P.Matousek,G. Gaborel, A.W. Parker, D. Phillips, G. D. Scholes,W. T. Toner and

M. Towrie, Laser Chem., 1999, 19, 97 (Chem. Abstr., 2000, 763901).13. M. E. Sigman, J. T. Barbas, S. Corbett, Y. B. Chen, I. Ivanov and R. Dabestani, J.

Photochem. Photobiol. A: Chem., 2001, 138, 269.14. K. L. Wiemers and J. F. Kauffman, J. Phys. Chem. A, 2001, 105, 823.15. T.-I. Ho, J.-H. Ho and J.-Y. Wu, J. Am. Chem. Soc., 2000, 122, 8575.16. J. H. Ho, T. L. Ho and R. S. H. Liu, Org. Lett., 2001, 3, 409.17. F. D. Lewis and W. Weigel, J. Phys. Chem. A, 2000, 104, 8146.18. A. K. Singh and S. Kanvah, J. Chem. Soc., Perkin Trans. 2, 2001, 395.19. M. L. Balevicius, A. Tamulis, J. Tamuliene and J.-M. Nunzi,Nato Sci. Ser., 3, 2000,

79, 437 (Chem. Abstr., 2001, 134, 100420).20. I. Grabchev, J. Photochem. Photobiol. A: Chem., 2000, 135, 41.

Photochemistry146

21. Y. Jiang and S.Wu,GanguangKexueYu GuangHuaxue, 2000, 18, 36 (Chem.Abstr.,2000, 132, 315705).

22. P. Wong-Wah-Chung, G. Mailhot and M. Bolte, J. Photochem. Photobiol. A:Chem., 2001, 138, 275.

23. C. T. Chen and Y. C. Chou, J. Am. Chem. Soc., 2000, 122, 7662.24. B. Nuber, A. Khong, S. R.Wilson andD. I. Schuster,Proc.-Electrochem. Soc., 2000,

161 (Chem. Abstr., 2001, 88062).25. T. Arai, Mol. Supramol. Photochem., 1999, 3(Organic Molecular Photochemistry),

131 (Chem. Abstr., 2000, 133, 303309).26. V. Papper and G. I. Likhtenstein, J. Photochem. Photobiol. A: Chem., 2001, 140,

39.27. L. Giglio, U.Mazzucato, G.Musumarra and A. Spalletti,Phys.Chem.Chem.Phys.,

2000, 2, 4005 (Chem. Abstr., 2000, 639762).28. T. Karatsu, H. Itoh, A. Nishigaki, K. Fukui, A. Kitamura, S. Matsuo and H.

Misawa, J. Phys. Chem. A, 2000, 104, 6993.29. M. Wang, J. Zhang, J. Liu and C. Xu, Wuli Huaxue Xuebao, 2000, 16, 677 (Chem.

Abstr., 2000, 133, 302883).30. E. J. Shin, J. Photosci., 1999, 6, 61 (Chem. Abstr., 2000, 133, 315481).31. E. J. Shin and T. W. Bae, J. Photosci., 1999, 6, 67 (Chem. Abstr., 2000, 588148).32. P.-H. Bong and J. H. Ryoo, J. Photosci., 1999, 6, 171 (Chem. Abstr., 2000, 133,

327089).33. S. Yamaki, M. Nakagawa, S. Morino and K. Ichimura, Macromol. Chem. Phys.,

2001, 202, 325 (Chem. Abstr., 2001, 137652).34. H. Mollersted and O. Wennerstrom, J. Photochem. Photobiol. A: Chem., 2001, 139,

37.35. M. Irie,Mol. Supramol. Photochem., 2000, 5, 111 (Chem.Abstr., 2001, 134, 107822).36. M. Irie, Gendai Kagaku, 2000, 357, 25 (Chem. Abstr., 2001, 134, 214767).37. M. Irie, Chem. Rev., 2000, 1685.38. T. Tsujioka, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 344, 51 (Chem.

Abstr., 2000, 2000).39. S. Kobatake, T. Yamada and M. Irie,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A,

2000, 344, 185 (Chem. Abstr., 2000, 764118).40. T. Yamaguchi, T, Inagawa, H. Nakazumi, S. Irie and M. Irie, Chem.Mater., 2000,

12, 869 (Chem. Abstr., 2000, 132, 327563).41. R. Sasai, H. Ogiso, I. Shindachi, T. Shichi andK. Takagi,Mol.Cryst.Liq.Cryst. Sci.

Technol., Sect. A, 2000, 345, 39 (Chem. Abstr., 2000, 764150).42. R. Sasai, H. Ogiso, T. Shindachi, T. Shichi and K. Takagi, Tetrahedron, 2000, 56,

6979.43. S. Irie and M. Irie, Bull. Chem. Soc. Jpn., 2000, 73, 2385.44. S. Irie and M. Irie, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 345, 179

(Chem. Abstr., 2000, 764173).45. T. Yamada, S. Kobatake and M. Irie, Bull. Chem. Soc. Jpn., 2000, 73, 2179.46. K. Higashiguchi, K. Matsuda, T. Yamada, T. Kawai andM. Irie,Chem.Lett., 2000,

1358.47. K.Higashiguchi, K.Matsuda, S. Kobatake, T. Yamada, T. Kawai andM. Irie,Bull.

Chem. Soc. Jpn., 2000, 73, 2389.48. H.Miyasaki,M.Murakami, A. Itaya, D. Guillaumont, S. Nakamura andM. Irie, J.

Am. Chem. Soc., 2001, 123, 753.49. M. Irie, T. Lifka, S. Kobatake and N. Kato, J. Am. Chem. Soc., 2000, 122, 4871.50. M. Irie, S. Kobatake and M. Horichi, Science, 2001, 291, 1769.


51. S. Kobatake, K. Shibata, K. Uchida and M. Irie, J. Am. Chem. Soc., 2000, 122,12135.

52. K. Uchida, E. Tsuchida, S. Nakamura, S. Kobatake and M. Irie, Mol. Cryst. Liq.Cryst. Sci. Technol., Sect. A, 2000, 345, 9 (Chem. Abstr., 2000, 764145).

53. S. Kobatake, K. Uschida, E. Tsuchida and M. Irie, Chem. Lett., 2000, 1340.54. T. Kawai and M. Irie, Nippon Shashin Gakkaishi, 2000, 63, 92 (Chem. Abstr., 2000,

133, 157019).55. K. Kodani, K. Matsuda, T. Yamada and M. Irie, Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2000, 344, 307 (Chem. Abstr., 2000, 764138).56. T. Kodani, K. Matsuda, T. Yamada, S. Kobatake and M. Irie, J. Am. Chem. Soc.,

2000, 122, 9631.57. A. Fernandez-Acebes,Chirality, 2000, 12, 149 (Chem. Abstr., 2000, 132, 327575).58. M. Fukudome, K. Kamiyama, T. Kawai and M. Irie, Chem. Lett., 2001, 70.59. J. Ern, A. T. Bens, H. D. Martin, S. Mukamel, S. Tretiak, K. Tsyganenko, K.

Kuldova, H. P. Trommsdorff and C. Kryschi, J. Phys. Chem. A, 2001, 105, 1741.60. K. Matsuda, K. Takayama and M. Irie, Chem. Commun., 2001, 363.61. T. Kawai, T. Sasaki and M. Irie, Chem. Commun., 2001, 711.62. L. N. Lucas, J. van Esch, R. M. Kellogg and B. L. Feringa, Chem. Commun., 2001,

759.63. M. M. Krayushkin, M. A. Kalik, D. L. Dzhavadov, L. G. Vorontsova, Z. A.

Starokova, A. Yu. Martynkin, V. L. Ivanov and B. M. Uzhinov, Russ. Chem. Bull.,2000, 49, 1757 (Chem. Abstr., 2001, 26848).

64. T. B. Norsten and N. R. Branda, J. Am. Chem. Soc., 2001, 123, 1784.65. M.-S. Kim, T. Kawai andM. Irie,Mol.Cryst.Liq.Cryst. Sci.Technol., Sect.A, 2000,

345, 251 (Chem. Abstr., 2000, 764185).66. M.-S. Kim, T. Kawai and M. Irie, Chem. Lett., 2000, 1188.67. K. Matsuda andM. Irie, J. Am. Chem. Soc., 2000, 122, 7195.68. K.Matsuda andM. Irie,Mol.Cryst.Liq.Cryst. Sci.Technol., Sect.A, 2000, 345, 155

(Chem. Abstr., 2000, 764169).69. K. Uchida, Y. Kawai, Y. Shimizu, V. Vill and M. Irie, Chem. Lett., 2000, 654.70. M. Yamada,M. Takeshita andM. Irie,Mol.Cryst.Liq.Cryst. Sci.Technol., Sect.A,

2000, 345, 107 (Chem. Abstr., 2000, 764161).71. M. Takeshita, M. Yamada, N. Kato and M. Irie, J. Chem. Soc., Perkin Trans. 2,

2000, 619.72. P. Fan, G. Pan, Z. Huang, Y. Ming and M. G. Fan, Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2000, 345, 33 (Chem. Abstr., 2001, 134, 78010).73. T. Fukaminato, S. Kobatake, T. Kawai and M. Irie, Proc. Jpn. Acad., Ser. B, 2001,

77B, 30 (Chem. Abstr., 2001, 244009).74. N. Ohtaka, Y. Hase, K. Uchida, M. Irie and N. Tamai,Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2000, 344, 83 (Chem. Abstr., 2000, 764102).75. H. Ishitobi, Z. Sekkat, M. Irie and S. Kawata, J. Am. Chem. Soc., 2000, 122, 12802.76. K. Kasatani, S. Kambe and M. Irie, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A,

2000, 345, 45 (Chem. Abstr., 2000, 764151).77. Q. Chen, T. Hiraga, L. Men, J. Tominaga and N. Atoda,Mol.Cryst. Liq.Cryst. Sci.

Technol., Sect. A, 2000, 345, 21 (Chem. Abstr., 2000, 764147).78. T. Mrozek, H. Goerner and J. Daub, Chem.-Eur. J., 2001, 7, 1028.79. M. Ben-Nun and T. J. Martinez, Chem. Phys., 2000, 259, 237 (Chem. Abstr., 2000,

133, 296058).80. B. Ceursters, H. N. T. Minh, J. Peeters and M. T. Nguyen,Chem. Phys. , 2000, 262,

243 (Chem. Abstr., 2001, 134, 185860).

Photochemistry148

81. O Sorkhabi, F. Qi, A. H. Rizvi and A. G. Suits, J. Am. Chem. Soc., 2001, 123, 671.82. M. Levitus, G. Zepeda, H. Dang, C. Godinez, T. A. V. Khoung, K. Schmieder and

M. A. Garcia-Garibay, J. Org. Chem., 2001, 66, 3188.83. A. Albini, M. Fagnoni and M. Mella, Pure Appl. Chem., 2000, 72, 1321 (Chem.

Abstr., 2000, 816917).84. J.-M. Yin, Y.-C. You, D.-B.Gao. Y.-A.MA, J.-Q. Zhuang andX.-S.Wang,Hecheng

Huaxue, 2000, 8, 134 (Chem. Abstr., 2000, 133, 104789).85. T. Hayamizu, M. Ikeda, H. Maeda and K. Mizuno, Org. Lett., 2001, 3, 1277.86. N. W. A. Geraghty and J. J. Hannan, Tetrahedron Lett., 2001, 42, 3211.87. D. Mangion, J. Kendall and D. R. Arnold, Org. Lett., 2001, 3, 45.88. X.-Y. Li, C. Zhou, Z.-R. Li, L. Qiu and F.-C. He, Huaxue Xuebao, 2000, 58, 189

(Chem. Abstr., 2000, 132, 315713).89. D. Shukla, C. Lu, N. P. Schepp, W. G. Bentrude and L. J. Johnston, J. Org. Chem.,

2000, 65, 6167.90. F. J. Hoogesteger, C. A. van Walree, L. W. Jenneskens, M. R. Roest, J. W.

Verhoeven, W. Schuddeboom, J. J. Piet and J. M. Warman, Chem.-Eur. J., 2000, 6,2948.

91. S.-R. Lin, S.-C. Lin, Y.-C. Lee, Y.-C. Chou, I.-C. Chen and Y.-P. Lee, J.Chem.Phys.,2001, 114, 160 (Chem. Abstr., 2001, 622); ibid., 2001, 114, 7396 (Chem. Abstr., 2001,291180).

92. Y. R. Lee, L. D. Wang, Y. T. Lee and S. M. Lin, J. Chem. Phys., 2000, 113, 5331(Chem. Abstr., 2000, 671445).

93. Y. R. Lee, L. D. Wang, Y. T. Lee and S. M. Lin, J. Chem. Phys., 2000, 113, 6107(Chem. Abstr., 2000, 710859).

94. J. A. Mueller, B. F. Parsons, L. J. Butler, F. Qi, O. Sorkhabi and A. G. Suits, J.Chem. Phys., 2001, 114, 4505 (Chem. Abstr., 2001, 155410).

95. J. A. Mueller, J. L. Miller, L. J. Butler, F. Qi, O. Sorkhabi and A. G. Suits, J. Phys.Chem. A, 2000, 104, 11261.

96. K. Tonokura and M. Koshi, J. Phys. Chem. A, 2000, 104, 8456.97. K. R. Edvardsen, T. Benneche and M. A. Tius, J. Org. Chem., 2000, 65, 3085.98. M. Z. Jin, L. Yang, L. M. Wu, C. You and Z. L. Liu, Chin. Chem. Lett., 2001, 12, 95

(Chem. Abstr., 2001, 187319).99. M. C. Jimenez, M. A. Miranda and R. Tormos, Chem. Commun., 2000, 2341.100. V. Nair, M. V. Nandakumar, G. N. Anilkumar, D. Maliakal, M. Vairamani, S.

Prabhakar and N. P. Rath, J. Chem. Soc., Perkin Trans. 1, 2000, 3795.101. W. Matsuda-Sentou and T. Shinmyozu, Eur. J. Org. Chem., 2000, 3195.102. M. C. Sajimon, D. Ramaiah, S. A. Kumar, N. P. Rath andM. V. George, Tetrahed-

ron, 2000, 56, 5421.103. M. C. Sajimon, D. Ramaiah, K. G. Thomas andM. V. George, J. Org.Chem., 2001,

66, 3182.104. M. C. Sajimon, D. Ramaiah, M. Muneer, N. P. Rath and M. V. George, J.

Photochem. Photobiol. A: Chem., 2000, 136, 209.105. H. E. Zimmerman and V. Cirkva, J. Org. Chem., 2001, 66, 1839.106. H. E. Zimmerman and V. Cirkva, Org. Lett., 2000, 2, 2365.107. M.Garavelli, F. Bernardi, V.Moliner andM.Olivucci,Angew.Chem. Int.Ed.Engl.,

2001, 40, 1466.108. S. Wilsey, J. Org. Chem., 2000, 65, 7878.109. W. M. Horspool, Chem. Dienes Polyenes, 2000, 2, 257.110. C.-C. Chou, R. K. Peddinti and C.-C. Liao,Heterocycles, 2001, 54, 61 (Chem.Abstr.,

2001,77722).


111. E. Cheung, K. C. W. Chong, V. Ramamurthy, J. R. Scheffer and J. Trotter, Org.Lett., 2000, 2, 2801.

112. P. A. Arnold, B. R. Cosofret, S.M. Dylewski, P. L. Houston and B. K. Carpenter, J.Phys. Chem. A, 2001, 105, 1693.

113. W. B. Lee, D. Oh, P. Won, S. Mi, D. H. Hwang, C. J. Cheong and H. Y. Moon, J.Photosci., 1999, 6, 57 (Chem. Abstr., 2000, 588182).

114. T. Bally, Z. D. Zhu, J. Wirz, M. Fulscher and J. Y. Hasegawa, J. Chem. Soc., PerkinTrans. 2, 2000, 2311.

115. I. R. Likhotvorik, E. Tipmann and M. S. Platz, Tetrahedron Lett., 2001, 42, 3049.116. G. Maier, C. Lautz and S. Senger, Chem.-Eur. J., 2000, 6, 1467.117. E. I. Klimova, M. M. Garcia, T. Klimova, C. A. Toledano, R. A. Toscano and L. R.

Ramirez, J. Organomet. Chem., 2000, 205, 89 (Chem. Abstr., 2000, 586632).118. A. de Meijere, D. Faber, U. Heinecke, R. Walsh, T. Muller and Y. Apeloig, Eur. J.

Org. Chem., 2001, 663.119. K. Mizuno, H. Sugita, T. Hirai and H. Maeda, Chem. Lett., 2000, 1144.120. K. Mizuno, K. Nire, H. Sugita and H. Maeda, Tetrahedron Lett., 2001, 42, 2689.121. K. Mizumo, H. Maeda, H. Sugita, S. Nishioka, T. Hirai and A. Sugimoto, Org.

Lett., 2001, 3, 581.122. K. Mizuno, H. Sugita, T. Hirai, H. Maeda, Y. Otsuji, M. Yasuda and K. Shima,

Tetrahedron Lett., 2001, 42, 3363.123. K. Mizuno, N. Ichinose and Y. Yoshimi, J. Photochem. Photobiol., C, 2000, 1, 167

(Chem. Abstr., 2001, 134, 245080).124. J. Castulik, J. Jonas and C. Mazal, Collect. Czech. Chem. Commun., 2000, 65, 708

(Chem. Abstr., 2000, 378684).125. F. Y. Liu, C. X. Li, G. H. Wu, H. Gao, F. Qi, L. S. Sheng, Y. W. Zhang, S. Q. Yu, S.

H. Chien and W. K. Li, J. Phys. Chem. A, 2001, 105, 2973.126. F. Liu, C. Li, H. Gao, L. Sheng and Y. Zhang, Wuli Huaxue Xuebao, 2000, 16, 758

(Chem. Abstr., 2000, 133, 266459).127. S. Hayashi, M. Nose and Y. Yamashita,Kenkyu Kiyo-Nihon Daigaku Bunrigakubu

Shizen Kagaku Kenkyushu, 2001, 36, 127 (Chem. Abstr., 2001, 306960).128. S. Okovytyy, L. Gorb and J. Leszczynski, Tetrahedron, 2001, 57, 1509.129. K. Yamamoto. Kenkyu Kiyo — Konan Joshi Daigaku, 1998, 35, 143 (Chem. Abstr.,

2001, 134, 162764).130. A. Ogawa, M. Imura, N. Kamada and T. Hirao, Tetrahedron Lett., 2001, 42, 2489.131. D. Mangion, D. R. Arnold, T. S. Cameron and K. N. Robertson, J. Chem. Soc.,

Perkin Trans. 2, 2001, 48.132. T. Shimizu, D. Miyasaka and N. Kamigata, J. Org. Chem., 2001, 66, 1787.133. N. Bulow and W. A. Konig, Phytochemistry, 2000, 55, 141 (Chem. Abstr., 2001, 134,

86387).134. M. Ben-Nun and T. J. Martinez, J. Am. Chem. Soc., 2000, 122, 6299.135. M. Ben-Nun, J. Quenneville and T. J. Martinez, J. Phys. Chem. A, 2000, 104, 5161.136. J. Saltiel, O. Dmitrenko, W. Reischl and R. D. Bach, J. Phys. Chem. A, 2001, 105,

3934.137. M. J. R. Reddy, C. V. Rao,K.M. Bushan,M. J. R. Reddy, V. R. Gopal and V. J. Rao,

Chem. Lett., 2001, 186.138. J. Hyakuta and K. Komuro, Jpn. Kokai Tokkyo Koho Jp., 2000, 219,685 (Chem.

Abstr., 2000, 133, 170276); Jpn. Kokai Tokkyo Koho Jp., 2000, 219,687 (Chem.Abstr., 2000, 133, 170277); Jpn. Kokai Tokkyo Koho Jp., 2000, 219,686 (Chem.Abstr., 2000, 133, 170278).

Photochemistry150

139. J. Hyakuta, Jpn. Kokai Tokkyo Koho Jp., 2000, 256,347 (Chem. Abstr., 2000,658109).

140. H.Nago and J.Momota, Jpn.KokaiTokkyoKoho, Jp., 2001, 114,755 (Chem.Abstr.,2001, 290840).

141. A. Hofmann and R. de Vivie-Riedle, J. Chem. Phys., 2000, 112, 5054.142. R. C. Dudek and P. M. Weber, J. Phys. Chem. A, 2001, 105, 4167.143. G. R. Krow, Y. B. Lee, W. S. Lester, N. Liu, J. Yuan, J. Q. Duo, S. B. Herzon, Y.

Nguyen and D. Zacharias, J. Org. Chem., 2001, 66, 1805.144. A. K. Singh and S. Kanvah, New J. Chem., 2000, 24, 639 (Chem. Abstr., 2000,

572445).145. G. Bartocci, G. Galiazzo, U. Mazzucato and A. Spaletti, Phys. Chem. Chem. Phys.,

2001, 3, 379 (Chem. Abstr., 2001, 54112).146. E. Marri, G. Galiazzo, U. Mazzucato and A. Spalletti, Chem. Phys., 2000, 260, 383

(Chem. Abstr., 2000, 698757).147. V. Bachler and H. Schaffner, Chem. Eur. J., 2000, 6, 959.148. A. G. Robinson, P. R. Winter, C. Ramos and T. S. Zwier, J. Phys. Chem. A, 2000,

104, 10312.149. B. D. Kim, G. S. Kim, B. Tu and S. C. Shim, Tetrahedron Lett., 2001, 42, 2369.150. A. E. Clark, E. R. Davidson and J. M. Zaleski, J. Am. Chem. Soc., 2001, 123, 2650.151. N. Choy, B. Blanco, J. H. Wen, A. Krishnan and K. C. Russell, Org. Lett., 2000, 2,

3761.152. G. B. Jones, J. M. Wright, G. Plourde, A. D. Purohit, J. K. Wyatt, G. Hynd and F.

Fouad, J. Am. Chem. Soc., 2000, 122, 9872.153. M. Schmittel, D. Rodriguez and J. P. Steffen, Angew. Chem. Int. Ed. Engl., 2000, 39,

2152.154. L. Gobbi, P. Seiler, F. Diederich and V. Gramlich,Helv.Chim.Acta, 2000, 83, 1711.155. S. K. Park and S. C. Shim, J. Photochem. Photobiol. A: Chem., 2000, 136, 219.156. B. E. Segmuller, B. L. Armstrong, R. Dunphy and A. R. Oyler, J. Pharm. Biomed.

Anal., 2000, 23, 927 (Chem. Abstr., 2000, 636004).157. S. Harich, J. J. Lin, Y. T. Lee and X. Yang, J. Chem. Phys., 2000, 112, 6656.158. D. Y. Kim, J. C. Choe and M. S. Kim, J. Chem. Phys., 2000, 113, 1714.159. X. C. Xing andM. Demuth, Eur. J. Org. Chem., 2001, 537.160. B. H. O. Cook and W. J. Leigh, Chem. Dienes Polyenes, 2000, 2, 197 (Chem. Abstr.,

2001, 134, 107825).161. J. Saltiel, S. J. Wang, L. P. Watkins and D. H. Ho, J. Phys. Chem. A, 2000, 104,

11443.162. Y. Sonoda, W. M. Kwok, Z. Petrasek, R. Ostler, P. Matiusek, M. Towrie, A. W.

Parker and D. Phillips, J. Chem. Soc., Perkin Trans. 2, 2001, 308.163. D. Walser, G. Zumofen, A. Renn and T. Plakhotnik, J. Phys. Chem. A, 2001, 105,

3022.164. J. P. Zhang, L. H. Skibsted, R. Fujii and Y. Koyama, Photochem. Photobiol., 2001,

73, 219.165. R. S. H. Liu and G. S. Hammond, Proc. Natl. Acad. Sci. U. S. A., 2000, 97, 11153

(Chem. Abstr., 2001, 134, 41776).166. P. Molnar, J. Deli, Z. Matus, G. Toth, D. Renneberg and H. Pfander, Helv. Chim.

Acta, 2000, 83, 1535.167. B. Lehmann, P. Knuschke and M. Meurer, Photochem. Photobiol., 2000, 72, 803.168. O. Dmitrenko, J. H. Frederick and W. Reischl. J. Photochem. Photobiol. A: Chem.,

2001, 139, 125.


169. M.-H. Chu, J.-Q. Guo, D.-K. Gao, S.-L. Sun, Y. Xiao and L.-Q. Wang, FaguangXuebao, 2000, 21, 64 (Chem. Abstr., 2000, 386349).

170. J. Filley, A. Miedaner, M. Ibrahim, M. R. Nimlos and D. M. Blake, J. Photochem.Photobiol. A: Chem., 2001, 139, 17.

171. T. Bach, C. Kruger and K. Harms, Synthesis, 2000, 305.172. C. Kruger and T. Bach, J. Inf. Rec., 2000, 25, 183 (Chem.Abstr., 2001, 134, 273394).173. S. Samajdar, A. Ghatak, S. Banerjee and S. Ghosh, Tetrahedron, 2001, 57, 2011.174. E. Galoppini, R. Chebolu, R. Gilardi and W. Zhang, J. Org. Chem., 2001, 66,

162.175. J. Zhuang, S. Wang, Y. Zheng, S. Zhao and W. Zhang, Huaxue Gongye Yu

Gongcheng (Tianjin, China), 2001, 18, 1 (Chem. Abstr., 2001, 242203).176. H. Nishino, A. Nakamura and Y. Inoue, PCT Int. Appl. WO 01 14,287 (Chem.

Abstr., 2001, 134,193014 ).177. T. V. Leshina,M. B. Taraban, V. F. Plyusin, O. S. Volkova andM. P. Egorov,Russ.

Chem. Bull., 2000, 49, 421 (Chem. Abstr., 2000, 469287).178. M. Wollenweber, M. Etzkorn, J. Reinbold, F. Wahl, T. Voss, J. P. Melder, C.

Grund, R. Pinkos, D. Hunkler, M. Keller, J. Worth, L. Knothe and H. Prinzbach,Eur. J. Org. Chem., 2000, 3855.

179. T. Yamato, K. Fujita, K. Futatsuki and H. Tsuzuki, Can. J. Chem., 2000, 78, 1089.180. K. Matohara, C. Lim, M. Yasutake, R. Nogita, T. Koga, Y. Sakamoto and T.

Shinmyozu, Tetrahedron Lett., 2000, 41, 6803.181. K. Mizuno, H. Maeda, Y. Inoue, A. Sugimoto, L. P. Vo and R. A. Caldwell,

Tetrahedron Lett., 2000, 41, 4913.182. T. Noh, K. Jeon, J. Yoon and Y. Jeong, Bull. Korean Chem. Soc., 1999, 20, 1351

(Chem. Abstr., 2000, 133, 104858).183. M. Sakamoto, A. Kinbara, T. Yagi, T. Mino, K. Yamaguchi and T. Fujita, Chem.

Commun., 2000, 1201.184. D. Dopp,Mol. Supramol. Photochem., 2000, 6, 101.185. M. D’Auria, Heterocycles, 2001, 54, 475 (Chem. Abstr., 2001, 77769; 2001, 134,

287687).186. A. Hilgeroth, Recent Res. Dev. Pure Appl. Chem., 1999, 3 (Pt. 1), 153 (Chem. Abstr.,

2000, 133, 30381).187. J. Hu, J. Zhang, F. Liu, K. Kittredge, J. K. Whitesell and M. A. Fox, J. Am. Chem.

Soc., 2001, 123, 1464.188. A. M. Somlai, D. Creed, F. A. Landis, S. Mahadevan, C. E. Hoyle and A. C. Griffin,

Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 371 (Chem. Abstr.,2000, 132, 341038).

189. A. Lalitha, K. Pitchumani and C. Srinivasan, J. Photochem. Photobiol. A: Chem.,2000, 134, 193.

190. G. Amaral, K. S. Xu and J. S. Zhang, J. Phys. Chem. A, 2001, 105, 1115.191. D. A. Micha and C. D. Stodden, J. Phys. Chem. A, 2001, 105, 2890.192. J. Lu, F.-W. Shao and K.-N. Fan, Chem. Phys. Lett., 2000, 329, 461 (Chem. Abstr.,

2000, 845120).193. A. Sugita, M. Mashino, M. Kawasaki and Y. Matsumi, Adv. Multi-Photon Pro-

cesses Spectroscop., 2001, 14, 151 (Chem. Abstr., 2001, 165547).194. P. Zou, W. S. McGivern and S. W. North, Phys. Chem. Chem. Phys., 2000, 2, 3785

(Chem. Abstr., 2000, 576842).195. S.-H. Lee, Y.-J. Jung and K.-H. Jung, Chem. Phys., 2000, 260, 143 (Chem. Abstr.,

2000, 704846).196. X. M. Zheng, W. M. Kwok and D. L. Phillips, J. Phys. Chem. A, 2000, 104, 10464.

Photochemistry152

197. X. Zheng and D. L. Phillips, J. Chem. Phys., 2000, 113, 3194 (Chem. Abstr., 2000,576729).

198. A. N. Tamovsky, M. Wall, M. Rasmusson, T. Pascher and E. Akesson, J. Chin.Chem. Soc., 2000, 47, 769 (Chem. Abstr., 2000, 651133).

199. X. Zheng and D. L. Phillips, J. Phys. Chem. A, 2000, 104, 6880; Chem. Phys. Lett.,2000, 324, 175 (Chem. Abstr., 2000, 434770).

200. X. M. Zheng and D. L. Phillips, J. Phys. Chem. A, 2000, 104, 6880.201. W. S.McGivern,O. Sorkhabi, A. G. Suits, A. Derecshei-Kovacs and S.W.North, J.

Phys. Chem. A, 2000, 104, 10085.202. A. Pal andM. Bandyopadhyay, Indian J.Chem. Technol., 2001, 8, 83 (Chem.Abstr.,

2001, 262910); Indian J.Chem., Sect. B:Org.Chem. Incl.Med.Chem., 2001, 40B, 290(Chem. Abstr., 2001, 302744).

203. A.Melchior, X. L. Chen, I. Bar and S. Rosenwaks,J.Phys.Chem. A, 2000, 104, 7927204. S. T. Tsai, Y. T. Lee and C. K. Ni, J. Phys. Chem. A, 2000, 104, 10125.205. P. Calza, C. Minero, A. Hiskia, E. Papaconstantinou and E. Pelizzetti,Appl.Catal.,

B, 2000, 29, 23 (Chem. Abstr., 2000, 804824).206. H. Shirayama and S. Taguchi,Mizu Shori Gijutsu, 2001, 42, 113 (Chem.Abstr., 2001,

293742).207. X. Chen, R.Marom, S. Rosenwaks, I. Bar, T. Einfeld, C.Maul andK.-H. Gericke, J.

Chem. Phys., 2001, 114, 9033 (Chem. Abstr., 2001, 346357).208. H. A. Scheld, A. Furlan and J. R. Huber, Chem. Phys. Lett., 2000, 326, 366 (Chem.

Abstr., 2000, 591035).209. X.-D. Min, Y.-L. Qu, L.-P. Duo, F.-T. Sang, B.-L. Yang and Q. Zhuang, Qian-

gjiguang Yu Lizishu, 2000, 12, 134 (Chem. Abstr., 2000, 463375).210. A. Yokoyama, K. Yokoyama and T. Takayanagi, J. Chem. Phys., 2001, 114, 1617

(Chem. Abstr., 2001, 32880).211. K. Yokoyama, A. Yokoyama and T. Takayanagi, J. Chem. Phys., 2001, 114, 1624

(Chem. Abstr., 2001, 32881).212. D. Xu, R. J. Price, J. Huang and W. M. Jackson, Z. Phys. Chem. (Muenchen, Ger.),

2001, 215, 253 (Chem. Abstr., 2001, 204889).213. N. Sogoshi, T. Wakabayashi, T. Momose and T. Shia, J. Phys. Chem. A, 2001, 105,

3077.214. A. S. Zyubin, A. M. Mebel and S. H. Lin, Chem. Phys. Lett., 2000, 323, 441 (Chem.

Abstr., 2000, 133, 111553).215. B. Kosmrlj and B. Sket, J. Org. Chem., 2000, 65, 6890.216. X. Zheng andD. L. Phillips,Laser Chem., 1999, 19, 71 (Chem.Abstr., 2000, 763892).217. S.-Y. Chiang, Y. C. Lee and Y. P. Lee, J. Phys. Chem. A, 2001, 105, 1226.218. S.-Y. Chiang, T.-T. Wang, J.-S. K. Yu and C.-H. Yu, Chem. Phys. Lett., 2000, 329,

185 (Chem. Abstr., 2000, 751355).219. A. Melchior, X. Chen, I. Bar and S. Rosenwaks, J. Chem. Phys., 2000, 112, 10787.220. H. Shirayama, Y. Tohezo and S. Taguchi, Water Res., 2001, 35, 1941 (Chem.Abstr.,

2001, 254335).221. K. Kavita and P. K. Das, J. Phys. Chem. A, 2001, 105, 315.222. K. Kavita and P. K. Das, J. Chem. Phys., 2000, 112, 8426 (Chem. Abstr., 2000, 133,

96666).223. H. J. Deyerl, L. S. Alconcel and R. E. Continetti, J. Phys. Chem. A, 2001, 105,

552.224. J.-P. Praly, G.-R. Chen, J. Gola and G. Hetzer, Eur. J. Org. Chem., 2000, 2831.225. A. Alberti, S. Bertini, M. Comoli, M. Guerrini, A. Mele and E. Vismara, Tetrahed-

ron, 2000, 56, 6291.


226. G. Mladenova, L. Chen, C. F. Rodriguez, K. W. M. Siu, L. J. Johnston, A. C.Hopkinson and E. Lee-Ruff, J. Org. Chem., 2001, 66, 1109.

227. M. A. O’Neill, F. L. Cozens and N. P. Schepp, Tetrahedron, 2000, 56, 6969.228. G. G. Gurzadyan and S. Steenken, Chem.-Eur. J., 2001, 7, 1808.229. D.W. Brousmiche, A. G. Briggs and P.Wan,Mol. Supramol.Photochem., 2000, 6, 1.230. K.Watanabe and Y.Matsumoto, Surf. Sci., 2000, 454–456, 262 (Chem.Abstr., 2000,

363934).231. P. A. Cook, M. N. R. Ashfold, Y.-J. Jee, K.-H. Jung, S. Harich and X. Yang, Phys.

Chem. Chem. Phys., 2001, 3, 1848 (Chem. Abstr., 2001, 305703).232. J.-H. Wang, K. Liu, S. Zhiyuan, H. Su and R. Bersohn, J. Chem. Phys., 2000, 113,

4146 (Chem. Abstr., 2000, 623034).233. S. M. Wu, J. J. Lin, Y. T. Lee and X. Yang, J. Chem. Phys., 2000, 112, 8027 (Chem.

Abstr., 2000, 133, 30447).234. S. M. Wu, J. J. Lin, Y. T. Lee and X. Yang, J. Phys. Chem. A, 2000, 104, 7189.235. M. A. O’Neill, F. L. Cozens and N. P. Schepp, J. Am. Chem. Soc., 2000, 122, 6017.236. D. P. DeCosta, N. Howell, A. L. Pincock, J. A. Pincock and S. Rifai, J. Org. Chem.,

2000, 65, 4698.237. M. Mella, M. Fagnoni and A. Albini, Tetrahedron, 2001, 57, 555.238. E. Modica, R. Zanaletti, M. Freccero and M. Mella, J. Org. Chem., 2001, 66, 41.239. S. A. Fleming and J. A. Pincock, 1999, Mol. Supramol. Photochem., 3(Organic

Molecular Photochemistry), 211 (Chem. Abstr., 2000, 133, 163778).240. H. Hitatsuka, T. Okamoto, S. Kuroda, T. Okutsu, H. Maeoka, M. Taguchi and T.

Yoshinaga, Res. Chem. Intermed., 2001, 27, 137 (Chem. Abstr., 2001, 309589).241. W. J. Leigh and T. R. Owens, Can. J. Chem., 2000, 78, 1459.242. J. E. Arguello, A. B. Penenory and R. A. Rossi, J. Org. Chem., 2000, 65, 7175.243. J. E. Arguello,M. Puiatti and A. B. Penenory,Molecules, 2000, 5, 455 (Chem.Abstr.,

2000, 433736).244. L. S. Alconcel, H. J. Deyerl, M. DeClue and R. E. Continetti, J. Am. Chem. Soc.,

2001, 123, 3125.245. H. Choi, R. T. Bise and D. M. Neumark, J. Phys. Chem. A, 2000, 104, 10112.246. D. Conroy, V. Aristov, L. Feng and H. Reisler, J. Phys. Chem.A, 2000, 104, 10288.247. J. O. Caceres, J. Tornero Lopez and A. Urena Gonzalez, Chem. Phys. Lett., 2000,

321, 349 (Chem. Abstr., 2000, 133, 30451).

Photochemistry154

4Photochemistry of Aromatic Compounds

BY ANDREWGILBERT

1 Introduction

During the year, a number of reviews have been published which provide anoverview for a variety of aspects of the photochemistry of aromatic compounds.Topics which have formed the subject of these reviews include the photochemis-try of hydroxy aromatic compounds,1 photoinduced ortho (2��2�) cycloaddi-tion of ethenes to triplet benzenes,2 perspectives of photoinduced electron trans-fer in organic synthesis,3 the synthetic potential of phthalimide SETphotochemistry,4 the synthesis of benzofurans using photocyclisation reactionsof aromatic carbonyl compounds,5 and the photocarbo-functionalisation offullerenes.6

2 Isomerisation Reactions

cis—trans Photoinduced interconversions of stilbenes and related systems arereviewed in Part II, Chapter 3 of this Volume.The results of an extensive study into the phototranposition reactions of 25

ortho, meta and para disubstituted benzenes in acetonitrile solution have beenreported by Pincock et al.7 Photostationary states are reached by methylben-zonitriles and trifluorobenzonitriles while some other derivatives, such asmethylanisoles and methoxybenzonitriles for example, are unreactive. In thepresence of 2,2,2-trifluoroethanol, all the photoreactive benzenes yield the etherderivatives of bicyclo[3.1.0]hex-3-en-2-ol, which in the case of benzene andalkylbenzenes arise from addition of the alcohol to the corresponding benzva-lene. However, for other reactive benzenes, carbenes or bicyclic diradicals areconsidered to be the probable intermediates. The latter feature has been exam-ined in detail with the six isomers of dimethylbenzonitrile.8 All of these alcoholaddition products are rationalised in terms of nucleophilic attack on the bi-cyclo[3.1.0]hex-3-en-1-yl cation intermediates [e.g. (1) from 3,4-dimethylben-zonitrile] formed by protonation of the photoisomer (2). It is concluded fromthese and earlier studies that the essential feature which controls the formation ofthe phototransposition isomers and the alcohol addition products is the position


155

of the cyano group relative to the other substituents.It has been earlier reported that, in a argon matrix, parent silabenzene under-

went photoisomerisation to give Dewar silabenzene.9 Further studies into theisomerisation of these systems have, apparently, been inhibited by the lack ofstable silabenzenes, but Japanese workers have recently synthesised the deriva-tive (3) in which the reactive silicon centre is protected by the bulky 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl group.10 Irradiation (320 nm) of (3) in C6D6

is reported to yield the silabenzvalene (4) which, inmoist air, is converted into thesingle stereoisomer (5), the structure of which was determined by X-ray crystal-lography.

3 Addition Reactions

Photoinduced (2��2�) cycloadditions involving arylethene moieties are re-viewed in Sections 1.1 and 1.2 of Part II, Chapter 2. The present section isconcerned with reactions which involve aromatic rings directly in the photo-process.Intramolecular meta photocycloaddition of 5-phenylprop-1-enes has been

used as the key step in a wide variety of synthetic sequences and interest in thephotochemistry of the corresponding bichromophores with heteroatoms in thetether between the benzene and ethene units continues. It is known that thephotoreactivity of 4-phenoxybut-1-enes is markedly influenced by the natureand position of the substituents on the benzene ring.11 Further work in this areahas been undertaken with the arene bearing carbomethoxy (6), carbomethoxy-methyl (7) and carbomethoxyethyl (8) substituents.12 As expected, for 2�-(6) only(9), derived from the initial ortho cycloadduct (10), was formed, the 3�- isomerproduced minor amounts of the substituted 1,6-bridged dihydrosemibullvalenecompound (11), and intractable polymer resulted from 4�-(6). In marked contrast,irradiation (300 nm) of the isomers of (7) and (8) all gave substituted derivatives ofthe intramolecular 2�,6�- (meta) cycloaddition product with the highest yieldsresulting from 2�-(7) and 2�-(8). Both these bichromophores and the 4�-(7) and4�-(8) isomers also yielded adducts having structures corresponding to (9) fromthe intramolecular ortho cycloadditon. The isomers of the two series (7) and (8) ofthe 4-phenoxybut-1-enes have been complexed with �-cyclodextrin and

Photochemistry156

irradiated in cellophane envelopes with a low-pressure mercury lamp.13 Thiswork provides the first example of using �-cyclodextrin for asymmetric inductionin the intramolecular meta photocycloaddition of benzene—ethene bi-chromophores. For example, ee values of 11.2 and 17% are observed for the twoadducts (12) and (13) (ratio 1 : 3) respectively from irradiation of complexed 3�-(7).It was reported last year that short irradiation (1 h) of 6-chloro-1,3-

dimethyluracil in mesitylene in the presence of trifluoroacetic acid (TFA) gavethe two adduct isomers (14) and (15).14 The same researchers have now reportedthat prolonged irradiation of this addend pair produced a complex mixture ofadducts of pentalenopyrimidine derivatives (see Scheme 1) including the noveldiazapentacyclo[6.4.01,3.02,6.04,8]dodecane (16).15

Hydrogen bonding between the addends has been used in the well-known(2��2�) photocycloadditions of ethenes to 1-cyanonaphthalene in order tocontrol the regio- and stereo-selectivities of the process.16 Thus the cyanoarenes(17) and the ethenes (18) give the endo adducts (19) selectively: this selectivitycontrol is increased from an endo : exo ratio of 3.3 : 1.0 to 13 : 1 respectively bylowing the temperature from ambient to �60 °C. Further studies into thephotocycloaddition of captodative ethenes to arenes having electron withdraw-ing substituents have been published and the type of product obtained from the1-acetonaphthones (20) is shown to be dependent upon the nature of the secondsubstituent.17 For example, while only the photosubstitution product (21) resultsfrom irradiation of (20a) with 2-morpholinoacrylonitrile, for (20b) both substitu-tion and addition processes occur whereas (20c) gives solely (22) and (23) isformed exclusively from (20d). It is noted that these adducts are thermally labileand readily revert to the starting materials on heating and that the presentphotocycloaddition reactions support the intermediacy of exciplexes as pro-posed earlier.18 Irradiation at wavelengths longer than 355 nm of 9-cyano-phenanthrene in the presence of cyclopentadiene or cyclohexa-1,3-diene is re-ported to yield both the arene dimer (24) and (2��2�) cycloadducts.19 Themechanism of the addition is suggested to be influenced by the ionisationpotential of the diene. The endo adduct isomers (25) and (26) from cyclopen-

II/4: Photochemistry of Aromatic Compounds 157

tadiene and the dimerisation of the phenanthrene are deduced to arise from theexcited singlet state of the arene but in the presence of Michler’s ketone thissystem also gives the exo isomer (27) and the (2��4�) cycloadduct (28).Electron-deficient arylethenes such as methyl cinnamate are reported to

undergo stereoselective (2��2�) photocycloaddition to the 5,6-positions ofchrysene in benzene solvent to give (29) by way of an excited singlet sandwichexciplex.20 Similarly, pyrene gives the two adducts (30) and (31) stereospecificallyand with endo selectivity in high yield. The same workers have described anintramolecular version of the addition to pyrene from the bichromophores (32).22

In this case, the efficiency of the reaction is very dependent upon the ethene

Photochemistry158

substituents. Thus while both (32a) and (32b) gave the intramolecular (2��2�)photoadducts (33a) and (33b) in 83 and 81% yields respectively, (32c) affordedonly a 22% yield of the adducts and (32d) was unreactive, although the corre-


sponding intermolecular process of pyrene and the ethene (34) resulted in theformation of (35) exclusively and in high yield. The regiospecific photocycloaddi-tion of (32) is explained by a sandwich-type singlet exciplex involving the pyreneand benzene rings. The (2��2�) photocycloadducts (36) and (37) from irradi-ation of 2-cyanonaphthalene in the presence of the cyclohexa-1,3-diene (38) havebeen used to synthesise the ‘cyclodimers’ (39) and (40) of the cyanoarene andbenzene in 64 and 30% yields respectively.23

Further studies into the application of the intramolecular photocycloadditionof ethenes to the furan ring to the synthesis of ginkgolide B (41) have beendescribed.24 Indeed the synthesis of the complex molecular architecture of thispotent PAF antagonist has now been achieved by using the stereoselectiveintramolecular photocycloaddition of (42) to construct the core skeleton of (41).Irradiation of (42) in hexane—benzene solution with wavelengths longer than 350nm gave an 85% yield of the adduct isomers (43) and (44) in a ratio of �25 : 1respectively. Regioselective cleavage of the cyclobutane ring in (43) and furtherelaboration provided the key pentacyclic intermediate for (41). Benzofuran hasbeen reported to undergo (2��2�) photocycloaddition to 2-alkoxy-3-cyano-pyridine in benzene solution to give a respective 32 : 25 ratio of the endo and exoisomers of (45) by the usual sequence of ortho cycloaddition yielding (46), ringopening to the cyclo-octatriene (47) and photochemical 4�-ring closure.25

Photochemistry160

Photochemical positional isomerisation in the pyridine and its dimerisation togive (48)26 also occur but neither theN-methylindole nor benzothiophene under-goes the addition process. The same series of pyridines give novel adducts with1-cyanonaphthalene.27 For example, 3-cyano-2-methoxypyridine gives a 32%yield of the pyridine dimer and 24% of the adduct (49) which is reasonablyproposed to arise from initial (2��2�) cycloaddition between the C-2 and C-3positions of the pyridine and the C-3 and C-4 positions of the naphthalene. Thecyclo-octatriene (50), formed from ring opening of the primary photoproduct,now unexpectedly undergoes an intramolecular (2��2�) photoaddition to yield(49) rather than a 4�-closure to give adducts of type (45). The adducts (49) arestable under ambient conditions but at 130 °C yield the isomer (51) quantitat-ively.Interesting photochemistry of 2-(1-naphthyl)ethyl benzoates (52) has been

described by Morley and Pincock.28 In both compounds, the naphthalene fluor-escence is quenched, and in the case of (52a) this is accompanied by a solvent-


dependent emission from the exciplex, but (52b) exhibited no such fluorescence.On the other hand, while (52a) is remarkably unreactive photochemically, (52b)undergoes an unprecedented intramolecular addition of the ester carbonyl to thenaphthalene ring followed by the reaction pathway outlined in Scheme 2 to givethe isomers (53) and (54). Novel intermolecular cycloaddition is reported fromstudies into the photoreactivity of 1,4-dicyanobenzene in the presence of 1,1-diphenylethenes.29 For these systems, it is suggested that the exciplex and/orcontact radical ion pair (55) collapses to the dihydroisoquinoline (56) which isoxidised in air to give (57), The reaction is controlled by the ability of the2-substituents on the ethene to stabilise the radical cation species and, further-more, while these additions occur in benzene, the reaction of the addend (58) isdiverted in acetonitrile and the isomer (59) results.The photochemistry of fullerenes continues to attract considerable attention.

Interestingly, photoinduced one-step multiple addition of secondary aminesoccurs to C60 under aerobic conditions to give tetra(amino)fullerene epoxide, therelevant section of which is shown in (60), in moderate to excellent yieldsdependent on the amine structure.30 Other workers have reported that in aspectroscopic study on amine—C60 systems a slow addition reaction was

Photochemistry162

observed that was ‘dramatically catalysed’ by UV radiation.31 These adductshave strong fluorescence emission in the 519 nm region and from this feature thedynamic properties of the aminofullerenes have been explored. (2��2�) Photo-cycloaddition of Z- and E-4-propenylanisole to C60 is reported to occur stereo-specifically to give the trans-substituted cyclobutane and hence it is concludedthat a stepwise mechanism operates in the reaction: results from studies withdeuteriated phenylethenes are consistent with the intermediacy of an openspecies in the rate-determining step.32 Photocycloaddition of 3-methyl-2-cyclo-hexen-1-one to C70 is reported to give an appreciablymore complexmixture thanthat observed from the corresponding reaction with C60, but NMR spectralstudies suggest that the reaction occurs preferentially at the two 6,6-bondsnearest to the pole of the C70 molecule.33

4 Substitution Reactions

In aerated aqueous solution (pH�6), acetophenone is reported to undergosubstitution with wavelengths �200 nm to give the 2- and 3-hydroxy isomers.34

The reaction is greatly inhibited by nitrogen degassing which is suggested toshow that the substitution process arises by attack of a ‘reactive’ oxygen speciesformed from acetophenone sensitisation. The mechanism of photoinducedchlorination of pyridine has been assessed by density functional theory and, ofthe transition states of the three possible pathways, that to form the 2-chloro-substituted product has the lowest activation energy (114.6 kJ mol�1) which is inagreement with the experimental result.35 Visible light irradiation of aromatichydrocarbons in the presence ofN-bromosuccinimide is reported to yield mono-bromides and dehydrogenated products from methyl-substituted and hydro-genated arenes respectively whereas anthracene yields solely the 9,10-dibromoderivative.36

In recent years, the photoreactions of arene—tetranitromethane systems havebeen subjected to detailed studies.37 Such processes with phenols, 1,2-dimethoxybenzene, and anisoles have been investigated by 15N NMR spectro-scopic examination of the photoreaction with 15N-enriched C(NO2)4.38 In theformation of nitrophenols and 1,2-dimethoxy-4-nitrobenzene, the reactions arededuced to arise from triplet excited states of the arenes or by free radicalencounters to give radical pairs from radical cations or phenoxy radicals and·NO2. The NMR signals of these nitro products appear in emission whereas, incontrast, the 15N NMR signals from the nitration products of anisole and the3,5-dimethylanisole appear in enhanced absorption which suggests the involve-ment of singlet radical pairs such as [anisole�·, ·NO2] for example: these areproposed to arise from decomposition of an unstable nitro-trinitromethyladduct intermediate.The irradiation of chlorobenzene in water is known to yield phenol deriva-

tives,39 but it has now been reported that unusual behaviour occurs from thechloroarene in ice.40 Under these conditions biphenyl, terphenyl and their chlor-inated derivatives are formed as a result, it is suggested, of a free radical process

Photochemistry164

in aggregates of the chlorobenzene even in very dilute solid solution. Theformation of triphenylene from this reaction is reasonably proposed to involvephotodehydrochlorination of the intermediate 2-chloroterphenyl (61). Thephotoformation of propylbenzene from 2-chloropropylbenzene in trifluoro-ethanol can readily be accounted for by radical intermediates but the productionof indane and trifluoroethoxypropylbenzene suggests the involvement of the2-propylphenyl cation.41Reaction pathways in this photosolvolysis process havebeen assessed by density function calculations and, indeed, the results stronglyimplicate the cation as an intermediate. Good yields of stannanes such as (62) areformed by an SRN1 mechanism from irradiation of chlorobenzenes in liquidammonia in the presence of NaSnMe3 and the reaction has been developed into aone-pot process to give phenylated compounds again in excellent yield.42 2-(4-N,N-Dimethylaminophenyl) heteroarenes (63) can be readily obtained by irradi-ation of 4-chloro-N,N-dimethylaniline in acetonitrile solution in the presence offurans, pyrroles or thiophenes.43 When the �-positions of the heteroarenes areblocked, the reaction occurs at the �-position with equal efficiency and theobserved high selectivity of the process is accounted for by the intermediacy ofthe N,N-dimethylamino cation (64) formed by heterolytic cleavage of the C—Clbond in the triplet excited aniline. Aryl bromides and iodides and phenylacetatedianions (65) in liquid ammonia solution react photochemically by an SRN1process to give arylated phenyl acetic acids (66) and (67),44 and irradiation of2,3-di-iodo-5-nitrothiophene in the presence of arenes or heteroarenes is re-ported to give the 2-aryl derivatives (68) in good to excellent yield.45 The lowefficiency of the latter reaction with 2,4-di-iodo-5-nitrothiophene is rationalised


in terms of the homolytic cleavage of the C—I bond occurring from the n* tripletstate which is the lowest state of the 2,3-di-iodo isomer, but the 2,4-di-iodothiophene has a ��* lowest state. Irradiation of aryl iodides in the presence ofazulene is reported to be a convenient method for arylating the electron rich1-position of azulene.46

The photoinduced substitution reactions of cyanoarenes continues to be atopic of much interest. Thus ortho and para dicyanobenzenes and 4-cyano-pyridine undergo photosubstitution with formamides and 1-alkyl-2-pyrrolidoneto yield, for example (69) and (70) respectively.47 Allylbenzene derivatives such as(71) are formed as 1:1:1 adducts from irradiation of 1,2,4,5-tetracyanobenzeneand tetramethylallene in methanol solution by a mechanism involving photo-induced electron transfer and described as a photo-NOCAS (photochemicalnucleophile—olefin combination, aromatic substitution) process.48 1,4-Dicyanobenzene behaves similarly but 1,4-dicyanonaphthalene undergoes reac-tions which are initially similar to the photo-NOCAS process but which yieldaddition products (72)—(75) with 1,1-dimethylallene, rather than the allyl com-pounds corresponding to (71). The efficiency of all these electron-transfer in-itiated processes is enhanced by the presence of biphenyl. Indeed, in the absenceof this co-donor, the photoinduced electron transfer in the dicyanonaphtha-lene—1,1-dimethylallene system is markedly reduced and instead an exciplex-mediated reaction to give the (4��2�) cycloadduct (76) becomes the majorpathway.

Photochemistry166

Irradiation of the co-crystals of 1,2,4,5-tetracyanobenzene and benzyl cyanide(respective ratio 1:2) leads to substitution at the aryl nitrile group giving thestilbene derivative (77) by the pathway outlined in Scheme 3.49 Inethanol/acetone solution, (77) is converted into the syn isomer which cyclises togive the isoindole derivative (78). The cyano group in 6-phenanthridinecarboni-trile is substituted on 254 nm irradiation of its propan-2-ol/water solutions toafford phenanthridine, (79) and (80) from the common intermediate, the 6-phenanthridinyl radical.50 Further studies by the same group have shown thatthe reaction proceeds exclusively from the ��* singlet of the cyanoheteroarene.51

The lowest triplet state of diacetylene has been laser-generated and the reactivityof this species with benzene and toluene has been investigated by time of flightmass spectrometry.52 The products are identified as phenylacetylene and isomersof phenyldiacetylene, and these reactions have been discussed in relation tohydrocarbon growth in sooting flames. Finally in this section, it is interesting tonote that phenylalanines (81) can be obtained in yields up to 50%, based onrecovered starting material, from irradiation of the protected glycines (82) in thepresence of di-t-butyl peroxide, benzophenone and substituted toluenes.53


5 Cyclisation Reactions

6�-Photoinduced electrocyclisations of a variety of aromatic systems continue toreceive wide attention both for their academic interest and commercial applica-tions. Stilbene derivatives have long been favourite compounds for study in thisarea. The reaction of p-methoxy-stilbenes and -�-arylstyrenes has been shown toprovide a convenient access to trihydro polyaromatic ketones such as (83) bynovel acid-catalysed hydrolysis of the cyclised intermediate (84) following a [1.9]hydrogen shift in the 4a,4b-trans-dihydrophenanthrene as illustrated in Scheme4.54 The process is versatile and good yields are reported for systemswith 2-furyl-,2-thienyl-, 3-furyl-, 3-thienyl, naphthyl- and phenanthryl- as the aryl unit in thestarting material. Similar photocyclisation has been used with N-[2-(o-styryl)phenylethyl]acetamides (85) and 1-methyl-1,2,3,4-tetrahydroisoquino-lines (86) to construct the phenanthrene ring system in new total syntheses of1-methyl-1,2,3,4-dihydronaphtho[1,2-f]isoquinolines.55 Picosecond time-resol-ved fluorescence spectroscopy of cis-1-(2-anthryl)-2-phenylethene has been usedto gain an understanding of the photocyclisation reaction by distinguishingbetween the s-cis and s-trans rotamers.56 Thus while the s-trans rotamer (87)undergoes solely cis�trans isomerisation, the s-cis rotamer (88) principallyyields the dihydrophenanthrene intermediate (89) which ring opens to (88) morerapidly than it is oxidised to the 1,2-naphth[a]anthracene (90). Irradiation of[n.2] metacyclophanes (91) in cyclohexane solution and the presence of iodineprovides a route to phenanthrene annulated polycyclic aromatic hydrocarbons(92) in yields up to 90%.57 The rates of reaction are dependent on substitutionwith the anti (91) [R�H and n�3] being appreciably greater than that of syn(91) [R�Me and n�3].

Photochemistry168

The photochromism of 1,8a-dihydro-2,3-diarylazulenes is reported to begreatly influenced by the nature of the aryl groups.58Thus while the 2,3-diphenylderivative (93) exhibits photochromism based solely on reversible isomerisationto the vinylheptafulvene (94), the dithienyl system (95) undergoes reversiblewavelength-dependent conversion to the 6�-cyclised isomer (96) and the hepta-fulvene (97). The efficiency of photocyclisation of cis-3-styrylthiophene under anitrogen atmosphere is decreased on increasing the solvent polarity and, follow-ing a separate oxidation, the process can afford good yields of (98), but irradi-ation in the presence of oxygen also results in cleavage to benzaldehyde and3-thiophenecarboxaldehyde and dimerisation to (99).59 The photoinduced cyc-lisation of the (arylvinyl)thienoquinolizinium salts (100) and (101) gives access toa series of novel heterohelicenes (102a) and (102b) respectively.60

Within the review period, a number of publications have appeared describing6�-photocyclisation of systems incorporating indole and benzothiophene moie-ties. Pan and co-workers have investigated the photochromic behaviour of thenovel 1,2-bis(1,3-dimethylindol-2-yl) cycloalkenes (103) and report that the ther-mal stability of the cyclised isomers is better than corresponding products fromthe 1,2-bis(1-ethyl-2-methylindol-3-yl)cycloalkenes (104), but that the absorp-tion maximum is at longer wavelength in the latter case.61 The same group alsonote that the 1-(3-methylbenzo[b]thiophen-2-yl)-2-(2-methylindol-3-yl)cyclo-alkenes (105) produce cyclised forms with absorption centred at 440 nm which isin the range of InGaN lasers.62 The 6�-photocyclisation of benzothiophenesystems (106) does not occur for the 4-nitrophenyl compound but the other


derivatives investigated yield not only the expected cyclised isomers (107), butalso the 6H-benzo[b]naphtha[2,3-d]thiopyran-6-ones (108) in respective yieldsof 73 and 6% for R�OMe.63

In recent years, considerable interest has been shown in the photochromicproperties which arise from the 6�-photoelectrocyclisation of 1,2-bis(methyl-thienyl)- and 1,2-bis(methylbenzothiophen-3-yl-perfluorocyclopentenes.A studyinto the influence of substituents on the phenyl rings of the bis(2-thienyl) systems(109) has revealed that although electron donor R groups shift the absorption ofthe open ring isomer to longer wavelengths the efficiency of the cyclisation isreduced, and for R�NMe2 no reaction occurs.64 Irradiation (366 nm) of the

Photochemistry170

optically active photochromic R and S enantiomers (110) in solution and assingle crystals is reported to induce reversible photocyclisation, and under thelatter conditions one diastereoisomer is formed exclusively, which in the case ofS-(110) is deduced from X-ray crystallography to have the (S,R,R) structure(111).65,66 Single crystals of the dithienyl and dibenzothienyl systems (112) and(113) undergo changes from colourless to red and green respectively on 366 nmirradiation.67 The dichroism of yellow and blue colours from the green cyclisedisomer of (113) under polarised light is attributed to two perpendicular electronictransitions at 465 and 600 nm respectively. It is interesting to note here that thedistyryl derivative (114) forms an amorphous state below the glass transitiontemperature (60 °C) in which reversible 6�-photocyclisation occurs.68 The type ofbisbenzothienylethenes considered above have two conformers: the anti parallelorientation (115) undergoes photocyclisation and the parallel (116) conformer isinactive. The efficiency of the photochromic process is, of course, dependentupon the ratio of the conformers and this aspect has been examined usingderivatives which have dimethyl and di-isopropyl substituents at the 2-posi-tions.69 Satisfyingly, the ratio of anti parallel:parallel of 70:30 (dimethyl) and 94:6(di-isopropyl), deduced from NMR spectroscopy, translates through to an in-crease in the quantum yield for the cyclisation from 0.55 to 0.80 (��282 nm) withthe reverse process (��517 nm) being essentially unaffected at around 0.35 foreach system. The increase in cyclisation efficiency which is reported on additionof �-cyclodextrin to aqueous solutions of (117) is attributed to an increase in theconcentration of the near-planar photoactive anti parallel as a result of its ease of


complexation.70 As part of a study into the properties of dinuclear complexeswith a photochromic bridge, Fraysse and co-workers have investigated thephotochemistry of the dithienyl ruthenium complex system (118).71 Reversiblecyclisation occurs on irradiation and an intervalence band arising from intra-molecular electron transfer between Ru(II) and Ru(III) is observed during oxida-tion of the cyclised isomer, but not from the open form (118).

Photochemistry172

1-Arylbuta-1,3-dienes undergo ready 6�-photoelectrocyclisation and a num-ber of examples of this type of process with fulgide systems have been recentlydescribed. One of the groups which has contributed much to this area over theyears has now reported that the thiofulgide (119) on 366 nm irradiation intoluene solution undergoes reversible cyclisation to give the thermally stablepurple photochrome (120) which absorbs at appreciably longer wavelength thanthe corresponding oxygen compound.72 Other workers have synthesised helio-chromic benzothienylfulgides and note that theE-isomer (121) for R�Ph photo-cyclises exclusively to the benzothiophene unit rather than the phenyl group.73

The formation of (122) by a 1,5-hydrogen shift in the cyclised compound (123)74

occurs in 20—27% yield overall depending on the substituent. The relationshipbetween the photoisomers of (121) is outlined in Scheme 5. Indolylfulgides (125)having diesters of crown groups have been synthesised and their photochromicproperties in the presence of Li�, Na� and K� have been studied.75 The associ-ation of the metal was stronger in both the E- and Z-isomers than the cyclisedcompound, and while for n�2 the presence of the ions did not influence thephotochromism, the Na�/n�3 and K�/n�4 systems, which had the largestassociation constants, did not cyclise. Geometries of the 3-furyl-, 3-pyrryl- and3-thienyl-fulgides and substituted 3-furyl-fulgides have been optimised at HF/6-31G and 6-31G* levels, fromwhich it is deduced that the cyclised isomers for the3-furyl- and thienyl compounds are more stable than the open E-form, whereasthese isomers are isoenergetic for the 3-pyrryl fulgide.76 Furthermore, it is notedthat formation of the -bond to give the cyclised isomer is enhanced by electrondonor substituents.

The photoformation of carbazoles from diaryl amines is a well-researchedprocess and is now reported to be first order and subject to significant solventeffects.77 The isomeric N,N-diphenylphenylenediamines have variable photo-reactivities in this process, but the N,N-dimethyl-N,N-diphenyl compounds


undergo mono- and di-cyclisations. 78 Interestingly, however, the recent accountof the formation ofN-methylcarbazole (41%) from the ortho isomer of the latterseries represents the first reported example of mono-cyclisation with concomi-tant loss of the N-methylaniline moiety.79 In an extension of earlier work,80 theinfluence of the methanesulfonyl group on the regioselectivity of the photo-cyclisation of the arylheteroarylamines (126) and (127) has been studied in somedetail.81 For example, in (127) with R�SO2Me, cyclisation is at the 2-positionand elimination occurs giving (128), whereas for R�Cl, the reaction involves the8-position and (129) results by the formal loss of HCl. Such differing regioselec-tivity is rationalised by radical cation and electrocyclisation mechanisms. Thereare indeed, numerous accounts of photodehydrohalogenation—cyclisation pro-cesses in the literature and several examples have been reported during thereview period. The process can, however, be markedly dependent on the halogen.Thus while 2-bromo-N-pyridinylbenzamides principally undergo photoreduc-tion to give N-pyridinylbenzamides (130) and give only minor amounts of thecyclised product, the 2-chloro-analogues (131) afford high yields of the benzo[c]-naphthyridinones (132).82The reaction arises from the triplet state of (131) and is

Photochemistry174

proposed to proceed by the n-complex (133) which is supported by laser flashphotolysis experiments showing a transient at 400 nm with a lifetime of 30 s.Irradiation of 2-bromo-2-methylpropananilides (134) (R1�H) results in dehyd-robromination giving the N-aryl-2-methylprop-2-enamides (135) exclusivelybut, in contrast, N-alkyl or N-phenyl substituted derivatives yield the indoloneand quinolinone cyclisation products (136) and (137) respectively as well asderivatives of (135).83 Products of type (136) are formed exclusively, albeit in lowyields, from N-methyl-substituted 2-chloro-2-phenylacetanilides and 2-chloro-acetanilide. Novel polycyclic heteroarene ring systems such as (138)84 and (139)85

can be synthesised using the photodehydrochlorination cyclisation of (140) and(141) respectively as the key reaction.


The regio- and stereo-chemically controlled photocyclisation of the aryl en-amide (142) has been used in the total synthesis of the antitumour alkaloids(�)-narciclasine (143) and (�)-pancratistatin (144),86 and a versatile, convenientand high-yielding route to benzo[a]carbazoles (145) and pyrido[2,3-a]car-bazoles (146) has been developed from the treatment of 2-(o-tolyl)- and 2-(3-methyl-2-pyridyl)-substituted indole-3-carbaldehydes (147) and (148) respective-ly with potassium t-butoxide in DMF at 70—80 °C with simultaneous exposureto a 400 W high pressure mercury arc lamp.87

Photochemistry176

TheZ- andE-isomers ofN-acetyl-�-dehydrophenylalanines (149) in methanolsolution are reported to undergo photoinduced cyclisation to give isoquinoline(150) and 1-azetine (151) respectively by the routes outlined in Scheme 6.88 In thepresence of benzophenone, only Z—E isomerisation of (149) occurs and so theformation of both (150) and (151) is deduced to arise from the singlet state of(149). The influence of substituents on these processes has also been described.89

The pyran ring in the nitrone spin trap (152) undergoes photochemical ringopening to (153) which cyclises back to (152) in the dark.90

The ortho quinone methide (154) formed photochemically (��313 nm) fromthe benzofurylcarbene (155), which in turn is the photoproduct of the diazirine(156) in a nitrogen matrix at 10 K, is reported to undergo light-induced cyclisa-tion (366—430 nm) to yield the allene (157).91 It is speculated that a 1,3-aryl shift in(157) gives the photostable benzocyclobutene (158), but irradiation of (157) withwavelengths in the 546—620 nm region reverses the cyclisation reaction and, byalternative ring closure of (154), the carbene (155) is reformed as outlined inScheme 7. Irradiation of diphenylethynyl ethenes of type (159) in propan-2-olsolution induces cyclisation to give the diphenylbenzocyclobutenes (160) inyields up to 21% dependent on the alkene ring size,92 and toluene solutions ofenyne-carbodiimides (161) are reported to afford the indoloquinolines (162) inexcellent yields by direct irradiation (for electron withdrawing substituents R1 orR2) or on triplet sensitisation.93


6 Dimerisation Processes

An improved synthesis has been described by Gan and co-workers which givesbetter yields and higher purities than previous routes to cis-syn-o,o�-dibenzene(163).94 The synthesis involves the (4��4�) photocycloaddition of the cyclohexa-1,3-diene (164) to benzene to give (165) as the key step followed by hydrolysis ofthe adduct and a thermal Cope rearrangement. Proximate benzene rings in astrained molecular environment as in ‘janusene’ (166) will undergo regiospecificphotodimerisation giving, in this case, (167) and this process has been used toprepare the benzoannelated[2.2.2.2]pagotetraene (168) which has a half-life of 25

Photochemistry178

min at 160 °C, by way of the maleic anhydride adduct (169).95 The mechanism ofthe earlier reported photodimerisation of o-acylstyrenes (170)96 has been inves-tigated and deduced to proceed by photorearrangement to the oxatricyclotriene(171) or to the ketene (172).97 The former isomer yields the benzobicyclo[3.2.1]-octanes (173) and (174) by the respective addition of the carbonyl group and theethene moiety of (170) to (171), and the isocoumarin (175) arises from similarreaction of the carbonyl group with (172).

Under an argon atmosphere, intramolecular photodimerisation of the linked1-naphthyl units in (176) occurs both by (2��2�) and (4��4�) cycloadditionsgiving (177) and (178) respectively but the novel 1,8-epidioxides (179) are alsoformed from irradiations under oxygen.98 The formation of (179) represents thefirst example of trapping a triplet biradical intermediate in aromatic cycloaddi-


tions and, on the basis of the anti stereochemistry of this product and thesyn-orientation of (178), an equilibrium between the two biradical intermediatesis proposed. The same group have also investigated the reactions ofN-(naphthyl-carbonyl)anthracene-9-carboximides (180), both in solution and in the solidstate, and report that for the formation of the (4��4�) cyclodimers (181) and(182) changing the reaction phase induces a novel reversal of diastereoselectiv-ity.99 Thus in acetone solution at �78 °C, the respective ratio of (181) to (182) is15:85 whereas at 60 °C in the solid state this is changed to 80:20. It is interestingto note here that the well-known (4��4�) photodimerisation of 2-pyridones inthe intramolecular linked system (183) leads, by subsequent cis-hydroxylation ofthe product (184) and nucleophilic addition, to the construction of both quater-nary carbons and four of the five stereogenic centres in the eight-membered ringof taxol.100

The photodimerisation of anthracene was first described in 1868 and yet theprocess continues to attract attention. Russian workers have reported that

Photochemistry180

pressure alone does not promote the photodimerisation in crystals despiteincreasing the number of excimer centres, but the application of pressure andshear stress does initiate the reaction.101 There is some evidence from this studythat the dimerisation actually occurs under the latter conditions in the absence ofradiation. Further details of a preliminary report102 of the photodimerisation of9-substituted acridizinium salts (185) have been published.103 The process isdependent on the phase and on the nature of the substituent and the anion. Forexample, inseparable mixtures of all four regioisomers were formed from(185a—c) in acetonitrile or methanol solution whereas the amino compound(185d) gave the syn and anti head-to-tail dimers in a 1 : 1 ratio. In the solid state,(185a and b).Br and (185c).ClO4 afforded the anti head-to-tail dimer (186) exclus-ively. X-Ray crystallographic data show that the salts which dimerise in the solidstate have lattices comprising pairs of monomers in an anti head-to-tail orienta-tion whereas for (185a).BF3, the two molecules are in a highly distorted synhead-to-head arrangement and no dimersiation is observed.

7 Lateral Nuclear Shifts

Over the years, the photo-Fries rearrangement of derivatives of aryl esters andanilides has attracted considerable attention and it is now reported that in theformer series, 2—12% of the product arises from the trivial mechanism of thephenol reacting with the acyl radical.104 Mayouf and Park have noted that whileirradiation of 2�-chlorobenzanilide in nitrogen-degassed acetonitrile solution inthe presence of sodium hydroxide yields mainly the photo-Fries product 2-amino-3-chlorobenzophenone and minor amounts of 2-phenylbenzooxazole(187), in contrast, 2�-bromobenzanilide under similar conditions gives reasonableyields of (187) and little of the Fries isomer.105 This type of lateral-nuclearrearrangement has also been used in the synthesis of ortho and para cyclo-phanes.106 In this application, irradiation of the macrocyclic N-phenylimides


(188) yields (189) and (190) as well as the secondary photo-Fries products, theamino cyclophanes (191) and (192): as expected, if the para position is blocked,only (189) and (191) (R�Me) are formed. Irradiation of the o-fluoro ester of3-hydroxy-6,7-dimethoxycoumarin (193) in benzene/ethanol solution gives therearranged isomer (194) which on treatment with potassium carbonate yields thecyclised product, 2,3-dimethoxyrotenoid (195), a member of a family of potentnaturally occurring insecticides and antifeedants.107 Photochemical lateral—nuclear migrations of a number of t-butyl ethers in methanol solution have beenstudied in some detail.108 The reaction is deduced to arise from the singlet excitedstate, and the formation of 1-methoxyadamantane from irradiation of 4-cyano-phenyl 1-adamantyl ether, is suggested, at least in this case, to involve an ionicintermediate. The photo-Claisen rearrangements of benzyl phenyl ethers

Photochemistry182

and benzyl 1-naphthyl ether in cation-exchangedY-zeolites and polyethylenes ofdiffering crystallinities have been reported.109 The ratios of products show thatthe reactions are more selective in the zeolites than in the polyethylenes andindicate that the supramolecular character of the reaction cage can be under-stood by such probe processes. However, the guest—host interactions can besubtle leading to quite different selectivities as shown by the current studycompared to the very high selectivity observed under similar conditions with thephoto-Fries rearrangement.110

Further studies have been reported into the photochemistry of 3,5-dimethoxybenzyl derivatives in alcohol solution.111While the 1,3-dimethoxy-5-methylene cyclohexa-1,3-dienes (196) are formed from the acetate and the phos-phate, the yields are low (ca. 16%) and the migration process arising from bondhomolysis does not appear to occur for the chloride, bromide and iodide.112 Thedominant process in these latter compounds is photosolvolysis involving hetero-lysis of the benzyl—X bond, although the same product is formed by thermalreaction of the solvent with (196).

The well-known photoWallach rearrangement of azoxybenzene into orthoand para hydroxyazobenzenes has been investigated in various cation-ex-changed faujasites and, as observed in isotopicmedia, the former product isomeris formed predominantly and from the S1 state.113

8 Miscellaneous Photochemistry of Aromatic Systems

Photoinduced intramolecular hydrogen atom transfer occurs for a range ofdisubstituted compounds with proximate interacting centres. ortho-Nitrobenzylcompounds are particularly reactive and the details of this process and thenature of the intermediates have been elucidated using time-resolved Raman andabsorption spectroscopies.114 Proton transfer in the ground and electronicallyexcited states of 4-methyl-2,6-diacetylphenol have been studied by steady-stateabsorption, emission and time-resolved spectroscopy in a variety of protic andaprotic solvents at 77 K and ambient temperature.115 From these investigations,it is predicted that the S0 and T1 states have appreciable barriers in the pathwayleading to proton transfer, whereas the reaction in the S1 state is much lessinhibited, and that the process is exothermic from the excited states and en-dothermic in the ground state. Similar investigations into photoinduced intra-molecular proton transfer between the enol (197) and the ketone (198) forms of10-hydroxybenzo[h]quinoline have led to the conclusion that the transfer isessentially barrierless and that the rate (385—405 nm excitation) is within low-


frequency large-amplitude vibrations incorporating the motion of atoms withinthe hydrogen bond.116 The competition between intra- and inter-molecularproton transfer of photoexcited 2-hydroxy derivatives of 2,5-diphenyl-1,3-oxazoles (199) in solutions of varying acidity has been studied.117 The emissioncharacteristics of the protropic forms were obtained and the equilibrium con-stants of the processes determined. It is interesting to note here that the well-catalogued conversion of 2-nitrobenzaldehyde to 2-nitrosobenzoic acid has beenproposed as an easy to perform laboratory experiment for use in assessing thelight intensity over the 300—410 nm wavelength range.118

1-Arylcyclohexenes (200) undergo deconjugation in variable yields to the3-aryl isomers by a photosensitised electron-transfer process,119 and it is reportedthat the 2,7-dihydroazepine derivative (201) gives the 1,2-dihydroaniline (202)and 1,2-dihydroazepine (203) derivatives in respective yields of 43 and 11% in aprocess that is triplet sensitised.120

Irradiation of dibenzonorcaradienes (204) having an acyl or alkoxycarbonylgroup at the 7-position are reported to undergo both cis—trans isomerisation andformation of substituted phenanthrenes (205) by way of a short-lived (��1—20ns) 1,3-biradical intermediate.121 Two groups report on the di-�-methane rear-rangement of naphthobarrelenes to give the corresponding semibullvalenes.122,123

In the case of the pyrazino system (206), rearrangement occurs exclusively by theazadi-�-methane route giving (206a) in 97% yield.123 Exposure of a series of [6,5]

Photochemistry184

open fulleroids (207) to ‘ambient light’ is reported to initiate a unimoleculardisrotatory closure to the [6,5] fullerene which then rearranges to the [6,6]closed isomer (208) by way of a biradical-like intermediate.124 Inhibition of therearrangement by oxygen supports a triplet state process.

Aromatic systems can be derived from a number of diverse photochemicalprocesses in aliphatic moieties. For example, the photochemical rearrangementof 2-phenylcyclohexa-2,5-dien-1-ones (209) has application as a regiospecific andefficient route to tetra- and penta-substituted phenols (210),125 and irradiation(365 nm) of benzene solutions of 1-(2-tolyl)-3,4-benzobicyclo[3.1.0]hexenones(211) gives a clean conversion to the naphthols (212) from the n�* triplet state.126

Further studies into the photochemistry of dihydroheteroarenes have shownthat the iminium ions of pyrimidines undergo ring contraction to afford five-membered ring systems.127 Thus irradiation of 1,4-dihydro-2,4,6-triphenyl-pyrimidine (213) in acid solution gives 2,3,5-triphenylpyrrole (214), while dihyd-ropyrazines (215) undergo ring contraction to 1,2,5-triphenylpyrroles (216)rather than to the isomeric 1,3,4-triaryl derivative. A new route to benz-


imidazoles such as (217) has been developed using IR radiation of o-phenylenediamine and a carboxylic acid adsorbed on Bentonite,128 and sunlightor artificial light has been employed in a new photocatalysed method forselective formation of mono- and poly-substituted pyridines.129 The photo-bromination of tetralin is the key step in a short and efficient route to 1,4-dibromonaphthalene,130 and 3,6-diamino-10-methylacridan (218) undergoes se-quential electron-proton-electron transfer processes to give (219) on irradi-ation.131 The use of intramolecular (2��2�) photocycloaddition of such systemsas (220) to synthesise cyclophanes with overlapping aromatic rings has beenreviewed.132

Each year there appear several publications describing the photodegradationof aromatic systems by a variety of routes. Studies in the area of gas-phasetwo-photon photochemistry of aromatic compounds have been summarised andkinetic and mechanistic data of the photodissociation and photoionisation ofthese systems have been systematised.133 Overall the process for benzene, inducedby 266 nm radiation, is ionisation from the S2 state and formation of C6H5

�.Dissociation rates have been measured employing a quadrupole ion trap/reflec-tron mass spectrometer for benzene, naphthalene and azulene and their per-deuteriated analogues.134 The radical cation of azulene formed from absorptionof two photons at 400 nm eliminates C2H2, H· and H2 with a rate constant equalto that of naphthalene within experimental error. Irradiation of phenylacetyleneat 193 nm yields acetylene and C6H4, some of which decomposes to hexatriyneand H2, but no evidence was obtained for the formation of C6H5, HC�C oratomic hydrogen which are observed in pyrolysis studies.135 The photofragmenttranslational energy distributions corresponding to F and CF3 elimination from

Photochemistry186

benzotrifluoride on 193 nm irradiation have been measured and the resultsindicate that the electronically excited state decays by internal conversion to ahighly vibrationally excited ground state before dissociation.136 Photodegrada-tion of chlorophenols and chlorophenoxyacetic acids using 300 nm radiation hasbeen studied in the presence of traces of ferric ions and anthraquinone sulfonateas sensitiser,137 and the previously unknown species 4-iminocyclohexa-2,5-dienylidene (221) has been detected from irradiation of 4-halogeno-anilines; itsreactions have been studied by nanosecond transient absorption spectroscopy.138

7-Amino-6-fluoroquinolones such as (222) in a phosphate buffer are reportedto undergo photoinduced reductive defluorination and oxidative fragmentationof the piperazine side chain to give (223).139 The process is considered to arisefrom electron-transfer quenching of the triplet state of the heteroarene by thephosphate anion leading to inefficient defluorination with the radical anion ofthe phosphate abstracting a hydrogen atom from the piperazine group resultingin its degradation. Dec-5-ene-1,3,7,9-tetrayne (224), not previously prepared, hasbeen obtained by sequential irradiation of 1,2:5,6-naphthalenetetracarboxylicdianhydride (225) in an argon matrix as outlined in Scheme 8,140 and in aceto-nitrile solution oxygenated polycyclic aromatic hydrocarbons including 9,10-phenanthrenequinone, 9-phenanthrenecarbaldehyde and 1,8-naphthalenedicar-boxylic anhydride undergo photodegradation to give diphenic acid and phthalicanhydride as well as unidentified compounds.141 Irradiation of ‘naphtho-o-car-borane’ (226) in benzene solution under oxygen results in the formation of the


quinone (227), but in the presence of a hydrogen donor, 5-ketonaphthocarborane(228) is also formed, whereas ‘benzocarborane’ undergoes regiospecific andstereoselective (2��2�) photodimerisation.142

Givens and co-workers report that the p-hydroxyphenacyl group provides anew versatile protecting unit for peptides and has fast release rates which aregreater than 108 s�1 with efficiencies in the 0.1—0.3 range.143 The protecting groupis released as p-hydroxyphenylacetic acid which does not interfere with thephotoprocess and, interestingly, a single flash (337 nm, �1 ns) of protectedbradykinin released sufficient of the nonapeptide to activate cell-surfacebradykinin receptors.

9 References

1. D.W. Brousmiche, A. G. Briggs and P.Wan,Mol. Supramol.Photochem., 2000, 6, 1.2. P. J. Wagner, Acc. Chem. Res., 2001, 34, 1.

Photochemistry188

3. A. Albini, M. Fagnoni and M. Mella, Chem. Beginning Third Millennium, Proc.Ger.-Ital.Meet. 1999 (pub. 2000) 83.

4. U. C. Yoon and P. S. Mariano, Acc. Chem. Res., 2001, 34 , 523.5. T. Horaguchi, Trends Heterocycl. Chem., 1999, 6, 1.6. K. Mikami and S. Matsumoto,Kikan Kagaku Sosetsu,1999, 43, 110.7. J. Foster, A. L. Pincock, J. A. Pincock, S. Rifai and K. A. Thompson,Can. J.Chem.,

2000, 78, 1019.8. N. Howell, J. A. Pincock, and R. Stefanova, J. Org. Chem., 2000, 65, 6173.9. G.Maier, G.Mihm, R. O.W. Baumgartner andH. P. Reisenauer,Chem. Ber., 1984,

117, 2337.10. K. Wakita, N. Tokitoh, R. Okazaki, N. Takagi and S. Nagase, J. Am. Chem. Soc.,

2000, 122, 5648.11. S. Y. Al-Qaradawi, K. B. Cosstick, and A. Gilbert, J. Chem. Soc., Perkin Trans. 1,

1992, 1145.12. K. Vizvardi, S. Toppet, G. J. Hoornaert, D. de Keukeleire, P. Bako and E. van der

Eycken, J. Photochem. Photobiol. A, 2000, 133, 135.13. K. Vizvardi, K. Desmet, I. Luyten, P. Sandra, G. J. Hoornaert, and E. van der

Eycken, Org. Lett., 2001, 3, 1173.14. K. Ohkura, K. Nishijima, A. Sakushima and K. Seki,Heterocycles, 2000, 53, 1247.15. K. Ohkura, K. Nishijima, and K. Seki, Chem. Pharm. Bull., 2001, 49, 384.16. A. Yokoyama and K. Mizuno, Org. Lett., 2000, 2, 3457.17. H. R. Memarian, M. Nasr-Esfahani and D. Dopp,New J. Chem., 2001, 25, 476.18. H. R. Memarian, M. Nasr-Esfahani, R. Boese and D. Dopp, Liebigs Ann./Recueil,

1997, 1023.19. T. Noh, K. Jeon, J. Yoon, and Y. Youngmee, Bull. Korean Chem. Soc., 1999, 20,

1351.20. H. Maeda, S. Waseda and K. Mizuno, Chem. Lett., 2000, 11, 1239.21. K. Mizuno, H. Maeda, Y. Inoue, A. Sugimoto, L. P. Vo and R. A. Caldwell,

Tetrahedron Lett., 2000, 41, 4913.22. H. Maeda, A. Sugimoto and K. Mizuno, Org. Lett., 2000, 2, 3305.23. T. Noh, S. Kang, M. Joo and H. Yu, Bull.Korean Chem. Soc., 2000, 21, 459.24. M. T. Crimmins, J.M. Pace, P. G. Nantermet, A. S. Kim-Meade, J. B. Thomas, S. H.

Watterson and A. S. Wagman, J. Am. Chem. Soc., 2000, 122, 8453.25. M. Sakamoto, A. Kinbara, T. Yagi, T. Mino, T. Fujita and K. Yamaguchi, Chem.

Commun., 2000, 1201.26. M. Sakamoto, M. Kimura, T. Fujita, T.Nishio, I. Iida and S. Watanabi, J. Am.

Chem. Soc., 1991, 113, 5859.27. M. Sakamoto, T. Yagi, T. Mino, K. Yamaguchi and T. Fujita, J. Am. Chem. Soc.,

2000, 122, 8141.28. K. Morley and J. A. Pincock, J. Org. Chem., 2001, 66, 2995.29. H. Ishii, Y. Imai, T. Hirano, S. Maki, H. Niwa and M. Ohashi, Tetrahedron Lett.,

2000, 41, 6467.30. H. Isobe, N. Tomita and E. Nakamura, Org. Lett., 2000 2, 3663.31. Q. J. Li, Q. J Gong, L. M. Du and W. J. Jin, Spectrochim. Acta, Part A, 2001, 57,

17.32. G. Vassilikogiannakis, M. Hatzimarinaki and M. Orfanopoulos, J. Org. Chem.,

2000, 65, 8180.33. J. Rosenthal, A. Khong, S. R. Wilson and D. I. Schuster, Proc.-Electrochem. Soc.,

2000, 216.34. Y.-M. Xu,Huaxue Xuebao, 2000, 58, 572.


35. J.-K. Hao, E.-C. Yang, Z.-G. Zhao, G.-L. Wang, Y.-Y. Cao, and Y.-X. Wang,Huaxue Xuebao, 2001, 59, 696.

36. W.-H. Zhang, Z.-M. Zong and X.-Y. Wei, Jiangsu Shiyou Huagong XueyuanXuebao, 2000, 12, 15.

37. See L. Eberson, M. P. Hartshorn and O. Persson, Acta Chem. Scand., 1998, 52, 745and 751; and references therein.

38. K. Schurmann and M. Lehnig, Appl.Magn. Reson., 2000, 18, 375.39. H.-R. Park, I.-J. Yang and M.-S. Kim, Bull. Korean Chem. Soc., 2000, 19, 1265.40. P. Klan, A. Ansorgova,D. Del Favero and I. Holoubek,TetrahedronLett., 2000, 41,

7785.41. K. Hori, T. Sonoda, M. Harada and S. Yamazaki-Nishida, Tetrahedron, 2000, 56,

1429.42. E. F. Corsico and R. A. Rossi, Synlett, 2000, 230.43. B. Guizzardi, M. Mella, M. Fagnoni and A. Albini, Tetrahedron, 2000, 56, 9383.44. G. C. Nwokogu, J.-W. Wong, T. D. Greenwood and J. F. Wolfe,Org. Lett., 2000, 2,

2643.45. M. D’Auria, C. Distefano, F. D’Onofrio, G. Mauriello and R. Racioppi, J. Chem.

Soc., Perkin Trans. 1, 2000, 3513.46. T.-I. Ho, C.-K. Ku and R. S. H. Liu, Tetrahedron Lett., 2001, 42, 715.47. M. Tsuji, K. Higashiyama, T. Yamauchi, H. Kubo and S. Ohmiya, Heterocycles,

2001, 54, 1027.48. D. Mangion, D. R. Arnold, T. S. Cameron and K. N. Robertson, J. Chem. Soc.,

Perkin Trans. 2, 2001, 48.49. Y. Ito, H. Nakabayashi, S. Ohba and H. Hosomi, Tetrahedron, 2000, 56, 7139.50. B. M. Vittimberga and D. F. Sears, J.Heterocycl. Chem., 2000, 37, 291.51. B. M. Vittimberga and D. F. Sears, J.Heterocycl. Chem., 2001, 38, 285.52. A. G. Robinson, P. R. Winter, C. Ramos and T. S. Zwier, J. Phys. Chem., 2000, 104,

10312.53. H. S. Knowles, K. Hunt and A. F. Parsons, Tetrahedron Lett., 2000, 41, 7121.54. T.-I. Ho, J.-H. Ho and J.-Y. Wu, J. Am. Chem. Soc., 2000, 122, 8575.55. E. Martinez, J. C. Estevez, R. J. Estevez and L. Castedo, Tetrahedron, 2001, 57,

1981.56. T. Karatsu, H. Itoh, A. Nishigaki, K. Fukui, A. Kitamura, S. Matsuo and H.

Misawa, J. Phys. Chem., 2000, 104, 6993.57. T. Yamato, K. Fujita, K. Futatsuki and H. Tsuzuki, Can. J. Chem., 2000, 78, 1089.58. T. Mrozek, H. Gorner and J. Daub, Chem.-Eur. J., 2001, 7, 1028.59. K. Song, L.-Z. Wu, C.-H. Yang and C.-H. Tung, Tetrahedron, 2000, 41, 1951.60. K. Sato, T. Yamagishi and S. Arai, J.Heterocycl. Chem., 2000, 37, 1009.61. G. Pan, P. Fan, Y. Ming and M. Fan,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A,

2000, 345, 27.62. P. Fan, G. Pan, Z. Huang, Y. Ming and M. G. Fan, Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2000, 345, 33.63. K. Sasaki, Y. Satoh, T. Hirota, T. Nakayama, Y. Tominaga and R. N. Castle, J.

Heterocycl. Chem., 2000, 37, 959.64. K. Uchida, T. Matsuoka, S. Kobatake, T. Yamaguchi and M. Irie, Tetrahedron,

2001, 57, 4559.65. T. Kodani, K. Matsuda, T. Yamada, S. Kobatake and M. Irie, J. Am. Chem. Soc.,

2000, 122, 9631.66. T. Kodani, K. Matsuda, T. Yamada and M. Irie, Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2000, 344, 307.

Photochemistry190

67. S. Kobatake, T. Yamada and M. Irie,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A,2000, 344, 185.

68. M.-S.Kim, T. Kawai andM. Irie,Mol.Cryst.Liq.Cryst. Sci.Technol., Sect.A, 2000,345, 251.

69. K. Uchida, E. Tsuchida, S. Nakamura, S. Kobatake and M. Irie, Mol. Cryst. Liq.Cryst. Sci. Technol., Sect. A, 2000, 345, 9.

70. M. Yamada,M. Takeshita andM. Irie,Mol.Cryst.Liq.Cryst. Sci.Technol., Sect.A,2000, 345, 107.

71. S. Fraysse, C. Coudret and J.-P. Launay, Eur. J. Inorg. Chem., 2000, 7, 1581.72. M. Badland, A. Cleeves, H. G. Heller, D. S. Hughes and M. B. Hursthouse, Chem.

Commun., 2000, 1567.73. Y. Yokoyama, H. Nakata, K. Sugama and Y. Yokoyama, Mol. Cryst. Liq. Cryst.

Sci. Technol., Sect. A, 2000, 344, 253.74. P. J. Darcy, H. G. Heller, P. J. Strydom and J. Whittall, J. Chem. Soc., 1981, 202.75. Y. Yokoyama, T. Ohmori, T. Okuyama, Y. Yokoyama and S. Uchida,Mol. Cryst.

Liq. Cryst. Sci. Technol., Sect. A, 2000, 344, 265.76. Y. Yoshioka, M. Usami and K. Yamaguchi, Mol. Cryst. Liq. Cryst. Sci. Technol.,

Sect. A, 2000, 345, 81.77. I. Fall, S. A. Ndiaye and J. J. Aaron, J. Soc. Ouest-Afr. Chim., 2000, 6, 107.78. H. Weller and K.-H. Grellmann, J. Am. Chem. Soc., 1983, 105, 6268.79. M. Chakrabarty, A. Batabyal and S. Khasnobis, Synth. Commun., 2000, 30, 3651.80. A. N. Frolov and M. V. Baklanov,Mendeleev Commun., 1992, 22.81. A. N. Frolov, Russ. J. Gen. Chem., 1999, 69, 1254.82. Y.-T. Park, C.-H. Jung, M.-S. Kim, K.-W. Kim, N. W. Song and D. Kim, J. Org.

Chem., 2001, 66, 2197.83. T. Nishio, H. Asai and T. Miyazaki,Helv. Chim. Acta, 2000, 83, 1475.84. J.-K. Luo, M. P. Cabal, R. F. Federspiel and R. N. Castle, J. Heterocycl. Chem.,

2000, 37, 997.85. J.-K. Luo, R. F. Federspiel and R. N. Castle, J. Heterocycl. Chem., 2000, 37, 171.86. J. H. Rigby, U. S. M. Umar and M. E. Mateo, J. Am. Chem. Soc., 2000, 122, 6624.87. C. B. de Konig, J. P. Michael and A. L. Rousseau, J. Chem. Soc., Perkin Trans. 1,

2000, 1705.88. H. Hoshina, K. Kubo, A. Morita and T. Sakurai, Tetrahedron, 2000, 56, 2941.89. H. Hoshina, H. Tsuru, K. Kubo, T. Igarashi and T. Sakurai,Heterocycles, 2000, 53,

2261.90. A. Alberti, M. Campredon, G. Giusti, B. Luccioni-Houze and D. Macciantelli,

Magn. Reson. Chem., 2000, 38, 775.91. T. Khasanova and R. S. Sheridan, J. Am. Chem. Soc., 2000, 122, 8585.92. G. B. Jones, J. M. Wright, G. Plourde, A. D. Purohit, J. K. Wyatt, G. Hynd and F.

Fouad, J. Am. Chem. Soc., 2000, 122, 9872.93. M. Schmittel, D. Rodriguez and J.-P. Steffen,Angew.Chem., Int.Ed., 2000, 39, 2152.94. H. Gan, M. G. Horner, B. J. Hrnjez, T. A. McCormack, J. L. King, Z. Gasyna, G.

Chen, R. Gleiter and N. C. Yang, J. Am. Chem. Soc., 2000, 122, 12098.95. M. Wollenweber, M. Etzkorn, J. Reinbold, F. Wahl, T. Voss, J.-P. Melder, C.

Clemens, R. Pinkos, D. Hunkler,M. Keller, J. Worth, L. Knothe and H. Prinzbach,Eur. J. Org. Chem., 2000, 3855.

96. S. V. Kessar and A. K. S. Mankotia, Chem. Commun., 1993, 1828.97. K. Oda, R. Nakagami, N. Nishizono and M. Machida, Chem. Lett., 2000, 1386.98. S. Kohmoto, T, Kobayashi, J. Minami, X. Ying, K. Yamaguchi, T. Karatsu, A.

Kitamura, K. Kishikawa and M. Yamamoto, J. Org. Chem., 2001, 66, 66.


99. S. Kohmoto, H. Masu, C. Tatsuno, K. Kishikawa, M. Yamamoto and K.Yamaguchi, J. Chem. Soc., Perkin Trans. 1, 2000, 4464.

100. Y. Lee, K. F. McGee, J. Chen, D. Rucando and S. McN. Sieburth, J. Org. Chem.,2000, 65, 6676.

101. A. A. Politov, B. A. Fursenko and V. V. Boldyrev,Dokl. Akad.Nauk, 2000, 371, 59.102. H. Ihmels, Tetrahedron Lett., 1998, 39, 8641.103. H. Ihmels, D. Leusser, M. Pfeiffer and D. Stalke, Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2001, 356, 433.104. H. J. Yoon, S. H. Ko, M. K. Ko andW. K. Chae, Bull.Korean Chem. Soc., 2000, 21,

901.105. A. M. Mayouf and Y.-T. Park, J. Photosci., 2000, 7, 5106. J. A. Heerklotz, C. Fu, A. Linden and M. Hesse,Helv. Chim. Acta, 2000, 83, 1809.107. K.-S. C. Marriott, M. Anderson and Y. A. Jackson,Heterocycles, 2001, 55, 91.108. D. P. DeCosta, A. Bennet, A. L. Pincock, J. A. Pincock and R. Stefanova, J. Org.

Chem., 2000, 65, 4162.109. W. Gu, M. Warrier, B. Schoon, V. Ramamurthy and R. G. Weiss, Langmuir, 2000,

16, 6977.110. W. Gu, M. Warrier, V. Ramamurthy and R. C. Weiss, J. Am.Chem. Soc., 1999. 121,

9467.111. F. L. Cozens, A. l. Pincock, J. A. Pincock and R. Smith, J.Org.Chem., 1998, 63, 434.112. D. P. DeCosta, N. Howell, A. L. Pincock, J. A. Pincock and S. Rifai, J. Org. Chem.,

2000, 65, 4698.113. A. Lalitha, K. Pitchumani and C. Srinivasan, J. Mol. Catal. A: Chem., 2000, 160,

429.114. A. Mandal, D. Guha, R. Das, S. Mitra and S. Mukherjee, J.Chem. Phys., 2001, 114,

1336.115. H. Takahashi, Y. Watanabe, M. Sakai and M. Tachikawa, Laser Chem., 1999, 19,

357.116. P.-T. Chou, Y.-C. Chen, W.-S. Yu, Y.-H. Chou, C.-Y. Wei and Y.-M. Cheng, J.

Phys. Chem., 2001, 105, 1731.117. A. O. Doroshenko, E. A. Posokhov and V. M. Shershukov, J. Gen.Chem., 2000, 70,

573.118. K. L. Willett and R. A. Hites, J. Chem. Educ., 2000, 77, 900.119. D. Mangion, J. Kendall and D. R. Arnold, Org. Lett., 2001, 3, 45.120. K. Saito and Y. Emoto,Heterocycles, 2001, 54, 567.121. A. Bogdanova and V. V. Popik, Org. Lett., 2001, 3, 1885.122. M. C. Sajimon, D. Ramaiah, K. S. Ajaya, N. P. Rath and M. V. George, Tetrahed-

ron, 2000, 56, 5421.123. C.-H. Chou, R. K. Peddinti and C.C. Liao,Heterocycles, 2001, 54, 61.124. M. H. Hall, H. Lu and P. B. Shevlin, J. Am. Chem. Soc., 2001, 123, 1349.125. Z. Guo and A. G. Schultz, Org. Lett., 2001, 3, 1177.126. D. J. Chang and B. S. Park, Tetrahedron Lett., 2001, 42, 711.127. J. Nagy, Z. Madarasz, R. Rapp, A. Szollosy, J. Nyitrai and D. Dopp, J. Prakt.

Chem., 2000, 342, 281.128. G. C. Penieres, I. A. Bonifas, J. G. C. Lopez, J. G. E. Garcia andC. T. Alvarez, Synth.

Commun., 2000, 30, 2191.129. B. Heller, D. Heller, H. Klein, C. Richter, C. Fischer, and G. Oehme, J. Inf. Rec.,

2000, 25, 15.130. O. Cakmak, I. Kahveci, I. Demirtas, T. Hokelek and K. Smith, Collect. Czech.

Chem. Commun., 2000, 65, 1791.

Photochemistry192

131. A. Marcinek, J. Zielonka, J. Adamus, J. Gebicki and M. S. Platz, J. Phys. Chem.,2001, 105 875.

132. J. Nishimura, Y. Nakamura, Y. Hayashida and T. Kudo,Acc. Chem.Res., 2000, 33,679.

133. V. K. Potapov and V. M. Matyuk,High Energy Chem., 2001, 35, 90.134. W. Cui, B. Hadas, B. Cao and C. Lifshitz, J. Phys. Chem., 2000, 104, 6339.135. O. Sorkhabi, F. Qi, A. H. Rizvi and A. G. Suits, J. Am. Chem. Soc., 2001, 123, 671.136. S.-T. Tsai, J. Phys. Chem., 2000, 104, 10125.137. S. Klementova and J. Matouskova, Res. J. Chem. Environ., 2000, 4, 25.138. K. Othmen, P. Boule, B. Szczepanik, K. Rotkiewicz and G. Graber, J. Phys.Chem.,

2000, 104, 9525.139. E. Fasani, M. Mella, S. Monti and A. Albini, Eur. J. Org. Chem., 2001, 391.140. T. Saito, H. Niino and A. Yabe, Chem. Commun., 2000, 1205.141. S. Matsuzawa, Polycyclic Aromat. Compd., 2000, 21, 331.142. A. Z. Bradley, A. D. Cohen, A. C. Jones, D. M. Ho andM. Jones, TetrahedronLett.,

2000, 41, 8695.143. R. S. Givens, J. F. W. Weber, P. G. Conrad, G. Orosz, S. L. Donahue and S. A.

Thayer, J. Am. Chem. Soc., 2000, 122, 2687.


5Photo-reduction and -oxidation

BY ALAN COX

1 Introduction

Topics which have formed the subjects of reviews this year include light-inducedoxidation and reduction reactions,1 zeolite as a medium for photochemicalreactions,2 photooxidation of alkanes, alkenes, and alkylbenzenes in zeolites,3

photoinduced electron transfer in clay interlayers,4 selective photooxidation oflower alkanes in polyphase,5 photoinduced electron transfer in organic syn-thesis,6 electron-transfer processes in photoinitiating systems,7 photoaminationby electron transfer,8 photoinduced electron-transfer cyclisation of acyclic andcyclic dienes.9 photoinduced electron transfer and energy transfer in fullerenes,10

vectorial electron-transfer pathways,11 photoinduced electron-transfer systemsand their analytical application in chemical sensing,12 photosensitised oxygena-tion of small ring olefins,13 photochemistry of �-benzoylpropionic acid deriva-tives,14 synthesis of benzofurans using photocyclisation of aromatic carbonylcompounds,15 the photochemistry of fullerenes,16 photocarbo-functionalisationreactions of fullerenes,17 photophysics of some new types of fullerene—porphyrindyads,18 photo- and electroactive fulleropyrrolidines,19 n,�* photochemistry be-yond ketones,20 photo- and radiation chemistry of quinones,21 and mechanismsof photooxidation of organic azides.22

Environmental purification using photooxidation on titanium dioxide cata-lysts,23 photocatalytic oxidationmechanisms of TiO2 for dyes,24 and stepwise andconcerted pathways in thermal and photoinduced electron-transfer bond-break-ing reactions,25 have also been discussed.

2 Reduction of the Carbonyl Group

A discussion of the n�* photochemistry beyond that of ketones has appeared.26

In particular, attention has been paid to recent studies on the photophysics andintermolecular photochemistry of n�* excited azoalkanes, and contrasts havebecome apparent with the analogous states of ketones. Some novel reactionmechanisms have been described.Solid state irradiation of 2-benzoyladamantane-2-carboxylic acids (1) to

which chiral auxiliaries have been attached either covalently bymeans of an ester


194

[(2), (3)], or ionically as a salt (4) leads to photoproducts (5) showing �96%diastereo- and enantiomeric excess.27 These reactions proceed via the inter-mediacy of (6). The kinetics of the photoinduced reduction of m-nitro-acetophenone with TiO2 powder have been obtained by measuring the rate offormation of m-H2NC6H4COMe,28 and Synechococcus sp. PCC 7942 has beenreported to photocatalyse the reduction of aryl methyl ketones to the corres-ponding (S)-alcohols with high enantioselectivities.29 Photolysis of mercapto-undecanophenone as a modified gold colloid has been observed to undergo aNorrish Type II reaction via a triplet state, and to generate free acetophenone insolution and the nonene-modifiedmonoprotected colloid via the triplet state anda 1,4-biradical intermediate.30 These observations may have implications for thedevelopment of a probe to ascertain the degree of conformational stability insuch environments. Following photoexcitation, xanthone and 1-azaxanthonereact with polyalkylbenzene donors to give ketyl radicals, and these are expectedto react either by one-step hydrogen abstraction, electron transfer followed byproton transfer, or by formation of a charge-transfer encounter complex.31

Results reported now suggest that the quenching is mainly by charge-transferencounter complex formation between the excited ketone and the ground-statepolyalkyl aromatic donor, and reactivities are dominated by reduction poten-tials except in the case of sterically hindered polyalkylbenzenes. It is suggestedthat �,�* and n,�* states form encounter complexes of distinct structure, and thata consequence of this is their differing abilities to react with hindered donors. Atime-resolved CIDNP study of the photochemical reduction of benzophenonewith triethylamine in acetonitrile solution has shown the presence of polarisationeffects on protons of the initial amine and recombination product of the ketyland aminoalkyl radical.32 This polarisation is apparent in the triplet state of thegeminate radical pair [Ph2CO·H MeC·HNEt2], and a mechanism has beenproposed which includes back hydrogen transfer and recombination as the twomain reaction pathways.Irradiation of hydrogen peroxide and dimethyl sulfoxide containing benzo-

phenone leads to the production of the benzophenone ketyl radical, togetherwith the methyl and methylsulfinic radicals.33 Replacement of the benzophenonewith decafluorobenzophenone, however, suppresses formation of the methylradicals. Taken with other observations, this suggests that the methyl radicals

II/5: Photo-reduction and -oxidation 195

are regenerated in a cyclic pathway in which they attack the hydrogen peroxide.The results of a study of the magnetic field effect on the photoinduced electron-transfer reaction between benzophenone and starburst dendrimers in aqueousmedia have been interpreted in terms of a radical pair mechanism.34 The infer-ence is drawn that dendrimers of higher generations act as both an electrondonor as well as a supercage in the photoreaction. A study has shown that therates and yields of the photopinacolisation of benzophenone in ethanol increasewhen sonication is simultaneously applied.35 This observation has been at-tributed partly to sonolytic decomposition, and partly to sonication inducingtriplet state quenching. The latter phenomenon may arise as a consequence ofeasier collisional deactivation processes which are favoured by the homogeneousdistribution of the activated species.The question of molecular size in relation to photoinduced electron-transfer

reactions has been addressed in the case of transfer from trimethoxybenzene toexcited quinones in both polar and apolar solvents using flash photolysis andphotoacoustic calorimetry.36 Comparisons of enthalpy, entropy, and volumechanges of these electron-transfer reactions were compared with those involvingtransfers from dimethylaniline to excited pyrene, and from tetramethylbenzidineto excited C60. Along with other data, the conclusion is drawn that reactant sizehas a negligible effect on the kinetics of these reactions, and non-specific solventeffects are only of importance for highly exothermic reactions. 1,4-Benzoquinoneand 2,6-dimethylbenzo-1,4-quinone have been reported to function as goodelectron acceptors from the photosynthetic system in cyanobacteria Synechococ-cus sp. PPC942.37 Synechococcus sp. cell-entrapped and DMBQ-embedded car-bon paste electrodes provide a steady-state current which has been ascribed tothe photoelectrochemical oxidation of water. Photochemical redox reactionsbetween o-quinones such as coenzyme PQQ (pyrroloquinolinequinone) (7) and

analogues of benzyl alcohol have been shown to occur by photoinduced electrontransfer from the substrate to the triplet excited state of the o-quinone, followedby proton and hydrogen atom transfer to yield the quinol and the correspondingoxidation products.38 High yields of two interconvertible anomeric naphtho-pyranylhemiacetals (8, 9) have been produced by irradiation (�irr �420 nm) of amixture of acenaphthylene and p-chloranil.39 These products arise from oxetaneformation followed by its hydration, and are stereoselectively converted into anidentical naphthopyranylacetal (10; R�Me, Et) in primary alcohols. Quinoneshave been photoreduced to the corresponding hydroquinones by 5,6-O-iso-propylidene--ascorbic acid rather than undergoing the analogous Paterno-Buchi reaction.40 A study has been made of the photoreduction of

Photochemistry196

o-benzoquinones at wavelengths corresponding to the S(��*) and S(n��*)transitions, (�max �400 and 600 nm), in the presence of dimethylaniline andderivatives, and the apparent rate constants for the transformations determinedby the free energy of electron transfer from the amine molecule to a photoexcitedo-quinonemolecule.41 A mechanism for the transformation has been proposed inwhich the rate-determining step is reversible formation of a triplet exciplex, andin which hydrogen transfer proceeds in parallel with electron transfer within theexciplex. A time-resolved FT-EPR spectroscopic study of the photoreduction ofduroquinone by triethylamine in methanol has shown that the spin polarised(CIDEP) duroquinone triplet undergoes deactivation by electron transfer fromtriethylamine to generate the duroquinone radical anion and amine radicalcation.42 Hydrogen transfer from the solvent to produce durosemiquinone rad-ical and hydroxymethyl radical also occurs. The durosemiquinone radical isreported to be transformed into duroquinone radical anion in the presence oftriethylamine in solution.Photoinduced one-electron reduction of 1,4-dihydroxyanthraquinone in the

presence of 1-benzyl-1,4-dihydroxynicotinamide or 5,5-dimethyl-1-pyrrolineN-oxide has been shown to occur by a radical-ion mechanism,43 and thecontrol of photoinduced electron transfer within a hydrogen-bonded por-phyrin—phenoxynaphthacenequinone photochromic system by reversiblychanging the electronic properties of the quinone electron acceptor has beendescribed.44 The carbonyl oxygen atoms of benzopyrones such as chromones andflavones in their lowest excited triplet states with mixed n�*—�,�* character arecapable of abstracting H atoms from solvents.45 Ketyl radicals are formed, andeven though these are indistinguishable from �-enol type radicals they undergodifferent reaction types. The photophysical properties of the porphyrinicphenoxynaphthacenequinones (11; M�H2, Zn) and (12) have been assessed witha view to determining their potential use as gated photoinduced electron-transfersystems.46 This has revealed that the photochemical isomerisation of the naph-thacenequinone moiety is prevented by its close association with the porphyrinring system. Photochemical redox reactions of the trimethyl ester of coenzymePQQ (PQQTME) with benzyl alcohol derivatives, THF, and cyclohexa-1,4-diene have been observed to give PQQTMEH2, the reduced PQQTME in thequinol form.47 Flash photolysis spectroscopy has enabled the lifetimes of thetriplet states of the o-quinones to be determined, and deuterium isotopic studiesindicate that the photoreduction occurs by electron transfer from the substrateto the triplet excited state of the o-quinone followed by proton and hydrogen


atom transfer to yield the quinol and the corresponding oxidation products. Theorientation of donor and acceptor molecules in the intermolecular electrontransfer between coumarin and dimethylaniline has been ascertained usingultrafast visible and IR polarisation spectroscopy.48

An examination of the use of keto esters as delivery systems for the controlledrelease of some aldehydes and ketones in sunlight has shown that the dominantprocess is a Norrish Type II fragmentation of the ester side chain.49 In addition,important subsidiary reactions include �-H abstraction from an alkyl side chainand intramolecular Paterno-Buchi reaction or epoxidation of the alkene. Theobservations have been rationalised using ab initio and density functional calcu-lations; the results of these investigations may find practical application in theperfumery industry. A silica gel surface has been shown able to provide a polarmedium capable of reducing the energy separation between the lowest 3(n,�*)and the upper 3(�,�*) states to a small value, and in some circumstances this cancause inversion of nearby 3(n,�*) and 3(�,�*) states.50 In valerophenone—p-methyl-

Photochemistry198

valerophenone and valerophenone—p-methoxyvalerophenone systems, internalfilter effects can be sufficiently strong that direct observation of energy-transferprocesses in solution is inhibited. Photoreactivity studies of valerophenone infrozen solution have shown that physical restraints present in the solid solventcavity are able to prevent reaction proceeding in parts of the molecule.51 Largerconformational changes are unable to occur, although some H abstractionprocesses are still apparent irrespective of the solvent used. The Norrish Type IIreaction was studied as a function of temperature, and semi-empirical PM3 andmolecular mechanics MM3 force field calculations have been performed toevaluate the stabilities of ground-state valerophenone conformations. A studyhas been made of the Norrish-Yang reaction of some �-benzoylpropionic acidderivatives as a function of substituent and reaction conditions.52 Both cyclic andopen-chain products such as cyclobutanes, pyrrolidines, tetrahydrofurans, �-lactones, and pinacols are formed, and these may be mostly obtained with highregio- and diastereo-selectivity. The results provide an insight into the factorsdetermining the stereochemistry of the Norrish-Yang reaction. Irradiation oftrans-2-phenylcyclohexyl 4-cyanobenzoate in methanol is reported to induce aNorrish Type II type reaction with formation of phenylcyclohex-1-ene and4-cyanobenzoic acid.53 The transformation is thought to occur by a singlet-stateintramolecular electron transfer which is followed by intramolecular protontransfer and finally cleavage of the 1,4-biradical. The corresponding stereoisomercis-2-phenylcyclohexyl 4-cyanobenzoate probably undergoes cis to transisomerisation before fragmentation. 1-(o-Tolyl)-1-benzoylcyclopropane (13)yields a single photoproduct (14) resulting from intramolecular hydrogen trans-fer from the methyl group to the carbonyl group to give a biradical intermediatewhich cyclises.54 By contrast, irradiation of 2H2-substituted 2-(o-tolyl)-2-ben-zoyloxirane induces hydrogen atom abstraction from the oxiranyl ring to give abiradical which undergoes transformation into a second oxiranyl ring-openedintermediate that subsequently rearranges. These differences in behaviour havebeen ascribed to increases in acidity and instability of the oxirane moiety.

A study of the excited state reactions of short-lived 2-methylbenzophenoneenols using a stepwise two-colour excitation time-resolved thermal lensing tech-nique has appeared.55 This reveals that with a 532 nm laser at which wavelengthonly the E-enol is excited, the increase of the transient absorption is apparent atwavelengths less than 420 nm, with no spectral changes corresponding to theZ-enol. These observations suggest that following excitation, it is only theE-enolwhich goes on to produce dihydroanthrone. Photolysis of o-tolualdehydes leadsto the formation of o-quinodimethanes, and these have been found to reactefficiently with [60]fullerene to form stable adducts.56 Such products possess ahydroxyl group which is available for further functionalisation.


An examination of the regioselective and threo-diastereoselective [2�2]photocycloaddition of benzophenone to chiral allylic alcohols of the formMe2C——CHCHR(OH) (R�Me, Et, CHMe2, CMe3) has revealed that the processis directed by the hydroxyl group.57 The product oxetanes (15) are obtained withboth high stereo- and regio-selectivity, and this is rationalised in terms of hydro-gen bonding which promotes regioselective cycloaddition, and a combination ofhydrogen bonding with 1,3-allylic strain which produces high �-facial differenti-ation. An unusual temperature dependence has been observed in the dia-stereoselectivity of the [2�2] photocycloaddition of benzophenone to cis- andtrans-cyclooctene through conformational control.58 In this reaction the lowerenergy substrate diastereomer, cis-cyclooctene (cis-16), affords trans-oxetane(trans-17), the higher energy product with increasing temperature, but (trans-16),the more strained diastereomer, retains its configuration in the cycloadduct (17)over a wide temperature range. These observations have been accounted for interms of the thermodynamic preference of the trans triplet diradical conformer,along with the kinetically controlled conversion of the cis into the trans tripletdiradical conformer. Irradiation of benzophenone in the presence of 5-methyl-2-furylphenylmethanol leads to the formation of two [2�2] adducts in a ratio of

1:1.59 Similar reactions with 4,4�-dimethoxybenzophenone, benzaldehyde or 4-methoxybenzaldehyde form adducts on the side of the furan proximate to themethyl group, but reactions involving 4,4�-dichlorobenzophenone lead to ad-ducts on the other side. These observations are rationalised in terms of a singleelectron-transfer process followed by a radical coupling reaction in which theregioselectivity is explained in terms of the stabilities of the intermediates. Amechanism has been reported which accounts for the regioselectivity and dia-stereoselectivity of the photoinduced cycloaddition reactions of 1-acetylisatin(18) with alkenes (19; R�H, Ph, Me) and (20) to give spiroxetanes such as (21),and with the related alkenes (22) and (23).60 For electron-rich alkenes, singleelectron processes involving (318*) and ion-radical pair formation operate, andthe regioselectivity of the cycloaddition depends upon charge and spin-densitydistribution in the ion-radicals; diastereoselectivity is also decided by ion-paircollapse. By contrast, with alkenes of high oxidation potential where singleelectron-transfer processes are not involved, regioselectivity is rationalised byfrontier molecular orbital considerations. The photocycloaddition reactions ofquinones with norbornadiene have been followed by the CIDNP method inwhich the relevant signals arise both from the 1,5-biradicals and from theirrelated radical ion pairs from which they are derived.61 The routes by which thebiradicals form and decay can be traced by using polarisations as labels. A studyhas shown that the Paterno-Buchi reactions of the silyl O,S-ketene acetals

Photochemistry200

(SKA), �,�-dimethyl-O,S-SKA (Me2C——C(SR1)OSiR3, SiR3/R1�TBDMS/Me,TMS/Me, TIPS/Me, TBDMS/But, TMS/But; (E)- and (Z)-EtCH——C(Sbut)OTBDMS) and aromatic aldehydes (ArC(O)H; Ar�Ph, p-NCC6H4, p-MeOC6H4, mesityl) give regio- and stereo-selectively trans-3-siloxyoxetanes in-dependent of the aldehyde, the substituents SR1 and SiR3, as well as the reactionmedium.62 The regioselectivity has been accounted for in terms of the relativestability of the 1,4-diradicals and the relative nucleophilicity of the sp2-carbons inO,S-SKA, and the S atom in O,S-SKA effects control of the trans selectivity.[2�2] Photocycloaddition of R3COR4 (R3�Me, Pri, Ph; R4�H, Me, Ph) with2-silyloxyfurans proceeds with stereoselective formation of the exo-oxetanes andoccurs in high yields.63 The regioselectivity for adducts (24; R1, R2�H, Me;R3�Pri, tert-BuMe2) and (25; same R1, R2, R3) is dependent upon the carbonyls,the substituents on the furan ring, and the excited state of the carbonyls.However, reactions with aldehydes are regiorandom and independent of theexcited state. It is suggested that an important factor in the approach direction ofthe electrophilic oxygen of the excited carbonyls is significant for exo-stereoselec-tion, and the Griesbeck model is successful in rationalising the regio- andexo-selective formation of oxetanes in the triplet-state photoreaction.The main product of irradiating benzene solutions of 2-alkynylcyclohex-2-en-

1-ones in the presence of an excess of 2-methylbut-1-en-3-yne at 350 nm iscis-fused 3,4,4a,5,6,8a-hexahydro-1(2H)-naphthalenone which arises by a 1,6-cyclisation of the common biradical intermediate, together with some bi-cyclo[4,2,0]octan-2-one.64

3 Reduction of Nitrogen-containing Compounds

An investigation of the excited-state dynamics of methylviologen has beendescribed.65 In particular, the photophysical and photochemical deactivationpathways have been studied in several polar solvents at room temperature, andthe results clearly show the strong electron-accepting character of the lowestsinglet excited state. This work also demonstrates for the first time that ahydrogen bonding solvent can function as the electron donor in an ultrafast


intermolecular electron-transfer reaction, and in addition is the first report of anefficient radiative decay pathway for methylviologen in fluid solution. A studyhas appeared of the photoreduction of methylviologen by eosin-Y (EY2�) in thepresence of triethanolamine in water—methanol mixtures.66 Both steady-stateand time-resolved investigations have been undertaken, and evidence is pres-ented which confirms that contributions are made by both the oxidative andreductive routes of 3(EY2�)* to the formation of methylviologen radical cation.Steady-state and time-resolved examinations of the photoreduction of methyl-viologen by 10-methylacridine orange in aqueous ethanol mixtures containingtriethanolamine have been reported.67 Rate constants have been measured forthe various processes, and the effects of added salts also determined. A report hasappeared of the C60-photosensitised reduction of methylviologen mediated bymolecular oxygen in organic solvents.68 Thus on irradiation of a system consist-ing of C60, electron donors such as triethanolamine and tetraphenylborate, C60·�

is formed. Subsequent introduction of molecular oxygen followed by furtherirradiation causes the C60·� to disappear with simultaneous appearance ofsuperoxide anion (O2·�). Addition of MV2� leads to electron transfer from O2·�

to MV2� in aprotic solvents, and by irradiating a system consisting of C60/elec-tron donor/O2/MV2�, MV·� was also observed to be generated. The actionspectrum for the photoreduction of methylviologen in a three-component systemconsisting of triethanolamine, (sulfonatophthalocyaninato)zincate(II) andmethylviologenhas been comparedwith the absorption and excitation spectra ofthe zinc complex alone, and this has enabled a quenching process for the systemto be determined.69 The distribution of the complexant species in the novelcomplex between pyranine, 8-hydroxy-1,3,6-pyrenetrisulfonate anion (26), andmethylviologen can be manipulated using ionic micellar aggregates, and thispermits control over competitive photochemical and photophysical pathwaysallowing maximisation of electron- and proton-transfer routes.70 Along withother observations, this may have implications for the development of a photo-catalyst whose properties can be adjusted by suitable disposition of the partnersin supramolecular aggregates. Comparison of the quenching of the electronicallyexcited singlet state of a series of simple N-alkylated pyridiniumyl-1,8-naph-thalimides and a series of polymethylene-linked 1,8-naphthalimide/viologendyads (27) has shown that attachment of the viologen promotes quenching.71

From flash photolysis and other studies, the conclusions have been drawn thatthe quenching can be ascribed to both intra- and inter-molecular processes andthat these arise by electron transfer from the excited state of 1,8-naphthalimide tomethylviologen. It has been reported that visible light excitation of [Ru(bpy)3]2�-

Photochemistry202

tethered titania will induce electron transfer to methylviologen to form thecation radical in an electron migration process which occurs on the titaniasurface.72

A new route to vicinal diamines by the photoreductive coupling of pyridine-,arene- and alkynecarboxaldimines has been described.73 Irradiation of 10-methylacridinium ion in acetonitrile containing allylic silanes and stannanesleads to allylated dihydroacridines (28), but with unsymmetrical allylsilanes allylgroups are introduced at the � position.74 Photoreduction of 10-methylacridin-ium by tributyltin hydride and tris(trimethylsilyl)silane, however, gives the corre-sponding 1,4-dihydroquinolines exclusively. These differences are accounted forin terms of nucleophilic versus electron-transfer pathways.

A study has compared the photosensitised reductive splitting of stereoisomericC5—C5�-linked dihydrothymine dimers [meso compound of (5R,5�S)- and(5S,5�R)-bi-5,6-dihydrothymines (29; R1�Me, R2�H, Me); racemic compoundof (5R,5�R)- and (5S,5�S)-bi-5,6-dihydrothymines (30 and 31; same R1, R2)] inaqueous solution with the one-electron oxidative splitting mechanism andphotorepair reaction of cyclobutane pyrimidine photodimers.75 Reaction withphotochemically generated hydrated electrons converts the C5—C5�-linkeddihydrothymine dimers to the corresponding 5,6-dihydrothymine derivatives,and time-resolved studies indicate that one-electron adducts of the C5—C5�-linked dimers undergo C5—C5�-bond cleavage to produce 5,6-dihydrothymin-5-yl radicals and the 5,6-dihydrothymine C5-anions leading to formation of 5,6-dihydrothymine derivatives by protonation at C5. Photoinduced reductive ringcontractions have been verified for 1,4-dihydro-6-methyl-2,4-diphenyl-pyrimidine, 1,4-dihydro-2,4,6-triphenylpyrimidine, 1,2-dihydro-3,6-diphenyl-1,2,4,5-tetrazine, 1,2-dihydro-2,4,6-triphenyl-1,3,5-triazine and 1,2-dihydro-1-methyl-2,4,6-triphenyl-1,3,5-triazine to give the fully unsaturated heterocycles.76

Dihydropyrazines such as (32; R1, R2�H, Cl, Me, F3C) are also reported toundergo photoreductive ring contraction to give 1,2,5-triarylpyrroles of the type(33).Both 1-methyl-3-phenylquinoxalin-2-one (34) and 3-phenylquinoxalin-2-one

(35) have been efficiently photoreduced in the presence of amines to give thesemireduced quinoxalin-2-ones (34-H)� and (35-H)� in unit quantum yield by anelectron-proton-electron transfer process.77 This is followed by an almost quanti-tative reversion to the parent substrate in a dark reaction. A study ofthe photochemistry of 5,10,15,20-tetrakis-(4-N-methylpyridyl)porphyrin indimethylformamide using �ex�347 nm induces photoreduction of the porphyrin


and subsequently formation of protonated products.78 The solvent acts as reduc-ing agent, and in air-saturated solutions chlorin molecules are formed, whereasin deoxygenated solution the transformation sequence is porphyrin � phlorin� porphomethene� porphyrinogen.Gramicidin S analogues containing a pair of -1-pyrenylalanine and - or

-p-nitrophenylalanine residues have been synthesised, and following photoexci-tation electron transfer from the excited pyrenyl group to the nitrophenyl groupwas observed to occur.79 Comparisons have been made between the rates ofelectron transfers in these examples and those observed in �-helix model poly-peptides. Rates of photoinduced electron transfer from the excited pyrenyl groupto the nitrophenyl group in �-helical polypeptides containing -1-pyrenylalanineand -4-nitrophenylalanine separated by 0—8 amino acid residues have beenmeasured.80 The rate constants show a complex dependence on the number ofspacer amino acids, but a simple exponential dependence on the edge-to-edgedistance between the two chromophores. The photolabile sugars 2,6-di-O-o-nitrobenzyl- and 3,6-di-O-o-nitrobenzyl-methylmannoside have been deprotec-ted by irradiating at 350 nm to afford methylglycosides.81 An examination of theeffects of modifying the surface of nanocrystalline titanium dioxide on thephotocatalytic degradation of nitrobenzene has been reported.82 Arginine, laurylsulfate, and salicylic acid have been found to bind TiO2 through their oxygen-containing functional groups, and arginine will facilitate the transfer of photo-generated electrons from the TiO2 conduction band to the adsorbed nitroben-zene. This study reveals that such amodification is an effective route to enhancedphotodecomposition of nitroromatic compounds. Azobenzene has been photo-catalytically reduced to hydrazobenzene in a 2e� process by irradiating at �ex

�300 nm in the presence of TiO2.83 Irradiation in the presence of TiO2 loadedwith nanometre-sized particles of Pt, however, leads to N——N bond cleavage by a4e� reduction. The photoreduction of the triplet states of the electron-deficientazaarenes 3,5,6-triphenyl-1,2,4-triazine, 3-phenyl-1,2,4-benzotriazine, 3-phenyl-1,2,4-phenanthro[9,10-e]triazine, and tetraphenylpyrimidine have been inves-tigated.84 In the presence of 1,4-diazabicyclo[2,2,2]octane (DABCO), the second-ary transient is ascribed to the radical anion, but in the presence of TEA ordiethylamine H-adduct radicals having maxima around 400 nm are observed. Aseparate group of workers also reports the photoreduction of 3,5,6-triphenyl-1,2,4-triazine in neat triethylamine to form 2,5-dihydro-3,5,6-triphenyl-1,2,4-triazine together with the products of reductive ring contraction, 3,5-diphenyl-1,2,4-triazole and 2,3-di-(3,5-diphenyl-1,2,4-triazole-1-yl)butane, the latter beingproduced as a mixture of racemic and meso-diastereoisomers.85 Fluorescence

Photochemistry204

quenching studies of naphthalene diimides have revealed their electron acceptorcapabilities.86 Although naphthalenediimides do not seem to produce O2(1�g), inthe presence of these compounds styrene has been photooxidised to benzal-dehyde, and it has been speculated that this may occur by radical chain reactionsinvolving the superoxide anion radical. Investigations of the photochemicalreduction of a series of aromatic imines to the corresponding amines by 2-phenyl-N,N-dimethylbenzimidazoline in the presence of magnesium perchloratehas shown that the reaction proceeds by a Mg2�-mediated photoinduced elec-tron-transfer mechanism.87 The quantum yields of triplet state and radical ionformation of various maleimides have been determined; these parameters are ofparticular importance in the use of such substrates as electron-transfer photo-initiators.88

4 Miscellaneous Reductions

A study of the photoinduced electron donor—acceptor interactions between C60

and aliphatic amines of various chain lengths, including diethylamine,triethylamine, tri-n-amylamine, propylethylamine, n-butylamine, n-heptylamine,dodecylamine and ethylenediamine, has established a correlation between struc-ture and the length of the alkyl chain in both the ground and excited states.89

Factors influencing dynamic properties of the C60/(aliphatic amine) such as �Het

and �Set have been investigated. ESR investigations of photoinduced electrontransfer between some water-soluble amine donors and the C60-�-cyclodextrininclusion complex have shown the presence of both the monoanion, C60

�, andthe dianion, C60

2�.90 This study also suggests that one of the most importantfactors affecting the half-life of the dianion radical is the stability of the corre-sponding donor cations. In some related work an examination has been made ofthe radical ions generated by photoinduced electron transfer between aminesand 3C60*/�-CD and C70*/�-CD.91 In both instances studied, rates were found tobe slower than in corresponding cases in solution, and for reversible systemsinvolving stable radical cations of amines, both C60·�/�-CD and C70·�/�-CDdecayed slowly by back electron transfer. In the presence of methylviologen,persistent MV·� was generated in equilibrium with C60·�/�-CD, and this sug-gests that C60/�-CD can act as an efficient photosensitiser and an electronmediator to produce MV·� for which nitrilotriethanol is used as sacrificialdonor. Irradiation of three-, four- and five-membered cyclic silicon compoundsin the presence of fullerene in benzonitrile as solvent leads to formation of thefullerene radical anion, C60·�, in tandem with rapid decay of the fullerene tripletstate suggesting that electron transfer occurs via 3C60*.92 Increases in the numberof silicon units are matched by decreases in the rate constant and quantum yieldfor electron transfer. FT-EPR has been used to study the energy and electrontransfer from porphyrins in their triplet excited state to C60 in toluene and inbenzonitrile.93 The primary route of electron transfer is shown to be oxidativequenching of magnesium tetraphenylporphyrin triplets. Dioxygen has beenreported to accelerate back electron-transfer processes between a fullerene rad-


ical anion and a radical cation of zinc porphyrin (ZnP) in photolytically gener-ated ZnP·�-C60·� and ZnP·�-H2P-C60·� radical ion pairs.94 In these systems,partial coordination of O2 to ZnP·� occurs and this facilitates an intermolecularelectron transfer from C60·� to O2. Consequently, molecular oxygen can act as anovel catalyst in the acceleration of back electron transfer in C60·�-ZnP·�radicalion pairs. Amodel system incorporatingC60 has been describedwhich shows thatC60 adducts can serve as visible-light harvesters which are capable of triggeringelectron-transfer processes between partners that do not absorb visible light.95

Introduction of a cyclopropyl grouping on the C60 chromophore renders itsuitable for participating in both triplet energy-transfer processes and in elec-tron-transfer processes. A study of photoelectron-transfer processes involvingC60 or C70 and zinc octaethylporphyrin (ZnOEP) in polar media has shown that,following selective excitation of ZnOEP, transient absorption bands attributableto the fullerenes can be observed.96 Analogously, following excitation of thefullerenes, decays of 3C60* and 3C70* can also be detected. Electron-transfer rateconstants and quantum yields of C60 and C70 formation via 3ZnOEP* and 3C60*or 3C70* have been determined, and were found to increase with solvent polarity.In benzonitrile solution, C70 forms a ground state charge-transfer complex with3,3�,5,5�-tetramethylbenzidine, and on selective excitation of C70 EPR singletsascribable to C70 mono- and di-anion are observed.97 In the photochemical andcathodic in situ reductions, identical EPR spectra of anion radicals have beenobtained.A study of the photochemistry of water-soluble isomeric bis(pyrrolidinium)

salts with C60(C4H10N�)2 as cationic moiety [36�(36a—36d) in which one pyr-rolidinium ring is fixed at the top 6-6 fusion as shown, the second is located at thedotted bond labelled eq�equatorial (36a), the dotted bond t4�trans-4 (36b),t3�trans-3 (36c), or t2�trans-2 (36d)] has been compared to bis(carboxylates)C60[C(CO2

�)2]2 and to �-CD-encapsulated C60.98 The electron-withdrawingcharacter of the pyrrolidinium groups confers enhanced electron-acceptor prop-erties on the bis(pyrrolidinium) salts, and photolysis of (36a—36d) gives singletstate absorptions that closely resemble observations on the pyrrolidine precur-sor. Intramolecular electron transfer and singlet-singlet energy transfer havebeen observed to occur competitively in the C60—oligo(naphthylenevinylene)dyad (37).99 Photoinduced charge separation and recombination in a tetra-thiophene-C60 dyad has been investigated in solvents of various polarities, and

Photochemistry206

has been found to occur with almost unit quantum yield and at about 1010 s�1 inpolar solvents, and to be totally absent in solvents such as toluene.100 Theobservation of a second charge-separated state of unprecedentedly long lifetimewas made in benzonitrile, and interpreted in terms of an equilibrium between thecharge-separated state and the triplet excited state. A comparative study hasbeen made of the photoinduced energy and electron-transfer processes in somefullerene—oligothiophene—fullerene triads (C60-nT-C60; T�thiophene, n�3, 6, 9)to those of mixtures of oligothiophenes (nT) with N-methylfulleropyrrolidine(MP-C60).101 Preferences have been observed for intra- and intermolecular en-ergy- and electron-transfer reactions as a function of conjugation length andsolvent permittivity, and these are found to be consistent with predictions madeusing the Weller equation for the change in free energy upon charge separation.In a study of photoinduced electron-transfer processes from oligothiophenes(nT)/polythiophene (poly-T) to fullerenes (C60/C70), it has been shown that selec-tive photoexcitation of the fullerene in polar solvents promotes electron transferfrom nT to the excited triplet state of the fullerene.102 The efficiency of electrontransfer is a maximum at n�4 and falls to smaller values at higher figuressuggesting that energy transfer may be occurring. In non-polar solvents,energy transfer is the dominant deactivation process. A series of noveldonor—bridge—acceptor dyads has been synthesised in which the pyrro-lidine[3�,4�:1,2][60]fullerene is covalently attached to the electron donor tetra-thiafulvalene either directly at the 2� position or through one or two vinylgroups.103 Observations suggest that intramolecular electron-transfer processesevolving from the fullerene singlet excited state generate the (C60·�)-(TTF·�) pair.Excitation of fulleropyrrolidines and fullerotriazolines covalently attached totetrathiafulvalene as electron donor leads to the formation of the fullereneexcited singlet state which then undergoes intramolecular electron transfer to thecharge separated state.104 Back electron transfer occurs following formation ofthe fullerene excited triplet state. C60has been used as a subunit for the construc-tion of molecules which exhibit light-induced electron transfer from a porphyrin


donor to a fullerene acceptor.105 A significant advantage of fullerenes overquinones, the preferred choice of nature, is the ability of fullerenes to accept up tosix electrons and the lower reorganisation energy of C60 compared to quinonesaccording to Marcus theory. Time-resolved optical and transient EPR spectro-scopies have been used to investigate photoprocesses associated with the com-plexation of a pyridine-functionalised C60 fullerene derivative to ruthenium- andzinc-tetraphenylporphyrins.106 The study has shown that following excitation inpolar solvents electron transfer from porphyrin to the fullerene occurs. Intra-molecular charge separation and charge recombination processes have beenobserved in a dyad comprising covalently linked C60 and N,N-di(6-tert-butyl-biphenyl)benzenamine, as well as in intermolecular electron transfer to meth-anofullerene.107 In moderately polar solvents, ion-pair recombination was foundto occur within a few nanoseconds giving the ground state and the triplet excitedstate of the C60 moiety, whereas in polar solvents decay occurred through twosteps. The existence of an equilibrium between the charge-transfer and tripletstates has been proposed.The solvent dependence of charge separation and charge recombination rates

in zinc porphyrin—C60 dyads have been examined in a range of different sol-vents.108 It has been shown that, irrespective of solvent polarity, the charge-separated state ZnP·�-C60·� is formed, but that it decays to different energystates depending upon its energy level with respect to those of the singlet andtriplet excited states of the C60 fragment. In non-polar solvents, charge recom-bination occurs to give first the C60 singlet state and subsequently, followingintersystem crossing, the C60 triplet state. In more polar solvents, the charge-separated state is lower than the C60 singlet excited state so that the C60 tripletstate is formed directly, whereas in benzonitrile the charge-separated state decaysdirectly to the ground state. An examination of electron-transfer processes in avariety of porphyrin-linked C60 dyads and triads has shown that, compared withC60 or naphthalenediimide with similar reduction potentials, accelerated photo-induced charge separation can be observed in the former.109 This has beenaccounted for by the small reorganisation energy in C60. Studies on por-phyrin—pyromellitimide—C60 triads suggest that the C60 moiety accelerates theelectron transfer via a through-bond process, or enhances the direct through-space electron transfer from the excited singlet state of the porphyrin. Thesestudies may have implications for the construction of a solar energy conversionsystem. Time-resolved transient absorption spectroscopy and fluorescence life-time measurements have been used to investigate photoinduced charge separ-ation and charge recombination processes in a homologous series of rigidlylinked, linear donor—acceptor arrays with different donor—acceptor separationsand diversified donor strengths.110 The series comprises the free base por-phyrin—C60 dyad (H2P-C60), zinc porphyrin—C60 dyad (ZnP-C60), ferrocene—zincporphyrin—C60triad (Fc-ZnP-C60), ferrocene—free base porphyrin—C60 triad (ZnP-H2P-C60), and zinc porphyrin—free base porphyrin—C60 triad (ZnP-H2P-C60). Thecyclophane-type molecular dyads (38; M�2H, Zn) in which a doubly bridgedporphyrin donor adopts a close, tangential orientation relative to the surface of afullerene acceptor have been prepared along with the porphyrin derivatives (39;

Photochemistry208

M�2H, Zn).111 Structural investigations indicate that the preferred conforma-tions of the latter compounds are such that one of the carbon spheres nests on theporphyrin surface resulting in an orientation analogous to that of the fullerenemoiety in the doubly bridged systems. Time-resolved luminescence studies haveshown (38; M�Zn) and (39; M�Zn) to have similar photophysical behaviour

suggesting that tight donor—acceptor distances can be present in singly bridgeddyads as a consequence of favourable fullerene—porphyrin ground-state interac-tions. A report has appeared of the synthesis and properties of novel porphin-fullerene dyads as well as their use in an investigation of light-induced energy andelectron transfer.112 It is suggested that the advantages of fullerenes overquinones is their ability to accept up to six electrons and the lower reorganisa-tion energy compared to quinones according to Marcus theory. Novel donor—acceptor compounds formed by phytochlorin and C60 fullerene residuals have


been examined in solution and in solid Langmuir-Blodgett films.113 The charge-transfer state has a relatively short lifetime in solution (�100 ps), but by contrastthe lifetime in films is found to be extraordinarily long for a dyad (�30 ns). Theconclusion is drawn that in the films the dyads have uniform orientation andperform a vectorial CT on photoexcitation, so that alternating the DA layer withthe layer composed of secondary donor molecules permits the CT distance to beincreased with concomitant increase in lifetime of the CT state. A study hasshown that photoinduced intermolecular electron transfer inmixtures of oligo(p-phenylenevinylene)s (OPVns, with n�2—7, the number of phenyl rings) andN-methylfulleropyrrolidine in o-dichlorobenzeneoccurs to the triplet state of thefullerene from the OPVn for n �2.114 This observation is in full agreement withthe calculated free energy change for charge separation.Irradiation (��350 nm) of deaerated mixtures of nitrobenzene and cyclo-

hexene leads to the formation of C6H5N(O)——NC6H5, C6H5N——NC6H5,C6H5NH2, and C6H5N(H)C6H5, and these products are also obtained when theirradiations are carried out in the presence of dispersions of TiO2, WO3, orCdS.115 It has been observed, however, that the relative product distributiondepends upon both the competitive adsorption—desorption equilibrium of thereagents used and the intermediates on the solid surfaces, as well as upon thediffering reducing powers of the photoexcited semiconductors. A study of thereactions of triplet 1-nitronaphthalene with trans-stilbene in both non-polar andpolar solvents has shown that in polar solvents the substituted naphthalene actsas an electron acceptor, but that in non-polar solvents only energy transfer totrans-stilbene is observed.116 The change from energy to electron transfer in linewith solvent polarity has been rationalised in terms of Marcus-Hush theory.Aryl-substituted tropylium ions have been photoreduced in deaerated acetoni-trile at room temperature using 9,10-dihydro-10-methylacridine (AcrH)2,2,4,6-triphenyl-4H-pyran, 10,10�-dimethyl-9,9�-bisacridane, or 2,2�,4,4�,6,6�-hexa-methyl-4,4�-bi-(4H-pyran) to 4-methoxyphenyltropylium perchlorate and 4-dimethylaminophenyltropylium perchlorate in an electron-transfer process.117

Following both steady-state and laser flash spectroscopic studies, a mechanismhas been proposed involving photoionisation of (AcrH)2.The reaction between hydrogen and photoexcited carbon dioxide over ZrO2

has been studied using kinetic isotope measurements, reaction temperaturedependence, and EPR.118 The results suggested that the hydrogen is activated inthe dark to react with the photoexcited CO2·�. An IR study has shown that thesurface species arising during the photoreduction of carbon dioxide with meth-ane over zirconium oxide are probably surface acetate and surface formate.119

Evidence from EPR studies suggests that photoexcitation of adsorbed carbondioxide gives CO2·�, which then reacts with methane in the dark; from theseobservations a mechanism to been proposed. Magnesium oxide has been re-ported to be a catalyst for the photoreduction of carbon dioxide to carbonmonoxide, and surface formate has been shown to be a reaction intermediate inthe process.120 Surface formate is also a reductant for the conversion of a secondmolecule of CO2 to CO. A study of the photocatalytic reduction of carbondioxide by cobalt and iron phthalocyanines indicates that although their

Photochemistry210

tetrasulfonated derivatives in aqueous solutions are readily reduced to [Co(I)-Pc]� and [Fe(I)Pc]�, they do not react with CO2.121 However, further reductionof [Co(I)Pc]� gives [Co(I)Pc·�]2�, a species which reacts rapidly with carbondioxide to produce CO and formate in a process whose photochemical yieldsare greatly enhanced by addition of p-terphenyl. Photolysis of the rhenium com-plex [Re(bpy)(CO3)P(OC6H13)3][BArF](2BArF�) (BArF�tetrakis[3,5-bis(tri-fluoromethyl)phenyl]borate) in compressed carbon dioxide and in the presenceof triethylamine leads to reduction of the medium CO2 to CO,122 and carbondioxide has also been photocatalytically and selectively reduced to formic acidusing macrocyclic Ni(II) and tris(2,2�-bipyridine)ruthenium(II) complexes im-mobilised into a Nafion membrane.123

The conditions necessary for the abiotic photoreduction of chloropropionicacid in solutions containingNa2S and quinones have appeared.124 Kinetic studieshave been reported for the photoinduced electron-transfer reduction from car-bazoles and anthracenes to various halomethanes in acetonitrile.125 The funda-mental parameters were determined by application of the Rehm-Weller Gibbsenergy relationship for one electron reduction, and good linear correlations wereobtained when these parameters were related to a range of thermodynamicparameters.Examination of the free energy dependence of electron transfer in some

donor—acceptor systems having hydrogen bonding appendages has shown thattwo types of electron transfer can operate.126 A unimolecular process occursbetween hydrogen bonded species and this obeys the Marcus equation, butwhere there is free diffusion electron transfer is bimolecular and Rehm-Wellerbehaviour is observed. The absence of the inverted region in bimolecular charge-separation reactions has been attributed to diffusion in the region of largedriving force. An investigation of the time resolved fluorescence quenching of apyrylium salt by toluene in acetonitrile solution gives rise to a non-exponentialdecay as a consequence of operation of the transient effect at higher concentra-tions.127 Following deconvolution, use of the Smoluchowski-Collins-Kimballmodel yields the intrinsic rate constant of the bimolecular electron-transferreaction; theMarcus electron transfer/diffusionmodel was also used. A study hasbeen reported of solvent and substituent effects on the efficiencies of photo-induced intramolecular electron-transfer processes in esters of 9-anthra-cenemethanol.128 Estimated rates of electron transfer were found to show a linearcorrelation with values, and values of �were calculated for methanol, sodiumdodecyl sulfate and Triton X. Observed variationswere accounted for in terms ofthe microviscosity and micropolarity of the interior of the micelle systems.Heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14]tetradecane has been used as a spacer

group for regulating photoinduced electron-transfer processes.129 Typical deriva-tives are (40; R1�H, R2�OH, X�O; R1, R2�O, X�O; R1�H, R2�OH, X�S;R1, R2�O, X�S), (41; X�O, S), and (42; R�O, C(CN)2, same X), and highefficiency is observed if the donor and acceptor groups are coplanar. It has beenreported that the product distribution from photolysis of methyl (p-nitro-phenyl)diazoacetate in an acetonitrile/methanol solvent system is altered byaddition of an electron-donating amine.130 Carbene-derived products are com-


pletely suppressed, and evidence suggests that single electron transfer to give thecarbene radical anion is the most likely pathway. Irradiation of some 2-O and3-O thiobenzoate derivatives such as (43) in dichloromethane solution contain-ing triethylamine induces solvent incorporation followed by cyclisation to thetricyclic product (44) via an electron-transfer process.131

5 Singlet Oxygen

A new method for the manufacture of O2(1�g) has been described and consists inpassing molecular oxygen over a sensitiser fabricated from an impregnatedpigment on a carrier under irradiation.132 The support may be one of a rangeincluding silica, alumina, or titania, and the photosensitiser can be selected fromMethylene Blue, Rose Bengal, a phthalocyanine, or a tetraphenylporphin. TheESR technique has been used to monitor the generation efficiency of O2(1�g)using C60 and C70 by following the signal intensity of TEMPO, the stablenitroxide arising from attack of O2(1�g) on TMP (2,2,4,4-tetramethyl-piperidine).133 Porphyrin—fullerene hybrids have been synthesised, and photo-physical properties such as quantum yields for formation of O2(1�g) and fluor-escence quenching determined.134 Efficiencies of O2(1�g) generation using somevinyl-linked benzoaza-15-crown-5-bipyridine ruthenium(II) complexes as sensi-tisers have been found to lie in the range 0.26—0.69.135 Lower values are charac-teristic of those compounds having lower potentials for oxidation of the con-jugated ligands. The photophysical properties and O2(1�g) generation efficiencyof tetrathiarubyrin have been investigated to elucidate the possibility of its use asa photodynamic therapy photosensitiser.136 The results show that the efficiencyof O2(1�g) generation during the oxygen quenching of the triplet state is close tounity, an observation which may be accounted for in terms of the hydrogen

Photochemistry212

bonding of ethanol impeding the deactivation pathway of the charge-transfercomplex with oxygen to the ground state, and the reduced probability of aggre-gate formation. Photoexcited TiO2 and ZnO are reported to be a convenientsource of O2(1�g).137 Their use in this respect has been demonstratedby analysis ofthe oxidation products of methyl oleate and 2,2,6,6-tetramethyl-4-piperidone.Rate constants have been determined for the quenching by O2 of triplet states

T1 for a series of naphthalene sensitisers of very different oxidation potential Eox,but of almost constant ET.138 An analysis of these and other results suggests thatquenching of these oxygen triplet states leads to O2(1�g

�), O2(1�g), and O2(3�g�)

with varying efficiencies by two different channels, each of which is capable ofproducing all three product states. Measurements of the phosphorescence life-time of O2(1�g) in supercritical and liquid carbon dioxide have shown that raisingthe pressure leads to corresponding reductions in the lifetime.139 Phosphor-escence quenching constants have been obtained, and bimolecular quenchingconstants and activation volumes derived. A new method has appeared fordetermining the rate constant of quenching of the excited electronic states ofmolecules by O2 from measurements of the kinetics of photosensitised lumines-cence of O2(1�g).140 This has been used in the case of quenching by molecularoxygen of the excited triplet states associated with the biopolymers of tetra-pyrrole in aqueous media.Photooxidations of alkenes by the O2(1�g) ene reaction, and which occur

within Methylene Blue doped NaY, have been observed to proceed with novelregiochemistry.141 This selectivity has been rationalised in terms of cationiccomplexation with the alkenes, and electrostatic interaction between the cationand the pendant oxygen atom on the developing perepoxide.

6 Oxidation of Aliphatic Compounds

The photocatalytic oxidation of methane to methanol by molecular oxygen onwater-preabsorbed porous TiO2-based catalysts has been reported, and Mo-containing porous TiO2 catalysts have been found to exhibit higher catalyticactivity than pure TiO2.142,143 Photocatalytic oxidation of methane to formalde-hyde on aWO3 surface has been achieved with greater than 90% selectivity from0.01—0.05% conversion using visible radiation.144 This high selectivity is a resultpartly of the powerful electron-accepting capability of its short-lived photo-induced O�centres which strongly polarise the adsorbed methane, as well as thestability of the W—O—W moiety during the photocatalytic process. Severalmaterials have been investigated as possible catalysts for the photooxidation ofpropane in a fixed bed flow reactor.145 The highest activity and selectivity forpropanone formation was achieved by alkali-ion-modified silica-supportedvanadium oxide, and this has been ascribed to the resistance of the catalyst tostructural changes and its ability to withstand being poisoned by water. Photo-catalytic oxidation of n-butane has been observed to occur at a steady state overa silica-supported vanadium oxide catalyst modified with Rb to form methylethyl ketone.146 Hydroxylation of cyclohexane has been catalysed by 5,10,15,20-


tetraphenylporphyrinatoiron(III) chloride (TPPFeCl) using O2 in a range ofsolvents.147 The rate of the reaction was found to be a function of the solvent andincreased in the order acetone� benzene� acetonitrile. These results may be ofimportance in the development of a model of cytochromeP450. Cyclohexane hasbeen photooxidised to cyclohexanone using alumina-supported vanadium oxideas specific catalyst.148 Evidence is advanced to suggest that the active species arestable isolated VO4 units on alumina. Titanium dioxide nanoparticles have beenderivatised with a Fe(III)-porphyrin by a procedure which leaves the amino-propylsilane function contained by the complex, and this has been characterisedusing various techniques.149 These show that the nature of the solvent is highlysignificant in determining the redox characteristics of the grafted polymer.Assessment of the photocatalytic activity of this grafted polymer has beenaccomplished by studying the monooxygenation of cyclohexane, and the resultsshow that increases in efficiency and selectivity are achieved. 8-Methyl-8-(1-methylethyl)bicyclo[5.1.0]oct-1(7)-ene (45), 8-ethyl-8-methylbicyclo[5.1.0]oct-1(7)-ene (46), and 9,9-dimethylbicyclo[6.1.0]non-1(8)-ene (47) have been subjec-ted to photooxygenation using polymer Rose Bengal as sensitiser.150 Both (45)and (46) yield dienes and enones, whereas (47) gives enones exclusively. Experi-mental data indicate that a photosensitiser-initiated free radical autoxidativeprocess is involved with likely intermediates being epoxides for (45) and (46) andhydroperoxides for (47). The absence of O2(1�g)-derived products may be at-tributed either to the relatively long C�—Hallylic distance in alkylcyclopropanes orto their relatively high IP. Alkenes are reported to undergo reaction withmolecular oxygen using the heterofullerenes C59HN and (C59N)2 as sensitisers.151

In particular, 2-methylbut-2-ene and �-terpinene undergo both ene and Diels-Alder photooxygenation reactions respectively to produce the correspondingperoxides. The seco-porphyrazine (48) is reported to induce [4�2] cycloaddi-tion of O2(1�g) to a variety of 1,3-dienes in chlorinated solvents to give thecorresponding endoperoxides under mild conditions.152

The kinetics of the chemiluminescence in the oxidation of cyclo-octene bymolecular oxygen have been studied.153 Cyclopentadiene has been photooxidisedby visible light using 2,9,16,23-tetrasulfophthalocyanines along with variouscentral metal ions as photosensitisers.154 The use of heterogeneous photo-sensitisers immobilised on the cationic exchange resin Amberlite IRA-400 was

Photochemistry214

also examined. 9,10-Dicyanoanthracene and lumiflavin have been reported toact as sensitisers for the photo-oxygenation of 3-substituted cholesterols and7-substituted cholesterols to give oppositely-positioned enol derivatives.155 Anene reaction involving O2(1�g) has been proposed, followed by subsequent rear-rangement of the initially formed 5�-hydroperoxides. Photo-oxidation of thetetranortriterpenoid cedrelone gives (49) whose structure has been established byboth NMR measurements and by X-ray crystallography.156 Addition of RoseBengal has been found to increase the rate of photo-oxidation. The photo-oxidation of �-pinene and trans,trans-1,4-diphenylbuta-1,3-diene using 9,10-dicyanoanthracene as sensitiser in mixed surfactant vesicles has been selectivelydirected towards products derived from either the O2(1�g) or superoxide radicalanion routes.157 This has been achieved by the appropriate choice of vesicles. Inone case studied, the sensitiser was incorporated within the bilayer membrane ofthe vesicles and the substrate solubilised in another set of vesicles, or by havingboth sensitiser and substrate incorporated in the bilayers of the same set.

Irradiation (��300 nm) of deoxygenated solutions of C60 in liquid diphenyl-methane results in the formation of Ph2CH radicals which react with electron-deficient C60 to give Ph2CHC60Hn (n�1, 3, 5).158 It is suggested that excitation ofthe fullerene leads to an increase in its solvation, and hence to an increase in theacidity of the methylene hydrogens in PHCH2. C60 has been alkylated usingvisible radiation in benzonitrile solutions containing the alkylcobalt(III) com-plexes, [RCo(DH)2py] (R�Me and PhCH2; (DH)2�bis(dimethylglyoximato);py�pyridine) to give R2C60.159 The transformation, which proceeds through theexcited state of the cobalt complex, is retarded by trapping agents such as the2,2,6,6-tetramethyl-1-piperidinyloxyl radical, and this observation suggests thatthe transformation proceeds by photocleavage of the cobalt—carbon bond of[RCo(DH)2py]. Photooxygenative partial ring cleavage of the bis(fulleroid) de-rivative (50; R1�R2�CO2Me; CO2CH2CF3, CO2But) has been investigated, andfound to constitute a useful high yield route to novel diketone derivatives (51;same R1, R2) having 12-membered rings on the surface of the fullerene; these arisevia (52; same R1, R2).160

Both experimental and theoretical approaches have been used to investigatethe Norrish Type I and Norrish Type II reactions of pentan-2-one included


within an alkali metal cation-exchanged ZSM-5 zeolite.161 Exchanging the ca-tions affects both the absorption state as well as the photochemical reactions ofthe included ketones, and molecular orbital calculations indicate that the zeoliteframework promotes delocalisation of the charge density of the alkali metalcations, resulting in significant changes in the photolysis of the ketones.Using visible radiation, ethanol has been photo-oxidised to a mixture consist-

ing largely of carbon dioxide together with small amounts of acetaldehyde,formic acid, and carbon monoxide.162 The vanadium-doped, supported TiO2

photocatalyst has a comparable activity and generates a similar product dis-tribution to analogously prepared TiO2 thin-filmmonolayer catalysts. An exam-ination of the photo-oxidation of aqueous solutions of isopropanol containingFe(III) on the surface of semiconductor electrodes has refuted the possibility thatthe Fe(III) ions act as electron acceptors from the oxidation intermediates of thesubstrate.163 A study has been made of the photocatalytic dehydrogenation ofpropan-2-ol on the (110) and (100) planes of TiO2, and both thermal andphotochemical pathways have been observed.164 It is found that in the presenceof light and with h �3.2 eV, the reaction proceeds readily and is not thermallyactivated, but on the (100) surface both thermally activated and photocatalyticpathways are observed. Differences are accounted for in terms of the site ge-ometry on the different surfaces, and it has been concluded that the photo-catalytic pathway is dominant on the (110) surface because hydrogen abstractionoccurs faster from the cation resulting from hole trapping than through protontransfer from the neutral molecule. The photocatalytic oxidation of propan-2-olon TiO2 powder and on a TiO2 monolayer catalyst anchored on porous Vycorglass (TiO2/PVG) has been studied by solid state NMR.165 Two adsorbed pro-pan-2-ol species were identified on the TiO2 powder, a hydrogen bonded speciesand a 2-propoxide species. Two parallel routes seem to be followed in theoxidation process, the first of which proceeds from the H-bonded propan-2-olspecies and which is followed by a condensation to give mesityl oxide, and asecond route which occurs through the relatively rapid and complete oxidationof 2-propoxide to carbon dioxide. Irradiation of diethyl ether—oxygen charge-transfer complexes in the presence of Sn(II) or Cu(II) salts is reported to givehigher yields of oxidation products such as ethyl acetate, acetaldehyde, ethanol,ethyl formate, and methanol than in their absence.166 Photolysis of oxygen-saturated tetrahydrofuran or dibutyl ether gives �-butyrolactone or butanol andbutyl butyrate.The mechanism of the photo-oxidation of decanethiol, self-assembled on

Photochemistry216

roughened silver, has been examined by surface-enhanced Raman spectroscopy(SERS), and in combination with an examination of the oxidation kinetics theresults show that, under the experimental conditions chosen, the oxidationmechanism is dominated by O3 and not by light.167 The slow rate of photo-oxygenation of diethyl sulfide in aprotic solvents is enhanced by addition ofalcohols, and an investigation has shown that this can be rationalised by theinteraction of the protic additives on the persulfoxide intermediate in competi-tion with cleavage processes.168 A kinetic analysis has rationalised this effect as ageneral acid catalysis.Studies of the quantum yields of the photocatalytic oxidation of formate in

aqueous TiO2 suspensions under periodic illumination have shown them to bealways smaller than, but at sufficiently high intermittence to approach valuesobtained under continuous illumination.169 The conclusion is drawn that photo-catalytic oxidation of formate in �10 nm TiO2 nanoparticle suspensions underperiodic illumination behaves kinetically as a homogeneous photochemicalsystem. Photolysis of matrix isolated cycloalkyl nitrites leads to the formation ofthe corresponding cycloalkyl ketones as complexes with HNO.170 However,cyclobutyl nitrite results in 4-nitrosobutanal formation.

7 Oxidation of Aromatic Compounds

A study of the catalytic performance of Mo complexes with Mo1—Mo4nucleari-ties grafted on mesoporous silica FSM-16 in the hydroxylation of benzene tophenol has appeared.171 The highest catalytic activity using hydrogen peroxide asoxidant is exhibited by a trinuclear Mo oxo complex grafted on FSM-16, and at300 K turnover numbers for phenol exceed 700. Studies of photoinduced intra-molecular electron transfer in the two donor—bridge—acceptor systems (53) and


(54) have been reported, and in all solvents examined fast electron transfer wasobserved.172 Investigations exclude a solvent-mediated electron-transfer path-way. From gas phase (U)HF ab initioMO calculations on (55), a less computa-tionally demanding case, the centre-to-centre distance between the two chromo-phores was evaluated. Irradiation of ‘naphtho-o-carborane’ (56) in the presenceof donors such as cyclohexa-1,4-diene induces a quantitative double hydrogenabstraction to give (57); supercoiled DNA is reported to behave similarly.173 Adiradical intermediate (58) has been proposed for these transformations. Thesame authors have also shown that the quinone, 5,8-diketonaphtho-o-carborane

has been produced by irradiating ‘naphtho-o-carborane’ under oxygen.174 In thepresence of the hydrogen donors acetonitrile or cyclohexa-1,4-diene, amixture ofthis same quinone and 5-ketodihydronaphthocarborane is formed. However,under similar conditions, photolysis of ‘benzocarborane’ leads to a highly stereo-and regiospecific dimerisation only . Excitation of bis[4,5-di(methylsulfanyl)-1,3-dithiol-2-ylidene]-9,10-dihydroanthracene (59) in chloroform solution produces(59·�), which in degassed conditions disproportionates to (59·2�), but which inaerated solutions gives 10-[4,5-di(methylsulfanyl)-1,3-dithiol-2-ylidene]an-thracene-9-(10)-one.175 The crystal structure of dication (59·2�) has been deter-mined and this indicates that the planar anthracene and 1,3-dithiolium ringsform a dihedral angle of 77.2° in contrast to the saddle shaped structure of (59). Astudy of the photoinduced electron-transfer quenching of singlet state excitedpyrene and 1,2,5,6-dibenzanthracene by 3-cyanopyridine and o-dicyanobenzenein protic and aprotic solvents has rationalised the charge separation efficiencies,�cs, in singlet-state photoelectron transfer using aprotic solvents and a modelbased upon the macroscopic properties of the solvent.176 Investigations of theelectron-transfer quenching of pyrene by the diphenyliodonium cation in a seriesof straight chain carboxylic acid solvents suggests that specific solvation of thepyrene by the polar head groups of the acids may be important.177 Hydrogenbonding between the carboxyl groups and the �-cloud of the pyrene may occur,leading to the electron-transfer quenching process not being diffusion controlled.It is suggested that the head groups of the carboxylic acids are involved in thesolvent relaxation. Some anthracene derivatives of [60]fullerene have beenfound to react with photochemically produced O2(1�g) at the anthryl group togive 9,10-epidioxides.178

An investigation of the photocatalytic oxidation of gaseous toluene on poly-crystalline TiO2 has found that use of Merck TiO2 leads to benzaldehyde as themain product, and the study shows that, in the absence of water vapour, thebenzaldehyde is held on the catalyst surface.179 Where TiO2 Degussa P25 is used

Photochemistry218

as an alternative catalyst, no gas-phase products are detected, and the mainmaterials formed are benzoate-like species which are strongly absorbed onto thecatalyst. An exploration of the liquid-phase photo-oxidation of ethylbenzene inair in the presence of Rose Bengal supported on a polymer has centred on theeffects of temperature and amount of sensitiser on the ethylbenzene conversionand the ethylbenzene hydroperoxide product selectivity, and on the kinetics.180

The active species in this process is thought to be O2(1�g). p-Xylene has beenphoto-oxygenated to p-tolualdehyde with 100% selectivity in a photoinducedelectron-transfer process by irradiating with visible light in the presence of10-methyl-9-phenylacridinium ion as excited electron acceptor.181 A study hasbeen reported of the photooxidation of toluene and p-xylene with molecularoxygen using visible light in the cation-exchanged zeolites X, Y, ZSM-5, andBeta.182 Large electric fields are thought to promote the photooxidation reactionby stabilising the internal charge-transfer state (R·�O2

�) formed following ex-citation by visible light, and a correlation was found to exist with measuredelectric field and product yield. This was highest for divalent cation-exchangedzeolites with high Si/Al ratios.Photosensitised electron transfer has been used to deconjugate some arylhex-

1-enes to the corresponding arylcyclohex-3-enes.183 Studies of substituent effectsin the aryl ring have provided useful insights into the mechanism of the reaction,and to its scope and limitations. Radical cations of 1,1-diarylethylenes, generatedby direct excitation using short-wavelength radiation within zeolites, have beenobserved to react with solvent hexane, whereas those generated by long-wavelength excitation of the diarylethylene/oxygen complex react with super-oxide anion as counter anion radical.184 These observations show that withinzeolites the 1,1-diarylethylene radical cations undergo abstraction of a hydrogenatom followed by reaction with superoxide anion, and further indicate thatreactive organic radical cations can be generated within zeolites in the absence ofa sensitiser. A mixture of o-(2-hydroxy-3-methylbut-3-enyl)phenols and o-(3-hydroxy-3-methylbut-1-enyl)phenols has been produced by the photoxygena-tion [O2(1�g)] of o-prenylphenols followed by reduction by triphenylphosphineat low temperature,185 and irradiation of oxygenated mixtures of perfluoroalkyliodides and �-chlorostyrenes in the presence of hexabutylditin has been reportedto lead to fluoroalkylated �,�-unsaturated ketones of the formRCOCH——CF(CF2)nCF3 (R�Ph, 4-ClC6H4, 4-MeC6H4, 1-naphthyl, 2-naphthyl;n�3, 5, 9).186

An investigation of the photo-oxidation of trans-1,2-dimethoxystilbene, trans-stilbene, and trans,trans-1,4-diphenylbuta-1,3-diene as well as 2,2,6,6-tetra-methylpiperidine inmixed surfactant vesicles has been carried out by using eithertetraphenylporphyrin or Methylene Blue as sensitiser incorporated in the bi-layers or aqueous inner compartments of one set of vesicles, with the substratesin the bilayer membranes of a second set of vesicles.187 Observations suggest thatO2(1�g), generated in either the bilayer or inner water pool of one vesicle, iscapable of diffusing out and may enter the bilayer of a second vesicle. Underthese conditions, trans-stilbene and trans,trans-1,4-diphenylbuta-1,3-diene areobserved to undergo 1,2-cycloaddition with the O2(1�g). In some related work by


the same authors, an investigation of the 9,10-dicyanoanthracene-sensitisedphotooxidation of �-pinene, trans-stilbene, and trans,trans-1,4-diphenylbuta-1,3-diene in mixed surfactant vesicles indicates that oxidation within the vesiclesselectively yields either the O2(1�g) mediated or the superoxide radical anionmediated products according to the locations of the substrate and sensitiser inthe reaction medium.188 Following photoinduced cis—trans isomerisation, cis-3-styrylthiophene has been converted to dihydronaphtho[1,2-b]thiophene whichcan be oxidised to naphtho[1,2-b]thiophene.189 Photoirradiation of 3-styryl-thiophene in the presence of oxygen gives (60) along with benzaldehyde and3-thiophenecarboxaldehyde as well as dimerisation to bis(naphtho[1,2-b]thiophene) (61). It has been suggested that the latter two reactions occur bycharge-transfer complex formation between oxygen and the substrate.

A rhodamine substituted with two 4-(1-pyrenyl)butyl moieties has been ob-served to show a biexponential fluorescence decay, and this has been interpretedas a reversible intramolecular photoinduced electron transfer.190 Fluorescencedecay measurements permitted the determination of different rate constantsof the excited state equilibrium. Photocyclisation of 3-chloro-N-(3-phen-anthryl)naphtho[1,2-b]thiophene-2-carboxamide is reported to give naph-tho[2�,1�:4,5]thieno[2,3-c]naphtho[1,2-f]quinolin-6(5H)-one as the only one oftwo possible isomers.191 This has been further converted to (62) and the corre-sponding triazole and tetrazole.

Secondary alcohols such as benzhydrol have been irradiated with visible lightin the presence of molecular oxygen within a titanium-substituted mesoporousmolecular sieve, Ti-MCM-41, to give the �-hydroperoxoalcohol, and subse-quently hydrogen peroxide.192 These peroxide species have been found to reactwith alkenes and sulfides with selective formation of epoxides and sulfoxidesrespectively. This procedure may represent a new method for activation ofoxygen in the presence of alcohols. Quantum yields (�obs) of the colloidal TiO2-sensitised photooxidation of ring methoxy-substituted benzylic alcohols havebeen determined, and the true quantum yields (�0) thence obtained.193 Inter- and

Photochemistry220

intramolecular deuterium isotope effects were found to be consistent with akinetically significant C�—Hbond-breaking process following the electron-trans-fer step.An examination of the dependence of the oxidation of phenol by O2(1�g)

photosensitised using [Ru(bpy)3]2� on such quantities as quantum yield offormation of the benzoquinone product as a function of [O2], [PhOH], tempera-ture, pH, and composition of the solvent has been reported.194 A mechanismconsistent with these data has been proposed and this involves formation of anendoperoxide intermediate from the reaction of O2(1�g) with phenol. A hetero-geneous copper catalyst employing the mesoporousmolecular sieveMCM-41 assupport has been developed in which different loadings of copper are impreg-nated onto the support.195 Evaluation of the performance showed that thecatalyst is able to increase the oxidation rate significantly, and studies are alsoreported of the effects of copper loading and catalyst dosage. Kinetic analysis ofthe photo-oxidation of phenol on naked TiO2 has indicated that 98% of thetransformation occurs by reaction with surface bound hydroxyl radicals, andthat the remaining 10% proceeds through direct reaction with holes.196 OnTiO2/F the reaction takes place almost exclusively by homogeneous hydroxylradicals. These observations may have implications for the use of alcohols as adiagnostic tool for analysing photocatalyticmechanisms. A study has been madeof the kinetics of the oxidation of the three isomeric trihydroxybenzenes byO2(1�g) as a function of pH and ionic strength in water, as well as benzene andacetonitrile.197 These results show that in aqueous media trihydroxybenzenesundergo spontaneous and fast photo-oxidation, and that they may have rel-evance to solar-promoted photo-oxidation under field conditions. Some por-phyrins and a chlorin possessing an aromatic group at the meso position havebeen synthesised and used as sensitisers to photooxidise various phenols andnaphthols to quinones.198 The reactions involve formation of O2(1�g) which addsto the substrate. In all of the cases studied generation of O2(1�g) was found to behighly efficient, and this is particularly so for 5,10,15,20-tetrakis(2,6-dichloro-phenyl)porphyrin, presumably because of its high O2(1�g) yield and its highphotostability.Aromatic aldehydes have been oxidised withmolecular oxygen in the presence

of photocatalysts such as meso-tetra-[4-(p-toluenesulfonyloxy)phenyl]por-phyrin and the corresponding Co(II) andMn(II) complexes.199 Measurements ofthe photooxidation of p-chlorobenzaldehyde showed that the kinetics are firstorder in the disappearance of substrate. The main intermediates in the directphotolysis (��200 nm) of acetophenone in aerated aqueous solution are 2-hydroxy- and 3-hydroxyacetophenone.200 Evidence is cited which indicates thatthe photodegradation occurs through attack on the aromatic ring by reactiveoxygen species which themselves originate from reaction of dissolved molecularoxygen with the excited organic substrate. Further hydroxylation to give dihyd-roxyacetophenone is observed.It has been reported that cleavage of p-methoxybenzyl 2-cyclohexylethyl ether

by 9,10-dicyanoanthracene in the presence of air to give a mixture of anisal-dehyde and 2-cyclohexylethanol may be accelerated by co-sensitisation with


biphenyl and driven in favour of cleavage products by replacing oxygen withbromotrichloromethane as sacrificial electron donor.201 Doubly heterogeneousconditions in which both sensitiser and ether are fixed on different silica beadswere used. The effects of oxygenated substituents on the [4�2] cycloaddition ofO2(1�g) in the photo-oxygenation of water-soluble naphthyl ethers have beeninvestigated.202 In cases such as (63), mesomeric interactions between oxygen andthe naphthalene ring lead to extreme reactivity. However, when a methylenelinker separates the oxygen atom from the aromatic ring as in (64), a mixture of1,4- (65; R�CH2CH(OH)CH2OH) and 5,8-endoperoxides (66) results. A sub-picosecond study has been reported of the electron-transfer kinetics of some rigiddyads and triads containing N,N-dimethylaniline (DMA) and dimethoxynaph-thalene (DMN) as donors and the dicyclovinyl group (CV) as acceptor.203 Therate of charge separation decreases exponentially with the number of -bonds inthe bridge for dyads such as DMN[n]DCV, and in triads such as DMA[4]DMN[8]DCV primary electron transfer occurs within 10 ps in solvents of lowand medium polarity. The rates of secondary electron transfer and the ensuingdeactivation processes were observed to depend upon the conformation.

Solutions of 3-acetyl-5-aryl-2-methylfurans in acetonitrile have been photo-oxygenated to 2,2-diacetyl-3-aroyloxiranes in the presence of Rose Bengal assensitiser through the corresponding endo-peroxide intermediate.204 Destructionof the product with water gives 3-acetyl-1-arylpent-2-ene-1,4-diones. However,direct irradiation of the same substrate in a stream of dry air affords 3-acetyl-1-aryl-2-hydroxypent-2-ene-1,4-diones. An investigation of the photosensitisedoxidation of furfural in butanol at 60 °C has been undertaken both in thepresence and in the absence of added water, and gives 2,5-dihydro-5-hy-droxyfuran-2-one and 2,5-dihydro-5-butoxyfuran-2-one.205 The same authorshave presented evidence to support the view that formic acid, an importantproduct in the photosensitised oxidation of furfural in butanol, is oxidised underthe conditions of the reaction and constitutes a source of water.206 Such an

Photochemistry222

observation could explain the formation of 2,5-dihydro-5-hydroxyfuran-2-one inthose cases where no water is added. Reaction of 4,7-dimethylbenzofurazan (67)in chloroform solution with O2(1�g) at 0 °C, generated by irradiation of C60, leadsto 4,7-dimethylbenzofurazan 4,7-endoperoxide (68), and is the first direct obser-vation of endoperoxide formation from a benzofurazan.207 Evidence for theintermediacy of the hydroperoxide has been obtained, and the rate constant forthe oxidation step measured. Irradiation of the neem triterpenoid nimbin (69)promotes oxidation of the furan ring with formation of two isomeric productscontaining a hydroxybutenolide; salannin (70; Tig�COCHMe——CHMe-(E))undergoes an analogous transformation.208

The mechanism of the polyoxometalate-mediated photocatalytic oxidation ofchlorinated organic compounds using 1,2-dichlorobenzene as a model has beenstudied and the possible role of hydroxyl radicals has been elucidated.209

8 Oxidation of Nitrogen-containing Compounds

Photolysis of (phenylamino)piperidine (71) in aqueous acetonitrile containingMethylene Blue and in the presence of oxygen has been reported to give the(phenylazo)pentanal (72).210 An examination of the photocatalytic oxidation ofZ(CONHNH2)2 (Z�bond, NHNH, CO) and Z�(CO2Et)2 (Z��NHNH,NHNHCOCH2CONHNH) in TiO2 dispersions has shown that photo-mineralisation of the N and C atoms occurs along with formation of N2, NH4

�,NO3

�, and CO2; carboxylic acids are also produced.211 These experimentalobservations along with the results of MO simulation of frontier orbital calcula-tions implicate a mechanism in which cleavage of the bonds between the carbon-yl group C atoms and the N atoms of the adjacent hydrazo groups occurs in theinitial photooxidation. �-Aminoalkyl radicals produced by photochemical in-duced electron transfer from tertiary amines such as N,N-dialkylanilines and

pyrrolidine derivatives have been added diastereoselectively to (5R)-5-men-thyloxy-2[5H]-furanone (73) and subsequently used to produce polycyclic mol-ecules and tetrahydroquinolines (74) in a tandem reaction.212 Facial dia-stereoselectivities in excess of 90% have been observed. Photo-oxidation of


thebaine (75) leads to the formation of hydrodibenzofuran (76) in a process whichoccurs by a [4�2] addition of O2(1�g) to the diene function followed by oxida-tion at the nitrogen atom, together with the benzofuran (77).213 A similar photo-oxidation of thebaine ammonium salt gives good yields of thebaine endoperox-ide (78). Structures have been synthesised in which a N,N-dimethylanilinechromophore is linked to a phenacyl ester of acetic acid, and it has been foundthat on irradiation these cleave to release acetic acid.214 Flash photolysis investi-gations suggest that an intramolecular charge-transfer state is formed whichpartitions between bond scission with formation of acetic acid, and a charge-recombination pathway which returns to the ground state. Such covalentlylinked electron donor—acceptor systems may form a useful photochemicallyremovable protecting group. Photoinduced intramolecular charge separationhas been observed in structures composed of either a bicyclohexylidene (79) or abicyclohexyl (80) substituted with an aniline donor and a dicyanoethylene elec-tron acceptor.215 Folding has been shown to occur on the nanosecond time-scalefor (80), and for (79) charge separation proceeds from either a fully foldedconformation or on a sub-nanosecond time-scale. The presence of the exocyclicdouble bond leads to efficient quenching as well as to an increased chargerecombination rate. Photoinduced charge separation has been studied in a seriesof rod-like donor—bridge—acceptor molecules in order to gain some insight intothe role of bridge energy levels on electron transfer rates.216 Structures of the typeANI-diMe-NI and ANI-diMeO-NI (ANI�4-aminonaphthalene-1,8-imide;NI�1,8:4,5-naphthalenediimide; diMe and diMeO�phenyl bridge substitutedat the 2 and 5 positions with methyl or methoxy groups respectively) wereexamined, and relative energies of the ion pair states suggest that 1*D-B-A�D-B�-A� occurs by a double electron-transfer process. Evidence seems to indicatethat electron transfer from the naphthalene 1,8-imide ring of 1*ANI to NI occurs

Photochemistry224

concomitantly with electron transfer from the p-dimethoxybenzene bridge to theelectron-deficient amine nitrogen atom in 1*ANI. Some secondary amines havebeen reported to undergo multiple addition to [60]fullerene under photochemi-cal aerobic conditions to produce a tetra(amino)fullerene epoxide.217

Quenching of 4-carboxybenzophenone triplets (3CB*) by amino acids in basicsolution occurs by electron transfer to 3CB* to give CB·� and the zwitterionaminium radical anion R2N·�CR2CO2

�.218 Values of the primary quenchingconstants have been obtained, and transfer of protons from aminium radicalswithin the solvent cage gives aminyl radicals, RN·CR2CO2· �, which undergo�-elimination of CO2·�. The rate constant for transfer of the proton fromR2N·�CR2CO2

� to CB·� within the solvent cage was also determined. Themechanismof the pyrene-sensitised photodecomposition ofN-phenylglycine hasbeen established as proceeding by electron transfer from theN-phenylglycine tothe excited singlet state of the pyrene by emissive exciplex formation.219

PhNHCH2· also participates as a reactive intermediate, and electron acceptorssuch as terephthalonitrile and diethyl isophthalate are reported to enhance theefficiency of the photodecomposition.The regioselectivities of photoinduced electron-transfer reactions of quinolinic

and trimellitic acid imides have been studied in the cases of potassium butyrateand hexanoate (81; n�3, 5 respectively) and the cysteine derivative (83), and givephotocyclisation products (82) and (84) with moderate selectivities for orthocyclisation.220 However, photoreaction of potassium propionate with the methylester of N-methyltrimellitic acid imide gives only the para addition product.These regioselectivities are rationalised in terms of donor—acceptor interactionsprior to electron transfer, and spin density magnitudes in the correspondingimide radical anions.

Irradiation of a 1:1 mixture of the E and Z isomers of N-methoxy-4-methoxyphenyl-4�-methylphenylmethanimine at �irr�360 nm using 9,10-dicyanoanthracene as photosensitiser in acetonitrile leads to an isomer ratio of4/96,221 and a study of the photooxidation of acetone semicarbazone in thepresence of TiO2 indicates that increases in solvent polarity enhance the yield ofproduct, and that the reaction rate increases with increase in the band gap of thesemiconductor.222 A structure—activity relationship has been proposed and areaction mechanism suggested.An examination of the photocatalytic oxidation of methylviologen in air-

saturated aqueous suspension has found that the initial photonic efficiencyincreases as the light intensity decreases.223 The consequences of increasing thesurface methylviologen concentration have also been elucidated. Studies of the


transient absorption of the 1:1 and 1:2 charge-transfer complexes of methylviolo-gen and iodide following ultrafast excitation in their charge-transfer band hasshown that excitation of the 1:1 complex results in formation of the MV·�/I·radical pair, while excitation of the 1:2 complex gives the MV·�/I· and MV·�/I2radical pairs.224

8-Hydroxyquinolines (85; R1, R2, R3�H, halo, C1—C6 alkyl, CHO, OH, OR,CO2H, CN, CO2R4, CONHR4, CONR4R5, CH2N(CH2CO2R5)CO2R4, R4 andR5�C1—C6 alkyl and C6—C14 aryl) have been irradiated in methylene dichloridesolution containing TPP with oxygen purging, followed by agitation with so-dium sulfate to yield the quinoline-5,8-diones (86; same R1, R2, R3, R4, and R5).225

It has been suggested that the reaction may proceed via the peroxide (87; sameR1, R2, R3, R4, and R5) which undergoes a sodium sulfate-mediated decomposi-tion. Photo-oxygenation of substituted 8-hydroxyquinolines gives substitutedquinoline-5,8-quinones.226

The products arising from photolysis of acridine-1,8-dione dyes have beenshown to be the result of a substituent-dependent process in which the cationradical and the solvated electron are the primary photoproducts.227 The anionradical arises from reaction of the ground-state molecule with a solvated elec-tron, and the anion radical and enolic form of the cation radical are apparent at480 and 550 nm respectively. Transients such as radical cations and radicals,produced sequentially in the oxidation of 3,6-diamino-10-methylacridan (88), anuncharged precursor of acriflavine, have been characterised using pulse radioly-sis and laser flash photolysis.228

An examination of the photophysics of coupled Cd(OH)2-coated Q-CdS withcolloidal TiO2 has appeared.229 The photoactivity of this coupled semiconductormay be enhanced by interaction between Cd(OH)2-coated Q-CdS and TiO2,leading to the possible formation of [CdS-TiO2(OH)2] and a photogeneratedhole CdS(h�) which gives an emissive complexwith the indole fromwhich indigois produced. Irradiated in the presence of cyanide ion and a sensitiser capableproducing O2(1�g), (�)-catharanthine (89) and (�)-16-O-acetylvindoline (90)have been reported to give (�)-3�-cyanocatharanthine and (�)-16-O-acetyl-3�-cyanovindoline respectively.230

Photochemical oxidation of 3-methylcarbazole in methanol leads to the for-mation of murrayaquinone-A, an alkaloid which has been isolated from Mur-raya euchrestifolia.231 This transformation has also been successfully applied tothe similar photooxidation of 3,6-dimethylcarbazole to 3,6-dimethylcarbazole-1,4-quinone. In a study of the photophysics and the mechanisms of the photo-chemical aromatisation of 1,2,3,4-tetrahydro-7H-pyrido[3,4-b]indole in 40%methanol/water, the rate of disappearance of substrate is linearly dependent

Photochemistry226

upon both the concentration of acid and the intensity of the exciting radiation.232

A two-step mechanism appears to be involved, in the first of which the excitedsubstrate reacts with ground state molecular oxygen to form an indolenine,followed subsequently by an acid-catalysed rearrangement to the correspondingdehydro derivative.A study of the kinetics of the dye-sensitised photo-oxidation of 2-amino-4-

hydroxy-6-methylpyrimidine has shown that rates are enhanced in alkalinemedia.233 The presence of the 4-hydroxyl group greatly influences the reactionrate and the experimental evidence suggests the involvement of a charge-transfermediated mechanism and participation of an initial excited encounter complex.Fourier-transform EPR investigations have been reported of radicals formed byelectron transfer from cytosine and 1-methylcytosine to the laser-induced tripletstate of anthraquinone-2,6-disulfonic acid.234 On the nanosecond timescale, themain products are derived from the base radical cations. The photo-oxidation ofuracil and cytosine has been carried out in the presence of peroxydiphosphate inaqueous solution and at neutral pH.235 Analysis of the results indicates that thetransformation probably occurs by production of the phosphate radical anionswhich add to the C-5 or C-6 position of the pyrimidine ring with formation of thepyrimidine radical. Following reaction with peroxydiphosphate both 5,6-dihyd-roxypyrimidine and isobarbituric acid are formed. It has been reported that therates of the TiO2-mediated photo-oxidation of uracil, thymine, and 6-methyl-uracil are retarded by the presence of Cu2�, and this has been accounted for interms of a short-circuiting role for Cu2�.236 Decreases in the photocatalyticactivity of TiO2 brought about by increasing the calcination temperature of theTiO2 have been explained by decreases in the extent of surface-bound peroxo-species. Methylene Blue-mediated photooxidation of guanosine has been re-ported to give spiroiminodihydantoin as the major product,237 and 2�-deoxyguanosine 5�-monophosphate (dGMP) has been oxidised by flavin adeninedinucleotide as sensitiser in a process for which direct evidence has been ob-tained for electron transfer from dGMP to either the triplet state of FAD oroxidised FAD radical.238

Ab initio calculations have been performed on the ground and lowest excited


state of pyrrole and pyrrole—water clusters and full geometry optimisation of the1�s* state implies that there is formation of a charge-transfer-to-solvent state.239

These studies indicate that such clusters form good models for studying themechanistic details of electron solvation processes occurring on excitation oforganic chromophores in water. The antiaromatic isophlorin, N21,N22-(1,2-diphenyletheno)-N23,N24-(carboethoxymethano)-5,10,15,20-meso-tetraphenyl-isophlorin (91) has been dioxygenated at the Cmeso—Cpyrrole-� double bond of thedipyrrylmethene group having the N21,N22-(1,2-diphenyletheno) bridge, andleads to the 19-benzoylisobilirubin (92) which has been characterised.240

N-(Arylamino)piperidines and N-(arylamino)pyrrolidines have been con-verted into the corresponding N-(arylamino) lactams.241 For example, photo-cyanation of the (nitrophenylamino)piperidine (93) has been achieved by irra-diating in oxygenated aqueous solution in the presence of trimethylsilyl cyanideand gives the cyanopiperidine (94). Photooxidation of (94) occurs in aqueousacetonitrile containing Methylene Blue, to produce the piperidinone (95).

The products of photolysis of 4,5-diphenyl-3-(4-methylphenyl)-4-oxazoline-2-thione in hydrocarbon solvents in the presence of O2(1�g) at �irr 450 nm are benzil,N-(4-methylphenyl)benzamide, and N,N-dibenzoyl-4-methylaniline, whereas inprotic solvents benzil,N-(4-methylphenyl)benzamide,N,N-dibenzoyl-4-methyl-aniline, and benzoic acid are formed.242 The suggestion is made that a dioxetaneis generated, which after cleavage gives two radicals which subsequently lead tothe above products. Chiral oxazolidine auxiliaries have been shown to be effec-tive in steering the diastereoselectivity and regioselectivity of the ene mode ofO2(1�g) reaction by means of a hydrogen bonding process.243 For example, (96;X�OCMe3, Ph, NHPh, NHC6H4NO2-4, NMePh) will react with molecularoxygen under photochemical conditions, and following treatment with PPh3 thealcohol (97; same X) is obtained.

Photochemistry228

An investigation of electron-transfer pathways from the lowest triplet excitedstates of (2-substituted)-10-methylphenothiazines has shown that quenchingoccurs by various electron acceptors in polar solvents such as propan-2-ol andacetonitrile.244 Two types of intermediate may be involved, a triplet contactradical ion pair (3CRIP) or a triplet exciplex (3Ex*), and a triplet solvent-separated radical ion pair (3SSRIP). Effects of magnetic fields and heavy atomson the efficiency of free ion formation are described.Multistep non-covalent andcovalent electron transfer have been successfully achieved in a catenane triad ofthe type [98.Q]Cl6 and consisting of phenothiazine as donor, [Ru(bipy)3], andcyclobis(paraquat-p-phenylene) (Q).245

Electron transfer rates have been measured for the charge separation processof the porphyrin—spacer—benzoquinones (99, X�Br, Cl, H) in which the spacersare trans-decalin and dihalosubstituted tricyclo[4.4.1.0]undecane including athree-membered ring.246 These show that rates for compounds having the three-membered rings are about 50—60 times larger than those with a trans-decalinspacer in THF. This acceleration has been attributed to an increase of theelectronic coupling and a decrease of the reorganisation energy.Ab initio calcula-tions suggest that this may arise from the bent geometry of the spacer or from themixing pathway induced by a very low lying antibonding orbital in thedihalosubstituted cyclopropane. A study has been reported of the photoinducedelectron transfer from the S1 state of ZnTTP to a covalently linked Ru(bpy)3 unitin the dyad TTP-CH2NHCORu(bpy)3, composed of 5,10,15,20-tetra(p-tolyl)por-phyrin (TTP) and ruthenium tris(2,2�-bipyridyl) subunits functionalised for con-


nection by an amide linkage.247 Strong fluorescence quenching has been observedin systems consisting of two porphyrins bridged by a biquinoxalinyl spacer, andthis has been interpreted as arising from long range (�8 A� ) through-biquinoxa-line bridge-mediated electron transfer from free base to porphyrin to the gold(III)porphyrin.248 Excitation of the caroteno—porphyrin—fullerene triad (C-P-C60)triggers electron transfer from the porphyrin first excited state or to the fullerenefirst excited state to yield C-P·�-C60·�, and this is followed by further electrontransfer to give C·�-P-C60·� as the final charge-separated state.249 Investigationssuggest that the energies of the charge-separated states of these fullerene-basedsystems are much less sensitive to changes in solvent dielectric constant than arethose of similar molecules possessing quinone electron acceptors.Irradiation of 3-methyl-2-(4-nitrophenyl)-2H-azirine (100; Ar�p-nitrophenyl)

in the presence of molecular oxygen in fluid solution and in low-temperaturematrices induces cleavage of the C—N bond of the azirine ring to give biradical(101), which in turn leads to acetonitrile oxide.250 A new synthetic protocol hasbeen described in which azidyl radicals and molecular oxygen can be added toelectron donor and electron acceptor substituted acyclic and cyclic alkenes toproduce 1,2-azidohydroperoxides, which themselves can be easily reduced.251

This reaction can be thought of as a complex sequence of photoinduced electrontransfer, addition, oxygen-trapping and subsequent electron-transfer processes.The MO LCAO quantum mechanical method in the AM1 approximation hasbeen used to consider hypothetical models of the interaction of deoxypeganine(102) with a solvent.252 Excited triplet states of deoxypeganine and some ana-logues have been calculated enabling a free-radical mechanism of photochemicaloxidation to be proposed. Helimeric mixtures of (�)-(M,7S)-isocolchicine (103)and (�)-(P,7S)-isocolchicine (104) have been photooxygenated using O2(1�g),and it has been found that cycloaddition occurs with high regioselectivity at the7a,11-positions and predominantly at the diene face to the amidic substituent atthe stereogenic centre, C-7.253 The two products are the syn endoperoxide (105)

Photochemistry230

and the anti endoperoxide (106). Monometallic colloidal dispersions such as Au,Pt, Pd, Rh, and Ru, and bimetallic nanoclusters such as Au/Pt, Au/Pd, Au/Rh,and Pt/Ru have been used as catalysts for visible light induced hydrogen gener-ation.254 It has been observed that the rate of electron transfer from methylviolo-gen cation radical to the metal nanoclusters is proportional to the hydrogengeneration rate. Free-radical intermediates are reported to be produced duringthe visible irradiation of aqueous Sulforhodamine B in the presence of TiO2 andair, and have been detected using the spin-trapping technique with 5,5-dimethyl-1-pyrroline N-oxide and N-tert-butyl-�-phenyl-nitrone.255 These are the hy-droxyl and hydroperoxyl radicals, together with the hydrated electron. Theirmechanism of generation has been discussed, but the main oxidising agent hasbeen suggested to be oxygen molecules. The photodegradation of methanolicMethyl Orange has been examined in the presence of ferric ions and hydrogenperoxide using the spin-trapping EPR technique.256 Intermediates producedwere detected by IR and GC—MS methods, and a mechanism suggested for thetransformation under both UV and visible light excitation. It has been reportedthat trifunctional electron donor—donor—acceptor molecules are capable ofundergoing the photoinduced charge separation D2-D1-A*�D2-D1

�-A�. fol-lowed by a charge migration step D2-D1

�-A� (CS1)�D2�-D1-A� (CS2) to give a

charge-separated state which is relatively long lived.257 Increases in chargemigra-tion rate occur in solvents of increased polarity within a series of alkyl ethers oralkyl acetates.


9 Miscellaneous Oxidations

Ketyl radicals and ketyl radical anions along with various sulfur radical cationshave been identified as transients following quenching of triplet 4-carboxy-benzophenone by methionine-containing peptides in aqueous solution, and thequantum yields of formation of these transients have been determined.258 Thepresence of such transients suggests that the triplet—triplet quenching processoccurs by electron transfer. Competitive donation of protons to the 4-car-boxybenzophenone radical anion takes place within the charge-transfer com-plex, and this competition occurs between protons on carbons adjacent to thesulfur radical centre and protons on the protonated amino groups of the radicalcation. A competition also exists between the two intramolecular two-centred,three-electron bonded species (SS)� and (SN)� which appear in the secondarykinetics. Visible light photooxidation of dilute aqueous and aqueous-ethanolicsolutions of sulfathiazole and succinylsulfathiazole have been studied kineticallyin the presence of riboflavin and Rose Bengal.259 The results may have micro-biological implications. An analysis of the kinetics of the photooxidation of3-(2-benzothiazolyl)-7-diethylaminocoumarin at 254 nm in halomethane sol-vents has shown that H-bond donation of the solvents is important in controll-ing the rate of product formation.260 The observations imply that the process ofactivation is controlled by diffusion of dye into the solvent cage.In a study of the photocatalytic decomposition of water to oxygen over pure

WO3, CeO2, and TiO2, it has been demonstrated that the yield of oxygen dependsupon both the type and surface of the cation present in the electron acceptor, andupon the salt counter ion. Highest long-term yields of molecular oxygen aregiven by Feaq3�.261

Dimethyl methylphosphonate has been photooxidised on powdered TiO2

using UV radiation to give CO, CO2 and formate ions together with water alongwith concurrent destruction of the PCH3 and POCH3 groupings.262 Studies weremainly carried out at 200 K under which conditions a hydrolytic pathway issuppressed. An examination of the SET-initiated photorearrangements of thecis- and trans-2-phenylallyl phosphites (107) to the corresponding phosphonates(108) has shown the process to occur with retention of configuration at thephosphorus atom.263

10 References

1. T. Slonka, Pr. Nauk. Inst. Technol. Nieorg. Nawozow Miner. Politech. Wroclaw,2000, 48, 220.

Photochemistry232

2. V. Ramamurthy, R. J. Robbins, K. J. Thomas and P. H. Lakshminarasimhan,Mol.Solid State, 1999, 2, 63.

3. S. Vasenkov and H. Frei,Mol. Supramol. Photochem., 2000, 5, 295.4. H. Usami and H. Fujimatsu,Nendo Kagaku, 2001, 40, 159.5. X.-h. Chen and S.-b. Li, Fenzi Cuihua, 2000, 14, 477.6. A. Albini, M. Fagnoni and M. Mella, Chem. Beginning Third Millennium, Proc.

Ger.-Ital.Meet., 1999, 83.7. J. Paczkowski, Z. Kucybala, F. Scigalski and A. Wrzyszczynski,Trends Photochem.

Photobiol., 1999, 5, 79.8. M.Yasuda, T. Yamashita, T. Shiragami andK. Shima,RecentRes.Dev.Photochem.

Photobiol., 1999, 3, 65.9. W.M.Horspool,Chem.Dienes Polyenes, 2000, 2, 257, ed. Z. Rappoport, JohnWiley

and Sons Ltd., Chichester, UK.10. H. Imahori and Y. Sakata,Kikan Kagaku Sosetsu, 1999, 43, 187.11. C. Konigstein, A. Launikonis, A. W. H. Mau, W. H. F. Sasse and G. J. Wilson, Z.

Phys. Chem. (Munchen), 1999, 213, 199.12. M. Granda-Valdes, R. Badia, G. Pina-Luis and M. E. Diaz-Garcia, Quim. Anal.

(Barcelona), 2000, 19 (Supl. 1), 38.13. A. A. Frimer, Spectrum (Bowling Green, OH,U. S.) 2000, 13, 9.14. P. Wessig, U. Lindemann and J. Schwarz, J. Inf. Rec., 2000, 25, 65.15. T. Horaguchi, Trends Heterocycl. Chem., 1999, 6, 1.16. Y. Fang, Y. Chen, J. Wang, R. Cai and Z. Huang,Huaxue Tongbao, 2000, 25.17. K. Mikami and S. Matsumoto,Kikan Kagaku Sosetsu, 1999, 43, 110.18. D. I. Schuster, Carbon, 2000, 38, 1607.19. M. Maggini and D. M. Dirk,Mol. Supramol. Photochem., 2000, 6, 149.20. W. M. Nau, EPA Newsl., 2000, 70, 6.21. T. Mukherjee, Proc. Indian Natl. Sci. Acad. Part A, 2000, 66, 239.22. S. V. Zelentsov, N. V. Zelentsova, A. B. Zhezlov and A. V. Oleinik, High Energy

Chem., 2000, 34, 164.23. Y. Nakamura and N. Torimoto,Kagaku to Kyoiku, 2000, 48, 198.24. H. Xing, C. Tian and Y. Wang, Shanghai Huanjing Kexue, 2001, 20, 63.25. C. Costentin, M. Robert and J.-M. Saveant, J. Phys. Chem. A, 2000, 104, 7492.26. W. M. Nau, EPA Newsl., 2000, 70, 6.27. E. Cheung, M. R. Netherton, J. R. Scheffer, J. Trotter and A. Zenova, Tetrahedron

Lett., 2000, 41, 9673.28. Y. Miyake and J. Miyuki, J. Chem. Eng. Jpn., 2000, 33, 372.29. K. Nakamura, R. Yamanaka, K. Tohi and H. Hamada,TetrahedronLett., 2000, 41,

6799.30. A. J. Kell, D. L. B. Stringle and M. S. Workentin, Org. Lett., 2000, 2, 3381.31. C. Coenjarts and J. C. Scaiano, J. Am. Chem. Soc., 2000, 122, 3635.32. S. A. Markaryan, Russ. J. Org. Chem., 2000, 36, 712.33. J. R.Woodward, T.-S. Lin, Y. Sakaguchi andH.Hayashi,Appl.Magn.Reson., 2000,

18, 333.34. Y. Akimoto, Y. Fujiwara and Y. Tanimoto, Chem. Phys. Lett., 2000, 236, 383.35. A. Gaplovsky, M. Gaplovsky, S. Toma and J.-L. Luche, J. Org. Chem., 2000, 65,

8444.36. C. Serpa and L. G. Arnaut, J. Phys. Chem. A, 2000, 104, 11075.37. M. Torimura, A. Miki, A. Wadano, K. Kano and T. Ikeda, J. Electroanal. Chem.,

2001, 496, 21.


38. S. Fukuzumi, S. Itoh, T. Komori, T. Suenobu, A. Ishida,M. Fujitsuka andO. Ito, J.Am. Chem. Soc., 2000, 122, 8435.

39. N. Haga, H. Takayanagi and K. Tokumaru, Chem. Lett., 2001, 448.40. M. G. Kulkarni and S. D. Kate, J. Chem. Soc. Perkin Trans. 1, 2000, 4242.41. S. A. Chesnokov, V. K. Cherkasov, Yu. V. Chechet, N. I. Nevodchikov, G. A.

Abakumov and O. N. Mamysheva, Russ. Chem. Bull., 2000, 49, 1506.42. J.-M. Lu and D Beckert, Res. Chem. Intermed. 2000, 26, 621.43. Z. C. Wu, J. Y. An, Y. Z. Hu and F. Tian, Chin. Chem. Lett., 2000, 11, 479.44. A. J. Myles and N. R. Branda, J. Am. Chem. Soc., 2001, 123, 177.45. T. Nakayama, Y. Torii, S. Miki and K. Hamanoue, Recent Res. Dev. Photochem.

Photobiol., 1999, 3, 103.46. A. J. Myles and N. R. Branda, Tetrahedron Lett., 2000, 41, 3785.47. S. Fukuzumi, S. Itoh, T. Komori, T. Suenobu, A. Ishida,M. Fujitsuka andO. Ito, J.

Am. Chem. Soc., 2000, 122, 8435.48. B. Akhremitchev, C. Wang and G. C. Walker, Laser Chem., 1999, 19, 403.49. S. Rochat, C. Minardi, J.-Y. De Saint Laumer and A. Herrmann,Helv. Chim. Acta,

2000, 83, 1645.50. T. Hasegawa, M. Kajiyama and Y. Yamazaki, J. Phys. Org. Chem., 2000, 13, 437.51. P. Klan, J. Janosek and Z. Kriz, J. Photochem. Photobiol., A, 2000, 134, 37.52. P. Wessig, U. Lindemann and J. Schwarz, J. Inf. Rec., 2000, 25, 65.53. J. A. Pincock, S. Rifai and R. Stefanova, Can. J. Chem., 2001, 79, 63.54. H. Kim, T. G. Kim, J. Hahn, D.-J. Jang, D. J. Chang and B. S. Park, J. Phys. Chem.

A, 2001, 105, 3555.55. T. Suzuki, T. Omori and T. Ichimura, J. Phys. Chem., 2000, 104, 11671.56. K. Okawa, Y. Nakamura and J. Nishimura, Tetrahedron Lett., 2000, 41, 3103.57. W. Adam, K. Peters, E. M. Peters and V. R. Stegman, J. Am. Chem. Soc., 2000, 122,

2958.58. W. Adam, V. R. Stegmann and S. Weinkoetz, J. Am. Chem. Soc., 2001, 123, 2452.59. M. D’Auria and R. Racioppi, ARKIVOC, 2000, 1, 145.60. J. Xue, Y. Zhang, T. Wu, H.-K. Fun and J.-H. Xu, J. Chem. Soc., Perkin Trans. 1,

2001, 183.61. M. Goez and I. Frisch, J. Inf. Rec., 2000, 25, 287.62. M. Abe, K. Fujimoto and M. Nojima, J. Am. Chem. Soc., 2000, 122, 4005.63. M. Abe, E. Torii and M. Nojima, J. Org. Chem., 2000, 65, 3426.64. B. Witte, L. Meyer and P. Margaretha,Helv. Chim. Acta, 2000, 83, 554.65. J. Peon, X. Tan, J. D. Hoerner, C. Xia, Y. F. Luk and B. Kohler, J. Phys. Chem. A,

2001, 105, 5768.66. S. D.-M. Islam, T. Konishi, M. Fujitsuka, O. Ito, Y. Nakamura and Y. Usui,

Photochem. Photobiol., 2000, 71, 675.67. S. D.-M. Islam, Y. Yoshikawa, M. Fujitsuka, O. Ito, S. Komatsu and Y. Usui, J.

Photochem. Photobiol., A, 2000, 134, 155.68. T. Konishi, M. Fujitsuka, O. Ito, Y. Toba and Y. Usui, Bull. Chem. Soc. Jpn., 2001,

74, 39.69. K. Kasuga, K. Nishie, M. Handa and T. Sugimori, Inorg. Chim. Acta, 2000, 307,

164.70. E. B. De Borba, C. L. C. Amaral, M. J. Politi, R. Villalobos and M. S. Baptista,

Langmuir, 2000, 16, 5900.71. T. P. Le, J. E. Rogers and L. A. Kelly, J. Phys. Chem. A, 2000, 104, 6778.72. K. Yoshinaga, I. Toyofuku, K. Yamashita, H. Kanehara and K. Ohkubo, Colloid

Polym. Sci., 2000, 278, 481.

Photochemistry234

73. P. J. Campos, J. Arranz and M. A. Rodriguez, Tetrahedron, 2000, 56, 7285.74. S. Fukuzumi,M. Fujita, S. Noura, K. Ohkubo, T. Suenobu, Y. Araki and O. Ito, J.

Phys. Chem. A, 2001, 105, 1857.75. T. Ito, H. Shinohara, H. Hatta, S.-i. Fujita and S.-i. Nishimoto, J. Phys. Chem. A,

2000, 104, 2886.76. J. Nagy, Z.Madarasz, R. Rapp, A. Szollosy, J. Nyitrai andD.Dopp, J.Prakt.Chem.

(Weinheim, Ger.), 2000, 342, 281.77. J. R. De la Fuente, A. Canete, A. L. Zanocco, C. Saitz and C. Jullian, J. Org. Chem.,

2000, 65, 7949.78. N. N. Kruk and A. A. Korotkii, J. Appl. Spectros., 2000, 67, 966.79. H. Sasaki and M. Sisido, Pept. Sci., 1999, 36th, 355.80. M. Sisido and H. Kusano, Pept. Sci., 1999, 36th, 65.81. S. Watanabe, T. Sueyoshi, M. Ichihara, C. Uehara and M. Iwamura, Org. Lett.,

2001, 3, 255.82. O. V. Makarova, T. Rajh, M. C. Thurnauer, A. Martin, P. A. Kemme and D.

Cropek, Environ. Sci. Technol., 2000, 34, 4797.83. H. Tada, M. Kubo, S. Ito and Y. Inubushi, Chem. Commun., 2000, 977.84. H. Gorner, D. Dopp and A. Dittmann, J. Chem. Soc., Perkin Trans. 2, 2000, 1723.85. D. Dopp, W. A. F. Youssef, A. Dittmann, A. M. Kaddah, A. A. Shalaby and Y. M.

Naguib, J. Inf. Rec., 2000, 25, 57.86. S. Alp, S. Erten, C. Karapire, B. Koz, A. O. Doroshenko and S. Icli, J. Photochem.

Photobiol., A, 2000, 135, 103.87. M. Z. Jin, L. Yang, L. M. Wu, Y. C. Liu and L. Z. Li, Chin. Chem. Lett., 2001, 12,

307.88. J. V. Sonntag and W. Knolle, J. Photochem. Photobiol. A, 2000, 136, 133.89. Q. J. Li, Q. J. Gong, L.M. Du andW. J. Jin, Spectrochim.Acta,Part A, 2001, 57, 17.90. J. Sun, Y. Liu, D. Chen and Q. Zhang, J. Phys. Chem. Solids, 2000, 61, 1149.91. A. Masuhara, M. Fujitsuka and O. Ito, Bull. Chem. Soc. Jpn., 2000, 73, 2199.92. Y. Sasaki, T. Konishi, M. Fujitsuka, O. Ito, Y. Maeda, T. Wakahara, T. Akasaka,

M. Kako and Y. Nakadaira, J. Organomet. Chem., 2000, 599, 216.93. D. M. Martino and H. van Willigen, J. Phys. Chem. A, 2000, 104, 10701.94. S. Fukuzumi, H. Imahori, H. Yamada, M. E. El-Khouly, M. Fujitsuka, O. Ito and

D. M. Guldi, J. Am. Chem. Soc., 2001, 123, 2571.95. T. W. Hamann, A. P. Bussandri, H. Van Willigen, S. Najah and J. C. Warner,

Proc.-Electrochem. Soc., 2000, 289.96. M. E. El-Khouly, M. Fujitsuka and O. Ito, J. Porphyrins Phthalocyanines, 2000, 4,

590.97. V. Brezova, D. Dvoranova, S. Rapta and A. Stasko, Spectrochim. Acta, Part A,

2000, 56, 2729.98. D. M. Guldi, J. Phys. Chem. B, 2000, 104, 1483.99. J. L. Segura, R. Gomez, N. Martin, C. Luo andD. M. Guldi,Chem.Commun., 2000,

701.100. M. Fujitsuka, O. Ito, T. Yamashiro, Y. Aso and T. Otsubo, J. Phys. Chem.A, 2000,

104, 4876.101. P. A. Van Hal, J. Knol, B.M.W. Langeveld-Voss, S. C. J. Meskers, J. C. Hummelen

and R. A. J. Janssen, J. Phys. Chem. A, 2000, 104, 5974.102. K. Matsumoto, M. Fujitsuka, T. Sato, S. Onodera and O. Ito, J. Phys. Chem. B,

2000, 104, 11632.103. N.Martin, L. Sanchez,M. A.Herranz andD.M.Guldi, J.Phys.Chem.A, 2000, 104,

4648.


104. N. Martin, L. Sanchez, B. Illescas, S. Gonzalez, H. M. Angeles and D. M. Guldi,Carbon, 2000, 38, 1577.

105. O. Kutzki, M. Wedel, F.-P. Montforts, S. Smirnov, S. Cosnier and A. Walter, Proc.— Electrochem. Soc., 2000, 172.

106. T. Da Ros, M. Prato, D. M. Guldi, M. Ruzzi and L. Pasimeni, Chem.— Eur. J. 2001,7, 816.

107. S. Komamine,M. Fujitsuka, O. Ito, K. Moriwaki, T. Miyata and T. Ohno, J. Phys.Chem. A, 2000, 104, 11497.

108. H. Imahori, M. E. El-Khouly, M. Fujitsuka, O. Ito, Y. Sakata and S. Fukuzumi, J.Phys. Chem. A, 2001, 105, 325.

109. H. Imahori, K. Tamaki, H. Tamada, K. Yamada, Y. Sakata, Y. Nishimura, I.Yamazaki, M. Fujitsuka, and O. Ito, Carbon, 2000, 38, 1599.

110. H. Imahori, K. Tamaki, D.M.Guldi, C. Luo,M. Fujitsuka, O. Ito, Y. Sakata and S.Fukuzumi, J. Am. Chem. Soc., 2001, 123, 2607. .

111. N. Armaroli, G. Marconi, L. Echegoyen, J.-P. Bourgeois and F. Diederich,Chem. —Eur. J., 2000. 6, 1629.

112. O. Kutzki, M. Wedel, F.-P. Montforts, S. Smirnov, S. Cosnier and A. Walter, Proc.— Electrochem. Soc., 2000, 172.

113. N. V. Tkachenko, A. Y. Tauber, V. Vehmanen, A. A. Alekseev, P. H. Hynninen andH. Lemmetyinen, Proc. — Electrochem. Soc., 2000, 10, 161.

114. P. A. vanHal, E. H. A. Beckers, E. Peeters, J. J. Apperloo andR. A. J. Janssen,Chem.Phys. Lett., 2000, 328, 403.

115. A. Maldotti, L. Andreotti, A. Molinari, S. Tollari, A. Penoni and S. Cenini, J.Photochem. Photobiol., A, 2000, 133, 129.

116. T. Fournier, G. D. Scholes, I. R. Gould, S. M. Tavender, D. Phillips and A. W.Parker, Laser Chem., 1999, 19, 397.

117. W. Abraham, D. Jacobi, U. Pischel and W. Schnabel, J. Inf. Rec., 2000, 25, 127.118. Y. Kohno, T. Tanaka, T. Funabiki and S. Yoshida, Phys. Chem.Chem. Phys., 2000,

2, 2635.119. Y. Kohno, T. Tanaka, T. Funabiki and S. Yoshida, Phys. Chem.Chem. Phys., 2000,

2, 5302.120. Y. Kohno, H. Ishikawa, T. Tanaka, T. Funabiki and S. Yoshida,Phys.Chem.Chem.

Phys., 2001, 3, 1108.121. J. Grodkowski, T. Dhanasekaran, P. Neta, P. Hambright, B. S. Brunschwig, K.

Shinozaki and E. Fujita, J. Phys. Chem. A, 2000, 104, 11332.122. H. Hori, Chorinkai Saishin Gijutsu, 2000, 4, 29.123. R. Ramaraj and J. R. Premkumar, Curr. Sci., 2000, 79, 884.124. K. K. Ngim and D. G. Crosby, ACS Symp. Ser., 2001, 777, 397.125. S. M. Bonesi and R. Erra-Balsells, J. Chem. Soc., Perkin Trans. 2, 2000, 1583.126. E. Prasad and K. R. Gopidas, J. Am. Chem. Soc., 2000, 122, 3191.127. X. Allonas, P. Jacques, A. Accary, M. Kessler and F. Heisel, J. Fluoresc., 2000, 10,

237.128. M. D. P. De Costa andM. K. A. D. Sriyani, J.Natl. Sci. Found. SriLanka, 1999, 27,

277.129. N.-R. Chiou, T. J. Chow, C.-Y. Chen,M.-A. Hsu andH. C. Chen,TetrahedronLett.,

2001, 42, 29.130. T. Mizushima, S. Ikeda, S. Murata, K. Ishii and H.-O. Hamaguchi, Chem. Lett.,

2000, 1282.131. A. L. Schreiber, M. A. Fashing and C. J. Abelt, J. Chem. Soc., Perkin Trans. 2, 2000,

953.

Photochemistry236

132. T. Matsuura and H. Suzuki, Jpn.Kokai Tokkyo Koho JP 2000, 211,902.133. A. Sienkiewicz, S. Garaj, E. Bialkowska-Jaworska and L. Forro, AIP Conf. Proc.,

2000, 544, 63.134. S. MacMahon, S. R. Wilson and D. I. Schuster, Proc. — Electrochem. Soc., 2000, 10,

155.135. A. A. Abdel-Shafi, P. D. Beer, R. J. Mortimer and F.Wilkinson, Phys. Chem.Chem.

Phys., 2000, 2, 3137.136. J.-H. Ha, G. Y. Jung, M.-S. Kim, Y. H. Lee, K. Shin and Y.-R. Kim, Bull. Korean

Chem. Soc., 2001, 22, 63.137. Y. Yamamoto, N. Imai, R. Mashima, R. Konaka, M. Inoue and W. C. Dunlap,

Methods Enzymol., 2000, 319, 29.138. R. Schmidt, F. Shafii, C. Schweitzer, A. A. Abdel-Shafi and F. Wilkinson, J. Phys.

Chem. A, 2001, 105, 1811.139. M. Okamoto and T. Takagi,Koatsuryoku no Kagaku to Gijutsu, 2000, 10, 192.140. N. N. Kruk and A. A. Korotkii, J. Appl. Spectrosc., 2000, 67, 560.141. E. L. Clennan and J. P. Sram, Tetrahedron, 2000, 56, 6945.142. X. Chen and S. Li, Chem. Lett., 2000, 314.143. X. Chen and S. Li, Fenzi Cuihua, 2000, 14, 243.144. K. A. Kolmakov and V. N. Pak, Zh. Prikl. Khim. (S-Peterburg), 2000, 73, 159.145. T. Tanaka, T. Ito, S. Takenaka, T. Funabiki and S. Yoshida,Catal. Today, 2000, 61,

109.146. T. Tanaka, T. Ito, T. Funabiki and S. Yoshida, Stud. Surf. Sci. Catal., 2000, 130B,

1961.147. J.-W. Huang, W.-Z. Huang, W.-J. Mei, J. Liu, S.-G. Hu and L.-N. Ji, J.Mol. Catal.

A: Chem., 2000, 156, 275.148. K. Teramura, T. Tanaka, T. Yamamoto and T. Funabiki, J. Mol. Catal. A: Chem.

2001, 165, 299.149. A. Molinari, R. Amadelli, L. Antolini, A. Maldotti, P. Battioni and D. Mansuy, J.

Mol. Catal. A: Chem., 2000, 158, 521.150. A. A. Frimer, M. Afri, S. D. Baumel, P. Gilinsky-Sharon, Z. Rosenthal and H. E.

Gottlieb, J. Org. Chem., 2000, 65, 1807.151. N. Tagmatarchis and H. Shinohara, Org. Lett., 2000, 2, 3551.152. A. A. Trabanco, A. G. Montalban, G. Rumbles, A. G. M. Barrett and B. M.

Hoffman, Synlett, 2000, 1010.153. Z. M. Komarenskaya, B. I. Chernyak, G. M. Mishchenko and Y. B. Trach, Theor.

Exp. Chem., 2000, 35, 330.154. O. Bartels, D. Wohrle, R. Gerdes, G. Schneider and G. Schulz-Ekloff, J. Inf. Rec.,

2000, 25, 251.155. W. Shuping, J. Zhiqin, L. Heting, Y. Li and Z. Daixun,Molecules, 2001, 6, 52.156. G. Gopalakrishnan, N. D. P. Singh, V. Kasinath, R. Malathi and S. S. Rajan,

Photochem. Photobiol., 2000, 72, 464.157. H. R. Li, C. H. Tung and L. Z. Wu, Chem. Commun., 2000, 1085.158. M. Fedurco, K. Klosterman, U. Kirbach, D. Scheller and L. Dunsch, Chem. Phys.

Lett., 2000, 319, 309.159. K. Ohkubo and S. Fukuzumi, Inorg. React.Mech. (Amsterdam), 2000, 2, 147.160. H. Inoue, H. Yamaguchi, S.-i. Iwamatsu, T. Uozaki, T. Suzuki, T. Akasaka, S.

Nagase and S. Murata, Tetrahedron Lett., 2001, 42, 895.161. H. Yamashita, M. Nishimura, H. Bessho, S. Takada, T. Nakajima, M. Hada, H.

Nakatsuji and M. Anpo, Res. Chem. Intermed., 2001, 27, 89.162. S. Klosek and D. Raftery, J. Phys. Chem. B, 2001, 105, 2815.


163. T. Ohno, S. Izumi, K. Fujihara, Y. Masaki and M. Matsumura, J. Phys. Chem. B,2000, 104, 6801.

164. D. Brinkley and T. Engel, J. Phys. Chem. B, 2000, 104, 9836.165. W. Xu and D. Raftery, J. Phys. Chem. B, 2001, 105, 4343.166. M. Shi, Chin. J. Chem., 2000, 18, 936.167. M. M. Ferris and K. L. Rowlen, Appl. Spectrosc., 2000, 54, 664.168. S. M. Bonesi and A. Albini, J. Org. Chem., 2000, 65, 4532.169. C. J. G. Cornu, A. J. Colussi andM.R.Hoffmann, J.Phys.Chem.B, 2001, 105, 1351.170. D. Puchowicz, J. Adamus and J. Gebicki, J. Chem. Soc.,PerkinTrans. 2, 2000, 1942.171. K. Zama, A. Fukuoka, Y. Sasaki, S. Inagaki, Y. Fukushima and M. Ichikawa,

Catal. Lett., 2000, 66, 251.172. M. Koeberg, M. de Groot, J. W. Verhoeven, N. R. Lokan, M. J. Shephard and M.

N. Paddon-Row, J. Phys. Chem. A, 2001, 105, 3417.173. A. Z. Bradley, A. J. Link, K. Biswas, D. Kahne, J. Schwartz, M. Jones, Z. Zhu and

M. S. Platz, Tetrahedron Lett., 2000, 41, 8691.174. A. Z. Bradley, A. D. Cohen, A. C. Jones, D. M. Ho andM. Jones, TetrahedronLett.,

2000, 41, 8695.175. A. E. Jones, C. A. Christensen, D. F. Perepichka, A. S. Batsanov, A. Beeby, P. J.

Low, M. R. Bryce, and A. W. Parker, Chem.—Eur. J., 2001, 7, 973.176. G. P. Zanini, H. A. Montejano and C. M. Previtali, J. Photochem. Photobiol., A,

2000, 132, 161.177. A. C. Bruce, J. J. Klein andM. R. V. Sahyun, J. Photochem.Photobiol.,A, 2000, 131,

27.178. H. Irngartinger, A. Weber and T. Escher, Eur. J. Org. Chem., 2000, 1647.179. G.Martra, V. Augugliaro, S. Coluccia, E. Garcia-Lopez, V. Loddo, L.Marchese, L.

Palmisano and M. Schiavello, Stud. Surf. Sci. Catal., 2000, 130A, 665.180. R. Alcantara, L. Canoira, P. G. Joao, J. G. Rodriguez and I. Vazquez, J.Photochem.

Photobiol., A, 2000, 133, 27.181. K. Ohkubo and S. Fukuzumi, Org. Lett., 2000, 2, 3647.182. A. G. Panov, R. G. Larsen, N. I. Totah, S. C. Larsen and V. H. Grassian, J. Phys.

Chem. B, 2000, 104, 5706.183. D. Mangion, J. Kendall and D. R. Arnold, Org. Lett., 2001, 3, 45.184. P. Lakshminarasimhan, K. J. Thomas, L. J. Johnston and V. Ramamurthy, Lan-

gmuir, 2000, 16, 9360.185. J.-J. Helesbeux, D. Guilet, D. Seraphin, O. Duval, P. Richomme and J. Bruneton,

Tetrahedron Lett., 2000, 41, 4559.186. M. Yoshida, M. Ohkoshi and M. Iyoda, Chem. Lett., 2000, 804.187. H.-R. Li, L.-Z. Wu and C.-H. Tung, J. Am. Chem. Soc., 2000, 122, 2446.188. H.-R. Li, L.-Z. Wu and C.-H. Tung, Tetrahedron, 2000, 56, 7437.189. K. Song, L.-Z. Wu, C.-H. Yang, C.-H. Tung, Tetrahedron Lett., 2000, 41, 1951.190. D. Pevenage,M. Van der Auweraer and F. C. De Schryver,Chem.Phys. Lett., 2000,

319, 512.191. J.-K. Luo, R. F. Federspiel and R. N. Castle, J. Heterocycl. Chem., 2000, 37, 171.192. A. M. Khenkin and R. Neumann, Catal. Lett., 2000, 68, 109.193. T. Del Giacco, M. Ranchella, C. Rol and G. V. Sebastiani, J. Phys. Org. Chem.,

2000, 13, 745.194. C. Li and M. Z. Hoffman, J. Phys. Chem. A, 2000, 104, 5998.195. X. Hu, F. L. Y. Lam, L. M. Cheung, K. F. Chan, X. S. Zhao and G. Q. Lu,

Sustainable Energy Environ.Technol.,Proc.Asia-Pac.Conf., 3rd. 51, Eds.X.Hu andP. L. Yue, World Scientific Publishing Co. Pte. Ltd, Singapore.

Photochemistry238

196. C.Minero, G.Mariella, V.Maurino, D. Vione andE. Pelizzetti,Langmuir, 2000, 16,8964.

197. M. I. Gutierrez, A. T. Soltermann, F. Amat-Guerri and N. A. Garcia, J. Photochem.Photobiol., A, 2000, 136, 67.

198. D. Murtinho, M. Pineiro, M. M. Pereira, A. M. d’A. Rocha Gonsalves, L. G.Arnaut, M. da Graca Miguel and H. D. Burrows, J. Chem. Soc., Perkin Trans. 2,2000, 2441.

199. T. An, Y. He, Y. Fang, X. Jin and H. Chen, J.Mol. Catal. A: Chem., 2000, 159, 143.200. Y.-M. Xu,Huaxue Xuebao, 2000, 58, 572.201. I. Leray, M. Ayadim, C. Ottermans, J. J. L. Habib and J. P. Soumillion, J.

Photochem. Photobiol., A, 2000, 132, 43.202. C. Pierlot, J. Poprawski, J. Marko and J.-M. Aubry, Tetrahedron Lett., 2000, 41,

5063.203. M. Seischab, T. Lodenkemper, A. Stockmann, S. Schneider, M. Koenberg, M. R.

Roest, J. W. Verhoeven, J. M. Lawson andM. N. Paddon-Row, Phys.Chem.Chem.Phys., 2000, 2, 1889.

204. S. Onitsuka, H. Nishino and K. Kurosawa,Heterocyl. Commun., 2000, 6, 529.205. A. Suzarte, M. Echeverria, A. Rosado and M. Rodriguez, Rev. CENIC, Cienc.

Quim., 2000, 31, 171.206. A. Suzarte and M. Echeverria, Rev. CENIC, Cienc. Quim., 2000, 31, 179.207. T. Takabatake, T. Miyazawa, M. Hasegawa and C. S. Foote, Tetrahedron Lett.,

2001, 42, 987.208. E. D. Morgan, A. P. Jarvis and G. R. Jones, ARKIVOC, 2000, 1, 304.209. R. R. Ozer and J. L. Ferry, J. Phys. Chem. B, 2000, 104, 9444.210. G. Cocquet, C. Ferroud and A. Guy, Tetrahedron, 2000, 56, 2975.211. K. Waki, J. Zhao, S. Horikoshi, N. Watanabe and H. Hidaka, Chemosphere, 2000,

41, 337.212. S. Bertrand, N. Hoffmann, S. Humbel and J. P. Pete, J. Org. Chem., 2000, 65, 8690.213. D. Lopez, E. Quinoa and R. Riguera, J. Org. Chem., 2000, 65, 4671.214. K. Lee and D. E. Falvey, J. Am. Chem. Soc., 2000, 122, 9361.215. F. J. Hoogesteger, C. A. Van Walree, L. W. Jenneskens, M. R. Roest, J. W.

Verhoeven,W. Schuddeboom, J. J. Piet and J. M. Warman, Chem.—Eur. J., 2000, 6,2948.

216. S. E. Miller, A. S. Lukas, E. Marsh, P. Bushard and M. R. Wasielewski, J. Am.Chem. Soc., 2000, 122, 7802.

217. H. Isobe, N. Tomita and E. Nakamura, Org. Lett., 2000, 2, 3663.218. G. L. Hug, M. Bonifacic, K.-D. Asmus and D. A. Armstrong, J. Phys. Chem. B,

2000, 104, 6674.219. S. Ikeda, S. Murata, K. Ishii and H. Hamaguchi, Bull. Chem. Soc. Jpn., 2000, 73,

2783.220. A. G. Griesbeck, M. S. Gudipati, J. Hirt, J. Lex, M. Oelgemoeller, H. Schmickler

and F. Schouren, J. Org. Chem., 2000, 65, 7151.221. Y. Kawamura, R. Takayama,M. Nishiuchi andM. Tsukayama, Tetrahedron Lett.,

2000, 41, 8101.222. R. K. Khandelwal and V. K. Vaidya, Orient. J. Chem., 2000, 16, 327.223. I. N. Martyanov and E. N. Savinov, J. Photochem. Photobiol., A, 2000, 134, 219.224. W. Jarzeba, S. Pommeret and J.-C. Mialocq, Chem. Phys. Lett., 2001, 333, 419.225. J. Cossy and D. Belotti, PCT Int. Appl. WO 01 12,597.226. J. Cossy and D. Belotti, Tetrahedron Lett., 2001, 42, 4329.


227. N. Srividya, P. Ramamurthy, V. T. Ramakrishnan, Phys. Chem. Chem. Phys., 2000,2, 5120.

228. A. Marcinek, J. Zielonka, J. Adamus, J. Gebicki and M. S. Platz, J. Phys. Chem. A,2001, 105, 875.

229. A. Kumar and A. K. Jain, J.Mol. Catal. A: Chem., 2001, 165, 265.230. G. Cocquet, P. Rool and C. Ferroud, J. Chem. Soc., Perkin Trans. 1, 2000, 2277.231. B. K. Chowdhury, S. Jha, B. Kar and S. C. Ranjan, Indian J. Chem., Sect. B: Org.

Chem. Incl.Med. Chem., 1999, 38B, 1106.232. C. Carmona, R. Ghanem, M. Balon, M. A. Munoz, P. Guardado, J. Photochem.

Photobiol., A, 2000, 135, 171.233. A. Pajares, J. Gianotti, G. Stettler, E. Haggi, S.Miskoski, S. Criado, F. Amat-Guerri

and N. A. Garcia, J. Photochem. Photobiol., A, 2000, 135, 207.234. J. Geimer, K. Hildenbrand, S. Naumov and D. Beckert, Phys. Chem. Chem. Phys.,

2000, 2, 4199.235. M. R. Kumar, M. T. Rao and M. Adinarayana, Indian J. Biochem. Biophys., 2000,

37, 13.236. M. R. Dhananjeyan, V. Kandavelu and R. Renganathan, J. Mol. Catal. A: Chem.,

2000, 158, 577.237. J. C. Niles, J. S. Wishnok and S. R. Tannenbaum, Org. Lett., 2001, 3, 963.238. C.-Y. Lu, S.-D. Yao and N.-Y. Lin, Chem. Phys. Lett., 2000, 330, 389.239. A. L. Sobolewski and W. Domcke, Chem. Phys. Lett., 2000, 321, 479.240. J.-I. Setsune, K. Kashihara and K.-I. Wada, Chem. Lett., 2001, 72.241. G. Cocquet, C. Ferroud, P. Simon and P.-L. Taberna, J. Chem. Soc., Perkin Trans.

2, 2000, 1147.242. I. S. Singh, Bull. Chem. Soc. Ethiop., 1999, 13, 127.243. W. Adam, K. Peters, E.-M. Peters and S. B. Schambony, J. Am. Chem. Soc., 2000,

122, 7610.244. E. Shimada, M. Nagano, M. Iwahashi, Y. Mori, Y. Sakaguchi and H. Hayashi, J.

Phys. Chem. A, 2001, 105, 2997.245. Y.-Z. Hu, S. Tsukiji, S. Shinkai, S. Oishi, H.Durr and I. Hamachi,Chem.Lett., 2000,

442.246. H. Tsue, H. Imahori, T. Kaneda, Y. Tanaka, T. Okada,K. Tamaki and Y. Sakata, J.

Am. Chem. Soc., 2000, 122, 2279.247. E. J. Shin, I. S. Kim and S. Y. Ahn, Bull.Korean Chem. Soc., 2000, 21, 328.248. E. K. L. Yeow, P. J. Sintic, N. M. Cabral, J. N. H. Reek, M. J. Crossley and K. P.

Ghiggino, Phys. Chem. Chem. Phys., 2000, 2, 4281.249. D. Kuciauskas, P. A. Liddell, S. Lin, S. G. Stone, A. L. Moore, T. A. Moore and D.

Gust, J. Phys. Chem. B, 2000, 104, 4307.250. H. Inui and S. Murata, Chem. Commun., 2001, 1036.251. A. G. Griesbeck, J. Steinwascher and T. Hundertmark, Peroxide Chemistry, 2000,

ed. W. Adam, Wiley-VCH Verlag GmbH: Weinheim, Germany, p. 60.252. M. A. Ashirmatov, Kh. N. Aripov, L. V. Molchanov, Kh. R. Nuriddinov and K. D.

Sargazakov, Khim. Prir. Soedin., 1992, 546.253. R. Brecht, F. Buettner, M. Boehm, G. Seitz, G. Frenzen, A. Pilz and W. Massa, J.

Org. Chem., 2001, 66, 2911.254. N. Toshima, Pure Appl. Chem., 2000, 72, 317.255. G. Liu, J. Zhao and H. Hidaka, J. Photochem. Photobiol., A, 2000, 133, 83.256. F. Chen, Y. Xie, J. He and J. Zhao, J. Photochem. Photobiol., A, 2001, 138, 139.257. R. J. Willemse, J. J. Piet, J. M. Warman, F. Hartl, J. W. Verhoeven and A. M.

Brouwer, J. Am. Chem. Soc., 2000, 122, 3721.

Photochemistry240

258. G. L. Hug, K. Bobrowski, H. Kozubek and B. Marciniak, Photochem. Photobiol.,2000, 72, 1.

259. A. Posadaz, E. Sanchez, M. I. Gutierrez, M. Calderon, S. Bertolotti, M. A. Biasuttiand N. A. Garcia, Dyes Pigm., 2000, 45, 219.

260. A. H. Gemeay, T. A. Fayed and H. A. El-Daly,Monatsh. Chem., 2000, 131, 749.261. G. R. Bamwenda, T. Uesigi, Y. Abe, K. Sayama and H. Arakawa, Appl. Catal., A,

2000, 205, 117.262. C. N. Rusu and J. T. Yates, J. Phys. Chem. B, 2000, 104, 12299.263. D. C. Hager, A. E. Sopchik and W. G. Bentrude, J. Org. Chem., 2000, 65, 2778.


6Photoreactions of Compounds ContainingHeteroatomsOther than Oxygen

BY ALBERT C. PRATT

1 Introduction

Reviews have been published on the photochemistry of 1,2-dithiins,1

fluoroquinolone antibiotics,2 fulleropyrrolidines,3 sultams,4 boron compounds,5,6

photocleavage processes of benzyl—heteroatom -bonds,7 photoamination byelectron transfer,8 the synthetic potential of phthalimide single electron transfer(SET) photochemistry,9,10 photo- and thermal-degradation mechanisms ofphotomerocyanines,11 molecular tailoring of photochromics,12 synthesis ofdihetarylethenes13 and their photochromism in confined reaction spaces,14 SETreactions of cyclic organosilanes,15 photophysics of fullerene—porphyrin dyads,16

solid state reactions of N-heterocycles,17,18 dimerisation of heterocycle-sub-stituted alkenes,19 photoisomerisation of pentaatomic heterocycles,20 n,�* excit-ed-state chemistry of azoalkanes,21 bimolecular photoreactions in solution,22

oxetanes from thiophenes and selenophenes23 and asymmetric photoreactions insolution24 and in crystalline ammonium carboxylate salts.25

2 Nitrogen-containing Compounds

2.1 E,Z Isomerisations. — Of the quinolyl-9-anthrylethenes (1), the 3-quinolylisomer is strongly fluorescent but does not undergo E,Z photoisomerisation. Incontrast 2- and 4-quinolyl-9-anthrylethenes fluoresce relatively strongly andundergo inefficient E,Z photoisomerisation in non-polar solvents but fluoresceweakly and undergo efficient photoisomerisation in polar solvents.26 2-Pyridyl-,4-pyridyl- and 2-pyrazinyl-anthrylethenes (2) exhibit solvent-dependent fluor-escence and efficient E,Z photoisomerisation, accompanied in non-polar sol-vents by efficient oxidative cyclisation. In polar solvents photocyclisation wasnot observed.27 The role of rotamers and intramolecular H-bonding between thenitrogen atom and the vinylic hydrogens in influencing the photophysical andphotochemical properties of the E,E-2,6-di(arylvinyl)pyridines (3) have beendiscussed.28 Pulsed and stationary fluorimetric techniques and laser flash photo-lysis have been used to investigate the excited states of the E,E- andZ,E-isomersof the three 1-pyridyl-4-phenyl-1,3-butadienes. Intramolecular hydrogen bond-


242

ing influences the excited-state properties of the Z,E-isomer of the 2�-pyridylderivative.29 The fluorescence and E,Z photoisomerisation of a series of triazine-stilbene fluorescent brighteners have been reported.30—32 Potential energy sur-faces have been calculated (AM1) for ground and first singlet excited-stateisomerisation about the carbon—carbon bonds of symmetrical carbocyaninesand correlated with polymethine chain length.33 In non-polar and low-polaritysolvents the cationic 3,3�-diethyl-2,2�-oxadicarbocyanines (4) form ion pairs. Thecounter ions affect the barrier height for isomerisation and AM1 calculationshave been used to rationalise the influence of these on the lifetimes of thephotoisomers.34

An unusual oxygen effect has been reported for the 9,10-dicyanoanthracene(DCA) SET sensitisation of oxime ether (5) [E:Z ratio�1:1] under oxygen,resulting in geometrical isomerisation with high Z-selectivity [photostationaryE:Z ratio�4:96]. Addition of superoxide anion, from DCA radical anion andoxygen, to the radical cation of (5) to give an open N,O-1,4 biradical wasproposed, with free rotation and subsequent loss of oxygen resulting in geometri-cal isomerisation.35 For a series of O-acyl-�-oxo oximes (6) geometricalisomerisation occurred from the triplet excited state whereas radical formationvia N—O bond homolysis was a singlet excited-state process.36 Efficient E,Zphotoisomerisation (��0.2—0.8) was the main process observed for aroylhyd-razones (ArCONHN——CAr2).37 Geometrical photoisomerisation was also ob-served for iminochromones (7) and (8), accompanied by irreversible formation ofproducts consistent with competing abstraction of hydrogen from the CH——Ngroup by the imide carbonyl group and �-cleavage,38 and for Z-1-methyl-N4-hydroxycytosine (9) in low-temperature matrices.39 The ONIOM method hasbeen used to investigate the first singlet excited-state photoisomerisation path-ways in protonated Schiff bases and extended to the isomerisation energy profileof the entire retinal protonated Schiff base.40

II/6: Photoreactions of Compounds Containing Heteroatoms Other than Oxygen 243

The enthalpy change and volume contraction accompanying E,Z photo-isomerisation of azobenzene and p-coumaric acid have been determined by ahybrid transient grating and photoacousticmethod.41 In marked contrast to thatobserved for stilbene, the photostationary E,Z ratio for azobenzene in zeolitecavities is very similar to that in cyclohexane.42 The geometrical photoisomerisa-tion of an azobenzene linker has been used to perturb the periphery of apolyamidoamine starburst dendrimer,43 to regulate the 1:1 vs. 1:2 stoichiometryof the ferric complex of a trihydroxamate siderophore,44 to control the catalyticactivity of a �-cyclodextrin bearing a histidine moiety,45 to photoswitch thepeptidomimetic inhibition of �-chymotrypsin,46 to photocontrol the formation oftriple helices between modified oligothymidine species and oligo-thymidine/oligodeoxyadenosine double helices, 47 to photomodulate the confor-mations of peptides48,49 and to modulate the fluorescence from the basal chromo-phore in a phosphorus(V) porphyrin.50 E,Z Photoisomerisation has been re-ported for amorphous films and solutions of triphenylamine derivativescontaining azobenzene branches,51 for substituted azobenzene amphiphiles inreversible optically-induced switching processes, 52 for self-assembled mono-layers of azobenzene and stilbene derivatives capped on colloidal gold clusters53

and for azobenzene derivatives containing a positively charged head group at theair/water interface.54,55

2.2 Photocyclisations. — 2-Azabicyclo[2.2.0]hex-5-enes (13)—(15) were ob-tained by acetone sensitised stereoselective photocyclisation of the 1,2-dihydro-pyridines (10)—(12) respectively,56,57 (14) and (15) being intermediates in a syn-thesis of nicotinic acetylcholine receptor agonist ABT-594 analogues. Electro-cyclic 4� ring-closure of 2-pyridone, 4-methoxy-2-pyridone and 4-benzyloxy-2-pyridone to 3-oxo-2-azabicyclo[2.2.0]hex-5-enes occurred with 20—23% enan-tiomeric excess at �20 °C in the presence of chiral lactam host (16).58 The singletexcited state of the alkaloid (�)-colchicine undergoes tropolone ring 4� elec-trocyclisation to give �- and �-lumicolchicines. Solvent—solute interactions in-volving the amide group determine the partitioning between the isomeric prod-ucts.59

Stilbene-type 6� electrocyclisation of (18) and (19) provided the phenanthrenering in a synthesis of 1-methyl-1,2,3,4-dihydronaphtho[1,2-f]isoquinolines (20).60

3-Styrylpyridine (21) underwent regioselective photoconversion to 2-azaphenan-threne (24) under anaerobic conditions, a rapid thermal 1,7-hydrogen shift

Photochemistry244

converting primary photoproduct (23) to the relatively stable 1,4-dihyd-ropyridine (27) which yielded (24). Anaerobic cyclisation of 3-styrylpyridinerotamer (28) yielded primary photoproduct (29) which reverted to startingmaterial rather than tautomerise to the less stable 1,2-dihydropyridine (26).However, in the presence of oxygen both regioisomeric dihydroazaphenan-threnes (27) and (29) were oxidised, giving a mixture of 2- and 4-azaphenan-threnes, (24) and (30). 3-Aminostyrylpyridine (22) exhibited analogous anaerobicregioselectivity to yield (25) whereas, in the presence of oxygen, both (25) and (31)were formed.61

Photochromic materials have been intensively studied in recent years due tothe prospects for application in photonic memory, switching or display devices.The photochromic 1,2-diarylcycloalkenes (32) underwent conrotatory 6� elec-trocyclisation on irradiation with UV light to give the closed forms (33) whoseabsorption, centred at 440 nm, is within the wavelength range of the InGaN bluelaser.62 The analogous 1,2-bis(1,3-dimethylindol-2-yl)-cyclopentenes and -cyclo-hexenes similarly yielded coloured cyclised forms. These have greater thermalstability than those of the 1,2-bis(1-ethyl-2-methylindol-3-yl)cyclopentenes andcyclohexenes.63

Fulgides (2,3-dialkylidenesuccinic anhydrides) also continue to attract interestas photochromic materials for technological applications. Z-Fulgide (34) is


non-photochromic whereas E-fulgide (36) gave closed form (38) which revertedto colourless E-open form (36) on irradiation with visible light. The introductionof a 5-dicyanomethylene group resulted in Z-isomer (35) being highly photo-chromic, undergoing facile conversion to E-isomer (37) which in turn underwentreversible closure to (39).64 Photochromic properties (UV/visible absorption,coloration, bleaching and fluorescence quantum yields, and photochromic cyclefatigue resistance) have been reported for a series of N-substituted indol-2-ylfulgimides (2,3-dialkylidenesuccinimides).65 The helical chirality of the hexa-triene portion of an open-form E-fulgide results in formation of a stereogenicquaternary carbon on the cyclohexadiene portion of the closed form because ofthe required photoinduced conrotatory ring closure. When an enantiomer ofresolved indolylfulgide (40), or either of the (R)-binaphthol derived indolylfulg-ides (41) or (42), was mixed with a nematic liquid crystal (4-cyano-4�-pentyl-biphenyl) the cholesteric phase was induced and the cholesteric pitches werereversibly changed by photoirradiation.66 The photochromic behaviour of threeindolylfulgenates containing crown-ether moieties has been investigated in thepresence and absence of Li�, Na� and K�. The association constants for the E-and Z-forms of (44) and (45) are greater than for the closed forms and forNa�-(44) and K�-(45) no photocoloration was observed. No effects of alkalimetal cations were observed for the photochromism of (43).67 Changes in theUV/visible absorption spectra resulting from 254 nm irradiation of variousfulgides and monoalkylidenesuccinic anhydrides have been reported.68 Ab initioMO studies at the HF/6-31G and HF/6-31G* levels have been reported for theopen and closed forms of 3-furyl, 3-pyrryl and 3-thienyl fulgides.69

Interest continues in the photochromism of benzopyrans involving photoin-duced conversion of the colourless closed form to the coloured open form and

Photochemistry246

thermal reversion to the original closed form. Carbazole 6,7-annelated 2,2-diphenyl-2H-1-benzopyrans exhibited enhanced colourability and kinetics ofthermal bleaching.70 Nanosecond laser flash photolysis studies of 3-phenyl-3-[1,2-dimethylindol-3-yl]-3H-naphtho[2,1-b]pyran, 2-phenyl-2-(2-thienyl)-2H-benzo[b]furano[3,2-f]benzopyran and 2,2-diphenyl-2H-benzo[b]furano[3,2-f]benzopyran have shown that, for each, both the singlet and triplet excited statesare involved in the photocoloration process.71,72,73 Photocoloration of the nitro-spirobenzopyranindolines (46) and (47) is a triplet-state process and open formE- and Z-merocyanines (59) and (59a) were observed, the quantum yield forcoloration with 308 nm pulses ranging from 0.3 to 0.8 in low-polarity solventsand decreasing to �0.2 with increasing polarity. Excitation of the E-merocyanine with 530 nm radiation generated the Z-isomer.74 In contrast to thenitrospiropyrans (46) and (47), the photochromism of spirobenzopyranindolines(48) and spironaphthopyranindolines (49) and (50) is dominated by ring openingvia the singlet excited state, the coloration quantum yield being largely indepen-dent of solvent polarity.75 For dinitrospirobenzopyran (51) the open chain col-oured merocyanine is the more thermally stable due to the presence of two nitrogroups. Pulsed nanosecond laser excitation of the merocyanine has revealedthree transients, proposed to be the merocyanine and spiropyran triplet excitedstates and an intermediate open form.76 Ferromagnetic intermolecular spin—spininteractions observed at low temperature for solid TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy)-substituted nitrospirobenzopyranindole (52) changed to anti-ferromagnetic interactions on photoconversion to the merocyanine form.77,78

Encapsulation of spiropyrans (53)—(55) in NaY zeolite cages changed the relativestabilities of the closed and open forms, resulting in bleaching of the colouredform on irradiation and recovery of the colour in the dark.79 A bis(spirobenzo-pyran) with a bridging 1,1�-diethynylferrocene unit behaved conventionally. Theaddition of transition metal cations such as Co(II) gave rise to additionalmerocyanine absorptions, suggestive of �-stacking between the spatially ar-ranged bis-spiropyran chromophores.80 A method has been developed for self-assembly of monolayers of spiropyrans on glass surfaces which stabilise thephotogenerated merocyanine intermediate.81 Femtosecond transient absorptionspectroscopy has been used to observe the time evolution of all intermediates inthe primary excited-state processes of spironaphthopyran (49) and spirooxazines


(56) and (57). The same mechanism applies to each, and rate constants have beendetermined for all processes in the kinetic scheme.82 Nanosecond laser flashphotolysis has been used to study the different photochromic behaviours of (60)and (62).83 Semiempirical AM1 calculations have been used to rationalise theobservation of two coloured isomeric keto forms of (62) which are three orders ofmagnitude longer-lived than the single coloured keto form (61) observed for(60).84 DFT or UHF/AM1 calculations show excellent agreement between ex-perimental and calculated �max values for the merocyanine forms of spiro[indo-line-naphthoxazines], spiro[indoline-naphthopyrans] and diarylnaph-thopyrans.85 Polarisation-propagator based ab initio methods also give fairlygood qualitiative �max predictions.86 Bichromophoric Z-(64) underwent simulta-neous dihydrophenanthrene formation and spiroxazine ring opening to yieldthermally stable (63) and small amounts of E-(64) on 366 nm irradiation at 295K.87

Dihydrophenanthrene formation is a thermally activated photoprocess andconsequently low-temperature irradiation of Z-(64) yielded fully open colouredisomer (65). Discontinuation of irradiation resulted in slow regeneration ofE-(64). Prolonged visible light irradiation of isomer (63) yielded small amounts ofZ-(64). Irradiation of dihydroindolizines (66) bearing a fluorene unit yieldedcoloured betaines (69) which absorb in the near IR (780—860 nm). However, theyundergo fast thermal 1,5-electrocyclisation to regenerate (66) within milli-seconds. The diphenyl (67) and dicyano (68) derivatives yield betaines with

Photochemistry248

half-lives of 400 and 330 s respectively.88 No visible colour change occurred onirradiation of ring-fused dihydroindolizines (70) in solution. In an ethanol matrixat 77 K; however, the colour of the Z-betaines (71) persists for periods rangingfrom seconds to a few minutes. Laser flash photolysis shows room-temperature


half-lives of a few nanoseconds forZ-betaines (71), due to ring-fusion accelerated1,5-electrocyclisation to regenerate (70).89 Depending on the substitution pat-terns in ring-opened delocalised betaines (74)—(76), either 6� electron 1,5-cyclisa-tion or 8� electron 1,7-cyclisation can occur. Thus (74) and (75) cyclised to (72)and (73) respectively whereas (76) cyclised to (77).90

Stereo- and regio-controlled photocyclisation of arylenamide (78) yielded (79),a key intermediate in an enantioselective synthesis of the antitumour alkaloids(�)-narciclasine and (�)-pancratistatin.91 Analogous photocyclisation ofdienamide (80) and its enantiomer in the presence of sodium borohydride andmethanol was used in the synthesis of (S)-(�)-pipecoline and of (S)-(�)- and(R)-(�)-coniine.92 Irradiation of ester (81) resulted in singlet excited-statecyclodehydration to isoquinolines (83), and competing rapid triplet isomerisa-

Photochemistry250

tion to E-(81). Strong electron-donating (OMe) or electron-withdrawing (CF3)p-substituents greatly reduce isoquinoline formation without affectingisomerisation, whereas the presence of a bulky chlorine in the ortho positionenhances isomerisation and completely suppresses cyclisation.93 In the presenceof triethylamine, (82) yielded predominantly dihydrobenzoquinolones (84). Elec-tron and proton transfers give enol-type biradical (85). Bulky t-butyl or phenylsubstituents in this biradical result in formation of derivatives analogous to (83),without affording (84).94 Semiempirical (AM1-SCI) calculations showed that

diphenylamine is non-planar, with intramolecular rotation therefore being re-quired to achieve the planarity necessary for cyclisation to the ring-closeddihydrocarbazole. Within a �-cyclodextrin cavity, rotation is restricted and thephotocyclisation rate constant is reduced, though the overall quantum yield forcarbazole formation is not affected.95 Oxidative photocyclisation of N,N�-diphenyl-m-phenylenediamine and of N,N�-dimethyl-N,N�-diphenyl-p-phenylenediamine gave bis-cyclisation products (86) and (87) respectively,whereas only monocyclisation to (88) was observed for N,N�-dimethyl-N,N�-diphenyl-o-phenylenediamine. The corresponding m-isomer yielded monocyclicproducts (89) and (90).96 Sensitised photolysis of enyne-ketenimines (91) yielded(92), involving elimination of a methyl group.97 Enyne-carbodiimides (93) simi-larly underwent C2—C6 cyclisation with formation of (96) in high yield viaintermediates (95) and (98). Where the N-phenyl terminus was blocked by amethyl group, as for enyne-carbodiimides (94), the C2—C6 cyclised product (99)eliminated a methyl group and abstracted hydrogen from the solvent to yieldproduct (97). 98

The first examples of C—O bond formation in the Norrish-Yang reaction havebeen reported. Irradiation of �-keto amides (100) resulted in �-hydrogen abstrac-tion followed by elimination of methanesulfonic acid to yield enolate diradicals


(101) which underwent regioselective cyclisation to (102).99 Norrish-Yang cyclisa-tion of �-benzoyl propionate derivatives may be used for the preparation ofcyclobutanes, pyrrolidines, tetrahydrofurans, �-lactams and pinacols.100 Irradi-ation of the anomeric gluco- and manno-configured N-glycosylsuccinimides(103) and (104) resulted in abstraction of H-2 and/orH-5 by the excited carbonyl.Stereoselective recombination of the resulting 1,4- and 1,5-biradicals gave an-nelated azacyclobutanols and azacyclopentanols respectively. The strained aza-cyclobutanols fragmented to give azepinedione derivatives. Thus �-gluco deriva-tive (103) gave bicyclic derivative (107) by H-2 abstraction whereas the �-glucoderivative (104) gave the tricyclic compound (108) by H-5 abstraction. The

Photochemistry252

�-manno derivative (105) underwent competingH-2 and H-5 abstraction to giveanalogous products. The �-manno derivative (106) in contrast yielded the en-amine derivative (109).101 The methylthiomethyl (MTM) esters (110) ofphthalimidopropionic and phthalimidobutyric acids cyclised to (113) whereasthose with longer or shorter spacer groups (111) underwent photodeprotectionto give the free carboxylic acids (115). In contrast the methylthioethyl (MTE)esters (112) underwent exclusive photocyclisation, yielding (114). Both cyclisa-tion and deprotection are initiated by SET from sulfur.102 Analogous SET fromnitrogen or sulfur to the phthalimido carbonyl group in the �-trimethylsilyl-methyl-substituted polysulfonamide (116), polythioether (117) and mixed oxy-gen—sulfur polyethers (118) and (119) resulted in desilylation and cyclisation tomacrocycles (120), (121), (122) and (123) respectively.103 N-Methyl-N-phenyl


2-benzoylbenzamides crystallised in the chiral space group P212121 and solid-state irradiation resulted in intramolecular cyclisation to phthalides (124) via aradical pair intermediate with good enantioselectivity.104

2.3 Photoadditions. — Intramolecular [2�2]-photoadditions of 1,3-bis-maleimidopropanes gave caged diimides (125) and (126).105 Hydrogen-bondingof chiral lactam hosts (16) and (17) to 2-quinolones resulted in enantioselectiveinter- and intra-molecular [2�2]-photocycloadditions with alkenes.106,107 Theintramolecular [2�2]-photocycloaddition of eniminium salts provides an alter-native route to enone-alkene adducts (132). For example (127)—(129), withelectron-deficient olefin tethers, displayed high degrees of stereospecificitywhereas for (130) and (131), with electron-rich olefin tethers, reduced levels ofstereocontrolwere observed, possibly due to competition between concerted andelectron-transfer pathways. Analogous intermolecular cycloadditions werechemically inefficient.108

Three [2�2]-dimers (133) were obtained on irradiation of pyrrolizin-3-one insolution — the syn head-to-head, anti head-to-head and syn head-to-tail dimers.109

In methanol cinnamoyldopamines (134)—(139) underwent E,Z-isomerisationwhereas in the solid state only (136), (137) and (138) were photoreactive. antiHead-to-tail [2�2]-dimerisation occurred for (138) whereas (137) gave the synhead-to-head dimer. In contrast (136) underwent novel [2�2]-photodimerisa-tion to give (140), the first example of solid-state photoaddition of an alkene to abenzene ring.110 2-Morpholino- and related amino-propenenitriles added withhigh regioselectivity to 1-naphthoic acid and its methyl ester to give the corre-sponding [2�2]- and [4�2]-adducts,111 to coumarin to give a [2�2]-adduct, to3-(2-benzothiazolyl)coumarin to give a [2�2]- (major) and a [4�2]-adduct,and to 2H-benzo[b]pyran-2-thione and 2H-benzo[b]thiin-2-thione to give

Photochemistry254

products derived from [2�2]-addition to the thione unit followed by elimin-ation of CH2——S.112 For 4-chloro-, 4-fluoro-, 4-methyl- and 2-methyl-1-acetonaphthones photoaddition and/or photosubstitution by 2-morpholino-propenenitriles were observed.113 4-Substituted 3-cyano-2-alkoxypyridines andbenzofuran yielded endo- and exo-[2�2]-photoadducts (141), involving initialaddition of the C-2 and C-3 positions of the singlet excited pyridine to the C-3and C-2 positions of benzofuran. Thermal ring-opening then gave a cycloocta-triene which photocyclised to (141).114 At low loading levels of E-2-styrylpyridinein zeolites, E- to Z-photoisomerisation was the only process observed. At higherloading levels syn head-to-tail photodimerisation and oxidative photocyclisa-tion were observed, product distributions being sensitive to the free volumeavailable inside the cage.115 1-Alkylthymines crystallise in two different polymor-phic forms. Crystals with hydrogen-bonded thymine bases in parallel sheets gavecyclobutane type photodimers, anti head-to-head from 1-pentyl-, 1-nonyl- and1-decyl-thymine and anti head-to-tail from 1-octylthymine.116 TheNH—Ohydro-gen-bond networks in crystals of E-4-methylcinnamamide and E-4-chloro-cinnamamide remained intact during crystal-to-crystal photodimerisation. Thelower photoreactivity of E-cinnamamide is due not only to greater separationbetween the carbon—carbon double bonds but also to partial disruption of thehydrogen-bond network during reaction.117 Efficient photoligation ofoligodeoxynucleotides (ODNs) in the presence of a template ODN has beenachieved based on the [2�2]-addition of a vinyl-containing nucleobase in oneODNwith the carbon—carbon double bond of a nucleobase in anotherODN, forexample 5-vinyldeoxycytidinewith thymine or 5-carboxyvinyldeoxyuridinewithcytosine. The concept has been used to demonstrate the reversible photopad-locking of a circular DNA and a convergent synthesis of branched ODNs.118,119

Within the hydrogen-bonded network in crystalline 4-(4-(2-(ethoxycar-bonyl)vinyl)-cinnamoylamino)benzoic acid, the amide-substituted double bondsaremuch closer together than the ester-substituted double bonds and irradiation


resulted in conversion to the anti head-to-tail dimer (142) with concomitantE- toZ-isomerisation of one of the ester-substituted double bonds.120 E-Cinnamamideand dicarboxylic acids (oxalic, fumaric and phthalic acids) form 1:1 hydrogen-bonded co-crystals. Phthalic acid and oxalic acid compel orientational controland photodimerisation to the syn head-to-head dimer of E-cinnamamide, incontrast to the anti head-to-tail dimer from E-cinnamide homocrystals. Thephotoreactive 1:1 co-crystals between E-4-methylcinnamamide or E-4-chloro-cinnamamide and oxalic acid showed similar orientational control. The 1:1E-cinnamamide/fumaric acid co-crystals yielded a mixed syn 1:1 photoadduct ofthe two different alkenes. Torsional vibrations may result in orientations withinmixed crystals that are more favourable for reaction than may be preciselypredicted from the crystal structure.121 2-Pyrones and maleimide form 1:1 com-plexes in the solid state. A combination of CH-� interactions, �-� stacking andhydrogen bonding between the components resulted in stereoselective formationof [2�2]-cycloadducts (143) on solid-state irradiation.122 Although 2-quinoloneyields the anti head-to-head photodimer in ethanol it is photoinert withincrystalline 1:2 inclusion complexes with three diol hosts.123

Irradiation of methyl phenylglyoxylate in the presence of 2-morpholino-propenenitrile gave oxetane (144).124 3,4-Dihydro-2-pyridone (DHP) photoreac-tedwith aromatic carbonyl compoundswith high regio- and diastereo-selectivity(�88%) to give oxetanes (145), which are useful intermediates in an efficientroute to 2-arylmethyl-3-piperidinols. The ability of DHP to bind to chiral lactamhost (16) through two hydrogen bonds may be used to differentiate the enan-tiotopic faces of its double bond.125 The thymine oxetanes (146) underwent highlyefficient photocycloreversion to the triplet excited states of the aromaticketones.126 1-Acetylisatin underwent efficient [2�2]-photocycloaddition to a

Photochemistry256

variety of styrene derivatives: for example, (147) and (148) are formed in 96%yield (ratio 0.61:1 respectively) from �-methylstyrene in benzene. For high oxida-tion potential alkenes the regioselectivity was rationalised by consideration offrontier MO interactions and the diastereoselectivity by the Salem-Rowlandrules for diradical intersystem crossing. For more electron-rich alkenes SET isinvolved, regioselectivity being rationalised by consideration of charge and spindensity distributions in the ion-radical pairs and diastereoselectivity by ion-radical pair collapse considerations.127 Diphenylacetylene gave oxetene (155) andboth regioisomeric oxetenes, (156)/(157), and (158)/(159), were formed from1-acetylisatin and 4-methoxy- and 4-chloro-substituted diphenylacetylenes, re-spectively. The oxetenes underwent spontaneous ring opening to the corre-sponding E- and Z-2-indolones (149)—(153). The �,�-unsaturated aldehyde (154)from phenylacetylene via oxetene (160) was not isolated; secondary intermolecu-lar hydrogen abstraction from the aldehydic C—H bond yielding the radical pair(165)/(166) occurred. Coupling, intramolecular nucleophilic attack of the hyd-roxyl group on the ketene and ketonisation of the resulting enol (167) furnishedboth diastereomers of (168).128 Cycloaddition of triplet 1,3,4-(2H)-isoquinoline-trione to diphenylacetylenes also yielded unstable oxetenes which rearranged toE- and Z-(161) and E- and Z-(162). Photoisomerisation of the E- to the Z-isomers, accompanied by oxidative cyclisation, resulted in formation of (163) and(164) in a high-yield one-pot synthesis.129 Anthracene, benz[a]anthracene anddibenz[a,c]anthracene gave [4�2]-adducts when irradiated in the presence of2-morpholinopropenenitrile.130 Direct irradiation of Z-�-(N-benzylaziridin-2-yl)acrylonitrile yielded two head-to-head dimers (170) by 1,3-dipolar cycloaddi-tion of photogenerated azomethine ylide (169) to the precursor aziridinyl-acrylonitrile. Analogous cycloadducts were obtained with acrylonitrile, methylacrylate, t-butyl acrylate, pent-2-enone, N-phenylmaleimide and methylpropiolate, the regiochemistry of the additions being contrary to that expectedfrom MO theory.131 Hydrogen bonding of the inert chiral lactam host (16) to2-pyridone in toluene resulted in [4�4]-photocycloaddition to cyclopentadieneto give a 2:3 mixture of endo and exo adducts in 87% and 84% ee respectively.132

The amino acridizinium salt (171) gave the syn and anti head-to-tail [4�4]-photodimers in equal amounts in solution whereas (172) yielded the anti head-to-tail [4�4]-photodimer along with both labile head-to-head dimers. Irradiationof (171) or (172) in the presence of supercoiled DNA led to pronounced strand


breaks.133 Whereas the N-methylated tethered pyrindinone-pyridone (173) yiel-ded exclusively intramolecular [4�4]-trans-cycloadduct (175), the nitrogen-unsubstituted system (174) yielded both trans- and cis-cycloadducts (176) and(177) respectively. Formation of the cis-adduct (177) involves formation of aself-assembled hydrogen-bonded dimer of (174). In toluene at 0 °C (174) wasquantitatively converted to cis-isomer (177), which is a key intermediate in asynthesis of the central features of the fusicoccins.134 The magnetic properties ofanthracene derivatives, and their [4�4]-photodimers, containing stable radicalsubstituents such as TEMPO and verdazyl, have been investigated.135,136

Diastereoselective intramolecular [4�4]-photocycloadditions of chiral acyc-lic imides (178) and (179) were compared in the solid state and in solution. For(178) reversal of diastereoselectivity occurred on changing the reaction phase.

Photochemistry258

Solid state photodimerisation of (179) resulted in almost 100% diastereoselectiv-ity.137 Molecular oxygen trapped the triplet syn- and anti-1,8-biradicals gener-ated on irradiation of 1-naphthyl-N-(1-naphthylcarbonyl)carboxamides (180)and (181) and gives evidence of stepwise aromatic cycloaddition. In the absenceof oxygen the biradicals were converted to [2�2]- and syn- and anti-[4�4]-cycloadducts. The anthryl derivatives (182) and (183) afforded the [4�4]-cyc-loadduct in quantitative yield even under an oxygen atmosphere.138 The 1:1crystalline furoic acid salt of 9-(N,N-dimethylaminomethyl)anthracene yieldedthe head-to-tail photodimer (184).139 There has been much interest in the photo-cycloaddition of tertiary amines R�N(CHR2)2 to [60]-fullerene. New alkaloid—fullerene systems have been reported from the photoreaction of tazettine,gramine, scandine and 10-hydroxyscandine to C60. All gave the expected [6,6]-monoadduct of type (185). The scandine and 10-hydroxyscandine [6,6]-mono-adducts underwent a secondary reaction involving [2�2]-cycloaddition of a


free vinyl group with a proximate C60 double bond.140 Photoinduced inter- andintra-molecular reactions of N-(�-hydroxyalkyl)tetrachlorophthalimides withalkenes resulted in the formation of medium to large sized heterocyclic rings,initiated by SET from the alkene. Capture of the radical cation (187) by the sidechain hydroxyl group of the radical anion (186) followed by radical pair recom-bination gave the products, for example (188) and (189) from �-methylstyrene.Rings of different structure and size can be readily constructed, for example the2-(2-hydroxyethoxy)ethyl ester ofN-tetrachlorophthaloylglycinewith �-methyl-styrene gave 13-membered lactones (190) and (191). Irradiation of (192) gavespirooxetane isomers (193) and (194).141 Irradiation of 5-(R)-menthyloxy-2[5H]furanone in the presence of benzophenone and tertiary cyclic amines resulted inregio- and stereo-specific addition to the less hindered face of the enone to yieldadducts (195). With secondary cyclic amines, chiral adducts (196) (�98% de)were obtained.142 Analogous reactions occurred with other unsaturated lactonesusing semiconductors (SiC, TiO2 or ZnS) as photosensitisers, rather than ben-zophenone, though with little selectivity at the asymmetric carbon �- to thenitrogen. SET from the amines to either benzophenone or the semiconductorgenerated the amine radical cation which, on deprotonation, resulted in C- orN-centred radicals which added to the enone in a radical chain process.143

Photochemistry260

Greater that 90% facial diastereoselectivity has been obtained in the photo-initiated tandem addition-cyclisation reactions of N-alkenyl and N-propargyl�-aminoalkyl radicals to (5R)-5-menthyloxy-2[5H]-furanone, the radicals beingformed following SET from a tertiary amine and loss of an �-proton. Forexample adducts (197)—(200) are obtained on irradiation of the furanone in thepresence of N-(1,1-dimethyl-2-propenyl)pyrrolidine with 4,4�-dimethoxybenzo-phenone as SET sensitiser. Analogous reactions with N,N-dialkylanilines alsoproceedwith high facial diastereoselectivity.144 The topochemical polymerisationonUV irradiation of the 1-naphthylmethylammoniumsalts of monomethylZ,Z-and E,E-muconic acids (MeO2CCH——CHCH——CHCO2H) and E,E-sorbic acid(MeCH——CHCH——CHCO2H) in the crystalline state has been investigated fromthe viewpoint of polymer crystal engineering.145

2.4 Other Processes. — Interest continues in excited-state intramolecular pro-ton transfer (ESIPT) processes. Spectroscopic studies on the photochromism ofthe Schiff bases N-salicylidene-1-decylamine146 and 7-ethylsalicylidenebenzyl-amine147 and on the photochromic (and liquid crystalline) properties of someN-[4-(4-n-alkoxybenzoyloxy)-2-hydroxybenzylidene]derivatives of methoxy- orethoxy-anilines148 have been reported. Spectroscopic and quantum-chemicalmethods have been applied to salicylidene alkylimines and to more rigid struc-tures (201).149 Salicylidene-N-methylimine and salicylidene-N-(�-methylben-zyl)imine have been the subject of theoretical studies.150,151 Investigations ofphotoinduced proton transfers in 2-hydroxy-1-(N-morpholinomethyl)naph-thalene and 7-hydroxy-8-(N-morpholinomethyl)quinoline,152 in the anion of2-(2�-acetamidophenyl)benzimidazole,153 in 2-(3,4,5,6-tetrafluoro-2-hydroxy-phenyl)benzoxazole,154 in o-hydroxy derivatives of 2,5-diphenyl-1,3,4-oxo-diazole,155—157 in 10-hydroxybenzo[h]quinoline158 and in ring-substituted [2,2�-bipyridyl]-3,3�-diols159 have been reported. In the singlet excited state of 9-acetoxy-2,7,12,17-tetra-n-propylporphycene, one tautomer is strongly favouredwhile both exist in equilibrium in the ground state.160 Studies on the excited-stateH-bonding interactions of p-methoxy-2-styrylquinolines,161 1-methyl-9H-py-rido[3,4-b]indole and 9-methyl-9H-pyrido[3,4-b]indole,162 and 2-(2�-hy-droxyphenyl)benzimidazole163 have been reported. Steady-state and picosecondtime-resolved spectroscopies have been applied to the investigation of theazo—enol and hydrazone—quinone tautomeric forms of a series of bisazo com-pounds.164,165 Nanosecond laser photolysis has been utilised to investigate theESIPT pathways and their rate constants for 2-(2,4-dinitrobenzyl)pyridine.166

Intermolecular proton transfer occurred in the solid state photochromism ofpyrazolones (202) and (203), involving conversion of the enolic forms to ketoforms. Compounds (204)—(206) are non-photochromic.167 Further investigationsof the photophysics of 7-azaindole, the doubly H-bonded dimer of which under-goes intermolecular phototautomerism and has been used as a model for H-bonded base pairs in DNA, have been reported.168,169 Earlier conclusions that thetautomerism occurs via concerted excited-state double proton transfer (ESDPT)have been strongly challenged and a stepwise mechanism has been pro-posed.170,171 ESDPT studies on 2-amino-4,6-dimethylpyrimidine and 2-amino-4-


methoxy-6-methylpyrimidine H-bonded dimers and acetic acid complexes havealso been reported,172 as have the kinetics of excited-state proton transfer ofdoubly protonated 2-aminoacridine.173

Time resolved laser spectroscopy has shown that in O-acyloxime triplets theenergy is localised on the imino portion of the molecule. In sufficiently flexibleoxime esters in non-vertical energy transfer, involving a change in geometrybetween ground and excited states, occurs.174 O-Alkyl aryl aldoxime ethers givealkoxy and aryliminyl radicals in very low yields on photolysis,175 whereasaldoxime esters undergo N—O bond cleavage and are convenient radical precur-sors. Oxime esters containing unsaturated alkyl groups yielded cyclised productsin good yield providing a ‘green’ alternative to organotin-mediated radicalprocesses. For example sensitised irradiation of (207) yielded methylenecyclo-pentane in 77% yield.176 Cyclohexyl, cycloheptyl and cyclooctyl nitrites in argonmatrices underwentO—NObond photocleavage and disproportionation to yielda complex of the ketone and HNO. Cyclobutyl nitrite and, to a lesser extent,cyclopentyl nitrite formed cycloalkyl radicals which underwent ring openingwith the formation of nitrosoaldehydes. The major differences in outcome fromthose which occurred in fluid solution were due to the influence of the rigidmatrix environment on the potential reaction pathways.177 Alkoxy radicals pro-duced on photolysis of N-alkoxythiazolethiones (208)—(211) underwentstereoselective 5-exo-trig cyclisation and were trapped by water-soluble thiols toafford disubstituted tetrahydrofurans with satisfactory to excellent dia-stereoselectivity.178 Photoconversion of N-cyclopentoxy- and carbohydrate-de-rivedN-alkoxythiazolethiones in the presence of hydrogen atom donors (R3SnH)yielded substituted aldehydes or formyl esters via regioselective fragmentation ofalkoxy radicals.179 Polymer supported reagents (212) and (213) can be used for thegeneration of alkyl or alkoxy radicals respectively under very mild conditions.Following irradiation of a dispersion of the reagent in the reaction medium witha tungsten lamp, the products are simply isolated by filtration and removal ofsolvent. With (212) N—O bond cleavage and decarboxylation yielded the corre-sponding alkyl radicals which were trapped by BrCCl3 to give the correspondingalkyl bromides. With (213) the alkoxy radicals underwent 5-exo-trig cyclisationto yield the corresponding phenyl 2-methyltetrahydrofurans.180 Photocleavageof the N—O bond of N-(9-anthroyloxy)-9-fluorenylideneamine and 1-(9-an-throyloxy)-2-pyridone yielded 9-anthroyloxy radicals with much lower reactiv-ity in decarboxylation, alkene additions, and hydrogen abstraction than ben-

Photochemistry262

zoyloxy and 1-naphthoyloxy radicals.181 Product and laser flash photolysisstudies on the radicals generated by photolysis of pyridine-2-thione esters (214)show that the initially formed radicals (215) undergo heterolytic fragmentationof the �-substituent to generate the olefin radical cation (216). Increased radicalreactivity and decreased cationic reactivity of (216) are important features ofradical cations that may possibly be capable of synthetic exploitation.182 Di-azeniumdiolates R2N—N(O) ——NOR� (R�Et; R� �Me, CH2Ph or 2-NO2C6H4)are photosensitive and two primary pathways operate. Extrusion of nitrousoxide (N2O) with simultaneous radical generation (R2N· and R�O·), which thenformed amines, aldehydes and alcohols, comprised the minor pathway. Cleavageof the N——N bond formed a carcinogenic nitrosamine (R2NN——O) and an alkoxynitrene (R�ON) which rearranged to a C-nitroso compound (R�N——O) andsubsequently tautomerised to the oxime.183 Photolysis (and thermolysis) of1,3,2,4-benzodithiadiazines (217) yielded stable 1,2,3-benzodithiazolyl radicals(218), possibly involving loss of a nitrogen from a ring-contracted 1,2,3-benzo-dithiazol-2-ylnitrene.184 The initial step following excitation of 1,4-dihydro-pyridines, for example 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine,may beradical formation rather that the purely intramolecular processes previouslyassumed responsible for their photochromic behaviour.185 Irradiation of azirine(219) yielded biradical (220) by C—N bond cleavage in solution or in low-tem-perature matrices where ketenimine (221) was concluded to be the product.186

The quantum yields for intersystem crossing of N-methylmaleimide,N-ethyl-maleimide,N-propylmaleimide and maleimide have been determined to be 0.03,0.07, 0.05 and unity respectively.187 The photoinducedSRN1 reaction of potassium


phthalimide with 1-iodoadamantane in DMSO in the presence of 18-crown-6yielded ring-substitution products 2-(1-adamantyl)phthalimide (12%) and 3-(1-adamantyl)phthalimide (45%) rather than N-substituted products.188 Photo-decarboxylative addition of glyoxylate and secondary or tertiary �-ketocar-boxylates (RCOCO2Na) to N-methylphthalimide resulted in the formation ofphthalimidines (222). In contrast primary �-ketocarboxylates gave solely acyla-tion products, for example (223) and/or (225). The primary product (223) under-goes ring expansion by ring—chain tautomerisation and subsequent furtherreaction with �-ketocarboxylate to give (225).189 Decarboxylative cyclisation ofphthalimido dipeptides (227) yielded cyclodipeptides (228)190 and the process hasalso been used to prepare macrocycloalkyne (226) from the corresponding�-phthalimidoalkynoic acid in 21% yield,191 and trans-pyrrolo[1,4]benzo-diazepines (229) fromN-phthalolylanthranilic acid derivatives (230). The prolinederivative (230b) yielded pure trans-(229b) in 86% enantiomeric excess. High

Photochemistry264

activation barriers to rotation about the central C—N bond in the intermediate(atropisomeric) 1,7-triplet biradicals result in preservation of their absolute axialchirality during reaction and diradical combination which proceeds with com-plete inversion of configuration at the stereogenic �-centre.192,193 With the moreflexible ethylene linked precursor N-phthaloyl-2-(�-alanyl)-2-azabicyclo[3.3.0]octanoate, approximately equal amounts of two diastereomers, (231) and (232),were isolated.194 Unsymmetrical imides (233) and (234) underwent photodecar-boxylation to yield o- and m-cyclised products (235) and (236), and (237) and(238) respectively, with modest regioselectivity favouring the o-isomer in eachcase. Photocyclisation of the imide (239) gave m- and o-isomers (241) and (243)respectively with preference for o-cyclisation. Unsymmetrical trimellitic acidimide (240) yielded p- and m-photoproducts (242) and (244) with preference forp-cyclisation. In contrast irradiation of N-methyltrimellitic acid imide in thepresence of potassium propionate gave solely the p-product (224). DFT and abinitio calculations for the imide radical anions were consistent with the observedregioselectivities being determined by differences in spin densities in the corre-sponding imide radical anions rather then donor—acceptor interactions prior toSET from either the carboxylate or sulfur donors to the imide.195 Photo-Fries-rearrangement of 12- and 14-memberedN-phenylimides occurred readily to giveo- and p-cyclophanes as primary products.196

In the presence of a phosphate buffer, antibacterial 7-amino-6-fluoro-quinolones underwent reductive defluorination and piperazine side chain oxida-tion, which are photoprocesses not observed in neat water. Norfloxacin (245)underwent quantitative defluorination to an unstablemajor product, though notto (248), the main product in neat water. A minor product (249) was character-ised. Enoxacin (246) yielded (251) and (252) whereas lomefloxacin (247) yielded(250) and (253)—(255). The reactions are initiated by SET quenching by phos-phate anion, an unexpectedly efficient reducing agent for excited states. This,coupled with the radical reactivity of the phosphate radical anion, led to the


unprecedented photoconversion of these 7-amino-6-fluoroquinolones.197,198 In-corporation of the cationic form of lomefloxacin (247) in anionic sodium dodecylsulfate micelles results in much increased photostability.199 Photolysis of clina-floxacin (256) yielded eight new degradation products from the two processes ofdechlorination followed by further reactions of the quinolone ring, and pyr-rolidine side-chain degradation.200 The bichromophoric sulfonylurea, chlorsul-furon (257), followed different reaction pathways depending on whether thebenzene or the triazine chromophore was excited. Chlorine substitution byhydrogen or hydroxyl in water occurred in the former case, whereas the mostefficient process in the latter case was S—N bond cleavage in the sulfonylureabridge.201 Photodegradation of the human pharmaceutical dichlofenac, 2-(2�,6�-dichlorophenyl)aminophenylacetic acid, occurs in lake water, the initial photo-product, 8-chlorocarbazole-1-acetic acid, photodegradingmore rapidly than theparent compound.202

Further modifications of the triacetyl derivative of 4-aminocyclopentene-trans,trans-3,5-diol, obtained by photohydration/acid-catalysed ring opening ofpyridine in aqueous perchloric acid, has led to a convenient synthesis of (�)-allosamizoline (258).203 cis/trans Interconversion generally occurred readily forN-alkyl-2-azetidinones, probably involving C-3—C-4 bond cleavage, whereasN-phenyl-2-azetidinones were unreactive, and N—CO bond cleavage/reclosuredid not lead to isomerisation of the �-lactam ring.204 Irradiation of furazans (259)in the presence of amines resulted in extrusion of benzonitrile, capture of thering-cleaved intermediate by the amine, cyclisation of the resulting N-acylaminoamidoxime and formation of the 3-amino-5-perfluoroalkyl-1,2,4-

Photochemistry266

oxadiazoles (260).205 Irradiation of 10-methylacridinium perchlorate (261) withallylic silanes and stannanes (262) led to the corresponding 5-allylated dihydro-acridines (265). With unsymmetrical allylsilanes and allylstannanes, the allylicgroups were introduced selectively at the �-position though, in the case ofallylstannanes, �-adducts were also obtained. SET from the organosilanes ororganostannanes to singlet excited 10-methylacridinium ion followed by radicalcoupling yielded the products.206 The 3-pyrazolines (263) underwent ring con-traction to (264) on irradiation.207 Irradiation of the triazolines (266) gave cyclo-butane cleavage products, in addition to the anticipated aziridines (267). Theseincluded pyridazinonorbornadiene (268), its isomer (269) and triazoles (272). Theunusual cleavage of (266), leading to (268) and (269), has been attributed to extrastabilisation, via (271), of diradical (270) provided by the pyridazine and pyridylnitrogens. Breakdown of (271) by route a yielded triazole (272) and norbor-


nadiene (268) whereas route b yielded (272) and rearranged product (269).Separate irradiation of (268) yielded (269) via a di-�-methane rearrangement,though this does not compete with formation of (269) during irradiation of(266).208 Irradiation of pyrazino- and quinoxalino-fused naphthobarrelenes re-sulted in triplet excited-state di-�-methane rearrangement via heteroaromatic-vinyl bridging, and not naphtho-vinyl bridging, to yield the correspondingsemibullvalenes.209 Photolysis of isoxazolone (273) in acetone at 300 nm gavepyrrole (276) via carbene (275). In contrast isoxazolone (274) yielded the acetonecycloaddition product (280), consistent with an electron-withdrawing groupclose to the nitrogen of the iminocarbene endowing it with 1,3-dipole (277)reactivity. In acetonitrile isoxazolone (274) yielded pyrrole (278), via cyclisationof carbene (275), and cycloaddition product (279).210,211

Irradiation of acridine and carbazole, either as a polycrystalline mixture or insolution, yielded the condensation product 9-carbazol-9-yl-acridine, possiblyinvolving SET.212 2,7-Dihydroazepine (281) photorearranged to 2,3-dihydro-azepine (282) which on further irradiation underwent ring contraction to give(283).213 Irradiation of 3,5,6-triphenyl-1,2,4-triazine in neat triethylamine gave2,5-dihydrotriazine (284), 3,5-diphenyl-1,2,4-triazole (285) and dimeric triazole(286).214 Photophysical studies of this and related electron-deficient azaarenes

Photochemistry268

have shown that the triplet state is involved in efficient SET from amines.Subsequent rapid proton transfer within the collision complex forms the hydro-gen-adduct radicals which react slowly to yield subsequent products.215 Aqueoussolutions of the sodium salt of N-bromo-4-methylbenzenesulfonamide (bro-mamine) yielded 4-methylbenzenesulfonamide, N,N-dibromo-4-methylben-zenesulfonamide and bromine as photoproducts.216 Irradiation of aldimines(R1CH——NR2) in propan-2-ol/acetone through Pyrex resulted in reductivedimerisation to the corresponding vicinal diamines [R1CH(NHR2CHR1NHR2]in good to excellent yields, the meso-diamine normally being in excess.217 Aro-matic imines (Ar1CH——NAr2) were efficiently photoreduced to the correspondingamines (Ar1CH2NHAr2) in the presence of 2-phenyl-N,N-dimethylbenzimidazoleas electron donor and magnesium cation as SET mediator.218 1H-Azepine-2,7-dione, on irradiation in aqueous acetonitrile containing either morpholine orpotassium hydroxide, underwent carbonyl photoreduction to give 7-hydroxy-1H-azepine-2-one.219 The use of catalytic amounts of �-lapachone, a triplet SETphotosensitiser, resulted in C-16—C-21 bond cleavage of the catharanthine rad-ical cation (287) and reaction with trimethylsilyl cyanide to yield 21�-cyano-16�-(methoxycarbonyl)cleavamine (288) in 88% yield.220

Light-controlled synthesis of peptides, employing photogenerated acids fordeprotection of N-t-Boc groups, has potential for parallel synthesis of address-able, combinatorial molecular microarrays, with photolysis of triarylsulfoniumor diaryliodonium hexafluoroantimonates in dichloromethane a source of thephotogenerated acid.221 Laser flash photolysis has been used to study photoacidgeneration from N-oxysuccinimidoarylsulfonates and 1,2-di(arylsulfonyl)hy-drazines. Sulfonic acids were generated following reaction of arylsulfonyl radicalwith molecular oxygen.222,223 Decahydroacridone dyes are efficient SET sensi-tisers for decomposition of diaryliodonium and triarylsulfonium salts. The re-sulting acridone radical cations release a proton. The dye singlet excited state isinvolved in the photosensitisation of triarylsulfonium salts whereas both singletand triplet excited states are involved in photoacid generation withdiaryliodonium salts.224 Quaternary ammonium dithiocarbamates quantitative-ly release a tertiary amine, for example diazabicyclo[2.2.2]octane from 1-phenacyl-(1-azonia-4-azabicyclo[2.2.2]octane)-N,N-dimethyldithiocarbamate,and are excellent photobase generators for use in polymer photocrosslink-ing.225—227 Preferential excitation—decomposition, using circularly polarised light,of one of the enantiomers of a racemic �-amino acid by the Norrish Type IImechanism (leucine, valine or isoleucine, all of which contain the necessary �-H


atom) yielded an enantiomerically enriched sample.228 Fluorescence quenching,laser flash photolysis and product characterisation have confirmed SET fromN-phenylglycine to singlet excited pyrene. The anilinomethyl radical is an inter-mediate in formation of the decomposition products N-methylaniline, anilineand formanilide.229 In neutral argon-saturated aqueous solution no dependenceof the dipeptide decomposition quantum yield on the sequence of amino acidsexists on 193 nm laser irradiation.230 The photocleavage of proteins, bovineserum albumin or lysozyme, by a series of 1-pyrenyl peptide probesPy(CH2)3CONHCH2COX (where X�Trp, Tyr, Phe or His) in the presence of anelectron acceptor has been investigated. Both BSA and lysozyme were photo-cleaved by the phenylalanine and histidine analogues while the tyrosine andtryptophan analogues did not cause fragmentation of either compound. Flashphotolysis of the probe—protein mixtures indicate that the initially producedpyrene cation radical is strongly quenched by the tyrosine and tryptophanresidues.231 It is of interest to biomedical processes related to cataract induction,photoageing, photodynamic therapy and stabilisation of biomaterials such asporcine or bovine pericardial tissues, that the FMN-sensitised intermolecularcross-linking of N-acetyl--tyrosine results in formation of threetyrosine—tyrosine products: C6,C6�-linked di-(N-acetyltyrosine), C6,O7�-linked di-(N-acetyltyrosine) and C6,C4�-linked di-(N-acetyltyrosine).232

Thymidine and uridine, also calf thymus DNA, sensitise the geometricalphotoisomerisation of Z-cyclooctene, producing the chiral E-isomer in enan-tiomeric excesses of up to 15%.233 Cytosine and 1-methylcytosine radical cations,generated by SET to triplet excited anthaquinone-2,6-disulfonic acid, underwentdeprotonation on the nanosecond timescale. Cytosine radical cation de-protonated at N-1 yielding cytosin-1-yl radical whereas 1-methylcytosine radicalcation deprotonated at the side-chain amino group to yield an aminyl radical.Each parent compound yielded an additional long-lived radical of unknownstructure on the nanosecond to microsecond timescale.234 Flavin adenine dinuc-leotide (FAD), a photonuclease model, has been used as a sensitiser of dGMP,which is a DNA model. Direct evidence of SET from dGMP was obtained.Sensitiser reactivity was not markedly influenced by the nucleotide environmentas shown by a comparison of nucleotide-free and -bound riboflavin.235 Irradi-ation of the 7-nitroindole nucleosides (289) yielded the 2�-deoxyribonolactones(290) and 7-nitrosoindole. The process provides a general route to the efficientpreparation of oligonucleotides containing the labile deoxyribonolactone moi-ety at a preselected position.236 Nitropiperonyl 2-deoxyriboside has been inves-tigated as a universal photocleavable DNA base analogue. Thus when it isincorporated into pentacosanucleotides (291), irradiation followed by piperidinetreatment caused specifically located strand cleavage to give the corresponding3�- and 5�-phosphates.237 The 2-(3,4-methylenedioxy-6-nitrophenyl)propoxycar-bonyl group is an effective photoremovable protecting group for the 5�-hydroxylprotection of nucleosides.238

Protected peptides, peptideamides and peptide N-alkylamides (Pep-tideCOXH) may be photolytically released from the peptidyl resin (292) onwhich they have been assembled. In this case, the 2-nitrobenzyl unit serves the

Photochemistry270

dual function of an anchoring linkage between the supporting resin and thegrowing peptide chain, and of latent reagent for release of the assembled pept-ide.239 The normal photocleavage of the �-methyl-6-nitroveratryl linker used inpeptide synthesis has been found to be accompanied by side product formationarising from competing reactions with the amino and thiol groups of othermolecules present in the reaction mixture.240 1-Acyl-7-nitroindolines have beeninvestigated as photolabile precursors of carboxylic acids, particularly neuro-active amino acids. 4-Methoxy substitution improved the photolysis efficiencywhereas the 4-N,N-dimethylamino analogue was photoinert.241 AM1 calcula-tions on the mechanism of 2-nitrobenzyl photochemistry suggest that a newmechanism, consistent with results from time resolved spectroscopy and acidcatalysis, must be considered.242 The recently introduced 2-nitrofluoren-9-yl-methoxycarbonyl peptide-protecting group underwent solvent-dependentphotocleavage. Although lacking an o-benzylic proton; a mechanism involvingsolvent-mediated proton transfer from the 9-position to the m-nitro group hasbeen proposed. The resulting intermediate (293) then breaks down as shown torelease the peptide, with simultaneous formation of 2-nitrodibenzofulvene.243

Irradiation of the �--glucopyranosylpyridinium chloride (294) in aqueouspotassium carbonate yielded a 1:1 mixture of photohydration products (295a)and (296), with aziridine (295a) being readily separable on a gram scale as thepentaacetate (295b).244 Irradiation of N-substituted (2-bromoacyl)anilides (297)resulted in competing cyclisation to oxindoles (299) and dehydrobromination toalkene (300), accompanied by secondary six-electron photocyclisation of (300) todihydrocarbostyrils (302). In contrast N-unsubstituted (2-bromoacyl)anilides(298) yielded only dehydrobromination products (301), cyclisation being pre-vented by the almost exclusive trans geometry around the amide carbon—nitro-


gen bond.245 Chlorine radical n-complexes have been identified as intermediatesin the photolysis of 4-(2-chlorobenzoylamino)pyridines which result in intra-molecular cyclisation to (303) via aryl radical attack on the complexed pyridinylring.246 Intramolecular photosubstitution to yield 2-phenyl-1,3-benzoxazole wasthe major process on irradiation of 2�-bromobenzanilide in acetonitrile accom-panied by photoreduction and photo-Fries type products. For 2�-chloro-benzanilide, benzoxazole formation is not the major process.247 Photolysis of theallal azidoformate (304) in the presence of an alcohol provided a convenientroute to �-2-amido allopyranosides (305), presumably via a transient aziridineintermediate.248 When 2�,3�,5�-tri-O-acetylbredinin (306) or 2�,3�-O-i-propylidenebredinin (307) were irradiated in dilute acetic acid, the 2-aminomalonamides (308) and (309) were obtained respectively. Appropriatemodifications of the 5�-position of (309) may be made and condensation withtriethyl orthoformate permits reconstruction of the imidazole base moiety, pro-viding convenient access to 5�-modified analogues of bredinin.249 Irradiation ofcyanoaromatics (ArCN) in the presence of formamides or pyrrolidones resultedin the formation of �-aryl amides (310)—(315) via an SET mechanism.250 Inaddition to five photoproducts previously identified from the short term irradi-ation of 6-chloro-1,3-dimethyluracil in mesitylene in the presence of tri-fluororacetic acid, two new secondary photoproducts 251 have been obtained. Sixadditional products, cyclobutaquinazolines and pentalenopyrimidines, havebeen isolated and identified from longer term irradiation.252 Orange to bluecolour changes accompanied the photoisomerisation of a series of anthra-isoxazoles to the corresponding phenoxazinequinones.253 Cation size plays

Photochemistry272

an important role in product formation in the singlet excited-state Wallachrearrangement of azoxybenzene to give predominantly o-hydroxyazobenzene incation-exchanged zeolites.254 Colourless thin films of theN,N�-dibenzyl dibrom-ide salts of 4,4�-, 5,5�- and 6,6�-biquinolines in poly(N-vinylpyrrolidine) undergophotocoloration, probably due to formation of the corresponding viologenradical cation.255 Photolysis, but not thermolysis, of 1-(1,2,4-triazol-4-yl)-2,4,6-trisubstituted pyridinium tetrafluoroborates in mesitylene and acetonitrile gavepredominantly the trisubstituted pyridine and 1-(2,4,6-trimethylphenyl)-1,2,4-triazole, possibly by SET from mesitylene but not involving the intermediacy offree 1,2,4-triazolyl cation. Photolysis ofN,N-dibenzoyl-4-amino-1,2,4-triazole inmesitylene yielded 1,2,4-triazole, dibenzoylimide and 1,2-bis(3,5-dimethyl-phenyl)ethane following formation of the 1,2,4-triazolyl free radical by cleanN—N bond homolysis, but no 1-(2,4,6-trimethylphenyl)-1,2,4-triazole was detec-ted.256 Photoheterolysis of the N—N bond of 1-(N-methyl-N-aryl)-2,4,6-trimethylpyridinium tetrafluoroborates generated the corresponding N-methyl-N-arylnitrenium ions. Time resolved infrared detection and computa-tional studies show that arylnitrenium ions are well described as 4-imino-cyclohexa-2,5-dienyl cations.257

Two new oxazolonaphthalimide hydroperoxides are very efficient in the


photocleavage of DNA and their absorption and fluorescence properties havebeen reported.258 Investigations of linkage-dependent singlet state quenching ofN-substituted 1,8-naphthalimides linked by 2,6-methylene spacers to a viologenunit,259 SET quenching of 1,8:4,5-naphthalene diimides fluorescence on thepicosecond timescale,260 the effect of substituents in a series of purpurin-18-N-alkylimides on the efficacy of in vivo photodynamic therapy,261 transient tripletsofN-(methoxytriethyleneglycol)mono- and di-substituted fulleropyrrolidines,262

radical anions from mono- and bis-N,N-dimethylfulleropyrrolidine deriva-tives,263 SET quenching of fluorescence in fluorescein—C60dyads,264 charge-separ-ation in carotene—porphyrin—fullerene triads,265 SET in donor—acceptorquinoxaline derivatives,266 radical-ion pairs and intersystem crossing indonor—acceptor dyads,.267 control of SET by hydrogen bonding within aporphyrin—phenoxynaphthacenequinone photochromic system,268 control offluorescence emission from 4-(2�-N,N-dimethylaminoethyl)amino-9-butylnaph-thalimde by solvent polarity,269 interaction of 4,4�-bipyridine singlet or tripletexcited states with triethylamine or 1,4-diazabicyclo[2.2.2]octane,270 sub-picosecond laser photolysis of 1-piperidino- and 1-pyrrolodino-anthra-quinone,271 magnetic field effects on the quenching of the triplet excited states of10-methylphenothiazine derivatives,272 fluorescence quenching of 2,3-diaza-bicyclo[2.2.2]oct-2-ene by aliphatic and aromatic amines,273 biphotonic photo-ionisation of 2,3-diazabicyclo[2.2.2]oct-2-ene,274 triplet excited 1,4-naph-thoquinonediazide-2-carboxylic acid,275 SET quenching of excited coumarindyes by diphenylamine and triphenylamine276 and SET from carbazole, N-acetylcarbazole and N-benzoylcarbazole to halomethanes277 have been pub-lished.Aspects of the photophysics of phenylalanine analogues,278 1-methyl-

and 1,2-dimethyl-2(1H)-pyridinimine,279 3-cyano-4-furyl-6-phenyl-2-(9-anthra-lylidene)-pyridine,280 4�-substituted-N-phenylphenothiazine derivatives,281 sub-stituted 2-(2-phenylethenyl)benzoxazoles and benzothiazoles,282 1-(N-ethylcar-bazolyl)-2-substituted-2-cyanovinylenes,283 1,3-dicarbazolylpropane,284 6-phenathridinecarbonitrile,285 tetraphenylporphyrin and octaethylporphyrin di-acids,286 2,3-dihydro-2,2,4-trimethyl-1H-1,5-benzodiazepine in aqueous cyclo-dextrin environments,287N,N-ditridecyl-3,4:9,10-perylenetetracarboxylicacid di-imide in chloromethane solvents288 and perylene diimide derivatives in aqueousand organic solvents289 have been reported.CASSCF calculations on simple 2H-azirines led to the conclusion that pho-

tolysis results in nitrile ylide formation from the n�* excited state via an S1/S0

conical intersection and that vinyl nitrene formation occurs via an S2/S1 conicalintersection from the ��* excited state.290 DFT/MRCI calculations have beenapplied in a study of the intramolecular charge-transfer states of N-pyrroloben-zene, N-pyrrolobenzonitrile and 4-N,N-dimethylaminobenzonitrile.291 Ab initiocalculations have been applied to the aromatic amino acids phenylalanine,tyrosine and tryptophan and the calculated excitation and emission energiessatisfactorily correspond to the measured values. Molecular electrostatic poten-tials change little on excitation, suggesting that H-bonding patterns of theseamino acids also change little on excitation, consistent with the structures and

Photochemistry274

activities of proteins and enzymes not being seriously modified by UV radi-ation.292

3 Sulfur-containing Compounds

cis-Cyclophane (316) and its trans-isomer (317) were interconverted on exposureto UV light.293 Hemithioindigo-containing lipids can be reversibly switchedbetween two geometric isomers in organic solvents or in phosphatidylserinevesicles, thermal reversion of the thermodynamically less stable E-isomer to theZ-isomer being slow in the dark.294 Irradiation of conjugated dithiepines (318) inbenzene containing traces of hydrochloric acid led to the non-conjugated isomer,by excited-state deprotonation, followed by reprotonation at the benzylic posi-tion.295 Irradiation of 2-oxo-2H-1-benzothiopyran-4-carbonitrile (319), or itsbenzopyran analogue (320), in the presence of 2,3-dimethylbut-2-ene, gave imine(324) by a triplet state process. The exclusion of cyclobutane formation impliesthat the rate of 1,5-cyclisation of the triplet biradical to give triplet vinyl nitrene(323) is much greater than the rate of intersystem crossing to the singlet biradical,the cyclobutane precursor.296 The corresponding 3-carbonitriles behaved differ-ently. Thus 2-oxo-2H-1-benzothiopyran-3-carbonitrile (321) reacted with anexcess of 2,3-dimethylbut-2-ene to give exclusively a cyclobutane. With 2-methylbut-1-en-3-yne, (321) yielded three adducts: two cyclobutanes and acyclobutene. 2-Oxo-2H-1-benzothiopyran (322), lacking a nitrile function at C-3and C-4, reacted with 2-methylbut-1-en-3-yne to yield three adducts: twocyclobutanes and a cyclobutene.297 Direct irradiation of 1,3-diheteroaryl-2-pro-


pen-1-ones (325)—(327) gave a mixture of dimeric cyclobutanes, consistent withthe reaction being under frontier orbital control and with only the more ther-modynamically stable dimers being formed. In contrast, when irradiated inacetonitrile containing benzophenone, 2-(2-thienyl)-1-nitroethene yielded a mix-ture of open-chain compounds (328)—(330) corresponding to dimerisation withloss of HNO2. 2-(2-Thienyl)-1,1-dicyanoethene underwent head-to-head [2�2]-dimerisation to give the trans cyclobutane in low yield.298 Irradiation of ahomogeneous solid film of substituted 7-methylisothiocoumarin (332) selectivelyyielded the head-to-head dimer, as also observed for isothiocoumarin (331). Incontrast the 5-trifluoromethyl derivative (333), with the substituent closer to thereactive centre, is non-selective, with all-cis head-to-head and head-to-tail dimersbeing produced in essentially equal amounts. The benzo derivative (334) isphotostable. The corresponding 7-methyl-5-trifluoromethyl- and 5,6-benzo-isocoumarins did not photodimerise under similar conditions.299 Enantioselec-tive intermolecular photoreaction via single-crystal to single-crystal transform-ation of inclusion complexes of thiocoumarin (also coumarin and cyclohex-2-enone) with optically active diol hosts have been reported. For example (�)-antihead-to-head dimer (335) has been obtained in 100% enantiomeric excess byirradiation of the solid 1:1 complex with (R,R)-(�)-trans-2,3-bis(hydroxy-diphenylmethyl)-1,4-dioxaspiro[4.4]nonane as host.300

Diarylethenes, particularly 1,2-dithienylperfluorocyclopentene derivativessuch as (336), have attracted much interest as photochromic materials. Thephotoreactive antiparallel conformation (336) underwent conrotatory cyclisa-tion to the closed isomer (360) onUV irradiation, whereas the parallel conforma-tion (341) was photoinactive. NMR spectroscopy showed that the methyl-substituted conformers (336) and (341) exist in a 65:35 ratio respectively in CDCl3whereas for bis(2-i-propyl-1-benzothiophen-3-yl)hexafluorocyclopentene themore space-demanding i-propyl groups reduce the proportion of parallel confor-mation (342) present, the ratio of (337) to (342) being 94:6 respectively. Thequantum yields for ring-opening of the closed forms (360) and (361) were essen-tially identical. For ring closure of the i-propyl-substituted compound they were

Photochemistry276

much higher (0.80 in hexane using 282 nm radiation) than for the methyl-substituted compound (0.55), which reflects the much greater proportion offavourable conformer (337) present for the former.301 The photogenerated col-oured closed isomers (344) and (360), containing 2-i-propyl groups, reverted tothe initial colourless open forms (337) and (347) respectively at temperaturesabove 60 °C whereas those containing 2-methyl groups, (343) and (359), requiredmuch higher temperatures for reversion to (336) and (349) respectively.302 Theaddition of �-cyclodextrin to an aqueous solution of the ammonium derivative(338) increased the quantum yield for cyclisation by a factor of 1.4 by increasing


the ratio of the active antiparallel conformer, more suitable than the inactiveparallel conformation for inclusion in the cyclodextrin cavity.303 Analogousreversible cyclisation/ring-opening photoprocesses have been reported for (339),(347),304 and (345)305 in solution, for (350), (351),306 (353),307 (354) and (355)308 insolution or as spin-coated amorphous films, and for (352)317 in a single crystal.Both (349)309 and (348) underwent conrotatory closure in the single crystallinestate. X-ray crystallography has revealed that, in the crystal, the thermal cyclo-reversion of the closed form (361) to (348) occurred in a conrotatory manner, abreach of the general Woodward-Hoffmann rules.310 The closed form (361) alsounderwent conrotatory ring opening to (348) on irradiation with 680 nm light.311

When optically active dithienylethene (363) was irradiated with 366 nm light insolution it underwent reversible photocyclisation to yield closed diasteromers(364) and (365) in equal amounts. However, when single crystals of (363) wereirradiated, a single diastereomer (364) was formed in �95% diastereomericexcess, the consequence of topochemically controlled crystalline state cyclisation

involvingminimal conrotation of the two thiophene rings.312,313 1,2-Bis(2-methyl-5-aryl-3-thienyl)perfluorocyclopentenes (346) and (356) also underwent revers-ible photochromic reactions in the single-crystal state. The rates of photocyclisa-tionwere independent of alkyl substitution at the 4-positions of the phenyl groupboth in solution and in the single-crystalline phase, photocyclisation activationenergies being practically zero. For the photocycloreversions, however, activa-tion energies were in the range 5—10 kJ mol�1 in the single-crystal state whereastheywere about 16 kJmol�1 in solution. The thermal stability of the closed formswas high, the half-life of the closed isomer (359) of (346) being estimated at 1900years at 30 °C.314 The photoreversible ring-closure/ring-opening process thatoccurred on irradiation of crystals of 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene resulted in the formation of steps, about 1 nmhigh and corresponding to one molecular layer, on the (100) single-crystallinesurface. These steps appeared on 366 nm irradiation and disappeared on irradi-ation with visible light (��550 nm). Valleys were formed simultaneously on the(010) surface on 366 nm irradiation and disappeared on subsequent exposure tovisible light. These surface changes arise from molecular structural changesoccurring within the diarylethenes packed in the single crystal.315 Polystyrenefilms containing compounds (346) or (349) turned blue or red respectively onexposure to �-radiation, colour intensities increasing linearly with the dose

Photochemistry278

absorbed, the colour change permitting an estimation of radiation dose. Excita-tion energy transfer from polymers to dithienylethenes may play a role in thecoloration process since different polymers display quite different colorationefficiencies.316,317 Irradiation of (366), (367) or (368), containing two 1,2-dithienylethene photochromes, resulted in cyclisation of only one of these moie-ties. Prolonged irradiation of (367) yielded the rearranged product (369) quanti-tatively.318 A system containing two dithienylperfluorocyclopentene moieties,linked to a fluorescent bis(phenylethynyl)anthracene reside underwent cyclisa-tion of only one of these moieties on irradiation at 313 nm, accompanied by areduction in fluorescence quantum yield from 0.83 to 0.001. A similar decrease inlaser emission intensity was observed on exposure to UV light. Reversal of bothobservations occurred by irradiation with visible light (� �500 nm).319 The bluefluorescence of the photochromic compound (357) was also suppressed by ringclosure on irradiation. The spectroscopic properties and reaction dynamics havebeen investigated and analysed, taking into account the presence of reacting andnon-reacting conformers. The presence of different conformers is argued to be arequirement for applications relying on efficient switching of the fluorescence.320

Similar photocontrol of fluorescence has been reported for the non-fluorinatedanalogue of porphyrinic dithienylethene (358), the intense emission from theopen form being eliminated by conversion to the non-fluorescent closed form onirradiation at 313 nm and restored on irradiation with wavelengths greater than480 nm, accompanying regeneration of the open form (358). The fluorescenceintensity may be conveniently regulated by toggling between open and closedforms by alternate UV (313 nm) and visible light irradiation (��480 nm),demonstrating the potential of (358) to act as a reversible data processing systemusing fluorescence detection.321

cis-1,2-Dicyano-1,2-dithienylethene underwent photochromic cyclisation asefficiently in colloidal solution as in amorphous films or in hexane solution. Thephotocyclisation efficiency in a polymer matrix was essentially independent ofthe nature of the polymer. In contrast only amorphous films of 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride coloured slightly onUV irradiationwhere-as colloidal solutions and polycrystalline samples showed no photochromism. Inpolymer matrices it showed significant dependence on the glass transition tem-perature and polarity of the matrix.322 The closure reactions for two ter-thiophene-substituted perfluorocyclopentenes occurred within about 2.7 ps in


hexane and within 1 ps in more polar acetonitrile, suggesting that charge transferin the excited singlet state is important in the photochromic process.323 Thequantum yields for the photoinduced closure and opening reactions of a series of1,2-dithienylperfluorocyclopentenes exhibited clear threshold behaviour as afunction of the S0—S1 excitation energy but were otherwise insensitive to thenature of substitutents.324 Both the closure and opening processes for thebis(nitronyl nitroxide) (340, n�0) occurred with almost 100% efficiency, andmagnetic susceptibility measurements showed that they are accompanied bychange of magnetic interaction between the two radical centres, associated withchanges in the planarity and aromaticity of the system and providing the basisformolecular switching devices for logic circuits.325,326 For the bis(nitronyl nitrox-ides) (340, n�1, 2) the p-phenylene spacers regulate the strength of the exchangeinteraction and highly efficient switching was observed by ESR spectro-scopy.327—330 For the diarylethene dimer (370) there are three, rather than two,photochromic states: open—open (OO), closed—open (CO) and closed—closed(CC). Bond alternation is disconnected at the open formmoieties of the OO- andCO-forms so that two spins cannot interact. In contrast the � system of theCC-form is fully delocalised and the exchange interaction between the radicalcentres is facilitated. On irradiation of the OO-form (370) with 313 nm lightsequential conversion to the CO- andCC-forms occurred. Cycloreversion occur-red using 576 nm light. ESR spectroscopy confirmed that the magnetic interac-tion was much greater in the CC-form than in either the OO- or CO-forms.331

Semiempirical MO calculations (AM1 and PM3) have been applied to theoptimisation of the conformers of photochromic dithienylethenes (cis-1,2-dicyano-1,2-dithienylethene, 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydrideand 1,2-bis(2,4,5-trimethyl-3-thienyl)perfluorocyclopentene in the ground andfirst excited singlet states. Charge distributions, energies and dipole momentshave been calculated, in addition to energy barriers between the open and closedforms.332

Efficient reversible photochromism requires very high reproducibility of theopen/ring-closed/open cycle. Some diarylethenes with thiophene rings ceasetheir photochromic cycles in less than several hundred cycles. An understandingof the various fatigue mechanisms is essential if highly fatigue-resistant materialsare to be developed for use in optoelectronic devices. Prolonged irradiation ofnon-substituted 1,2-bis(3-thienyl)perfluorocyclopentene with 313 nm radiationyielded (375), resonance structure (371) rationalising cyclisation to (373), withsubsequent dehyrogenation yielding (375). Blocking the dehydrogenation stepby incorporating 2-and 2�-methyls, for example as in (372), did not produce aproduct analogous to (375) due to the difficulty of eliminating a methyl group.

Photochemistry280

Rather, elimination of hydrogen fluoride occurred from (374) to yield (376). Withmethyls in the 4- and 4�-positions of the thiophene rings no by-product analog-ous to (375) was obtained. In the presence of oxygen, compound (371) yieldedminor by-product (377).333 The stable by-product (378), from the closed isomer(359), was obtained from 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene(349).334 The dihydroazulene—dithienylethene conjugate (380) underwent photo-conversion to both isomeric dihydrothienobenzothiophene (379) and vinyl-heptafulvene (382). In contrast the dihydroazulene—diphenylethene conjugate(381) yielded only the vinylheptafulvene (383) on irradiation. Vinylheptafulvenes(382) and (383) reverted thermally to the dihydroazulene forms (380) and (381)respectively.335

Thiofulgides (384) cyclised to thermally stable coloured isomers (387) whichshowed large bathochromic shifts of 40—60 nm of their long-wavelength absorp-tion bands relative to the oxygen analogues (388) obtained from (385). Whitelight resulted in cycloreversion of (387) to (384).336 The alkyl-substituted fulgides(386) were irradiated with 366 nm light. The resulting closed forms (389) under-went a thermal 1,5-sigmatropic hydrogen shift to yield heliofulgides (390) whichyielded the open-form (391) on irradiation with 366 nm light. Reversion to (390)occurred on standing.337


Structure—property relationships have been proposed based on a combinationof molecular modelling and experimental determination of photochromic par-ameters (absorption wavelength of open and closed forms, rate constants ofthermal bleaching and coloration ability) for photochromic thiophene-sub-stituted [3H]-naphtho[2,1-b]pyrans. The calculations were used to make quali-tative predictions on the variation of the absorption wavelength of the openform.338 For the crowned spirobenzothiopyran (58) the stability of the photo-induced open coloured isomer was enhanced by the metal ion complexing abilityof the crown ether moiety, especially Li�, and by metal ion affinity, especially byAg�, for the thiophenolate anion.339 Spectrokinetic parameters have beenreported for a series of thiophene-fused 2H-chromenes which includes2,3-dimethyl-8,8-diphenyl[8H]chromene[7,8-d]thiophene, 2,3-dimethyl-7,7-diphenyl[7H]chromene[6,5-d]thiophene, 2,3-dimethyl-6,6-diphenyl[6H]chromene[5,6-d]thiophene and 2,3-dimethyl-5,5-diphenyl[5H]chromene[8,7-d]thiophene,340 and also for a range of 5-methoxycarbonyl-8,8-diaryl[8H]chromene[7,8-d]thiophenes and 8-methoxycarbonyl-5,5-diaryl[5H]chromene[8,7-d]thiophenes.341 Fluorescence was observed for severaloligothiophene-substituted chromenes, the absorbed light inducingoligothiophene fluorescence rather than ring opening of the chromene. Thephotochromism/fluorescence ratio depended on the polythiophene chain lengthand on the chromene substitution site.342—344

Oxidative photocyclisation of the 9-(arylvinyl)thieno[3,2-a]quinoliziniumperchlorates (392) and (393) in methanol containing iodine yielded the corre-sponding thiaazonia[5]helicenes, for example (394) from (392). The isomeric9-arylvinylthieno[2,3-a]quinolizinium perchlorates underwent analogous cyc-lisation.345 Irradiation of N,N-dibenzyl-�,�-unsaturated thioamides (395)—(398)in benzene yielded �-thiolactams (400)—(403) respectively. From (395) and (396),for which two diastereomeric �-thiolactams are possible, only the Z-isomer wasobtained. The unsaturated thioamides (396) and (397), although achiral, crystal-

Photochemistry282

lised in chiral form and solid-state photocyclisation resulted in the formation ofthe corresponding optically active �-thiolactams (401) and (402) in high enan-tiomeric excess. Consideration of the absolute configurations of crystalline (�)-(396) and its cyclisation product (�)-(Z)-(401) were consistent with the involve-ment of a zwitterionic intermediate (399) which undergoes conrotatory cyclisa-tion to yield the Z-�-thiolactam.346

The 4-aryl-4-methyl-2,6-diphenyl-4H-thiopyrans (404) photorearranged byselective migration of the aryl groups to form the corresponding 2H-thiopyrans(408) quantitatively via the 6-aryl-5-methyl-1,3-diphenyl-2-thiabicyclo[3.1.0]hex-3-enes (406) as intermediates.347 For the 3,5-substituted 4H-thiopyrans (405),direct conversion to hexasubstituted 2H-thiopyrans (409) occurred without in-termediates (407) being observable by NMR spectroscopy.348 4,4-Diphenyl-2,6-di(4-methoxyphenyl)-4H-thiopyran-1,1-dioxide photoconverted to 3-(4-methoxyphenyl)-6,6-diphenyl-2-thiabicyclo[3.1.0]hex-3-ene-2,2-dioxide by athia-di-�-methane rearrangement involving initial vinyl—vinyl bridging.349 Simi-lar formation of syn- (major) and anti-thiabicyclo[3.1.0]hex-3-ene-2,2-dioxidesoccurred for 4-methyl-2,4,6-triphenyl-4H-thiopyran-1,1-dioxide.350 Photolysis ofN-phenyl-O-benzylthiocarbamate (PhNHCSOCH2Ph), N-phenyl-O-phenyl-thiocarbamate (PhNHCSOPh) and N-phenyl-S-phenylthiocarbamate(PhNHCOSPh) in acetone containing traces of benzophenone resulted inhomolysis of the N—CS, O—CS and S—CO bonds and the resulting free radicalsyielded the products by hydrogen-abstraction, dimerisation, disproportionationand/or fragmentation processes.351


Details of the photochemical reactions of N-acylbenoxazole-2-thiones withalkenes have been reported.352 Initial [2�2]-cycloaddition of the alkene to thecarbon—sulfur double bond yielded the unstable aminothietane (410), the regio-chemistry of which was determined by formation of the more stable diradicalintermediate. Carbon-sulfur bond cleavage, followed by intramolecular acyltransfer from nitrogen to sulfur, resulted in formation of 2-substituted benz-oxazoles (411) whereas the analogous steps initiated by carbon—oxygen bondcleavage led to iminothietanes (412). Irradiation of a series of N-3- or N-4-alkenylthioglutarimides (413) gave thietanes (414) as primary photoproducts.For thio- or dithio-glutarimides (413; X�O, S; n�2; R1�R2�R3�Me),thietanes (411) were the major products isolated whereas in all other cases theirfission products were obtained. Products from Norrish Type II �-hydrogenabstraction were very minor.353 Irradiation of 2-trimethylsilyl-2-phenyl-1,3-

dithiane or 2-pentamethyldisilanyl-2-phenyl-1,3-dithiane in propan-2-ol yieldedbenzyltrimethylsilane or benzylpentamethyldisilane in 34% and 28% yield re-spectively, the outcome of initial carbon—sulfur bond cleavage.354 Laser flashphotolysis studies with a series of dithiane-carbonyl adducts (415) support amechanism for deprotection involving SET from the dithiane moiety to excitedbenzophenone, followed by benzophenone radical anion facilitated O-de-protonation, coupled to carbon—carbon bond scission and release of the car-bonyl compound.355 The method has been applied to the deprotection of calix-arene and dibenzocrown ether derivatives.356 Irradiation of the 2-O-thiobenzo-ate derivative (418) of methyl 4,6-benzylidene-�--glucopyranoside indichloromethane containing triethylamine resulted in solvent incorporation andcyclisation to diastereoisomers (416) and (417). The 3-O-thiobenzoate derivative(419) similarly yielded (421) and (422). SET from triethylamine to the tripletexcited thiobenzoyl group of (419) yielded a radical anion which abstracted ahydrogen atom from the triethylamine radical cation. The resulting thiolateanion reacted with dichloromethane, generating chloromethyl sulfide (420) withcyclisation to the adjacent hydroxyl group completing conversion to (421) and

Photochemistry284

(422).357 Irradiation of the N-t-butyl-benzothiazole-2-sulfenamide (423) in car-bon tetrachloride in the presence of water yielded benzothiazole, 2-mercapto-benzothiazole, 2-chlorobenzothiazole and benzothiazol-2-one.358 The resin-bound thiohydroxamic acid linker (424) has potential as an efficient tracelesslinker, revealing an aliphatic C—H bond on photolysis at 350 nm. Thus irradi-ation of resin bound N-methylindole-3-acetic acid (425) in the presence of avariety of hydrogen donors (Me3CSH, Bu3SnH, (Me3Si)3SiH) resulted in decar-boxylative release of 1,3-dimethylindole.359

2,3-Diiodo-5-nitrothiophene (426), on irradiation in the presence of aromaticcompounds (benzene, thiophene, 2-bromothiophene, 2-chlorothiophene), gavehigh yields of the corresponding 2-aryl derivatives (427) and (428). 2-Iodo-5-nitrothiophene (429) underwent an analogous conversion to (430) in the presenceofm-xylene, and 2-iodo-5-nitroimidazole behaved similarly. Homolytic cleavageof the carbon—iodine bond was proposed to occur from the lowest triplet �,*state. In contrast the di-iodo compound (426) convertedm-xylene to a mixture of3-methylbenzaldehyde and m-tolualdehyde by an SET process. For the isomeric2,4-diiodo-5-nitrothiophene (431) substitutions occurred in very low yields, PM3calculations showing that the lowest triplet is �,�*. With thiophene, (432) wasobtained whereas with benzene a mixture of the anticipated product (433) andthe transposed product (427) was formed, transposition occurring from theinitially formed radical. 2-Bromo-5-nitrothiazole has a lowest �,�* excited statewith insufficient energy to cleave the carbon—bromine bond and, in the presenceof benzene or indene, replacement of the nitro group occurred to yield 2-bromo-5-phenylthiazole or 2-bromo-5-(1H-inden-2-yl)thiazole respectively.360 Steady-state and pulsed techniques, and also semi-empirical quantum-mechanical calcu-lations, have been applied to an investigation of the photosubstitution reactionsof 2-iodo-5-nitrothiophene, 2-iodo-5-cyanothiophene, 2-bromo-5-cyano-thiophene and 4-iodonitrobenzene.361

In water, direct photolysis of 4-ClC6H4CH2SCOEt yielded 4-chlorobenzal-dehyde and 4-chlorbenzyl alcohol, and 2-MeNHCOOC6H4CH2SEt was con-verted to a mixture of the corresponding sulfoxide, 2-MeNHCOOC6H4Me andtwo unidentified oxidation products.362 The solid-state photoreactions of two-component molecular crystals of 2-thienylacetic acid with acridine yielded 9-(2-thienyl)methyl-9,10-dihydroacridine and biacridane, also obtained from sol-ution-phase irradiation. In the solid state bis(2-thienyl)acetic acid-acridine and


bis(2-thienyl)acetic acid-phenanthridine yielded bis(2-thienyl)methane and 9,9-bis(2-thienyl)methyl-9,10-dihydroacridine or 6-(di-2-thienylmethyl)-5,6-dihyd-rophenanthridine respectively. In solution, the bis(2-thienyl)methyl radical frombis(2-thienyl)acetic acid dimerised to give 1,1,2,2-tetrakis(2-thienyl)ethane.363 Thelack of racemisation on triplet sensitisation and of quenching of racemisation bydienes, and the much greater impact on singlet photophysics by the sulfinylsubstituent than on triplet behavour, led to the conclusion that photoracemisa-tion of a series of aryl methylsulfoxides is intimately tied to non-radiative singletdecay. Activation energies for sulfoxide photoracemisation are low.364

CIDNP measurements have been used to study the SET quenching of singletsensitisers naphthalene and 9,10-dimethylanthracene by triphenylsulfoniumhexafluoroantimonate. Formation of phenyl radicals and the 9,10-dimethyl-anthracenyl cation respectively were observed.365 CIDNP has also been used toinvestigate the equilibrium between the open-chain protonated, open-chaindeprotonated and cyclic (two-centre, three-electron bond between sulfur andnitrogen) forms of the methionine radical cation, generated by photoinducedSET to 4-carboxybenzophenone.366 Quenching of the fluorescence of 3-car-boxyethyl-7-methylthioxanthen-9-one by di- and tri-methoxybenzenes dis-played Rehm-Weller behaviour, whereas with methyl-substituted benzenes thebehaviour followed a sigmoidal curve arising from exciplex quenching.367 Rapidsolvent-dependent intramolecular SET quenching occurred on excitation of thefullerene moiety of �-extended tetrathiafulvalene-containing fulleropyrrolidinedyads.368 Bis[4,5-di(methylthio)-1,3-dithiol-2-ylidene]-9,10-dihydroanthraceneformed a transient radical cation, with a half life of approximately 80 s on flashphotolysis in chloroform. Disproportionation to the dication occurred in de-gassed solutions whereas in aerated solutions 10-[4,5-di(methylthio)-1,3-dithiol-2-ylidene]anthracene-9(10H)one was obtained.369 Time-resolved visible andnear-IR absorption spectroscopy370 and EPRmeasurements371 have been used toinvestigate charge separation in photoexcited polythiophene—fulleropyrrolidinedyads. Photoexcitation of the oligothiophene moiety in somefullerene—oligothiophene—fullerene triads, with three, six or nine thiophene units,resulted in very fast (1012—1013 s�1) intramolecular SET to the fullerene moiety,

Photochemistry286

whereas in oligothiophene/fullerene mixtures intermolecular triplet energytransfer occurred.372 Excitation of the phenothiazine moiety inphenothiazine—bridge—pyromellitdiimide and phenothiazine—bridge—pyrromel-litdiimide—nitroxide radical systems, where the bridge is a semi-rigid biphenyl-4,4�-bis(methylene) unit, resulted in efficient singlet initiated SET from thephenothiazine to the pyromellitdiimide unit to give charge-separated stateswhose decay kinetics were determined by the interplay between spin conversionand back electron transfer.373

4 Compounds Containing Other Heteroatoms

4.1 Silicon and Germanium. — The stable silabenzene (434) yielded silabenz-valene (435) on irradiation.374 The disilanylethynylbiphenyl (436) was convertedto reactive silacyclopropene (437) on irradiation. In the presence of methanol,(437) was converted to the E-adduct (438) and to two dimers, a 1,2- and a 1,4-disilacyclohexadiene. Irradiation of (438) yielded only the Z-isomer (439). In thepresence of acetone, photoadducts (437) yielded two acetone adducts, in additionto some 4,4�-bis(trimethylsilylethynyl)biphenyl, the latter consistent with liber-ation of dimethylsilene from either (437) or its adduct with acetone.375 A series oftrimethylsilyl-substituted cyclopropenes has been investigated to distinguishbetween the possible occurrence of cyclopropylidene intermediates (445), pro-duced by a fast 1,2-silyl shift in a 1-silyl-substituted cyclopropene (440), orvinylcarbene intermediates (442) in the formation of allenes (443) from cyclo-propenes (440). For example 254 nm irradiation converted tetrakis(trimethyl-silyl)cyclopropene (441) quantitatively to allene (444). The alkenyl cyclopropenes(446), offering an intramolecular trap for a cyclopropylidene intermediate, yiel-ded only allenes (447), without bridged spiropentanes (448). Alkenyl cyclo-propenes (449) and (450) similarly yielded only allenes, (451) and (452) respective-ly, without bridged spiropentanes analogous to (448). The experimental results,supported by computational considerations, therefore rule out the involvementof cyclopropylidene intermediates in these rearrangements.376 The efficientphotodeprotection of t-butyldimethylsilyl enol ethers occurred in the presence ofdichloronaphthoquinone or chloranil as sensitiser and propan-2-ol as solvent.Under the same conditions silyl alkyl ethers were inert. For example (453) wasconverted to 4-t-butyldimethylsilyloxycyclohexanone in 98% yield.377 Directphotolysis of benzylsilanes (454) and (455) in solution resulted predominantly inthe formation of the corresponding 6-silylisotoluene derivatives (456) and (457),secondary photolysis of which accounted for most of the subsequently isolatedproducts. Thus (458) was produced quantitatively from 1-benzyl-1-methyl-silacyclobutane (454) in methanolic hexane whereas irradiation of 1-benzyl-1-phenylsilacyclobutane (455) yielded 1-benzyl-1-phenylsilene and a complexproduct mixture consistent with competing formation of benzyl and 1-phenyl-silacyclobutyl radicals from isotoluene (457). Benzyldimethylphenylsilane alsoyielded the corresponding isotoluene derivative whereas benzyltrimethylsilanewas essentially photostable.378


Spectroscopic detection of 9-phenyl-9-silaanthracene, 9-(2,4,6-tri-i-propyl-phenyl)-9-silaanthracene, and 9-(2,4,6-tri-t-butylphenyl)-9-silaanthracene, from254 nm photolysis of the corresponding 9,10-dihydro compounds at 77 K, hasbeen reported379 and photophysical processes and reaction intermediates havebeen investigated.380 o-Phenol-containing alkoxyvinylsilanes (459), on irradi-ation at 254 nm, and (460), on irradiation at 350 nm, underwent E,Z-isomerisa-tion followed by spontaneous cyclisation, to give (461) or (462) respectively, withefficient elimination of the corresponding alcohol, and show promise as photo-removable silyl protecting groups.381

Photochemistry288

Dimerisation of diaminosilenes is temperature dependent, yielding either sili-con—silicon doubly bonded disilenes or (-NR2)-bridged dimers. Thuscophotolysis of a 1:1 mixture of silacyclopropenes (464) and (464-d12) yieldeddiaminosilenes (463) and (463-d12). When (463) and (463-d12) were trapped at75 °C by added bis(trimethylsilyl)acetylene, scrambling was observed, with (465),(465-d12) and (465-d6) being obtained in a 3:3:2 ratio, consistent with the inter-mediacy of the bridged silene dimer (466).382 In contrast trapping of the di-aminosilenes at room temperature by triethylvinylsilane yielded a mixture of(468) and (468-d12), consistent with the intermediacy of disilene (467). Stericcongestion in bis(dialkylamino)organosilylboranes leads to homolytic cleavageof the silicon—boron bond on irradiation, yielding pairs of organosilyl andbis(dial-kylamino)boryl radicals, both of which may be trapped by addedTEMPO. The organosilyl radicals induce silylation of alkenes, silylative cyclisa-tion of dienes and radical polymerisation of methyl acrylate, methyl methac-rylate and vinyl acetate, and may provide an alternative to organotin-basedradical processes. For example irradiation of dimethylphenylsilylbis(di-i-propylamino)borane [PhMe2Si-B(Pri2N)2] in the presence of 1-octene yieldeddimethylphenylsilyloctane. Reaction with alkyl halides also occurred, methyl-cyclopentane being obtained by photoreductive cyclisation of 1-bromo-5-hexene.383

Photolysis (��300 nm) of the 1-disilagermirene (469) resulted in the migrationof the silyl substituent and almost quantitative formation of the stable endocyclicsilicon—germanium double bond isomer, 2-disilagermirene (470).384 Steady-stateand laser flash photolysis of triphenylsilyltrimethylgermane in hydocarbon sol-vents resultedmainly in silicon—germaniumbond homolysis, dimethylgermyleneextrusion and concerted [1,3]-trimethylgermyl migration to the o-position ofone of the phenyl rings. Trimethylsilyltriphenylgermane and 1,1,1-trimethyl-


2,2,2-triphenyldigermane underwent analogous photochemistry.385 Chemicallyinduced dynamic electron polarisation (CIDEP) signals of the triphenylsilyl andtriphenylgermyl radicals were observed by direct photolysis of hexaphenyl-disilane and hexaphenyldigermane in cyclohexane or tetrahydrofuran and areexplained by a triplet mechanism. No signals could be observed from hexa-phenyldistannane within the 80 ns time resolution used.386 Analogous to the60-fullerene SET sensitised reaction of cyclic disiliranes (471) with benzonitrilewhich yields adducts (473), involving reaction of the disilirane radical cation withbenzonitrile,387 cyclic digermiranes (472) afford bisgermylated adducts (474).388 Intoluene 1,4-addition of (472) to C60 occurred via an exciplex mechanism to give(475).389 Steady-state and nanosecond laser flash photolysis and matrix isolationtechniques showed that photolysis of the 7,8-digermabicyclo[2.2.2]octadienes(476) yielded mainly tetraalkyldigermenes (R2Ge——GeR2), triplet excited 1,4-diphenylnaphthalene and rearranged product (477).390

4.2 Phosphorus. — Photolysis generated radical species (481) and (480) fromcaged ATP (479) and monomethyl phosphate (478) respectively. SET from thebenzyl anion formed by photodeprotonation of (479) to the aromatic ring of(479) resulted in co-formation of the radical anion of (479) and cyclic aminoxyl(481). The radical pathway represented only �10% of the reaction outcome,normal photorelease of ATP with concomitant generation of 2-nitroso-acetophenone being the major pathway.391 Addition—elimination, rather thanelimination—addition, occurred in the preparative scale photolysis of the tri-i-propylphenyl-containing 7-(2,4,6-trialkylphenyl)-7-phosphanorbornene 7-ox-ides (482) and (483) in the presence of alcohols. Aryl H-phosphinates (485) andelimination products were obtained via the intermediate five-coordinate adduct(487).392 A (reversible) addition—elimination mechanism is also involved in thephotofragmentation of phosphabicyclooctene (484) in the presence of water oralcohols to give the phosphorylated product (486).393 Thionophosphates (488) inacetonitrile underwent efficient phototransformation to thiolophosphates (491)via a non-chain radical pathway. In the presence of hydrogen-donating species

Photochemistry290

such as propan-2-ol, tetrahydrofuran, toluene and cyclohexene, the methylmandelate-derived thionophosphate yielded (492)—(495) respectively, radical(490) being responsible for radical generation from the hydrogen donor.394

Photolysis of phosphorus—silicon betaine (496) yielded silathiirane (497) as pri-mary photoproduct.395

Direct irradiation of optically active phosphites (R)-(498) and (R)-(499) yieldedshort-lived singlet radical pairs, and a high degree of retention of configurationoccurred in the formation of the phosphonates (R)-(501) and (R)-(502) respective-ly, consistent with significantly higher rates of radical combination than radicalrotation within the radical pair. In contrast direct irradiation of the opticallyactive acetophenone derivative (S)-(500) or triplet sensitisation of (R)-(499) yiel-ded primarily triplet radical pairs and almost complete randomisation ofstereochemistry at the stereogenic centres in product phosphonates, (503) and(502) respectively, by a combination of cage and non-cage processes.396 Thetransient radical cation (504) has been detected in the dicyanoanthracene-induced photorearrangement of dimethyl 2-(4-methoxyphenyl)allylphosphite tophosphonate (506). The lifetime of (504) is approximately 100 times less than that


of 4-methoxystyrene, corresponding to cyclisation to distonic radical cationintermediate (505).397

4.3 Other Elements. — Irradiation of 2-acetylselenophene in the presence of2,3-dimethylbut-2-ene or 2,3-dimethylmaleic anhydride resulted in cyclobutaneformation, involving [2�2]-cycloaddition of the alkene to the acetyl-substitutedcarbon—carbon double bond of the selenophene ring, and oxetane formation,involving the acetyl group of the selenophene and the alkene.398 PhotoinducedSET from 9,10-dimethoxyanthracene (DMA) to silaselenide (507) resulted ingeneration of radical (508) and phenylselenide anion (509) by mesolysis of theresulting radical anion. The alkylsilyl radical (508) may be used for alkyl radicalgeneration by phenylselenyl group transfer from the alkyl phenyl selenides (510).The resulting radical (511) may then undergo reaction to yield another radical(512) which may be scavenged by reaction with diphenyl diselenide, produced byreaction of anion (509) with oxygen, to yield phenyl selenide (513). The generalityof this catalytic process has been demonstrated by a variety of conversions, for

Photochemistry292

example intramolecular conversions of (514) and (515) to (516) and (517) respect-ively, and by intermolecular reaction of (518) with (519) to yield (520).399 1,3-Diselenyl-substituted allenes (521) and (522) photorearranged to (523) and (524),by a sequence of 1,2-shifts involving biradical and carbene intermediates. Fur-ther irradiation of (523) and (524) yielded isomeric enediynes (525) and (526), viaC—Se bond homolysis, radical coupling and diselenide elimination.400

Photolysis of ‘naphthocarborane’ (527) in benzene containing 1,4-cyclo-hexadiene yielded (528), possibly via the biradical (529). In the presence ofsupercoiled cyclic DNA, (527) caused efficient single strand photocleavage.401 Inthe presence of oxygen, quinone (530) and ketone (531) were formed. In contrastto (527), ‘benzocarborane’ underwent highly efficient regio- and stereo-specific[2�2]-photodimerisation.402 The interaction of singlet excited dibenzoyl-methanatoboron difluoride (532) with unsaturated carbonyl compounds hasbeen investigated and the role of excimers evaluated in the process leading toadducts (533).403

Irradiation of the ion pair (534) resulted in outer-sphere charge transfer withformation of the corresponding radicals (535) and (536). These fragmented andthe resulting butyl radicals dimerised to give octane with a quantum yield of1.5�10�3 at 280 nm.404


5 References

1. E. Block, Phosphorus, Sulfur, Silicon Relat. Elem., 1999, 153—154, 173—192.2. E. Fasani, A. Albini, M. Mella, M. Rampi and F. B. Negra, Int. J. Photoenergy,

1999, 1, 7—11.3. M. Maggini and D. M. Guldi,Mol. Supramol. Photochem., 2000, 6, 149—196.4. D. Dopp, Int. J. Photoenergy, 2001, 3, 49—56.5. A. Pelter, R. T. Pardasani and P. Pardasani, Tetrahedron, 2000, 56, 7339—7369.6. R. Littger, J. Taylor, G. Rudd, A. Newlon, D. Allis, S. Kotiah and J. T. Spencer,

Spec. Publ. R. Soc. Chem., 2000, 253, 67—76.7. S. A. Fleming and J. A. Pincock,Mol. Supramol. Photochem., 1999, 3, 211—281.8. M. Yasuda, T. Yamashita, T. Shiragami andK. Shima,RecentRes.Dev.Photochem.

Photobiol., 1999, 3, 65—76.9. U. C. Yoon and P. S. Mariano, Acc. Chem. Res. 2001, 34, 523—533.10. M. Oelgemoller, EPA Newsl., 2000, 69, 11—23.11. V. Malatesta, J. Hobley and C. Salemi-Delvaux, Mol. Cryst. Liq. Cryst. Sci.

Technol., Sect. A, 2000, 344, 69—76.12. H. G. Heller, K. S. V. Koh, M. Kose and N. G. Rowles, Adv. Colour Sci. Technol.,

2001, 4, 6—11.13. M. M. Krayushkin, Chem.Heterocycl. Compd. (N.Y.), 2001, 37, 15—36.14. M. Irie,Mol. Supramol. Photochem., 2000, 5, 111—141.15. M. Kako and Y. Nakadaira, Bull. Chem. Soc. Jpn., 2000, 73, 2403—2422.16. D. I. Schuster, Carbon, 2000, 38, 1607—1614.17. Y. Wang, J. Meng and T. Matsuura, Trends Heterocycl. Chem., 1999, 6, 21—36.18. Y. Ito,Mol. Supramol. Photochem., 1999, 3, 1—70.19. M. D’Auria,Heterocycles, 2001, 54, 475—496.20. M. D’Auria, Adv.Heterocycl. Chem., 2001, 79, 41—88.21. W. M. Nau, EPA Newsl., 2000, 70, 6—29.22. K. Venkatesan,Mol. Solid State, 1999, 3, 89—131.23. F. Vargas and C. Rivas, Int. J. Photoenergy, 2000, 2, 97—101.24. S. R. L. Everitt and Y. Inoue,Mol. Supramol. Photochem., 1999, 3, 71—130.25. J. R. Scheffer, Can. J. Chem., 2001, 79, 349—357.26. E. J. Shin, J. Photosci., 1999, 6, 61—65.27. E. J. Shin and T. W. Bae, J. Photosci., 1999, 6, 67—70.28. L. Giglio, U.Mazzucato, G.Musumarra and A. Spalletti,Phys.Chem.Chem.Phys.,

2000, 2, 4005—4012.29. G. Bartocci, G. Galiazzo, U. Mazzucato and A. Spalletti, Phys. Chem.Chem. Phys.,

2001, 3, 379—386.30. I. Grabchev and T. Philipova, Dyes Pigments, 2000, 44, 175—180.31. I. Grabchev, J. Photochem. Photobiol. A: Chem., 2000, 135, 41—44.32. I. Grabchev and V. Bojinov, Z.Naturforsch., 2000, 55A, 833—836.33. J. Park, Dyes Pigments, 2000, 46, 155—161.

Photochemistry294

34. K. Kasatani, H. Okamoto and S. Takenaka, ITE Lett. Batt., New Technol. Med.,2000, 1, 946—951.

35. Y. Kawamura, R. Takayama,M. Nishiuchi andM. Tsukayama, Tetrahedron Lett.,2000, 41, 8101—8106.

36. R. Mallavia, R. Sastre, F. Amat-Guerri, J. Photochem. Photobiol. A: Chem., 2001,138, 193—201.

37. D. G. Belov, B. G. Rogachev, L. I. Tkachenko, V. A. Smirnov and S. M. Aldoshin,Russ. Chem. Bull., 2000, 49, 666—668.

38. A. Gaplovsky, J. Donovalova, M. Lacova, R. Mracnova and H. M. El-Shaaer, J.Photochem. Photobiol. A: Chem., 2000, 136, 61—65.

39. T. Stepanenko, L. Lapinski, A. L. Sobolewski, M. J. Nowak and B. Kierdaszuk, J.Phys. Chem. A, 2000, 104, 9459—9466.

40. T. Vreven and K. Morokuma, J. Chem. Phys., 2000, 113, 2969—2975.41. K. Takeshita, N. Hirota andM. Terazima, J.Photochem.Photobiol.A:Chem., 2000,

134, 103—109.42. M.Kojima, T. Takagi and T. Goshima,Mol.Cryst.Liq.Cryst., 2000, 344, 179—184.43. S. Ghosh and A. K. Banthia, Tetrahedron Lett., 2001, 42, 501—503.44. T. Masuda, S. Arai, S. Tamagaki and T. Nagasaki, Tetrahedron Lett., 2000, 41,

2411—2414.45. W. Lee and A. Ueno,Macromol. Rapid Commun., 2001, 22, 448—450.46. A. J. Harvey and A. D. Abell, Tetrahedron, 2000, 56, 9763—9771.47. H. Asanuma, X. Liang, T. Yoshida, A. Yamazawa and M. Komiyama, Angew.

Chem. Int. Ed., 2000, 39, 1316—1318.48. C. Renner, R. Behrendt, S. Sporlein, J. Wachtveitl and L. Moroder, Biopolymers,

2000, 54, 489—500.49. C. Renner, J. Cramer, R. Behrendt and L.Moroder,Biopolymers, 2000, 54, 501—514.50. D. R. Reddy and B. G. Maiya, Chem. Commun., 2001, 117—118.51. A. Honma, T. Kanbara and K. Hasegawa, Mol. Cryst. Liq. Cryst., 2000, 345,

125—130.52. E. Markava, D. Gustina, I. Muzikante, L. Gerca, M. Rutkis and E. Fonavs, Mol.

Cryst. Liq. Cryst., 2001, 355, 381—400.53. J. Zhang, J. K. Whitesell and M. A. Foxe, Chem.Mater., 2001, 13, 2323—2331.54. Y. O. Oh, H. Y. Jung and Y. S. Kang,Mol. Cryst. Liq. Cryst., 2000, 349, 91—94.55. H. Kang, B. M. Lee, J. Yoon and M. Yoon, J. Colloid Interface Sci., 2000, 231,

255—264.56. G. R. Krow, J. Yuan, Y. Fang, M. D. Meyer, D. J. Anderson, J. E. Campbell and P.

J. Carroll, Tetrahedron, 2000, 56, 9227—9232.57. G. R. Krow, Y. B. Lee, W. S. Lester, N. Liu, J. Yuan, J. Duo, S. B. Herzon, Y.

Nguyen and D. Zacharias, J. Org. Chem., 2001, 66, 1805—1810.58. T. Bach, H. Bergmann and K. Harms, Org. Lett., 2001, 3, 601—603.59. A. L. P. Nery, F. H. Quina, P. F. Moreira, Jr., C. E. R. Medeiros, W. J. Baader, K.

Shimizu, L. H. Catalani and E. J. H. Bechara, Photochem. Photobiol., 2001, 73,213—218.

60. E. Martınez, J. C. Estevez, R. J. Estevez and L. Castedo, Tetrahedron, 2001, 57,1981—1986.

61. F. D. Lewis, R. S. Kalgutkar and J.-S. Yang, J. Am. Chem. Soc., 2001, 123,3878—3884.

62. P. Fan, G. Pan, Z. Huang, Y. Ming and M. G. Fan, Mol. Cryst. Liq. Cryst., 2000,345, 33—38.

63. G. Pan, P. Fan, Y. Ming and M. Fan,Mol. Cryst. Liq. Cryst., 2000, 345, 27—32.


64. Z. Sun, R. S. Hosmane and M. Tadros, J.Heterocycl. Chem., 2000, 37, 1439—1441.65. Y. Liang, A. S. Dvornikov and P. M. Rentzpis, J. Mater. Chem., 2000, 10,

2477—2482.66. T. Sagisaka and Y. Yokoyama, Bull. Chem. Soc. Jpn., 2000, 73, 191—196.67. Y. Yokoyama, T. Ohmori, T. Okuyama, Y. Yokoyama and S. Uchida,Mol. Cryst.

Liq. Cryst., 2000, 344, 265—270.68. S. S. Deshmukh and S. Banerjee, Asian J. Chem., 2001, 13, 481—484.69. Y. Yoshioka, M. Usami and K. Yamaguchi, Mol. Cryst. Liq. Cryst., 2000, 345,

81—88.70. M.M. Oliveira, L. M. Carvalho, C.Moustrou, A. Samat, R. Guglielmetti and A. M.

F. Oliveira-Campos,Helv. Chim. Acta, 2001, 83, 1163—1171.71. P. Fan, G. Pan, J. Wei, Y. Ming, A. Zhu, M. G. Fan and W. M. Hung,Mol. Cryst.

Liq. Cryst., 2000, 344, 283—288.72. G.-L. Pan, J.-Q.Wei, P. Fan, A.-P. Zhu, Y.-F.Ming,M.- G. Fan and S. D. Yao,Res.

Chem. Intermed., 2000, 26, 829—838.73. P. Fan, J. Wei, Y. Ming, A. Zhu, Y. Ming, M. G. Fan, W. Wang and S. Yao,Mol.

Cryst. Liq. Cryst., 2000, 344, 289—294.74. H. Gorner, Phys. Chem. Chem. Phys., 2001, 3, 416—423.75. A. K. Chibisov and H. Gorner, Phys. Chem. Chem. Phys., 2001, 3, 424—431.76. J. Takeda, Y. Ikeda, D. Mihara, S. Kurita, A. Sawada and Y. Yokoyama, Mol.

Cryst. Liq. Cryst., 2000, 345, 191—196.77. S. Takeuchi, Y. Ogawa, A. Naito, K. Sudo, N. Yasuoka, H. Akutsu, J.-I. Yamada

and S. Nakatsuji,Mol. Cryst. Liq. Cryst., 2000, 345, 167—172.78. S. Nakatsuji, Y. Ogawa, S. Takeuchi, H. Akutsu, J.-I. Yamada, A. Naito, K. Sudo

and N. Yasuoka, J. Chem. Soc., Perkin Trans. 2, 2000, 1969—1975.79. I. Cascades, S. Constantine, D. Cardin, H. Garcia, A. Gilbert and F. Marquez,

Tetrahedron, 2000, 56, 6951—6956.80. M. Takase and M. Inouye,Mol. Cryst. Liq. Cryst., 2000, 344, 313—318.81. L. de Leon and M. C. Biewer, Tetrahedron Lett., 2000, 41, 3527—3530.82. S. A. Antipin, A. N. Petrukhin, F. E. Gostev, V. S. Marevtsev, A. A. Titov, V. A.

Barachevsky, Y. P. Strokach and O. M. Sarkisov, Chem. Phys. Lett., 2000, 331,378—386.

83. P. Fan, Y. Zhang, A. Zhu, Y. Ming, M. G. Fan, W. Lin, S. Yao and Y. Yokoyama,Mol. Cryst. Liq. Cryst., 2000, 344, 151—156.

84. Y. Zhang, P. Fan and M. G. Fan, Res. Chem. Intermed., 2000, 26, 785—791.85. F. Maurel, A. Samat, R. Guglielmetti and J. Aubard,Mol. Cryst. Liq. Cryst., 2000,

345, 75—80.86. Y. Shigemitsu, H. Jørgen, H. J. Aa. Jensen, H. Koch and J. Oddershede,Mol.Cryst.

Liq. Cryst., 2000, 345, 89—94.87. F. Ortica, D. Levi, P. Brun, R. Guglielmetti, U. Mazzucato and G. Favaro, J.

Photochem. Photobiol. A: Chem., 2001, 138, 123—128.88. S. A. Ahmed, T. Hartmann, V. Huch, H. Durr and A.-M. A. Abdel-Wahab, J. Phys.

Org. Chem., 2000, 13, 539—548.89. R. Fromm, R. Born, H. Durr, J. Kannengießer, H. D. Breuer, P. Valat and J.

Kossanyi, J. Photochem. Photobiol. A: Chem., 2000, 135, 85—89.90. Y. Tan, T. Hartmann, V. Huch, H. Durr, P. Valat, V. Wintgens and J. Kossanyi, J.

Org. Chem., 2001, 66, 1130—1137.91. J. H. Rigby, U. S. M. Maharoof and M. E. Mateo, J. Am. Chem. Soc., 2000, 122,

6624—6628.92. F. Bois, D. Gardette and J.-C. Gramain, Tetrahedron Lett., 2000, 41, 8769—8772.

Photochemistry296

93. H. Hoshina, H. Tsuru, K. Kubo, T. Igarashi and T. Sakurai,Heterocycles, 2000, 53,2261—2274.

94. K. Maekawa, T. Igarashi, K. Kubo and T. Sakurai, Tetrahedron, 2001, 57,5515—5526.

95. D. Sur, P. Purkayastha and N. Chattopadhyay, J. Photochem. Photobiol.A: Chem.,2000, 134, 17—21.

96. M. Chakrabarty, A. Batabyal and S. Khasnobis, Synth. Commun., 2000, 30,3651—3668.

97. M. Schmittel, D. Rodrıguez and J.-P. Steffen, Angew. Chem. Int. Ed., 2000, 39,2152—2155.

98. M. Schmittel, D. Rodrıguez and J.-P. Steffen, Molecules, 2000, 5, 1372—1378(http://www.mdpi.org/molecules/list00.htm).

99. P. Wessig, J. Schwarz, U. Lindemann and M. C. Holthausen, Synthesis, 2001,1258—1262.

100. P. Wessig, U. Lindemann and J. Schwarz, J. Inf. Recording., 2000, 25, 65—68.101. S. Thiering, C. E. Sowa and J. Thiem, J. Chem. Soc., PerkinTrans. 1, 2001, 801—806.102. A. G. Griesbeck, M. Oelgemoller and J. Lex, J. Org. Chem., 2000, 65, 9025—9032.103. U. C. Yoon, S. W. Oh, J. H. Lee, J. H. Park, K. T. Kang and P. S. Mariano, J. Org.

Chem., 2001, 66, 939—943.104. M. Sakamoto, N. Sekine, H. Miyoshi, T. Mino and T. Fujita, J. Am. Chem. Soc.,

2000, 122, 10210—10211.105. D. Laurenti, C. Santelli-Rouvier, G. Pepe and M. Santelli, J. Org. Chem., 2000, 65,

6418—6422.106. T. Bach and H. Bergmann, J. Am. Chem. Soc., 2000, 122, 11525—11526.107. T. Bach, H. Bergmann and K. Harms, Angew. Chem. Int. Ed., 2000, 39, 2302—2304.108. X. Cai, V. Chang, C. Chen, H.-J. Kim and P. S. Mariano, Tetrahedron Lett., 2000,

41, 9445—9449.109. X. L.M. Despinoy and H. McNab, ARKIVOC, 2000, 1, 252—258.110. Y. Ito, S. Horie and Y. Shindo, Org. Lett., 2001, 3, 2411—2413.111. A. Kugelberg, D. Dopp and H. Gorner, J. Inf. Recording., 2000, 25, 187—194.112. S. Neubauer, A. Blecking, D. Dopp and G. Henkel, J. Inf. Recording., 2000, 25,

195—201.113. H. R.Memarian,M.Nasr-Esfahani andD.Dopp,NewJ.Chem., 2001, 25, 476—478.114. M. Sakamoto, A. Kinbara, T. Yagi, T. Mino, K. Yamaguchi and T. Fujita, Chem.

Commun., 2000, 1201—1202.115. A. Lalitha, K. Pitchumani, C. Srinivasan, J. Photochem. Photobiol. A: Chem., 2000,

134, 193—197.116. Y. Inaki, E. Mochizuki, N. Yasui, M. Miyata and Y. Kai, J. Photopolym. Sci.

Technol., 2000, 13, 177—182.117. H. Hosomi, Y. Ito and S. Ohba, Acta Crystallogr., 2000, B56, 682—689.118. K. Fujimoto, S. Matsuda, N. Ogawa, M. Hayashi and I. Saito, Tetrahedron Lett.,

2000, 41, 6451—6454.119. K. Fujimoto, N. Ogawa, M. Hayashi, S. Matsuda and I. Saito, Tetrahedron Lett.,

2000, 41, 9437—9440.120. F. Nakanishi, K. Honda, M. Yoshida and N. Feeder,Mol. Cryst. Liq. Cryst., 2001,

356, 15—22.121. Y. Ito, H. Hosomi and S. Ohba, Tetrahedron, 2000, 56, 6833—6844.122. T. Obata, T. Shimo,M. Yasutake, T. Shinmyozu,M. Kawaminami, R. Yoshida and

K. Somekawa, Tetrahedron, 2001, 57, 1531—1541.


123. B. Hatano, S.-Y. Hirano, T. Yanagihara, S. Toyota and F. Toda. Synthesis, 2001,1181—1184.

124. C. van Wolven, D. Dopp and M. A. Fischer, J. Inf. Recording., 2000, 25, 209—214.125. T. Bach, H. Bergmann, H. Brummerhop, W. Lewis and K. Harms, Chem. Eur. J.,

2001, 7, 4512—4521.126. A. Joseph and D. E. Falvey, J. Am. Chem. Soc., 2001, 123, 3145—3146.127. J. Xue, Y. Zhang, T. Wu, H.-K. Fun and J.-H. Xu, J. Chem. Soc., Perkin Trans. 1,

2001, 183—191.128. J. Xue, X.-L. Wang, H. K. Fun and J.-H. Xu, Org. Lett., 2000, 2, 2583—2586.129. Y. Zhang, S.-P. Qian, H.-K. Fun and J.-H. Xu, Tetrahedron Lett., 2000, 41,

8141—8145.130. U. Neumann, J. Weber and D. Dopp, J. Inf. Recording., 2000, 25, 203—208.131. K. Ishii, Y. Shimada, S. Sugiyama andM.Noji, J. Chem. Soc.,PerkinTrans. 1, 2000,

3022—3024.132. T. Bach, H. Bergmann and K. Harms, Org. Lett., 2001, 3, 601—603.133. (a) H. Ihmels, B. Engels, K. Faulhaber and C. Lennartz, Chem. Eur. J., 2000, 6,

2854—2864; (b) H. Ihmels, D. Leusser, M. Pfeiffer and D. Stalke, Mol. Cryst. Liq.Cryst., 2001, 356, 433—441.

134. K. F. McGee Jr., T. H. Al-Tel and S. McN. Sieburth, Synthesis, 2001, 1185—1196.135. T. Ojima, H. Akutsu, J.-I. Yamada and S. Nakatsuji, Chem. Lett., 2000, 918—919.136. T. Ojima, H. Akutsu, J.-I. Yamada, S. Nakatsuji, Polyhedron, 2001, 20, 1335—1338.137. S. Kohmoto, H. Masu, C. Tatsuno, K. Kishikawa, M. Yamamoto and K.

Yamaguchi, J. Chem. Soc., Perkin Trans. 1, 2000, 4464—4468.138. S. Kohmoto, T. Kobayashi, J. Minami, X. Ying, K. Yamaguchi, T. Karatsu, A.

Kitamura, K. Kishikawa and M. Yamamoto, J. Org. Chem., 2001, 66, 66—73.139. H. Ihmels, D. Leusser, M. Pfeiffer and D. Stalke, Tetrahedron, 2000, 56, 6867—6875.140. L.-W. Guo, X. Gao, D.-W. Zhang, S.-H. Wu, H.-M.Wu and Y.-J. Li, J.Org.Chem.,

2000, 65, 3804—3810.141. J. Xue, L. Zhu, H.-K. Fun and J.-H. Xu, Tetrahedron Lett., 2000, 41, 8553—8557.142. Z.-Y. Wang, T.-Y. Jian and Q.-H. Chen, Chin. J. Chem., 2001, 19, 177—183.143. S. Marinkovic and N. Hoffmann, Chem. Commun., 2001, 1576—1578.144. S. Bertrand, N. Hoffmann, S. Humbel and J. P. Pete, J. Org. Chem., 2001, 66,

8690—8703.145. A. Matsumoto, S. Nagahama and T. Odani, J. Am. Chem. Soc., 2000, 122,

9109—9119.146. J. Zhao, B. Zhao,W. Xu, J. Liu, Z.Wang and Y. Li, Spectrosc. Spect.Anal., 2001, 21,

98—100.147. D. Guha, A. Mandal, A. Koll, A. Filarowski and S. Mukherjee, Spectrochim. Acta,

Part A, 2000, 56, 2669—2677.148. S. Sakagami, T. Koga and A. Takase, Liq. Cryst., 2000, 27, 1551—1554.149. M. I. Knyazhansky, A. V.Metelitsa,M. E. Kletskii, A. A.Millov and S. O. Besugliy,

J.Mol. Struct., 2000, 526, 65—79.150. M. Z. Zgierski and A. Grabowska, J. Chem. Phys., 2000, 113, 7845—7852.151. M. Z. Zgierski, J. Chem. Phys., 2001, 115, 8351—8358152. E. J. A. de Bekker, A. Pugzlys and C. A. G. O. Varma, J. Phys. Chem. A, 2001, 105,

399—409.153. S. Santra, G. Krishnamoorthy and S. K. Dogra, Chem. Phys. Lett., 2000, 327,

230—237.154. K. Tanaka, M. Deguchi, S. Yamaguchi, K. Yamada and S. Iwata, J. Heterocycl.

Chem., 2001, 38, 131—136.

Photochemistry298

155. A. O. Doroshenko, E. A. Posokhov, A. A. Verezubova and L.M. Ptyagina, J. Phys.Org. Chem., 2000, 13, 253—265.

156. A. O. Doroshenko, E. A. Posokhov and V. M. Shershukov, Russ. J. Gen. Chem.,2000, 70, 573—578.

157. A. D. Doroshenko and E. A. Posokhov,High Energy Chem., 2000, 34, 93—100.158. P.-T. Chou, Y.-C. Chen, W.-S. Yu, Y.-H. Chou, C.-Y. Wei and Y.-M. Cheng, J.

Phys. Chem. A, 2001, 105, 1731—1740.159. L. Kaczmarek, P. Borowicz and A. Grabowska, J. Photochem. Photobiol.A:Chem.,

2001, 138, 159—166.160. M. Gil, J. Jasny, E. Vogel and J. Waluk, Chem. Phys. Lett., 2000, 323, 534—541.161. S.-L. Wang and T.-I. Ho, Spectrochim. Acta, Part A, 2001, 57, 361—366.162. C. Carmona, M. Galan, G. Angula, M. A. Mun oz, P. Guardado and M. Balon,

Phys. Chem. Chem. Phys., 2000, 2, 5076—5083.163. J. C. Penedo, M. Mosquera and F. Rodrıguez-Prieto, J. Phys. Chem. A, 2000, 104,

7429—7441.164. R. Karpicz, V. Gulbinas and A. Undzenas, J. Chin. Chem. Soc., 2000, 47, 589—595.165. R. Karpicz, V. Gulbinas, A. Stanishauskaite, A. Undzenas, Chem. Phys., 2001, 269,

357—366.166. Y. Ikeda, J. Takeda and S. Kurita,Mol. Cryst. Liq. Cryst., 2000, 345, 197—202.167. X.-C. Tang, D.-Z. Jia, K. Liang, X.-G. Zhang, X. Xia and Z.-Y. Zhou, J. Photochem.

Photobiol. A: Chem., 2000, 134, 23—29.168. P.-T. Chou, G.-R. Wu, C.-Y. Wei, C.-C. Cheng, C.-P. Chang and F.-T. Hung, J.

Phys. Chem. B, 2000, 104, 7818—7829.169. J. Catalan and M. Kasha, J. Phys. Chem. A, 2000, 104, 10812—10820.170. A. Douhal, M. Moreno and J. M. Lluch, Chem. Phys. Lett., 2000, 324, 75—80.171. A. Douhal, M. Moreno and J. M. Lluch, Chem. Phys. Lett., 2000, 324, 81—87..172. M. A. El-Kemary, H. S. El-Gezawy, H. Y. El-Baradie and R. M. Issa, Chem. Phys.,

2001, 265, 233—242.173. R. Yang and S. G. Schulman, J. Fluorescence, 2001, 11, 109—112.174. X. Allonas, J. Lalevee, J.-P. Fouassier,H. Tachi,M. Shirai andM. Tsunooka,Chem.

Lett., 2000, 1090—1091.175. A. J. McCarroll and J. C. Walton, J. Chem. Soc., Perkin Trans. 2, 2000, 1868—1875.176. A. J. McCarroll and J. C. Walton, J. Chem. Soc., Perkin Trans. 2, 2000, 2399—2409.177. D. Puchowicz, J. Adamus and J. Gebicki, J. Chem. Soc., Perkin Trans. 2, 2000,

1942—1945.178. J. Hartung, R. Kneuer and K. Spehar, Chem. Commun., 2001, 799—800.179. J. Hartung, T. Gottwald and R. Kneuer, Synlett, 2001, 749—752.180. L. D. Luca, G. Giacomelli, G. Porcu and M. Taddei, Org. Lett., 2001, 3, 855—857.181. Y. Saitoh, M. Kaneko, K. Segawa, H. Itoh and H. Sakuragi, Chem. Lett., 2001,

82—83.182. B. C. Bales, J. H. Horner, X. Huang, M. Newcomb, D. Crich andM.M. Greenberg,

J. Am. Chem. Soc., 2001, 123, 3623—3629.183. A. Srinivasan,N. Kebede, J. E. Saavedra, A. V. Nikolaitchik, D. A. Brady, E. Yourd,

K. M. Davies, L. K. Keefer and J. P. Toscano, J. Am. Chem. Soc., 2001, 123,5465—5472.

184. I. V. Vlasyuk, V. A. Bagryansky, N. P. Gritsan, Y. N. Molin, A. Y. Makarov, Y. V.Gatilov, V. V. Shcherbukhin and A. V. Zibarev, Phys. Chem. Chem. Phys., 2001, 3,409—415.

185. J. Sworakowski, S. Nespu� rek, J. Lipinski, A. Lewanowicz and E. SY liwinska, Mol.Cryst. Liq. Cryst., 2001, 356, 163—173.


186. H. Inui and S. Murata, Chem. Commun., 2001, 1036—1037.187. J. von Sonntag and W. Knolle, J. Photochem. Photobiol. A: Chem., 2000, 136,

133—139.188. M. B. Maquieira, A. B. Pen en ory and R. A. Rossi, Molecules, 2000, 5, 457—458

(http://www.mdpi.org/molecules/list00.htm).189. A. G. Griesbeck, M, Oelgemoller and J. Lex, Synlett, 2000, 1455—1457.190. A. Bartoschek, A. G. Griesbeck and M. Oelgemoller, J. Inf. Recording., 2000, 25,

119—126.191. D. J. Yoo, E. Y. Kim, M. Oelgemoller and S. C. Shim, Heterocycles, 2001, 54,

1049—1055.192. A. G. Griesbeck, W. Kramer and J. Lex, Angew. Chem. Int. Ed., 2001, 40, 577—579.193. W. Kramer and A. G. Griesbeck, J. Inf. Recording., 2000, 25, 235—238.194. A. G. Griesbeck, W. Kramer, A. Bartoschek and H. Schmickler,Org. Lett., 2001, 3,

537—539.195. A. G. Griesbeck,M. S. Gudipati, J. Hirt, J. Lex,M. Oelgemoller, H. Schmickler and

F. Schouren, J. Org. Chem., 2000, 65, 7151—7157.196. J. A. Heerklotz, C. Fu, A. Linden and M. Hesse, Helv. Chim. Acta, 2000, 83,

1809—1824.197. E. Fasani, M. Mella, S. Monti and A. Albini, Eur. J. Org. Chem., 2001, 391—397.198. S. Monti, S. Sortino, E. Fasani and A. Albini, Chem. Eur. J., 2001, 7, 2185—2196.199. S. Sortino, G. De Guidi and S. Giuffrida,New J. Chem., 2001, 25, 197—199.200. M. J. Lovdahl and S. R. Priebe, J. Pharm. Biomed. Anal., 2000, 23, 521—534201. M. Caselli, G. Ponterini and M. Vignali, J. Photochem. Photobiol. A: Chem., 2001,

138, 129—137.202. T. Poiger, H.-R. Buser and M. D. Muller, Environ. Toxicol. Chem., 2001, 20,

256—263.203. H. Lu, P. S. Mariano and Y.-F. Lam, Tetrahedron Lett., 2001, 42, 4755—4757.204. R. Alcazar, P. Ramırez, R. Vicente, M. J. Manchen o, M. A. Sierra and M. Gomez-

Gallego,Heterocycles, 2001, 55, 511—521.205. S. Buscemi, A. Pace and N. Vivona, Tetrahedron Lett., 2000, 41, 7977—7981.206. S. Fukuzumi,M. Fujita, S. Noura, K. Ohkubo, T. Suenobu, Y. Araki and O. Ito, J.

Phys. Chem. A, 2001, 105, 1857—1868.207. J. A. Finke, R. Huisgen and R. Temme,Helv. Chim. Acta, 2000, 83, 3333—3343.208. D. Margetic, D. N. Butler and R. N. Warrener, Aust. J. Chem., 2000, 53, 959—963.209. C.-H. Chou, R. K. Peddinti and C.-C. Liao,Heterocycles, 2001, 54, 61—64.210. M. Cox, F. Heidarizadeh and R. H. Prager, Aust. J. Chem., 2000, 53, 665—671.211. M. Cox, R. H. Prager and D. M. Riessen, ARKIVOC, 2001, 2, 2—16.212. H. Koshima,Mol. Cryst. Liq. Cryst., 2001, 356, 483—486.213. K. Saito and Y. Emoto,Heterocycles, 2001, 54, 567—570.214. D. Dopp, W. A. F. Youssef, A. Dittmann, A. M. Kaddah, A. A. Shalaby and Y. M.

Naguib, J. Inf. Recording., 2000, 25, 57—63.215. H. Gorner, D. Dopp and A. Dittmann, J. Chem. Soc., Perkin Trans. 2, 2000,

1723—1733.216. H.S. Yathirajan, P. Nagendra, K. N. Mohana, K. M. Lokanathrai, K. S. Rangappa

and A. S. Ananda Murthy, Indian J. Chem., 2000, 39A, 1218—1221.217. (a) P. J. Campos, J. Arranz andM. A. Rodrıguez,Tetrahedron, 2000, 56, 7285—7289;

(b) A. Padwa, W. Bergmark and D. Pashayan, J. Am. Chem. Soc., 1969, 91,2653—2660..

218. M. Z. Jin, L. Yang, L. M. Wu, Y. C. Liu and Z. L. Liu, Chin. Chem. Lett., 2001,307—308.

Photochemistry300

219. Y. Fukai, T.Miyazawa,M.Kojoh, T. Takabatake andM.Hasegawa, J.Heterocycl.Chem., 2001, 38, 531—534.

220. G. Cocquet, P. Rool and C. Ferroud, Tetrahedron Lett., 2001, 42, 839—841.221. J. P. Pellois, W. Wang and X. Gao, J. Comb. Chem., 2000, 2, 355—360.222. F. Ortica, C. Coenjarts, J. C. Scaiano, H. Liu, G. Pohlers and J. F. Cameron,Chem.

Mater., 2001, 13, 2297—2304.223. C. Coenjarts, F. Ortica, J. Cameron,G. Pohlers, A. Zampini, D. Desilets, H. Liu and

J. C. Scaiano, Chem.Mater., 2001, 13, 2305—2312.224. C. Selvaraju, A. Sivakumar and P. Ramamurthy, J. Photochem. Photobiol. A:

Chem., 2001, 138, 213—226.225. H. Tachi, M. Shirai and M. Tsunooka, J. Photopolym. Sci. Technol., 2000, 13,

153—156.226. H. Tachi, T. Yamamoto,M. Shirai andM. Tsunooka, J. Polym. Sci.:Part A: Polym.

Chem., 2001, 39, 1329—1341.227. M. Tsunooka, H. Tachi, T. Yamamoto, K. Akitomo and M. Shirai, J. Photopolym.

Sci. Technol., 2001, 14, 153—154.228. H. Nishino, A. Kosaka, G. A. Hembury, H. Shitomi, H. Onuki and Y. Inuoe, Org.

Lett., 2001, 3, 921—924.229. S. Ikeda, S. Murata, K. Ishii and H. Hamaguchi, Bull. Chem. Soc. Jpn., 2000, 73,

2783—2792.230. M. Mulcahy, J. G. McInerney, D. N. Nikogosyan and H. G rner, Biol. Chem., 381,

1259—1262.231. A. Buranaprapuk, C. V. Kumar, S. Jockusch andN. J. Turro,Tetrahedron, 2000, 56,

7019—7025.232. H.-R. Shen, J. D. Spikes, C. J. Smith and J. Kopecek, J. Photochem. Photobiol. A:

Chem., 2000, 133, 115—122.233. T. Wada, N. Sugahara, M. Kawano and Y. Inoue, Chem. Lett., 2000, 1174—1175.234. J. Geimer, K. Hildenbrand, S. Naumov and D. Beckert, Phys. Chem. Chem. Phys.,

2000, 2, 4199—4206.235. C.-Y. Lu, S.-D. Yao, N.-Y. Lin, Chem. Phys. Lett., 2000, 331, 389—396.236. M.Kotera, Y. Roupioz, E. Defrancq, A.-G. Bourdat, J. Garcia, C. Coulombeau and

J. Lhomme, Chem. Eur. J., 2000, 6, 4163—4169.237. M. C. Pirrung, X. Zhao and S. V. Harris, J. Org. Chem., 2001, 66, 2067—2071.238. P. Berroy, M. L. Viriot and M. C. Carre, Sensors Actuators B, 2001, 74, 186—

189.239. K. S. Kumar, M. Roice and V. N. R. Pillai, Tetrahedron, 2001, 57, 3151—3158.240. M. Rinnova, M. Novakova, V. Kasicka and J. Jiracek, J. Peptide Sci., 2000, 6,

355—365.241. G. Papageorgiou and J. E. T. Corrie, Tetrahedron, 2000, 56, 8197—8205.242. K. Schaper, D. Dommaschke, S. Globisch and S. A. Madani-Mobarekeh, J. Inf.

Recording., 2000, 25, 339—354.243. B. Henkel and E. Bayer, J. Peptide Sc., 2001, 7, 152—156.244. F. Glarner, B. Acar, I. Etter, T. Damiano, E. A. Acar, G. Bernardinelli and U.

Burger, Tetrahedron, 2000, 56, 4311—4316.245. T. Nishio, H. Asai and T. Miyazaki,Helv. Chim. Acta, 2000, 83, 1475—1483.246. Y.-T. Park, C.-H. Jung, M.-S. Kim and K.-W. Kim, J. Org. Chem., 2001, 66,

2197—2206.247. A. M. Mayouf and Y.-T. Park, J. Photosci., 2000, 7, 5—8.248. C. Kan, C. M. Long, M. Paul, C. M. Ring, S. E. Tully and C. M. Rojas, Org. Lett.,

2001, 3, 381—384.


249. S. Shuto, K. Haramuishi, M. Fukuoka and A. Mutsuda, J. Chem. Soc., PerkinTrans. 1, 2000, 3603—3609.

250. M. Tsuji, K. Higashiyama, T. Yamauchi, H. Kubo and S. Ohmiya, Heterocycles,2001, 54, 1027—1032.

251. K. Ohkura, K.-I. Nishijima, S. Uchiyama, A. Sakushima and K.-I. Seki, Chem.Pharm. Bull., 2001, 49, 384—390.

252. K. Ohkura, K.-I. Nishijima and K.-I. Seki,Heterocycles, 2001, 54, 65—68.253. K. Takagi, A. Mizuno, H. Iwamoto, M. Oota, K. Shirai and M. Matsuoka. Dyes

Pigments, 2000, 45, 201—208.254. A. Lalitha, K. Pitchumani and C. Srinivasan, J. Mol. Catal. A: Chem., 2000, 160,

429—435.255. M. Nanasawa, T. Tomoda and M. Hirai, Mol. Cryst. Liq. Cryst., 2000, 344,

163—168.256. R. A. Abramovitch, J. M. Beckert, H. H. Gibson Jr., A. Belcher, G. Hundt, T. Sierra,

S. Olivella, W. T. Pennington and A. Sole, J. Org. Chem., 2001, 66, 1242—1251.257. S. Srivastava, P. H. Ruane, J. P. Toscano, M. B. Sullivan, C. J. Cramer, D.

Chiapperino, E. C. Reed andD. E. Falvey, J.Am.Chem. Soc., 2000, 122, 8271—8278.258. W. Yao and X. Qian, Dyes Pigments, 2001, 48, 43—47.259. T. P. Le, J. E. Rogers and L. A. Kelly, J. Phys. Chem. A, 2000, 104, 6778—6785.260. S. Alp, S. Erten, C. Karapire, B. Koz, A. O. Doroshenko and S. Icli, J. Photochem.

Photobiol. A: Chem., 2000, 135, 103—110.261. A. Rungta, G. Zheng, J. R.Missert,W. R. Potter, T. J. Dougherty andR. K. Pandey,

Bioorg.Med. Chem. Lett., 2000, 10, 1463—1466.262. K. Kordatos, T. Da Ros,M. Prato, S. Leach, E. J. Land and R. V. Bensasson,Chem.

Phys. Lett., 2001, 334, 221—228.263. V. Brezova, M. Gembicka and A. Stasko, Fullerene Sci. Tech., 2000, 8, 225—248.264. B. Jing, D. Zhang and D. Zhu, Tetrahedron Lett., 2000, 41, 8559—8563.265. J. L. Bahr, D. Kuciauskas, P. A. Liddell, A. L. Moore, T. A. Moore and D. Gust,

Photochem. Photobiol., 2000, 72, 598—611.266. R. Czerwieniec, J. Herbich, A. Kapturkiewicz and J. Nowacki, Chem. Phys. Lett.,

2000, 325, 589—598.267. G. P. Wiederrecht, W. A. Svec, M. R. Wasielewski, T. Galini and H. Levanon, J.

Am. Chem. Soc., 2000, 122, 9715—9722.268. A. J. Myles and N. R. Branda, J. Am. Chem. Soc., 2001, 123, 177—178.269. X. Poteau, A. I. Brown, R. G. Brown, C. Holmes and D. Matthew, Dyes Pigments,

2000, 44, 91—105.270. L. Boilet, G. Burdzinski, G. Buntinx, G. Lefumeux and O. Poizat, J. Phys.Chem.A,

2001, 105, 10271—10277.271. T. Nakayam, R. Yamauchi, H. Shin andK.Hamanoue, J.Phys.Chem.A, 2000, 104,

9698—9704.272. E. Shimada, M. Nagano, M. Iwahashi, Y. Mori, Y. Sakaguchi and H. Hayashi, J.

Phys. Chem. A, 2001, 105, 2997—3007.273. U. Pischel and W. M. Nau, J. Phys. Org. Chem., 2000, 13, 640—647.274. U. Pishcel, X. Allonas and W. M. Nau, J. Inf. Recording., 2000, 25, 311—321.275. G. Bucher, H. Wandel and W. Sander, J. Phys. Org. Chem., 2001, 14, 197—200.276. S. Nad and H. Pal, J. Photochem. Photobiol. A: Chem., 2000, 134, 9—15.277. S. M. Bonesi and R. Erra-Balsells, J. Chem. Soc., Perkin Trans. 2, 2000, 1583—1595.278. A. Rzeska, K. Stachowiak, J. Malicka, L. Lankiewicz and W.Wiczk, J. Photochem.

Photobiol. A: Chem., 2000, 133, 33—38.279. H. Traore, M. Saunders and S. Blasiman, Aust. J. Chem., 2000, 53, 951—957.

Photochemistry302

280. M. A. EI-Kemary, J. Photochem. Photobiol. A: Chem., 2000, 137, 9—14.281. P. Borowicz, J. Herbich, A. Kapturkiewicz, R. Anulewicz-Ostrowska, J. Nowacki

and G. Grampp, Phys. Chem. Chem. Phys., 2000, 2, 4275—4280.282. I. Petkova, P. Nikolov and V. Dryanska, J. Photochem. Photobiol. A: Chem., 2000,

133, 21—25.283. M.C. Castex, C. Olivero, G. Pichler, D. Ades, E. Cloutet and A. Siove, Synth.Met.,

2001, 122, 59—61.284. Z. Chen, Z. Zhang, X. Yuan, L. Song andF. Bai, Spectrochim.Acta,Part A, 2001, 57,

499—503.285. B. M. Vittimberga and D. Sears, J. Heterocycl. Chem., 2001, 38, 285—291.286. V. S. Chirvony, A. vanHoek, V. A. Galievsky, I. V. Sazanovich, T. J. Schaafsma and

D. Holten, J. Phys. Chem. B, 2000, 104, 9909—9917.287. D. Sur, P. Purkayastha and N. Chattopadhyay, Indian J. Chem., 2000, 39A,

389—391.288. S. A. El-Daly and T. A. Fayed, J.Photochem.Photobiol.A:Chem., 2000, 137, 15—19.289. S. Icli, S. Demic, B. Dindar, A. O. Doroshenko and C. Timur, J. Photochem.

Photobiol. A: Chem., 2000, 136, 15—24.290. C. Bornemann and M. Klessinger, Chem. Phys., 2000, 259, 263—271.291. A. B. J. Parusel, Phys. Chem. Chem. Phys., 2000, 2, 5545—5552.292. P.S. Kushwah and P.C. Mishra, J. Photochem. Photobiol. A: Chem., 2000, 137,

79—86.293. R. Ballardini, V. Balzani, J. Becher, A. D. Fabio,M. T. Gandolfi, G.Mattersteig,M.

B. Nielsen, F. M. Raymo, S. J. Rowan, J. F. Stoddart, A. J. P. White and D. J.Williams, J. Org. Chem., 2000, 65, 4120—4126.

294. K. Eggers, T. M. Fyles and P. J. Montoya-Pelaez, J. Org. Chem., 2001, 66,2966—2977.

295. Y. Wan, A. Kurchan and A. Kutateladze, J. Org. Chem., 2001, 66, 1894—1899.296. D. Schwebel, M. Soltau and P. Margaretha, Synthesis, 2001, 1111—1113.297. D. Schwebel and P. Margaretha,Helv. Chim. Acta, 2000, 83, 1168—1174.298. M. D’Auria, L. Emanuele, G. Mauriello and R. Racioppi, J. Photochem. Photobiol.

A: Chem., 2000, 134, 147—154.299. M. A. Kinder, J. Kopf and P. Margaretha, Tetrahedron, 2000, 56, 6763—6767.300. K. Tanaka, E. Mochizuki, N. Yasui, Y. Kai, I. Miyahara, K. Hirotsu and F. Toda,

Tetrahedron, 2000, 56, 6853—6865.301. K. Uchida, E. Tsuchida, S. Nakamura, S. Kobatake and M. Irie, Mol. Cryst. Liq.

Cryst., 2000, 345, 9—14.302. S. Kobatake, K. Uchida, E. Tsuchida and M. Irie, Chem. Lett., 2000, 1340—1341.303. M. Yamada, M. Takeshita andM. Irie,Mol. Cryst. Liq. Cryst., 2000, 345, 107—112.304. S. Kobatake, T. Yamada and M. Irie,Mol. Cryst. Liq. Cryst., 2000, 344, 185—190.305. K. Uchida, T. Matsuoka, S. Kobatake, T. Yamaguchi and M. Irie, Tetrahedron,

2001, 57, 4559—4565.306. H. Utsumi, D. Nagahama, H. Nakano and Y. Shirota, J. Mater. Chem., 2000, 10,

2436—2437.307. M. -S. Kim, T. Kawai and M. Irie,Mol. Cryst. Liq. Cryst., 2000, 345, 251—255.308. M. -S. Kim, T. Kawai and M. Irie, Chem. Lett., 2000, 1188—1189.309. T. Yamada, S. Kobatake and M. Irie, Bull. Chem. Soc. Jpn., 2000, 73, 2179—2184.310. S. Kobatake, K. Shibata, K. Uchida and M. Irie, J. Am. Chem. Soc., 2000, 122,

12135—12141.311. T. Yamada, S. Kobatake, K. Muto and M. Irie, J. Am. Chem. Soc., 2000, 122,

1589—1592.


312. T. Kodani, K. Matsuda, T. Yamada, S. Kobatake and M. Irie, J. Am. Chem. Soc.,2000, 122, 9631—9637.

313. T. Kodani, K. Matsuda, T. Yamada andM. Irie,Mol. Cryst. Liq. Cryst., 2000, 344,307—312.

314. M. Irie, T. Lifka, S. Kobatake and N. Kato, J. Am. Chem. Soc., 2000, 122,4871—4876.

315. M. Irie, S. Kobatake and M. Horichi, Science, 2001, 291, 1769—1772.316. S. Irie and M. Irie,Mol. Cryst. Liq. Cryst., 2000, 345, 179—184.317. S. Irie and M. Irie, Bull. Chem. Soc. Jpn., 2000, 73, 2385—2388.318. A. Peters and N. R. Branda, Adv.Mater. Opt. Electron., 2000, 10, 245—249.319. T. Kawai, T. Sasaki and M. Irie, Chem. Commun., 2001, 711—712.320. J. Ern, A. T. Bens, H.-D. Martin, S. Mukamel, S. Tretiak, K. Tsyganenko, K.

Kuldova, H. P. Trommsdorff and C. Kryschi, J. Phys. Chem. A, 2001, 105,1741—1749.

321. T. B. Norsten and N. R. Branda, J. Am. Chem. Soc., 2001, 123, 1784—1785.322. K. Kasatani, S. Kambe andM. Irie,Mol. Cryst. Liq. Cryst., 2000, 345, 45—50.323. N. Ohtaka, Y. Hase, K. Uchida,M. Irie andN. Tamai,Mol.Cryst.Liq.Cryst., 2000,

344, 83—88.324. K. Kuldova, K. Tsyganenko, A. Corval, H. P. Trommsdorff, A. T. Bens and C.

Kryschi, Synth.Met., 2001, 122, 163—166.325. K. Matsuda andM. Irie, Chem. Lett., 2000, 16—17.326. K. Matsuda andM. Irie,Mol. Cryst. Liq. Cryst., 2000, 345, 155—160.327. K. Matsuda andM. Irie, J. Am. Chem. Soc., 2000, 122, 8309—8310.328. K. Matsuda andM. Irie, J. Am. Chem. Soc., 2000, 122, 7195—7201.329. K. Matsuda andM. Irie, Polyhedron, 2001, 20, 1391—1395.330. K. Matsuda andM. Irie, Chem. Eur. J., 2001, 6, 3466—3473.331. K. Matsuda andM. Irie, J. Am. Chem. Soc., 2001, 123, 9896—9897.332. Kazuo Kasatani, ITE Lett. Batt.New Tech.Med., 2001, 2, 220—224.333. K. Higashiguchi, K. Matsuda, T. Yamada, T. Kawai andM. Irie,Chem. Lett., 2000,

1358—1359.334. K. Higashiguchi, K.Matsuda, S. Kobatake, T. Yamada, T. Kawai andM. Irie,Bull.

Chem. Soc. Jpn., 2000, 73, 2389—2394.335. T. Mrozek, H. Gorner and J. Daub, Chem. Eur. J., 2001, 7, 1028—1040.336. M. Badland, A. Cleeves, H. G. Heller, D. S. Hughes and M. B. Hursthouse, Chem.

Commun., 2000, 1567—1568.337. Y. Yokoyama, H. Nakata, K. Sugama and Y. Yokoyama, Mol. Cryst. Liq. Cryst.,

2000, 344, 253—258.338. N. Rebiere, C. Moustrou, M. Meyer, A. Samat, R. Guglielmetti, J.-C. Micheau and

J. Aubard, J. Phys. Org. Chem., 2000, 13, 523—530.339. M. Tanaka, K. Kamada and K. Kimura, Mol. Cryst. Liq. Cryst., 2000, 344,

319—324.340. M.-J. R. P. Queiroz, R. Dubest, J. Aubard, R. Faure, R. Guglielmetti, Dyes Pig-

ments, 2000, 47, 219—229.341. C. D. Gabbutt, J. D. Hepworth, B. M. Heron, S. M. Partington, Dyes Pigments,

2000, 47, 73—77.342. S. Coen, C. Moustrou, M. Frigoli, M. Julliard, A. Samat and R. Guglielmetti, J.

Photochem. Photobiol. A: Chem., 2001, 139, 1—4.343. M. Frigoli, C. Moustrou, A. Samat, R. Guglielmetti, R. Dubest and J. Aubard,Mol.

Cryst. Liq. Cryst., 2000, 344, 139—144.344. M. Frigoli, C. Moustrou, A. Samat and R. Guglielmetti,Helv.Chim.Acta, 2000, 83,

3043—3052.

Photochemistry304

345. K. Sato, T. Yamagishi and S. Arai, J.Heterocycl. Chem., 2000, 37, 1009—1014.346. M. Sakamoto, M. Takahashi, W. Arai, T. Mino, K. Yamaguchi, S. Watanabe and

T. Fujita, Tetrahedron, 2000, 56, 6795—6804.347. M. Taghizadeh and H. Pirelahi, J. Photochem. Photobiol. A: Chem., 2001, 139,

45—51.348. A. Mouradzadegun and H. Pirelahi, Phosphorus, Sulfur Silicon Relat. Elem., 2000,

157, 193—199.349. A. Mouradzadegun and H. Pirelahi, Phosphorus, Sulfur Silicon Relat. Elem., 2000,

165, 149—154.350. A. Mouradzadegun and H. Pirelahi, J. Photochem. Photobiol. A: Chem., 2001, 138,

203—205.351. A.M. Gaber, M.M. Aly and A. M. Fahmy, Phosphorus, Sulfur Silicon Relat. Elem.,

2000, 166, 243—251.352. T. Nishio, I. Iida andK. Sugiyama, J. Chem. Soc.,PerkinTrans. 1, 2000, 3039—3046.353. K. Oda, T. Ishioka, Y. Fukuzawa, N. Nishizono and M. Machida, Heterocycles,

2000, 53, 2781—2788.354. A. M. Reddy, S. Tsutsui and K. Sakamoto, Chem. Lett., 2001, 476—477.355. P. Vath and D. E. Falvey, J. Org. Chem., 2001, 66, 2887—2890.356. Y.Wan, O. Mitkin, L. Barnhurst, A. Kurchan and A. Kutateladze,Org. Lett., 2000,

2, 3817—3819.357. A. L. Schreiber, M. A. Fashing and C. J. Abelt, J. Chem. Soc., Perkin Trans. 1, 2000,

953—955.358. A. Gaplovsky, B. Jakubıkova, R. Hercek and J. Donovalova, J. Trace Microprobe

Techniques, 2000, 18, 419—424.359. J. R. Horton, L. M. Stamp and A. Routledge, Tetrahedron Lett., 2000, 41,

9181—9184.360. M. D’Auria, C. Distefano, F. D’Onofrio, G. Mauriell and R. Racioppi, J. Chem.

Soc., Perkin Trans. 1, 2000, 3513—3518.361. L. Latterini, F. Elisei, G. G. Aloisi andM. D’Auria, Phys. Chem.Chem. Phys., 2001,

3, 2765—2770.362. D. Vialaton andC. Richard, J.Photochem.Photobiol.A:Chem., 2000, 136, 169—174.363. H. Koshima, D. Matsushige, M. Miyauchi and J. Fujita, Tetrahedron, 2000, 56,

6845—6852.364. W. Lee and W. S. Jenks, J. Org. Chem., 2001, 66, 474—480.365. M. Goez and G. Eckert, J. Inf. Recording., 2000, 25, 281—285.366. M. Goez and J. Rozwadowski, J. Inf. Recording., 2000, 25, 301—306.367. M. Dossot, D. Burget, X. Allonas and P. Jacques,New J.Chem., 2001, 25, 194—196.368. M.A. Herranz, N. Martın, L. Sanchez, C. Seoane and D. M. Guldi, J. Organomet.

Chem., 2000, 599, 2—7.369. A. E. Jones, C. A. Christensen, D. F. Perepichka, A. S. Batsanov, A. Beeby, P. J.

Low, M. R. Bryce and A. W. Parker, Chem. Eur. J., 2001, 7, 973—978.370. M. Fujitsuka, K. Matsumoto, O. T. Yamashiro, Y. Aso and T. Otsubo, Res. Chem.

Intermed., 2001, 27, 73—88.371. A. Cravino, G. Zerza, M. Maggini, S. Bucella, M. Svensson, M. R. Andersson, H.

Neugebauer and N. S. Sariciftci, Chem. Commun., 2000, 2487—2488.372. P. A. van Hal, J. Knol, B. M.W. Langeveld-Voss, S. C. J. Meskers, J. C. Hummelen,

R. A. J. Janssen, Synth.Met., 2001, 116, 123—127.373. Y. Mori, Y. Sakaguchi and H. Hayashi, Bull. Chem. Soc. Jpn., 2001, 74, 293—304.374. K. Wakita, N. Tokitoh, R. Okazaki, N. Takagi and S. Nagase, J. Am. Chem. Soc.,

2000, 122, 5648—5649.375. S. K. Park, J. Photochem. Photobiol. A: Chem., 2000, 135, 155—162.


376. A. de Meijere, D. Faber, U. Heinecke, R. Walsh, T. Muller and Y. Apeloig, Eur. J.Org. Chem., 2001, 663—680.

377. M. Z. Jin, L. Yang, L. M. Wu, Y. C. Liu and Z. L. Liu, Chin. Chem. Lett., 2001, 12,95—98.

378. W. J. Leigh and T. R. Owens, Can. J. Chem., 2000, 78, 1459—1468.379. K. Nishiyama, M. Oba, H. Takagi, I. Fujii, N. Hirayama, Narisu, H. Horiuchi, T.

Okutsu and H. Hiratsuka, J. Organomet. Chem., 2000, 604, 20—26.380. H. Hiratsuka, M. Tanaka, H. Horiuchi, Naris, T. Yoshinaga, M. Oba and K.

Nishiyama, J. Organomet. Chem., 2000, 611, 71—77.381. M. C. Pirrung, L. Fallon, J. Zhu and Y. R. Lee, J. Am. Chem. Soc., 2001, 123,

3638—3643.382. M. Takahashi, S. Tsutsui, K. Sakamoto, M. Kira, T. Muller and Y. Apeloig, J. Am.

Chem. Soc., 2001, 123, 347—348.383. A. Matsumoto and Y. Ito, J. Org. Chem., 2000, 65, 5707—5711.384. V. Y. Lee, M. Ichinohe and A. Sekiguchi, J. Am. Chem. Soc., 2000, 122, 9034—9035.385. W. J. Leigh and N. P. Toltl, Organometallics, 2000, 19, 3232—3241.386. I. S. M. Saiful, Y. Ohba, K. Mochida and S. Yamauchi, Phys. Chem. Chem. Phys.,

2001, 3, 1011—1014.387. Y. Sasaki,M. Fujitsuka,O. Ito, Y.Maeda, T.Wakahara, T. Akasaka, K.Kobayashi,

S. Nagase, M. Kako and Y. Nakadaira,Heterocycles, 2001, 54, 777—787.388. Y.Maeda, S. Takahashi, T.Wakahara, T. Akasaka, Y. Sasaki,M. Fujitsuka, O. Ito,

K. Kobayashi, S. Nagase, M. Kako and Y. Nakadaira, ITE Lett. Batt., NewTechnol.Med., 2000, 1, 408—411.

389. T. Akasaka, Y. Maeda, T. Wakahara, T. Mizushima, W. Ando, M. Walchli, T.Suzuki, K. Kobayashi, S. Nagase, M. Kako, Y. Nakadaira, M. Fujitsuka, O. Ito, Y.Sasaki, K. Yamamoto and T. Erata, Org. Lett., 2000, 2, 2671—2674.

390. K. Mochida and T. Kayamori, Organometallics, 2000, 19, 3379—3386.391. J. E. T. Corrie, B. C. Gilbert, V. R. N. Munasinghe and A. C. Whitwood, J. Chem.

Soc., Perkin Trans. 2, 2000, 2483—2491.392. G. Keglevich, M. Trecska, Z. Nagy and L. T ke, Heteroat. Chem., 2001, 12, 6—9.393. S. Jankowski, J. Rudzinski, H. Szelke, G.Keglevich,J.Organomet.Chem., 2000, 595,

109—113.394. V. K. Yadav, R. Balmurugan, M. Parvez and R. Yamdagni, J. Chem. Soc., Perkin

Trans. 1, 2001, 323—332.395. I. V. Borisova, N. N. Zemlyanskii, A. K. Shestakova, V. N. Khrustalev, Y. A.

Ustynyuk and E. A. Chernyshev, Russ. Chem. Bull., 2000, 49, 1583—1592.396. W. Bhanthumnavin and W. G. Bentrude, J. Org. Chem., 2001, 66, 980—990.397. D. Shukla, C. Lu, N. P. Schepp, W. G. Bentrude and L. J. Johnston, J. Org. Chem.,

2000, 65, 6167—6172.398. F. Vargas and C. Rivas, J. Photochem. Photobiol. A: Chem., 2001, 138, 1—5.399. G. Pandey, K. S. S. P. Rao and K. V. N. Rao, J. Org. Chem., 2000, 65, 4309—4314.400. T. Shimizu, D. Miyasaka and N. Kamigata, J. Org. Chem., 2001, 66, 1787—1794.401. A. Z. Bradley, A. J. Link,K. Biswas,D. Kahne, J. Schwartz,M. Jones Jr., Z. Zhu and

M. S. Platz, Tetrahedron Lett., 2000, 41, 8691—8694.402. A. Z. Bradley, A. D. Cohen, A. C. Jones, D. M. Ho and M. Jones Jr., Tetrahedron

Lett., 2000, 41, 8695—8698.403. Y. L. Chow, S. S. Wang, H. Huang and J. -Q. He, Res. Chem. Intermed., 2000, 26,

643—666.404. H. Kunkely and A. Vogler, Z. Naturforsch., 2001, 55B, 431—432.

Photochemistry306

7Photoelimination

BY IAN R. DUNKIN

1 Introduction

This chapter deals with photoinduced fragmentations of organic and selectedorganometallic compounds, in particular reactions accompanied by loss of smallmolecules such as nitrogen, carbon monoxide or carbon dioxide. Photodecom-positions which produce two or more larger fragments and other miscellaneousphotoeliminations are reviewed in the final section. Photofragmentations ofcarbonyl compounds, taking place, for example, by Norrish Type I and IIprocesses, are discussed in Part II, Chapter 1.A number of papers have appeared whichmay be of general interest within the

context of photoelimination chemistry. Vauthey has published in the EPANewsletter a very readable review of transient grating techniques for investigat-ing ultrafast processes.1 Photochemically generated radical ion pairs of rigiddonor—bridge—acceptor molecules have been studied by field dependentCIDNP,2 and the effect of bridge length on the exchange interaction and backelectron transfer determined. Persistent contact ion pairs have been generated insolid argon by Hg-lamp irradiation of N,N,N�,N�-tetramethylbenzidine in thepresence of CCl4 and Xe as electron acceptors.3 This was an extension of anearlier study of contact ion pairs from tetramethyl-p-phenylenediamine.A gener-alized photochemical theory of the vacuum-UV laser ablation of polymers hasbeen advanced,4 while molecular interactions with solid surfaces during theisotopically selective IR multiphoton dissociations of SF6 and CF3I in pulsedgas-dynamic flows have been shown to result in noticeable increases in productyields without substantial decreases in selectivity.5

2 Elimination of Nitrogen from Azo Compounds and Analogues

Although azoisobutyronitrile (AIBN) is extensively used as a radical initiator(e.g. in the synthesis of polymers), diffusion constants of AIBN and the radicalformed from its photolysis were until recently unknown. These have now beendetermined by transient grating and Taylor dispersion methods for benzenesolutions at 22 °C.6 The diffusion constant for the radical was found to be smallerthat that of AIBN, and this is attributed to radical—solvent interactions.


307

Stereochemical inversion in the photoelimination of N2 from (1) (Scheme 1)showed a strong dependence on the viscosity of the reaction medium.7 The ratio[(2inv)]:[(2ret)] varied from 81:19 in the low viscosity solvent n-hexane to 46:54in 1,4-butanediol. This observation can be explained on the assumption that themore viscous solvents hinder the otherwise preferred inversion process simply byfriction, but this does not appear to resolve uncertainties as to the exact mechan-ism of the reaction.

Photoelimination of N2 and methyl acetate from the �3-1,3,4-oxadiazoline (3)(Scheme 2) has been studied by both steady-state (300 nm) and laser-flash(308 nm) techniques.8 In benzene, 300 nm photolysis of (3) gave (6) and (7) as theonly identified products, presumably arising via diazo compound (4) and carbene(5); there was no insertion of the carbene into solvent molecules. No transientabsorption was detected following laser flash-photolysis of (3) in 1,1,2-trifluoro-trichloroethane, but in the presence of pyridine carbene (5) was trapped, at a ratefaster than the time resolution of the spectrometer (�20ns), as an ylide with�max�350 nm. Computations at several levels of theory suggest that carbene (5)might be better represented as the bicyclic zwitterion (5a).

3 Elimination of Nitrogen from Diazo Compounds and Diazirines

3.1 Generation of Alkyl, Alicyclic and Heterocyclic Carbenes. — Vibrationallyexcited vinyl chloride in its electronic ground state has been generated inmolecular beams by photolysis of 3-methyl-3-chlorodiazirine, and its unimolecu-

Photochemistry308

lar dissociation dynamics investigated.9 In these conditions, both HCl elimin-ation and C—Cl bond fission occur. The silylene (12) (Scheme 3) was produced inhigh yield in Ar matrices via 1-phenylsilene (11) by photolysis of phenylsilyl-diazomethane (8).10 The diazo compound (8) was also apparently interconvertedwith its diazirine isomer (9) under these conditions. Carbene (10) was notobserved directly. In matrices doped with O2, the thermal reaction of (12) withoxygen could be monitored by IR spectroscopy; the only primary productdetected was dioxasilirane (14), presumably arising by cyclization of the silanoneO-oxide (13).

Argon-matrix photolysis of 3-noradamantyldiazirine (15) gave adamantene(16) and protoadamant-3-ene (17), which could be interconverted photochemi-cally.11 A transient absorption of (16) (�max�325 nm) was also observed inflash-photolysis experiments with (15) in benzene solutions, but noradamantyl-carbene, the initial N2-loss product from (15), was not observed in this study.Rate constants for reactions of (16) with methanol, cyclohexa-1,3-diene,tris(trimethylsilyl)silane, acetic acid and O2 were determined. UV irradiation ofthe spiro diazirine (18) in benzene produced a mixture of dimeric azines, but inpentane a mixture of insertion products (19) was obtained together with traces of1,3-bishomoprismane (20).12 Photolysis of (18) in a nitrogen matrix13 showed theformation of its diazo isomer, but not the corresponding carbene; on warm up,traces of (20) were obtained. In contrast to its photochemistry, (18) gives mainly(21) on thermolysis.The photoelimination of N2 from diazocyclopentadiene has been known for a

long time to yield the triplet carbene, cyclopentadienylidene (22), which has beendetected by EPR and matrix IR and UV-visible spectroscopy. Although it wasalso known that (22) undergoes a photochemical transformation to a terminalalkyne, the exact structure of this secondary photoproduct remained unknown.Maier and Endres have now shown that, when (22) is irradiated in matrices at313nm, triplet 2-penten-4-yn-1-ylidene is generated in its (s-E)-(E)-conformer(23), which is converted into 3-ethynylcyclopropene (24) by 436nm light.14 Theyhave also shown that when (22) and the eliminated N2 are present in the same

II/7: Photoelimination 309

matrix cage, irradiation with light of ��570 nm induces a partial back reactionto diazocyclopentadiene. The same authors have also reported a matrix study of4H-imidazol-4-ylidene (25), generated in solid argon by 313nm photolysis of4-diazo-4H-imidazole.15 Photoexcitation of (25) at �570nm yields the ring-opened singlet carbene (26), which can be converted into (27) by irradiation at�310nm. Carbene (26) could not be observed in N2 matrices, probably owing toefficient back reaction with nitrogen to regenerate the diazo precursor. It wasalso shown to react with CO, yielding the corresponding ketene.

Cyclopent[a]acenaphthylenylidene (28) has been generated from the corre-sponding diazo precursor compound, and has been shown to give spirocyclo-propanes with alkenes.16 With trans-�-methylstyrene, the carbene addition wasstereospecific, and with 2,3-dimethylbutadiene both 1,2- and 1,4-addition wereobserved. Competition experiments for the reaction of (28) with styrenes gave alinear Hammett correlation with ��0.38. Accordingly, (28) is regarded as anucleophilic singlet carbene in these reactions. Nevertheless, some triplet prod-ucts (e.g. the dimer and H-abstraction products) were also obtained from reac-tions of (28).Photolysis of benzotriazole in Ar andN2 matrices has been studied by both IR

and UV-visible absorption spectroscopy (Scheme 4).17 The reactions are compli-cated by the existence of the 1H (29) and 2H (30) tautomers of the triazole. At254nm, the 1H form (29) photolysesmore quickly than the 2H form, yielding the

Photochemistry310

diazoimine (31) by N—NH bond scission. Irradiation of (31) at 420 nm resultedpredominantly in cycloreversion to (29), but a minor pathway led to ketenimine(33), presumably via iminocarbene (32), and ultimately to cyanocyclopentadiene(34). Although the 2H tautomer (30) was also photolysed slowly in these experi-ments, it was likely that it reacted by initial photoinduced tautomerization to(29).

3.2 Generation of Aryl and Heteroaryl Carbenes. — Three novel triplet an-thryl(aryl)carbenes (35) were generated by irradiating the corresponding diazoprecursors in rigid matrices at low temperatures and were characterized by EPRspectroscopy.18 The anthryl and aryl groups appear to act as good reservoirs forthe unpaired electrons and also confer kinetic stability. Thus, in comparisonwiththe EPR signals of most triplet carbenes, which disappear below 90K, the EPRsignals of (35a) in 2-methyltetrahydrofuran glasses persisted to 120K, those of(35b) to 130K, and those of the very bulky (35c) to 175K, where the sample wasfluid. The triplet benzanthracenylidene (36) has been obtained in n-hexanematrices at 1.7K by in situ photolysis of the corresponding diazo compound, andESR and hole burning studies were performed to determine its zero-field split-ting parameters.19


Sulfur ylides (37) formed from arylchlorocarbenes and trimethylene sulfidehave been studied by flash-photolysis of the diazirine precursors.20 In preparativeexperiments, these intermediates gave thioacetal products when the ylides under-went ring opening induced by HCl. Absolute rate constants have been deter-mined for the reactions of chlorophenylcarbene, bromophenylcarbene andchloro-p-nitrophenylcarbene with tetramethylethylene in a range of solvents.21

The carbenes were generated from diazirine precursors and showed similarreactivity in pentane, Freon-113, benzene, anisole, THF, ethyl acetate andacetonitrile. Thus, solvation of the carbenes has little influence on their reactivitytowards tetramethylethylene.2-Benzofurylchlorocarbene (38) has been isolated in low-temperaturematrices

by photolysis of the corresponding diazirine and has been found to possess aninteresting photochemistry of its own.22 By choice of wavelength, (38) can beselectively interconverted with the ring-opened quinone methide (39) and thestrained allene (40); and there is evidence that the latter undergoes a photo-induced 1,3-aryl shift to give the benzocyclobutadiene (41).

Carbonyl oxides (R1R2COO), derived from the photolysis of diphenyl-diazomethane23,24 and phenylmethyldiazomethane24 in the presence of O2, havebeen subjected to kinetic studies at 295K. Reaction of benzophenone O-oxidewith sulfoxides afforded predominantly sulfones, but in the case of Ph2SO somediphenyl sulfide was also formed.23 The latter product led to the postulate ofparallel reaction pathways: (i) nucleophilic attack of the carbonyl oxide at thesulfur atom of the sulfoxide and (ii) formation of a cyclic intermediate by1,3-dipolar addition of Ph2COO to the S——O bond. In the formation of thecarbonyl oxides, contributions by quantum chain processes involving tripletketones and singlet oxygen have been identified.24

The influence of the reaction environment has been investigated for thephotolysis of four racemic 1,2-diaryldiazopropanes (42; Ar1, Ar2�phenyl, bi-phenyl).25 In solution, mixtures of products were obtained, containing E and Zstereoisomers of products from both aryl and hydrogenmigration to the carbenecentre generated by loss of N2. Photolysis of the crystalline compounds, however,gave the H-shifted products as their Z isomers (43) with �99% selectivity inmost cases. Photolysis of the compounds in amorphous solids did not reproducethis selectivity, demonstrating that rigidity alone is not sufficient. The observedproducts can be rationalized by considering the conformations of the diazocompounds in the crystal and modelling reaction trajectories. The ability tocontrol reaction pathways, including stereochemistry, in this way, even for suchhigh energy reactions as diazo photolysis, suggests that there could be manyworthwhile applications of crystal photochemistry in synthesis.Several photoaffinity probes containing aryl(trifluoromethyl)diazirine moie-

ties (44) have been reported.26—28 One of these reports describes a complex

Photochemistry312

trifunctional probe, containing the photolabel, a biotin tag and a moenomycinligand,27 and another a simple approach for the preparation of biotinyl photo-probes from unprotected carbohydrates,28 which should facilitate research intocarbohydrate receptors.

3.3 Photolysis of Diazo Carbonyl Compounds and Sulfur Analogues. — Laserflash photolysis of methoxycarbonyl-2-naphthyldiazomethane in Freon-113 sol-ution containing THF led to the observation of a transient absorption(�max�330nm), which was assigned to the ether ylide (45).29 The rate of formationof the transient had a first-order dependence on THF concentration. Thisappears to be the first reported direct observation of a carbene-ether ylide. Themechanism of the reaction of ketocarbenes with methanol has been investigatedin kinetic studies of the photolysis of a series of p-substituted phenyl-2-diazo-propiophenones (46; X�MeO, Me, H, F).30 A wide difference in the activationenthalpies for electron-donating and electron-withdrawing substituents wasnoted, the former being consistent with diffusion-controlled processes. Qualitat-ive energy surfaces for the singlet and triplet carbenes were proposed to accountfor the kinetic results and observed products.

Ketene ylides have been detected following flash-photolysis of 2-diazo-1,3-diphenylpropane-1,3-dione, (PhCO)2CN2, in the presence of amines (althoughnot including pyridine).31 It was also found that the triplet state of the startingmaterial had a lifetime of several microseconds — unusual for a diazo compound— but that it was not a precursor of the ketene, whichmust therefore have resultedfrom singlet excited state fragmentation. Product distributions from photolysisof methyl (p-nitrophenyl)diazoacetate in MeCN—MeOHwere greatly altered bythe addition of the electron-donating amine N,N,N�,N�-tetramethyl-p-phenylenediamine.32 In particular, the �-methoxy product from trapping of thecorresponding carbene byMeOHwas completely suppressed. Other amines hadsimilar but less dramatic effects. To account for this observation, it was proposedthat single-electron transfer to the carbene generated the carbene radical anionas the key intermediate. Some confirmation of this proposal was derived from theobservation of the radical cation of the amine in flash-photolysis experiments.The hydration of the carbene formed by flash-photolysis of 4-diazochroman-

3-one (47) has been studied.33 A short-lived species, identified as the enol


tautomer of the lactone, 4-hydroxyisochroman-3-one, was detected.2-Ethoxycarbonyl-1-silacyclobutanes (49; X�Cl, N3, NCO, NCS) have been

synthesized photochemically from the silyl-�-diazoacetates (48) by intramolecu-lar C—H insertion of the intermediate carbenes.34 The silacyclobutanes undergofacile thermal ring expansion by a 1,3(C�O) shift, yielding the oxasilacyclo-hexenes (50).

Novel surface modifications of platinum by the 3-pyridyl �-diazoketone (51)and its 4-pyridyl isomer, together with the ketenes formed by photolysis of thediazoketones, have been studied by means of ultra high vacuum reflection-absorption IR spectroscopy.35 This approach is claimed to have potential as thebasis for a large range of surface modifications.In a laser flash-photolysis study of diphenylsulfonyldiazomethane (52), the

sulfene (53) and the ylide formed by trapping of this sulfene by pyridinewere bothobserved.36 The reactions of (53) with other nucleophiles (e.g. acetate, azide,cyanide and MeOH) were also examined. Photolysis of the stereoisomeric �-diazo sulfoxides (54) in argon matrices gave the sulfine (55) by hetero-Wolffrearrangement of the sulfinyl carbene, which was not itself detected.37 On furtherUV irradiation, (55) rearranged to (56) or lost COS to give (57). Novel diazosul-fonyldiazomethanes have been patented as photoacid generators for chemicallyamplified resists.38

4 Elimination of Nitrogen from Azides

A critical review of the complex literature on the photo-oxidation of organicazides has been published and a reaction scheme proposed which appears toexplain most of the available experimental and theoretical results.39 A study ofthe photolysis of 4,4�-diazidostilbenes in polymer matrices has revealed thatcis—trans isomerization competes with degradation of the azido group.40

Photochemistry314

Although the majority of photochemical studies of azides in the review periodhave been concerned with aryl or heteroaryl azides, an interesting exception wasprovided by the report of a photoinduced amidoglycosylation. Photolysis of theallal azidoformate (58) in the presence of alcohols yielded the 2-amido-allopyranosides (59), presumably by nitrene addition to the C——C bond followedby ring opening of the resulting aziridine.41 Yields were modest but potentiallyuseful (35—40%) for simple alcohols (MeOH, EtOH, PriOH), but significantlylower for a number of more complex alcohols.

The effects of substitution on the yield of high-spin nitrenes from the photoly-sis of 2,6-diazidopyridines42 and the part played by orbital control in the selectivephotolysis of azido groups in 2,4,6-triazido-3,5-dichloropyridine43 have beeninvestigated. In the former study, it was found that the progressive introductionof cyano groups disfavours the formation of high-spin products, probably owingto enhancement of pyridine-ring fragmentation. Azidopyridine (60), upon irradi-ation, has the possibility of N2 elimination from the azido group and fragmenta-tion of either or both triazole rings, yielding potentially nitrene, carbene, car-benonitrene and dicarbenonitrene species with triplet, quintet or septet spinstates. Photolysis of (60) at 77K in 2-methyltetrahydrofuran led to the detectionof several EPR signals.44 Besides triplet signals belonging to isolated carbene andnitrene centres, a quintet signal was also observed, which was attributed to thecarbenonitrene (61). A photochemical synthesis of novel mesoionic amides [e.g.(62)] starting from azidotetrazolium salts has been described.45

Photoaffinity labels containing aryl azide groups have been developed byseveral research groups. Efficient syntheses of 4-azidotetrafluoroaniline havebeen reported, and the potential of this compound as a heterobifunctionalphotoaffinity label was tested in model photolyses in cyclohexane.46 A tyrosinederivative containing a 5-azido-2-nitrobenzoyl moiety has been prepared, andthe structures of its photo-cross-linking products have been investigated.47 Tes-tosterone derivatives with various azidoaryl groups have been synthesized to


provide reagents with different linker lengths for the photoaffinity labelling ofsex-hormone binding globulins and androgen receptors.48 Arylazide-1,3-disub-stituted cyclohexanes have been prepared as leukotriene B4 photoaffinityprobes.49 8-Aminohydrocinchonidinewas coupled with 4-azidosalicylic acid andlabelled with 125 I to provide a photoaffinity label for proteins,50 and 12-[(4-azidosalicyl)amino]dodecanoic acid was used to prepare acetylated ganglio-sides, which were then radioiodinated to give photolabels for erythrocyte mem-brane proteins.51

5 Photoelimination of Carbon Monoxide and Carbon Dioxide

Rotational and vibrational distributions have been determined for the COfragments produced by vacuum-UV photodissociation of OCS in the150—155 nm region, which takes place through the 2 1�� state of OCS.52 As one ofthe few small molecules with competing chemically distinct reaction channels atsimilar energies, HNCO continues to be the subject of both experimental andtheoretical studies. In the review period, three computational studies of thephotodissociation of HNCO have been published.53—55 The pathway for S1�S0

internal conversion has received particular attention.54,55

Photolysis of ketene at 193 nm has been studied by measuring the yields ofatomic hydrogen formed when very dilute mixtures of ketene and argon orketene and H2 were subjected to single pulses from an ArF laser.56 Quantumyields for four reaction channels were determined: H2CCO�h giving (i)CH2(3B1)�CO (0.628), (ii) CH2(1A1)�CO (0.193), (iii) HCCO�H (0.107) and (iv)C2O(b1��)�H2 (0.072). The [H] profile was found to depend mainly on the rateof the reaction H�HCCO�CH2�CO. A theoretical study has been made ofthe photodissociation of formaldehyde to give H2�CO, including classicaltrajectory calculations by MP2 and density functional theory methods.57 Thepredicted translational energy distributions of the products were in better agree-ment with experiment than for previous Hartree-Fock calculations, and goodrepresentations of product rotational distributions and the CO vibrational statepopulations were also obtained. The photodissociation of formic acid has beeninvestigated both experimentally and theoretically.58 Ab initio calculations wereperformed for five reaction channels on the S0, S1 and T1 potential energysurfaces; and the vibrationally excited products were detected using time-resol-ved FTIR after laser photolysis at 248 or 193 nm. At 248 nm, the HCOOHmolecule is first excited to the S1 state but the dissociation takes place on the S0

surface, giving vibrationally excited CO, CO2 and H2. At 193nm, an additionaldissociation pathway which produces OH and HCO radicals was identified.The sequential photolysis (308 and 248 nm) of 1,2;5,6-naphthalenetetracar-

boxylic dianhydride (63) (Scheme 5) has been investigated in Ar matrices.59

Dec-5-ene-1,3,7,9-tetrayne (67) was tentatively identified as the final product,and naphthyne intermediate (64) and ketene (65) were detected directly by IRspectroscopy. It seems unclear, however, whether the ketene (65) lies on thepathway to (67) or whether it decomposes to other, unidentified products. The

Photochemistry316

likely immediate precursor of the final product, the naphthadiyne (66), was notdetected. All IR identifications were made on the basis of comparisons withspectra predicted by density functional theory.

A series of aroyl-substituted phenylacetic acids and p-acetylphenylacetic acidhave been shown to undergo photodecarboxylation with quantum yields in therange 0.2—0.7, when irradiated with 254—350 nm light in aqueous solutions atpH�pKa.60 Quantum yields decreased when the pH was lowered. In most casesthe product arising from protonation of the corresponding arylmethyl carbanionwas obtained in high yield. Mesityl cyclohexanecarboxylate lost CO2 to givecyclohexylmesitylene in good yield upon excitation at 254nm in neutralacetonitrile solutions.61 In the presence of ethanol and acid, however, the sameester underwent transesterification upon irradiation. Quenching of the 4-car-boxybenzophenone triplet by amino acid anions in basic aqueous solution hasbeen investigated in a nanosecond laser flash-photolysis study.62 Rapid decar-boxylation was observed with rate constants estimated at 8.7�1010 s�1, which isat least an order of magnitude faster than the decarboxylation of aliphaticacyloxy radicals in aqueous media. The pyrene-sensitized photodecompositionof N-phenylglycine has been shown to be accelerated by the addition of anelectron acceptor, such as terephthalonitrile.63 A mechanism involving electrontransfer from the amino acid to singlet excited pyrene through exciplex forma-tion and the intermediacy of the radical PhNHCH2· was proposed.The photodecarboxylative addition of �-keto carboxylates (RCOCO2Na) to

N-methylphthalimide gave alkylation products (68; R�Pri, Bus, But) in yields


of 73—86%, while glyoxylate (HCOCO2Na) gave the reduction product (68;R�H) in 52% yield.64 In contrast, pyruvate (MeCOCO2Na) gave a 53% yield ofthe ring-expansion product (69). An intramolecular application of this photo-chemistry was provided by stereoselective syntheses of pyrrolo[1,4]ben-zodiazepines (70; R1�Me, H; R2�H, Me, Pri, Bui) from the precursors (71);65

yields were in the range 54—83%. Quantum yields for the 350nm photodecar-boxylation of 6-carboxypterin (72) in aqueous solutions were shown to bedependent on both pH and oxygen concentration.66 A study has beenmade of thephotodecarboxylation of chromone-2-carboxylic acid in both aerated and de-aerated ethanol; and ketohydroperoxide intermediates in the aerated reactionwere detected by chemiluminescence.67

Dimethylvinylidene (73), together with the �-lactone (74), dimethyl-propadienone (75) and dimethylketene, were observed as products of the photo-lysis of the bis-peroxy ester (76) in argon matrices.68 Expected intramolecularrearrangement products of the carbene (73), but-2-yne and 1-methylcyclo-propene, were not, however, detected. Identifications were made by comparisonof experimental and computed IR spectra.

5.1 Photoelimination of CO from Organometallic Compounds. — A review ofthe quantitative photochemistry of organometallic complexes and the mechan-isms of their photoreactions has been published.69 This contains sections on thephotoelimination of CO from selected Fe, W and Rh carbonyl complexes.

Photochemistry318

Reviews of the photochemistry of Group 8 and Group 6 cyclopentadienyl metalcarbonyl compounds have also appeared.70,71

A detailed experimental and theoretical study has been made of the ultrafast267nm photodissociation of Group 6 metal hexacarbonyls M(CO)6 (M�Cr,Mo, W) in the gas phase.72 Five consecutive processes were identified followingexcitation: the first two correspond to relaxation along a Jahn-Teller activecoordinate and internal conversion, while in the third the molecules change overto a repulsive ligand-field surface and dissociate, giving M(CO)5 in the S1 state.Thereafter, the excited M(CO)5 molecules relax in an ultrashort time through aJahn-Teller induced conical intersection to the S0 state, a pathway which corre-sponds to a pseudorotation. The total times taken to reach the S0 state ofM(CO)5were found to be 110, 165 and 195 fs for M�Cr, Mo and W, respectively. In S0,M(CO)5 eliminates a second CO molecule in about 1 ps, owing to excess vibra-tional energy, but this step can be suppressed in solution by cooling.Nanosecond time-resolved infrared spectroscopy has been used to study the

photolysis of M(CO)6 (M�Cr,Mo,W) in supercritical fluids (CO2, Kr and Xe).73

The sensitivity of the (CO) IR bands to the molecular structure assists greatly inidentifying reactive species. For the first time organometallic noble gas com-plexes [e.g. M(CO)5(Kr)] have been observed in solution. Moreover, evidencewas obtained for �1-O bound CO2 in the complexes M(CO)5(CO2) formed insupercritical CO2. Time-resolved infrared spectroscopy on the nanosecond time-scale has also been used to investigate the photoelimination of CO from[(C5Me5)Cr(CO)2]2.74 In this case, loss of terminal CO bands was accompaniedby the appearance of a single band in the bridging CO region, consistent with theformation of the triply bridged species (C5Me5)Cr(-CO)3Cr(C5Me5).Room-temperature photolysis of M(CO)6 (M�Cr, Mo, W) in the presence of

tetracyanoethylene (TCNE) or fumaronitrile (FN) yielded trans-(�2-TCNE)2M(CO)4 or trans-(�2-FN)2M(CO)4, respectively, with no evidence for thecorresponding cis complexes.75 UV irradiation of Cr(CO)6 in heptane containingan excess of AsPh3 gave only trans-Cr(CO)4(AsPh3)2, in contrast to previousstudies of the reaction in the presence of �-alumina, which gave mixtures of thecis and trans complexes.76 Propene complexes, Cr(CO)5(�2-C3H6) and(C5R5)Mn(CO)2(�2-C3H6) (R�H, Me), have been synthesized by UV photolysisof Cr(CO)6 and (C5R5)Mn(CO)3, respectively, in liquid propene under highpressure.77 Similarly, (C5H5)Mn(CO)2(N2O) has been prepared in near-criticalN2O at room temperature and identified by its (CO) and (N2O) IR bands.78

This complex has a lifetime of about 5 minutes at room temperature and appearsto decay by two pathways, one of which may involve O-atom transfer, to give(C5H5)Mn(CO)2(N2). Aldol-type condensations of cyclic ketones can be initiatedby UV irradiation of W(CO)6 and CCl4; a mechanism involving intermediatecarbene complexes of tungsten has been proposed.79 A metal—carbene activespecies has also been proposed for the polymerization of alkynes and strainedcyclic alkenes by the W(CO)6/CCl4)/h system, with NMR evidence to supportthis suggestion.80 The ‘photocatalytic’ role of Fe(CO)5 in the silylation of olefinswith vinylsilanes and hydrosilanes has also been investigated.81 Benzenetricar-bonylchromium(0), when photolysed in CHCl3, gives CrCl3 with a quantum yield


of 1.4, consistent with a radical mechanism.82

The photochemistry of some chromium aminocarbene complexes,(CO)5Cr[C(NR1

2)R2] (R1�H, Me, Bz; R2� H, Me, Ph), has been investigated insolution by flash photolysis and in low-temperature matrices.83 Some of thesecomplexes were known to undergo efficient photoreactions with imines to form�-lactams, supposedly via metal—ketene complexes. The only photochemicalprocess observed in this study, however, was CO loss, and the major product inall cases was apparently cis-(CO)4Cr[C(NR1

2)R2].The photochemical reactions of the niobium and tantalum complexes (77;

M�Nb, Ta) and their indenyl analogues with CO, H2 and N2 have been studiedin solution at room temperature84 and at low temperatures in polyethylenematrices and liquid xenon.85 The reactions occur via initial CO loss. A note-worthy observation with H2 was that either classical or non-classical dihydridescould result. Thus, in n-heptane saturated with H2, the tantalum complex (77;M�Ta) gave the classical dihydride (78; M�Ta), while the niobium complex(77;M�Nb) gave both the classical dihydride (77;M�Nb) and the non-classicalisomer (79). The 267 nm photolysis of (C5H5)Ir(CO)2 in cyclohexane solution atroom temperature has been examined by picosecond time-resolved IR spectro-scopy.86 Alkane C—H bond activation was observed directly, with formation of(C5H5)Ir(CO)(cyclohexyl)(H) following CO loss, although about 80% of theexcited molecules relaxed without dissociation. The rate of activation of thecyclohexane was fast enough (2 ps) to suggest a negligible activation barrier.Comparison of the photochemistry of a series of rhodium dicarbonyl complexes,XRh(CO)2 (X�C5H5, C5H4Me, C5HMe4, C5Me5, �5-C9H7 and acac), under avariety of experimental conditions has shown that the photoefficiency of COelimination is substantially dependent on the unique ligand X and the excitationwavelength;87 quantum yields varied over three orders of magnitude in the orderC5H5�C5H4Me�C5Me5 �acac��5-C9H7.

Photolysis of Co2(CO)6(alkyne) complexes in frozen Nujol at about 90Kresulted in CO loss, to give Co2(CO)5(alkyne) complexes in which CO lossappeared to be from an axial position.88 Conversion to a second isomer, presum-ably with an equatorial vacancy, was observed on annealing at 140K. Photo-lyses of some phosphine substituted derivatives, axial-Co2(CO)5(PR1

3)(C2R22)

(R1�Bu, Ph, OPh; R2�H, Ph), gave two isomeric CO-loss products in each case.UV irradiation of the iron complex (80) in the presence of P(OR)3 (R�Ph, Bu, Pr,Et, Me) led to regioselective substitution of two CO ligands on different ironcentres, to give mixtures of cis and trans complexes (81).89

Studies of the photoinduced replacement of CO in cyclopentadienyl(dicar-bonyl)iron thiocarboxylate complexes90 and in a heterometallic osmium—manga-nese complex91 have also been reported. UV irradiation of Fe(CO)3[P(OPh)3]2

Photochemistry320

gave the orthometallated iron hydride (82).92 The reactions of this hydride with aseries of alkynes (R1C�CR2) were studied, and in some cases double carbonyla-tion was observed, yielding complexes of structure (83).

6 Photoelimination of NO and NO2

Photochemical reactions of cycloalkyl nitrites c-CnH2n�1ONO (n�4—8) havebeen studied in argon matrices.93 The larger ring compounds, cyclohexyl, cyclo-heptyl and cyclooctyl nitrites, gave complexes of the corresponding cycloalkylketones with HNO, presumably via initial O—N cleavage followed by dispropor-tionation of the resulting cycloalkyloxyl radicals and NO. In the case of cyclo-butyl nitrite, ring opening occurred, to give 4-nitrosobutanal as the majorproduct, while cyclopentyl nitrite gave a mixture of 5-nitrosopentanal and thecyclopentanone-HNO complex.Excitation at 400nm of the charge-transfer complex between tetranitro-

methane and naphthalene in acetonitrile and dichloromethane has been inves-tigated on the femtosecond timescale.94 The excitation produces a radical ionpair, comprising the naphthalene radical cation and the tetranitromethanideradical anion. The latter eliminates NO2 to give tetranitromethanide within200 fs.In the search for versatile methods of NO generation for biomedical applica-

tions, a possibility for achieving controlled photochemical release of NO from asolid substrate has been demonstrated.95 In this work, a gold substrate was firstderivatized with monolayers of dithiothreitol (DTT-SH), in which a thiol groupis exposed. Attempts to nitrosate these layers in situ with NaNO2 were, however,unsuccessful. Nitrosation of the surface was subsequently accomplished byderivatization with previously prepared S-nitrosodithiothreitol (DTT—SNO).The DTT—SNO layer was found to be thermally stable, and NOwas released byirradiation with visible light.The dynamics of NO ejected in the photodissociation of methyl nitrite on

Ag(111) surfaces have been studied at 248 and 351 nm, with and without thickspacer layers of hexane, and at various coverages ofMeONO.96,97 The photoejec-tion of NO appears to be dominated by direct excitation of MeONO; there wasno evidence for NO ejection as a result of substrate excitation.


7 Miscellaneous Photoeliminations and Photofragmentations

7.1 Photoelimination from Hydrocarbons. — Vacuum-UV photolysis of jet-cooled methane has been investigated in detail by photofragment translationalspectroscopy98,99 and, in one study, the results compared with similar photolysesof silane and germane.98 Products arise via cleavage of one C—H bond, to giveH�CH3, or by cleavage of two C—Hbonds, to give H�H�CH2. A photochemi-cal model has been applied to the role of methane photochemistry in theatmosphere of Titan.100 Three significant dissociation channels for propane at157nm have been identified: elimination of atomic hydrogen, molecular hydro-gen and methyl radical.101 Interestingly, elimination of H2 from the centralcarbon of propane (2,2-H2 elimination) was found to be more favourable than H2

elimination from vicinal carbons (1,2-H2 elimination). A similar study of H-atomdynamics in the photodissociation of jet-cooled ethyl radical has also beenpublished.102

A theoretical study of the photodynamics of ethylene has identified eightconical intersections involving the optically accessible V state, which are likely tobe relevant to the photochemistry of ethylene.103 Experimentally, H-atom andH2

elimination from ethylene excited at 157nm have been investigated, and threedifferent molecular elimination processes observed: 1,1, 1,2-cis and 1,2-trans.104

HCC radicals have been generated by laser photodissociation of acetylene at193 nm, and their reactions with acetylene studied both experimentally andtheoretically.105 The 193 nm photodissociation of HCC radicals, to give C2

mainly in the B 1�g state, has also been investigated.106 Photofragments from the157nm photodissociation of propyne and its isotopomer MeCCD have beenexamined in similar experiments.107 H-atom elimination from both the methylgroup and terminal alkyne carbon was observed; elimination of H2 also occurredbut with much smaller yields. The 243nm photodissociation of vibrationallypre-excited CD3CCH resulted in both methyl C—D and acetylenic C—H bondrupture, with the former process predominating.108 The photofragmentation ofphenylacetylene at 193 nm gave acetylene and C6H4 as the only detected primaryproducts.109 Some of the C6H4 molecules subsequently decomposed to 1,3,5-hexatriyne and H2. There was no evidence for the formation of phenyl andethynyl radicals, even though these had been observed in the pyrolytic decompo-sition of phenylacetylene.Photodissociation of 4-ethyltoluene at 266 nm in n-heptane solution proceeds

by C—H bond fission of the CH2 group to give the corresponding benzyl radicalat a relatively slow rate (4.0�107 s�1).110 Since the S1 [��*(benzene)] state popu-lated by the initial excitation does not correlate adiabatically with the dissocia-tive *(C—H) state, it was proposed that the photodissociation takes place viaintersystem crossing to the T1 [��*(benzene)] state, which in turn crosses to the*(C—H) state.

7.2 Photoelimination from Organohalogen Compounds. — The photolysis ofsimple organohalogen compounds continues to attract a large amount of verysophisticated experimentation, and our knowledge of ultrafast fundamental

Photochemistry322

processes has increased as a consequence. In the review period, reports on thistype of research have included studies of the photodissociation of CH3Cl,111

CH3Br,111 CH3I,111—113 CH2BrCl,114 CH2BrI,115,116 CH2ClI,117 CH2Br2,118 CH2I2,119,120

CF2I2,116,121,122 CHFCl2123 and CBrClF2.124,125 In the photodissociation of CH2I2,formation of isodiiodomethane (H2C—I—I) from the reaction of the initial frag-ments, CH2I and I, has been found to be favoured by solvation,119,120 while relatedisodihalomethanes have also been observed in other systems: H2C—Cl—I fromCH2ClI,117 H2C—Br—Br from CH2Br2118 and H2C—I—Br from CH2BrI.116 The effectof the surface on the formation of CH3 fragments has been investigated for thephotodissociation of CH3Br adsorbed on CaF2(111) surfaces modified either byelectron impact or by H-atoms.126 CF2Br and Br were the major products, andC2F4Br2 and Br2 the minor products, when CF2Br2 was adsorbed on highlyordered pyrolytic graphite and irradiated at 225—350nm.127

Besides halogenated methanes, there have also been studies of the fragmentphotodynamics of a number of halogenated C2 and C3 molecules: CH3CFCl2,128

CH2ClCH2I,129 CF3CH2I,130 CF3CF2I,112 CH2——CHCl,131 CH2——CFCl,132,133

CF3CF2CF2I,112 (CF3)2CFI,112 and CH2——CClCH3.134 To take two examples, fiveprimary dissociation channels were found for CH2——CFCl at 193nm [elimin-ation of Cl (by a fast process), HCl, HF, Cl (by a slow process) and F],132 andthree primary channels for CF2——CFCl at the same wavelength (to giveCFCl�CF2, C2F2Cl�F and C2F3�Cl).133 The elimination of HCl fromCH2——CHCl has been found to proceed by competing three- and four-centrechannels.131 IR spectroscopy was employed to study the photolysis of CD3CD2Iin solid parahydrogen at 4.4K.135 Under these conditions, the iodide precursorexisted in both monomeric and dimeric units. The monomers underwent com-peting reactions to give CD3CD2·�I or CD2——CD2�I2; the dimers gaveCD2——CD2�C2D6�I2, either directly or via CD3CD2· radicals, followed by aslow disproportionation proceeding by quantum mechanical tunnelling of a Datom.In a comparative study of the A-band photodissociation of partially fluor-

inated alkyl iodides, CF3CH2I, C6F13CH2CH2I and C8F17CH2CH2I, eliminated Iatoms in both ground (2P3/2) and excited (2P1/2) states were detected by two-photon laser induced fluorescence.130 It was found that F atoms at the �-positionincrease the quantum yield of excited I atoms but at the �-position have far lesseffect, and that excited I atoms tend to be the major product over the entireA-band (222—305 nm).A theoretical study has been made of competing C—Cl and C—Br bond fission

in 1[n�*(CO)] photoexcited bromoacetyl chloride.136 Although computed abso-lute rate constants were smaller than those measured experimentally, calculatedbranching ratios were close to experimental values.The triplet �-ketocarbene (84) has been detected in flash-photolysis experi-

ments as the HBr-loss primary product in the photolysis of 2-bromophenol.137

The triplet ketocarbene had UV absorptions with �max�360, 375 and 388nm,and its identity was confirmed by product studies. An alternative pathway gavethe ring-contracted ketene (85), possibly via the singlet ketocarbene. The princi-pal photoproducts of 2-chloro-, 2-bromo- and 2-fluoroaniline in aqueous sol-


utions were found to be 2-aminophenol, aniline and 1-cyanocyclopenta-1,3-diene.138 In the formation of 2-aminophenol, the fluoro derivative reacted signifi-cantlymore efficiently than the chloro and bromo congeners; so it was concludedthat the reactionwas a heterolytic process, probably the substitution of halide bywater. Although a definitive conclusionwas not reached, it seemed likely that thering-contracted product, cyanocyclopentadiene, was formed via initial elimin-ation of the corresponding hydrogen halide to give iminocarbene (86). Photo-chemical reactions of a series ofN-(2-bromoalkanoyl)anilines (87) gave HBr-lossproducts (88), (89) and (90) in yields and proportions depending on the substitu-ents R andX.139 Some cyclic analogues (91; n�1—2; X�Cl, Br) underwent similarphotoreactions.

Chlorobenzene in ice exhibits unusual photochemistry when irradiated at254nm.140 Thus, biphenyl and terphenyl, together with chlorinated derivatives,and triphenylene were formed in ice, possibly via free radicals, in contrast toliquid water, in which phenolic products are formed almost exclusively. Thephotolysis of C60Cl6 in the presence of a spin trap has been examined in an EPRstudy.141 A C—Cl bond underwent homolytic cleavage to give a stable fullereneradical of the cyclopentadienyl type.

7.3 Photofragmentations of Organosilicon and Organogermanium Com-pounds. — The literature on the gas-phase laser photolysis of organosilicon com-pounds for chemical vapour deposition has been reviewed.142 Time-resolvedphotoionization mass spectrometry has been used to study the kinetics of theformation of Si2H2 by 193nm photolysis of disilane.143 No reaction of Si2H2 withH2, CH4, SiH4 or Si2H6 was observed, but decay rates for Si2H2 reacting with O2,NO and HCl were measured and exhibited negative dependence on the totalpressure.1-Benzyl-1-methylsilacyclobutane (92; R�Me) undergoes a rearrangement to

(93) in quantitative yield when photolysed in methanolic hexane solution, by asequential two-photon process involving intermediate (94; R�Me); whereas the1-phenyl analogue (92; R�Ph), under similar conditions, gives a complex mix-ture of products consistent with competing formation of 1-benzyl-1-phenylsilene

Photochemistry324

and benzyl- and phenylsilacyclobutyl radicals.144 The silene intermediate wasdetected directly in flash-photolysis experiments with �max at 315 nm; while theradical intermediates were shown to arise by secondary photolysis of the otherprimary photoproduct (94; R�Ph). Photolysis of the dihydro-9-silaanthracene(95; R�Ph) produced 9-phenyl-9-silaanthracene (96; R�Ph); the parent dihydrocompound (95; R�H) gave (96; R�H), but in very low yield.145 These reactionswere also studied at 77K in 3-methylpentane glasses, and this showed that theunsubstituted silaanthracene (95; R�H) decomposed to carbon-centred radicalsand silenes, while the phenyl derivative (95; R�Ph) gave radicals as well as (96;R�Ph).146

The stereospecific formation of 1,3-disilacyclobutanes has been observed tooccur in the photolysis of organometallic precursors, as exemplified by theconversion of the meso compound (97) exclusively into the trans product (98)(Scheme 6).147 The racemic mixture diastereoisomeric with (97) gave only the cisstereoisomer of (98). Paramagnetic intermediates formed by photolysis of thesilanorbornadiene derivative (99) in the presence of electron-density donors(PPh3 and O2) have been investigated by spin-chemistry methods (CIDNP andmagnetic field effects).148 The results have provided the second example of areaction of triply excited dimethylsilylene. Cyclotetrasilenes (100; R1�Pri,R2�Pri, But) have been generated photolytically from ladder oligosilanes(101) and trapped as Diels-Alder adducts with 2,3-dimethylbuta-1,3-diene oranthracene.149 Both photolysis and thermolysis of betaines(R1

3P�—CR2R3—SiR4R5—S�) containing the fragment �P—C—Si—S� have beenshown to follow two main pathways: (i) elimination of Ph3P (R1�Ph) andformation of a silathiirane and (ii) a elimination of R3P——CR2R3 and generationof a silanethione R4R5Si——S.150

In an investigation of the formation of aerosol particles in the gaseous photo-lysis of mixtures of allyltrimethylsilane and acrolein, it was shown that the silaneunderwent a retroene elimination of propene to give 2-methyl-2-silapropene, aswell as C—Si homolysis to give allyl and trimethylsilyl radicals.151 The decomposi-tion of 1,3-dimethyldisiloxane152 and its diethyl analogue153 induced by IR lasersor UV photolysis has been examined as a means of producing nano-structured


hydridoalkylsilicones. With the diethyldisiloxane, IR laser-induced thermolysisis dominated by 1,1-H2 and ethylene elimination, while UV photolysis resultsmainly in 1,1-H2 and ethane elimination; this difference influences the composi-tion of the resulting nanotextured films.

The photodissociation of jet-cooled silane and germane by Lyman-� light(121.6 nm) yields H atoms with low kinetic energies, consistent with a three-bodyfragmentation to, primarily, H�H�SiH2 (or GeH2).98 The IR multiphotonexcitation of propyltrimethylgermane in the collisionless regime yields propene,with a threshold energy above the dissociation energy of the starting compound,in agreement with a recombination mechanism involving H atoms.154 EPRsignals belonging to triphenylsilyl and triphenylgermyl radicals were observedfollowing photolysis of hexaphenyldisilane and hexaphenyldigermane in sol-ution, but the triphenylstannyl radical could not be similarly detected within theavailable time resolution (ca. 80 ns).155 The photochemistry of trimethylsilyl-triphenylgermane (Ph3GeSiMe3), triphenylsilyltrimethylgermane (Ph3SiGeMe3)and 1,1,1-trimethyl-2,2,2-triphenyldigermane (Ph3GeGeMe3) in hydrocarbonsolvents has been studied by steady state and flash photolysis.156 In each case, themajor products were derived from either homolysis of the Ge—Si or Ge—Ge bondor from extrusion of dimethyl- or diphenylgermylene. The 350nm photolysis ofthe siladigermirane (102; Mes�2,4,6-trimethylphenyl) in toluene in the presence

of MeMgI gave a complex product mixture (after work-up with NH4Cl), fromwhich five products were isolated and identified: Mes2GeHMe, MesGeHMe2,(But2MeSi)MesGeHMe, m-(di-t-butylmethylsilyl)toluene and p-(di-t-butyl-methylsilyl)toluene.157 The first of these products was thought to arise by addi-tion of MeMgI to photoextruded dimesitylgermylene, the second by formationof dimesitylmethylgermylmagnesium iodide from the first product, followed byelimination of MesMgI to give mesitylmethylgermylene and then addition ofMeMgI. The third product was supposed to derive from addition of MeMgI toMes2Ge——SiBut2, followed by elimination of MesMgI and a second addition ofMeMgI, while the most reasonable explanation for the two aromatic productswas the addition of di-t-butylmethylsilyl radicals to the solvent, toluene, followedby H-atom abstraction.

Photochemistry326

7.4 Photofragmentations of Organosulfur, Organoselenium and Organotel-lurium Compounds. — The photodissociations of dimethyl sulfide158,159 and itsfully deuteriated isotopomer159 have been investigated by velocity map imaging.Electronic excitation of dimethyl sulfide in the first absorption band producedMeS· and Me· radicals with substantial translational but little vibrational en-ergy. The dissociation dynamics of ethylene sulfide have been studied by meansof tunable synchrotron radiation, and the results have suggested the existence ofa reaction channel giving S(3P) in conjunction with triplet ethylene, C2H4 (3B1u),and have allowed the first experimental measurement of the energy of the latterspecies near its equilibrium geometry, in which the two methylene groups lie inperpendicular planes.160

A number of alkoxyl and cycloalkoxyl radicals (RO·), along with the 4-nitrobenzenethiyl radical (4-NO2C6H4S·), have been generated by flash photoly-sis of 4-nitrobenzenesulfenate esters (103), and rate constants determined fortheir �-scission or 1,5-H abstraction reactions.161 The cinnamyloxy radical(PhCH——CHCH2O·) has also been generated from the corresponding 4-nitro-benzenesulfenate, and was found to undergo an unprecedented epoxide ringclosure, to give the oxiranyl benzyl radical.162 Calculations (B3LYP/6-31G*)suggested that the closed form of the radical is about 20 kJmol�1 more stablethan the open form; so the ring closure appears to be thermodynamically driven.The 2,2-diphenylcyclobutylcarbinyl radical, along with the 2-pyridylthiyl rad-ical, was generated from (104), by photo-induced O—N cleavage followed by

decarboxylation, and the kinetics of its ring opening were investigated.163 As aresult, the 2,2-diphenylcyclobutylcarbinyl radical was proposed as a useful calib-rated radical clock, which is somewhat faster than the cyclopropylcarbinylradical. The sulfine (55), generated in argon matrices by photoelimination of N2

from (54), gave (57) by photoelimination of COS, as well as the rearrangementproduct (56), as mentioned earlier in this chapter (Section 3.3).37 Note also thephotoelimination reactions of betaines containing the fragment �P—C—Si—S�

described above (Section 7.3).150

Laser-induced photolysis of gaseous selenophene and tellurophene affordsbut-1-en-3-yne and ethyne as major products, with very minor amounts ofbutadiyne, and results in chemical vapour deposition of selenium and telluriumfilms.164

7.5 Photolysis of o-Nitrobenzyl Derivatives and Related Compounds. — Thephotoinduced transfer of hydrogen from methylene groups to nitro in o-nitro-benzyl compounds has been examined by time-resolved resonance Raman andabsorption spectroscopy.165 Although these processes are not themselves photo-


eliminations, the data acquired in this study are relevant to an understanding ofthe more usual photocleavages of o-nitrobenzyl ethers or esters. EPR spectrahave been obtained for radical species generated by photolysis of a series ofo-nitrobenzyl compounds, including the caged ATP (105) and the caged mono-methyl phosphate (106).166 The photolysis of caged ATP has been investigatedpreviously and the accepted mechanism for its photofragmentation leads to thegeneration of ATP� with no role postulated for free radicals. This latest studyshows, however, that the photolysis of (105) is quite complicated: the resultingreactions include photoisomerization, photofragmentation, electron transfer,intramolecular addition and spin-trapping reactions of the nitroso group pro-duced via molecular rearrangement. Unwanted complexity was also uncoveredin the photochemical cleavage of an �-methyl-6-nitroveratryl-based photolabilelinker for peptide synthesis.167 Fortunately it was found that the undesired effectscould be largely reduced by the choice of appropriate reaction conditions.

Photolysis of 1-acyl-7-nitroindolines (107) in aqueous solution releases thecarboxylic acid (RCO2H) and a 7-nitrosoindole, and it was suggested that thisreaction would provide a convenient source of photochemically generated car-boxylic acids, particularly neuroactive amino acids.168 The effect of electron-donor substituents (X) in the 4-position was investigated as part of this research,and it was found that a methoxy group improved the photolysis efficiency bymore than two-fold, but a 4-dimethylamino group suppressed the reactioncompletely. Indirect phosphorylation of hydroxylic solvents has been accom-plished by UV photolysis of the nitrobenzyl ester (108), by a mechanism whichseems to involve photo-induced de-esterification followed by dissociation of theresulting species, (HO)2P(O)C(NOH)CO2H.169

An examination of wavelength selectivity in the removal of photolabile pro-tecting groups, including o-nitrobenzyl derivatives, has been published.170 Forsome groups, the order of reactivity at 254 nm was found to be reversed at491nm. The syntheses of photolabile phosphotriester derivatives of dinucleosidephosphates, containing o-nitrobenzyl or o-nitroveratryl moieties, have been

Photochemistry328

reported.171 Photolabile protecting groups for nucleosides, based on o-nitro-phenylethylcarbonate groups, have been the subject of a patent,172 and a novelphotoscissile poly(ethylene glycol)-based hydrogel has been developed, whichexploits nitrocinnamate pendant groups. 173

7.6 Other Photofragmentations. — The photodynamics of the Lyman-� photo-dissociation of HCN174,175 and DCN175 have been investigated both theoreticallyand experimentally, and an improved value of the dissociation energyD0(H—CN)obtained. At this wavelength,HCN fragments toH�CN,with CN in bothA andB states, whereas for DCN no significant branching to CN(B) occurs. Time-of-flight mass spectrometry has been utilized to study the irradiation of CH3CN bysoft X-rays, which results in the formation of CF3

�, CF2� and CN� fragments.176

Photolysis of p-(�-hydroxyethyl)toluene at 266 nm in n-heptane results inC—OH bond fission.110 The dissociation rate was found to be �1.0�109 s�1,which is much greater than that of the C—H bond fission observed under thesame conditions for p-ethyltoluene (see Section 7.1). In contrast to p-ethyl-toluene, the initially populated S1 [��*(benzene)] state of p-(�-hydroxy-ethyl)toluene crosses adiabatically to the dissociative np(O) *(C—O) state, thusallowing rapid C—OH bond fission. A series of ten substituted aryl t-butyl ethersgave as the major products the corresponding phenols, as well as t-butyl sub-stituted phenols, when irradiated at 254nm.177 Quenching studies with 2,3-dimethylbutadiene indicated that the photoreactions took place from the singletexcited state; quantum yields and singlet lifetimes were found to correlatereasonably well with h values, with ��0.77, consistent with polarity of bondbreaking in the transition state of the type O(��)· · ·C(��). The photochemicaldissociation of alkylperoxy radicals on activated silica surfaces has been exam-ined, and parallel pathways involving rupture of both O—Oand C—Obonds werefound.178

The photorelease of diethyl phosphate from the p-hydroxyphenacyl derivative(109), a potentially useful means of achieving fast release for monitoring physio-logical responses, has been shown to proceed via the triplet excited state.179

Photolyses of aldoxime esters (ArCH——NOCOR), containing a range of alkyland cycloalkyl groups, resulted in N—O bond cleavage and the formation ofaryliminyl (ArCH——N·) and alkyl (R·) radicals.180 The process was favoured by4-methoxyacetphenone, added as a photosensitizer, and by methoxy substitu-ents on the aryl ring; 4-nitro and pentafluoro substitution, on the other hand,were deleterious. The analogous photolyses of aldoxime ethers (ArCH——NOR)gave alkoxy and aryliminyl radicals, but only in very low yields.181 o-Quinonemethide (110) has been generated in water by thermolysis and photolysis of(2-hydroxybenzyl)trimethyl iodide (111).182 Alkylations of various amines andsulfides, including amino acids and glutathione, were accomplished in goodyields by Michael additions to (110) generated in this way.Photodissociation dynamics of s-triazine at 193 and 248nm have been studied

by probing the HCN fragments using coherent anti-Stokes Raman spectroscopy(CARS).183 Room-temperature photolysis of the benzodithiadiazine (112) affordsradical (113) in nearly quantitative yield, in an extraordinary reaction that


involves a ring contraction and loss of a nitrogen atom.184 Radical (113) and aseries of substituted analogues were also produced by thermolysis of the corre-sponding benzodithiadiazine precursors, and EPR spectra of these species wereobtained. Carbazolyl nitrenium cations, which can be in either the singlet ortriplet state, are generated by photolysis and thermolysis of 1-(carbazol-9-yl)-2,4,6-triphenylpyridinium tetrafluoroborate.185

Photorelease of the cyclopentadienyl radical is among the topics covered in areview of the electronic spectra and photoreactivity of cyclopentadienyl com-plexes.186 UV irradiation of CpRh(C2H4)2 (Cp��5-C5H5) gives products arisingfrom the initial photoelimination of CpRh.187 The synthesis of nanoparticles bythe laser-induced photodissociation of ferrocene has been investigated.188,189

The monomeric carbenoid complex [LiCH2SPh(pmdta)] (pmdta�N,N,N�,N,N-pentamethyldiethylenetriamine) undergoes extrusion of themethylene group when photolysed in toluene, with formation of CH4 andLiSPh(pmdta).190 In refluxing toluene, the thermal reaction follows a dimerizing�-elimination pathway, to give LiSPh(pmdta) and ethylene.The 157nm photodissociation of polyamides191 and the photodegradation of

polyoxymethylene192 at 122, 147 and 193nm have been examined. The latterstudy was aimed at understanding the photochemical evolution of organicmolecules in comets, and the main products identified were H2CO, CO, HCO2H,CO2, MeOH, MeOCHO,MeOCH2OMe and C3H6O3 (trioxane).

8 References

1. E. Vauthey, EPA Newsl., 2000, 70, 30.2. M. Wegner, H. Fischer, S. Grosse, H.-M. Vieth, A. M. Oliver and M. N. Paddon-

Row, Chem. Phys., 2001, 264, 341.3. B. Godicke, A. Langenscheidt, H. Meyer and A. Schweig, Chem. Phys., 2000, 261,

339.4. M. C. Castex, N. Bityurin, C. Olivero, S. Muraviov, N. Bronnikova and D. Riedel,

Appl. Surf. Sci., 2000, 168, 175.5. G. N. Makarov and A. N. Petin, Quantum Electron., 2000, 30, 738.6. M. Terazima, Y. Nogami and T. Tominaga, Chem. Phys. Lett., 2000, 332, 503.

Photochemistry330

7. W. Adam, V. Martı, C. Sahin and A. V. Trofimov, J. Am. Chem. Soc., 2000, 122,5002.

8. J. R. Snoonian and M. S. Platz, J. Phys. Chem. A, 2001, 105, 2106.9. S. H. Cho, W.-H. Park, S. K. Kim and Y. S. Choi, J. Phys. Chem. A, 2000, 104,

10482.10. H. Bornemann and W. Sander, J. Am. Chem. Soc., 2000, 122, 6727.11. E. L. Tae, Z. Zhu and M. S. Platz, J. Phys. Chem. A, 2001, 105, 3803.12. K.Mlinaric-Majerski, J. Veljkovic andM. Kaselj,Croat.Chem.Acta, 2000, 73, 575.13. The authors in ref. 12 give�196 °C (77K) as the temperature of the matrix, but this

is the boiling point of N2 and is clearly quoted in error; N2 matrices normallyrequire temperatures below 25K.

14. G. Maier and J. Endres, J.Mol. Struct., 2000, 556, 179.15. G. Maier and J. Endres, Eur. J. Org. Chem., 2000, 2535.16. H. Durr, A.-M. A. Abdel-Wahab, M. T. Ismail and O. S. Mohamed, J. Photochem.

Photobiol. A, 2000, 132, 167.17. M. Kiszka, I. R. Dunkin, J. Gebicki, H. Wang and J. Wirz, J. Chem. Soc., Perkin

Trans. 2, 2000, 2420.18. H. Itakura and H. Tomioka, Org. Lett., 2000, 2, 2995.19. B. Kozankiewicz,M. Aloshyna, A. Sienkiewicz,M.Orrit, P. Tamarat, C.M.Hadad,

J. R. Snoonian and M. S. Platz, J. Phys. Chem. A, 2000, 104, 5213.20. Y. N. Romashin, M. T. H. Liu and R. Bonneau, Tetrahedron Lett., 2001, 42, 207.21. S. Çelebi, M.-L. Tsao and M. S. Platz, J. Phys. Chem. A, 2001, 105, 1158.22. T. Khasanova and R. S. Sheridan, J. Am. Chem. Soc., 2000, 122, 8585.23. A. M. Nazarov, E. M. Chainikova, P. V. Krupin, S. L. Khursan, I. A. Kalinichenko

and V. D. Komissarov, Russ. Chem. Bull., 2000, 49, 1496; Izv. Akad. Nauk, Ser.Khim., 2000, 1504.

24. A. M. Nazarov, A. I. Voloshin, V. D. Komissarov and V. P. Kazakov, Dokl. Akad.Nauk, 2000, 371, 634; Chem. Abstr., 2000, 133, 134955p.

25. M. A. Garcia-Garibay, S. Shin and C. N. Sanrame, Tetrahedron, 2000, 56, 6729.26. C. Morita, K. Hashimoto, T. Okuno and H. Shirahama, Heterocycles, 2000, 52,

1163.27. T. Ruhl, L. Hennig, Y. Hatanaka, K. Burger and P.Welzel,TetrahedronLett., 2000,

41, 4555.28. Y. Hatanaka, U. Kempin and P. Jong-Jip, J. Org. Chem., 2000, 65, 5639.29. J.-L. Wang, T. Yuzawa, M. Nigam, I. Likhotvorik and M. S. Platz, J. Phys. Chem.

A, 2001, 105, 3752.30. D. D. Sung, J. P. Lee, Y. H. Lee, W. S. Ryu and Z. H. Ryu, J. Photosci., 2000, 7, 15.31. F. Ortica, G. Pohlers, J. C. Scaiano, J. F. Cameron and A. Zampini,Org. Lett., 2000,

2, 1357.32. T. Mizushima, S. Ikeda, S. Murata, K. Ishii and H. Hamaguchi, Chem. Lett., 2000,

1282.33. Y. Chiang, S. J. Eustace, E. A. Jefferson, A. J. Kresge, V. V. Popik and R.-Q. Xie, J.

Phys. Org. Chem., 2000, 13, 461.34. G. Maas and S. Bender, Chem. Commun., 2000, 437.35. J. L. Pitters, K. Griffiths, M. Kovar, P. R. Norton and M. S. Workentin, Angew.

Chem. Int. Ed., 2000, 39, 2144.36. F. Ortica, G. Pohlers, C. Coenjarts, E. V. Bejan, J. F. Cameron, A. Zampini, M.

Haigh and J. C. Scaiano, Org. Lett., 2000, 2, 3591.37. W. Sander, A. Strehl, A. R. Maguire, S. Collins and P. G. Kelleher, Eur. J. Org.

Chem., 2000, 3329.


38. Y. Ozawa, A.Watanabe, A. Seki, K. Takemura and S. Nagura (Shin-Etsu ChemicalIndustry Co. Ltd.), Japanese Patent 2001 106,669, 17 Apr 2001;Chem. Abstr., 2001,134, 303026q.

39. S. V. Zelentsov, N. V. Zelentsova, A. B. Zhezlov and A. V. Oleinik, High EnergyChem., 2000, 34, 164;Khim. Vysokikh Energii, 2000, 34, 201.

40. L. N. Karyakina and A. V. Gubinov, High Energy Chem., 2000, 34, 256; Khim.Vysokikh Energii, 2000, 34, 300.

41. C. Kan, C. M. Long, M. Paul, C. M. Ring, S. E. Tully and C. M. Rojas, Org. Lett.,2001, 3, 381.

42. S. V. Chapyshev, R. Walton and P. M. Lahti,Mendeleev Commun., 2000, 114.43. S. V. Chapyshev, R. Walton and P. M. Lahti,Mendeleev Commun., 2000, 187.44. S. V. Chapyshev, R. Walton and P. M. Lahti,Mendeleev Commun., 2000, 138.45. S. Araki, H. Hattori, H. Yamamura and M. Kawai, J. Heterocycl. Chem., 2000, 37,

1129.46. K. A. H. Chehade and H. P. Spielmann, J. Org. Chem., 2000, 65, 4949.47. E. L. Mishchenko, L. A. Kozhanova, A. Y. Denisov, N. P. Gritsan, Y. Y. Mar-

kushin, M. V. Serebriakova and T. S. Godovikova, J. Photochem. Photobiol. B,2000, 54, 16.

48. E. Mappus, C. Chambon, B. Fenet, M. Rolland de Ravel, C. Grenot and C. Y.Cuilleron, Steroids, 2000, 65, 459.

49. D. Durand, P. Hullot, J.-P. Vidal, J.-P. Girard, J. L. Baneres, J. Parello, A. Muller,C. Bonne and J.-C. Rossi, Bioorg.Med. Chem. Lett., 2000, 10, 811.

50. L. W. Deady, J. Desneves and L. M. Tilley, J. Labelled Compd. Radiopharm., 2000,43, 977.

51. T. Pacuszka and M. Panasiewicz, J. Labelled Compd. Radiopharm., 2000, 43, 1255.52. R. Itakura, A. Hishikawa and K. Yamanouchi, J. Chem. Phys., 2000, 113, 6598.53. L. Zhao and Z. Li, Sci. China, Ser. B: Chem., 2001, 44, 31.54. D. R. Yarkony, J. Chem. Phys., 2001, 114, 2614.55. R. Schinke and M. Bittererova, Chem. Phys. Lett., 2000, 332, 611.56. G. P. Glass, S. S. Kumaran and J. V. Michael, J. Phys. Chem. A, 2000, 104, 8360.57. X. Li, J. M. Millam and H. B. Schlegel, J. Chem. Phys., 2000, 113, 10062.58. H. Su, Y. He, F. Kong, W. Fang and R. Liu, J. Chem. Phys., 2000, 113, 1891.59. T. Sato, H. Niino and A. Yabe, Chem. Commun., 2000, 1205.60. M. Xu and P. Wan, Chem. Commun., 2000, 2147.61. T. Mori, T. Wada and Y. Inoue, Org. Lett., 2000, 2, 3401.62. G. L. Hug, M. Bonifacic, K.-D. Asmus and D. A. Armstrong, J. Phys. Chem. B,

2000, 104, 6674.63. S. Ikeda, S. Murata, K. Ishii and H. Hamaguchi, Bull. Chem. Soc. Jpn., 2000, 73,

2783.64. A. G. Griesbeck, M. Oelgemoller and J. Lex, Synlett, 2000, 1455.65. A. G. Griesbeck, W. Kramer and J. Lex, Angew. Chem. Int. Ed., 2001, 40, 577.66. G. Suarez, F. M. Cabrerizo, C. Lorente, A. H. Thomas and A. L. Capparelli, J.

Photochem. Photobiol. A, 2000, 132, 53.67. H. Kawata, T. Kumagai, T. Morita and S. Niizuma, J. Photochem. Photobiol. A,

2001, 138, 281.68. S. C. Reed, G. J. Capitosti, Z. Zhu andD. A.Modarelli, J.Org.Chem., 2001, 66, 287.69. A. J. Lees, Coord. Chem. Rev., 2001, 211, 255.70. T. E. Bitterwolf, Coord. Chem. Rev., 2001, 211, 235.71. T. E. Bitterwolf, Coord. Chem. Rev., 2000, 206-207, 419.72. S. A. Trushin, W. Fuß and W. E. Schmid, Chem. Phys., 2000, 259, 313.

Photochemistry332

73. M.W. George,M. Poliakoff, X.-Z. Sun andD. C. Grills,Laser Chem., 1999, 19, 133.74. J. J. Turner, M.W. George, I. P. Clark and I. G. Virrels, Laser Chem., 1999, 19, 245.75. I� . A. Morkan and A. Uztetik-Morkan, Z.Naturforsch., B, 2000, 55, 1153.76. S. Luukkanen, M. Haukka, E. Eskelinen, T. A. Pakkanen, V. Lehtovuori, J.

Kallioinen, P. Myllyperkio and J. Korppi-Tommola, Phys. Chem. Chem. Phys.,2001, 3, 1992.

77. J. L. King, K. Molvinger andM. Poliakoff, Organometallics, 2000, 19, 5077.78. K. Molvinger, G. I. Childs, M. Jobling, M. Roper, M. W. George andM. Poliakoff,

Chem. Lett., 2000, 1260.79. Ç. Bozkurt, J. Organomet. Chem., 2000, 603, 252.80. G. Bhukta, R. Manivannan and G. Sundararajan, J. Organomet. Chem., 2000, 601,

16.81. B. Marciniec and M. Majchrzak, Inorg. Chem. Commun., 2000, 3, 371.82. L. Federici and P. E. Hoggard, Inorg. React.Mech., 2000, 2, 179.83. K. O. Doyle,M. L. Gallagher,M. T. Pryce and A. D. Rooney, J.Organomet.Chem.,

2001, 617-618, 269.84. G. I. Childs, D. C. Grills, S. Gallagher, T. E. Bitterwolf andM.W. George, J.Chem.

Soc., Dalton Trans., 2001, 1711.85. G. I. Childs, S. Gallagher, T. E. Bitterwolf andM.W. George, J.Chem. Soc.,Dalton

Trans., 2000, 4534.86. J. B. Asbury, K. Hang, J. S. Yeston, J. G. Cordaro, R. G. Bergman and T. Lian, J.

Am. Chem. Soc., 2000, 122, 12870.87. N. Dunwoody, S.-S. Sun and A. J. Lees, Inorg. Chem., 2000, 39, 4442.88. T. E. Bitterwolf, W. B. Scallorn and C. A. Weiss, J. Organomet.Chem., 2000, 605, 7.89. H. Sun, X. Huang, Z. Hu, Y. Ma and J. Yang, J. Organomet. Chem., 2000, 613, 1.90. K.M. Tawarah, I. Jibril andM. Z. Bani-Fwaz,TransitionMet.Chem., 2000, 25, 659.91. V. A.Maksakov, I. V. Slovokhotova and S. P. Babailov,Russ.Chem. Bull., 2000, 49,

747; Izv. Akad.Nauk, Ser.Khim., 2000, 746.92. M. Barrow, N. L. Cromhout, D. Cunningham, A. R. Manning and P. McArdle, J.

Organomet. Chem., 2000, 612, 61.93. D. Puchowicz, J. Adamus and J. Gebicki, J. Chem. Soc.,PerkinTrans. 2, 2000, 1942.94. M. Rasmusson, E. Aakesson, L. Eberson and V. Sundstroem, J. Phys. Chem. B,

2001, 105, 2027.95. R. Etchenique, M. Furman and J. A. Olabe, J. Am. Chem. Soc., 2000, 122, 3967.96. J. E. Fieberg and J. M. White, J. Chem. Phys., 2000, 113, 3839.97. C. Kim, W. Zhao and J. M. White, Surf. Sci., 2000, 464, 240.98. P. A. Cook, M. N. R. Ashfold, Y.-J. Jee, K.-H. Jung, S. Harich and X. Yang, Phys.

Chem. Chem. Phys., 2001, 3, 1848.99. J.-H. Wang, K. Liu, Z. Min, H. Su, R. Bersohn, J. Preses and J. Z. Larese, J. Chem.

Phys., 2000, 113, 4146.100. E. H. Wilson and S. K. Atreya, J. Geophys. Res. (Planets), 2000, 105, 20263.101. S. M. Wu, J. J. Lin, Y. T. Lee and X. Yang, J. Chem. Phys., 2000, 112, 8027.102. G. Amaral, K. Xu and J. Zhang, J. Chem. Phys., 2001, 114, 5164.103. M. Ben-Nun and T. J. Martınez, Chem. Phys., 2000, 259, 237.104. J. J. Lin, C. C. Wang, Y. T. Lee and X. Yang, J. Chem. Phys., 2000, 113, 9668.105. B. Ceursters, H. M. T. Nguyen, J. Peeters and M. T. Nguyen, Chem. Phys., 2000,

262, 243.106. A. M. Mebel, M. Hayashi, W. M. Jackson, J. Wrobel, M. Green, D. Xu and S. H.

Lin, J. Chem. Phys., 2001, 114, 9821.107. S. Harich, J. J. Lin, Y. T. Lee and X. Yang, J. Chem. Phys., 2000, 112, 6656.


108. X. Chen, Y. Ganot, I. Bar and S. Rosenwaks, J. Chem. Phys., 2000, 113, 5134.109. O. Sorkhabi, F. Qi, A. H. Rizvi and A. G. Suits, J. Am. Chem. Soc., 2001, 123, 671.110. M. Fujiwara and K. Mishima, Phys. Chem. Chem. Phys., 2000, 2, 3791.111. G. Amaral, K. Xu and J. Zhang, J. Phys. Chem. A, 2001, 105, 1115.112. A. V. Baklanov, M. Aldener, B. Lindgren and U. Sassenberg, Chem. Phys. Lett.,

2000, 325, 399.113. J. Lu, F. Shao and K. Fan, Chem. Phys. Lett., 2000, 329, 461.114. S.-H. Lee, Y.-J. Jung and K.-H. Jung, Chem. Phys., 2000, 260, 143.115. P. Zou, W. S. McGivern and S. W. North, Phys. Chem. Chem. Phys., 2000, 2, 3785.116. X. Zheng and D. L. Phillips, J. Chem. Phys., 2000, 113, 3194.117. A. N. Tarnovsky, M. Wall, M. Rasmusson, T. Pascher and E. A� kesson, J. Chin.

Chem. Soc. (Taipei), 2000, 47, 769.118. X. Zheng, W. M. Kwok and D. L. Phillips, J. Phys. Chem. A, 2000, 104, 10464.119. X. Zheng and D. L. Phillips, J. Phys. Chem. A, 2000, 104, 6880.120. W. M. Kwok, C. Ma, A. W. Parker, D. Phillips, M. Towrie, P. Matousek and D. L.

Phillips, J. Chem. Phys., 2000, 113, 7471.121. P. Farmanara, V. Stert, H.-H.Ritze andW.Radloff, J.Chem.Phys., 2000, 113, 1705.122. H. A. Scheld, A. Furlan and J. R. Huber, Chem. Phys. Lett., 2000, 326, 366.123. X. Chen, R.Marom, S. Rosenwaks, I. Bar, T. Einfeld, C.Maul andK.-H. Gericke, J.

Chem. Phys., 2001, 114, 9033.124. A. Yokoyama, K. Yokoyama and T. Takayanagi, J. Chem. Phys., 2001, 114, 1617.125. A. Yokoyama, K. Yokoyama and T. Takayanagi, J. Chem. Phys., 2001, 114, 1624.126. T. G. Lee and J. C. Polyani, Surf. Sci., 2000, 462, 36.127. M. J. Dorko, T. R. Bryden and S. J. Garrett, J. Phys. Chem. B, 2000, 104, 11695.128. A. Melchior, X. Chen, I. Bar and S. Rosenwaks, J. Chem. Phys., 2000, 112, 10787.129. X. Zheng and D. L. Phillips, Laser Chem., 1999, 19, 71.130. K. Kavita and P. K. Das, J. Phys. Chem. A, 2001, 105, 315.131. S.-R. Lin, S.-C. Lin, Y.-C. Lee, Y.-C. Chou, I. Chen and Y.-P. Lee, J. Chem. Phys.,

2001, 114, 160.132. Y. R. Lee, L. D. Wang, Y. T. Lee and S. M. Lin, J. Chem. Phys., 2000, 113, 5331.133. Y. R. Lee, L. D. Wang, Y. T. Lee and S. M. Lin, J. Chem. Phys., 2000, 113, 6107.134. J. A. Mueller, B. F. Parsons, L. J. Butler, F. Qi, O. Sorkhabi and A. G. Suits, J.

Chem. Phys., 2001, 114, 4505.135. N. Sogoshi, T.Wakabayashi, T.Momose and T. Shida, J.Phys.Chem.A, 2001, 105,

3077.136. A. J. Marks, J. Chem. Phys., 2001, 114, 1700.137. F. Bonnichon, C. Richard and G. Grabner, Chem. Commun., 2001, 73.138. K. Othmen and P. Boule, J. Photochem. Photobiol. A, 2000, 136, 79.139. T. Nishio, H. Asai and T. Miyazaki,Helv. Chim. Acta, 2000, 83, 1475.140. P.Klan, A. Ansorgova, D. Del Favero and I. Holoubek,TetrahedronLett., 2000, 41,

7785.141. R. G. Gasanov, O. G. Kalina, A. A. Popov, P. A. Dorozhko and B. L. Tumanskii,

Russ. Chem. Bull., 2000, 49, 753; Izv. Akad. Nauk, Ser.Khim., 2000, 752.142. J. Pola, Proc. Indian Natl. Sci. Acad., Part A, 2000, 66, 107.143. Y. Nakajima, K. Tonokura, K. Sugimoto and M. Koshi, Int. J. Chem.Kinet., 2001,

33, 136.144. W. J. Leigh and T. R. Owens, Can. J. Chem., 2000, 78, 1459.145. K. Nishiyama, M. Oba, H. Takagi, I. Fujii, N. Hirayama, Narisu, H. Horiuchi, T.

Okutsu and H. Hiratsuka, J. Organomet. Chem., 2000, 604, 20.

Photochemistry334

146. H. Hiratsuka, M. Tanaka, H. Horiuchi, Naris, T. Yoshinaga, M. Oba and K.Nishiyama, J. Organomet. Chem., 2000, 611, 71.

147. Y. Zhang, F. Cervantes-Lee and K. H. Pannell, J. Am. Chem. Soc., 2000, 122, 8327.148. T. V. Leshina, M. B. Taraban, V. F. Plyusnin, O. S. Volkova and M. P. Egorov,

Russ. Chem. Bull., 2000, 49, 421; Izv. Akad.Nauk, Ser.Khim., 2000, 420.149. H. Matsumoto, S. Kyushin, M. Unno and R. Tanaka, J. Organomet. Chem., 2000,

611, 52.150. I. V. Borisova, N. N. Zemlyanskii, A. K. Shestakova, V. N. Khrustalev, Y. A.

Ustynyuk and E. A. Chernyshev,Russ.Chem.Bull., 2000, 49, 1583; Izv.Akad.Nauk,Ser.Khim., 2000, 1594.

151. K. Semba and H. Morita, J. Photochem. Photobiol. A, 2000, 134, 97.152. J. Pola, M. Urbanova, Z. Bastl, J. Subrt and P. Papagiannakopoulos, J. Mater.

Chem., 2000, 10, 1415.153. M. Urbanova, Z. Bastl, J. Subrt and J. Pola, J.Mater. Chem., 2001, 11, 1557.154. G. P. Zhitneva and Y. N. Zhitnev,High Energy Chem., 2000, 34, 340.155. I. S. M. Saiful, Y. Ohba, K. Mochida and S. Yamauchi, Phys. Chem. Chem. Phys.,

2001, 3, 1011.156. W. J. Leigh, N. P. Toltl, P. Apodaca, M. Catstruita and K. H. Pannell, Or-

ganometallics, 2000, 19, 3232.157. M. S. Samuel, K. M. Baines and D. W. Hughes, Can. J. Chem., 2000, 78, 1474.158. P. Quintana, R. F. Delmdahl, D. H. Parker, B. Martınez-Haya, F. J. Aoiz, L.

Ban ares and E. Verdasco, Chem. Phys. Lett., 2000, 325, 146.159. B. Martınez-Haya, P. Quintana, L. Ban ares, P. Samartzis, D. J. Smith and T. N.

Kitsopoulos, J. Chem. Phys., 2001, 114, 4450.160. F. Qi, O. Sorkhabi and A. G. Suits, J. Chem. Phys., 2000, 112, 10707.161. J. H. Horner, S.-Y. Choi and M. Newcomb, Org. Lett., 2000, 2, 3369.162. J. Amaudrut and O. Wiest, Org. Lett., 2000, 2, 1251.163. S.-Y. Choi, J. H. Horner and M. Newcomb, J. Org. Chem., 2000, 65, 4447.164. J. Pola, Z. Bastl, J. Subrt and A. Ouchi, Appl. Organomet. Chem., 2000, 14, 715.165. H. Takahashi, Y. Watanabe, M. Sakai and M. Tachikawa, Laser Chem., 1999, 19,

357.166. J. E. T. Corrie, B. C. Gilbert, V. R. N. Munasinghe and A. C. Whitwood, J. Chem.

Soc., Perkin Trans. 2, 2000, 2483.167. M. Rinnova, M. Novakova, V. Kasicka and J. Jiracek, J. Peptide Sci., 2000, 6, 355.168. G. Papageorgiou and J. E. T. Corrie, Tetrahedron, 2000, 56, 8197.169. J. M. Carrick, B. A. Kashemirov and C. E. McKenna, Tetrahedron, 2000, 56, 2391.170. C. G. Bochet, Tetrahedron Lett., 2000, 41, 6341.171. T. V. Abramova, J. P. Leonetti, V. V. Vlassov and B. Lebleu,Russ. J.Bioorg.Chem.,

2000, 26, 174.172. W. Pfleiderer, S. Buhler and H. Giegrich (Nigu Chemie GmbH), German Patent

19,952,113, 3 May 2001; Chem. Abstr., 2001, 134, 311401y.173. Y. Zheng, F. M. Andreopoulos, M. Micic, Q. Huo, S. M. Pham and R. M. Leblanc,

Adv. Funct.Mater., 2001, 11, 37.174. E. Soares Barbosa, R. McCarroll, T. P. Grozdanov and P. Rosmus, Phys. Chem.

Chem. Phys., 2000, 2, 3131.175. P. A. Cook, S. R. Langford,M.N. R. Ashfold and R.N. Dixon, J.Chem.Phys., 2000,

113, 994.176. T. Ibuki, K. Okada, T. Gejo and K. Saito, Chem. Phys. Lett., 2000, 328, 147.177. D. P. DeCosta, A. Bennett, A. L. Pincock, J. A. Pincock and R. Stefanova, J. Org.

Chem., 2000, 65, 4162.


178. M.Mel’nikov, V. I. Pergushov andN.Osokina, Spectrochim.Acta,Part A, 2000, 56,2517.

179. P. G. Conrad, II, R. S. Givens, B. Hellrung, C. S. Rajesh, M. Ramseier and J. Wirz,J. Am. Chem. Soc., 2000, 122, 9346.

180. A. J. McCarroll and J. C. Walton, J. Chem. Soc., Perkin Trans. 2, 2000, 2399.181. A. J. McCarroll and J. C. Walton, J. Chem. Soc., Perkin Trans. 2, 2000, 1868.182. E. Modica, R. Zanaletti, M. Freccero and M. Mella, J. Org. Chem., 2001, 66, 41.183. J. H. Kim and H. L. Kim, Chem. Phys. Lett., 2001, 333, 45.184. I. V. Vlasyuk, V. A. Bagryansky, N. P. Gritsan, Y. N. Molin, A. Y. Makarov, Y. V.

Gatilov, V. V. Schcherbukhin and V. Zibarev, Phys. Chem. Chem. Phys., 2001, 3,409.

185. D. Bogdahl,Heterocycles, 2000, 53, 2679.186. A. Vogler and H. Kunkely, Coord. Chem. Rev., 2001, 211, 223.187. J. Muller, C. Hirsch, A. Guo and K. Qiao, Z. Anorg. Allg. Chem., 2000, 626, 2069.188. K. Elihn, F. Otten,M. Boman, P. Heszler, F. E.Kruis, H. Fissan and J.-O. Carlsson,

Appl. Phys. A, 2001, 72, 29.189. P. Heszler, K. Elihn, M. Boman and J.-O. Carlsson, Appl. Phys. A, 2000, 70, 613.190. T. Ruffer, C. Bruhn, A. H. Maulitz, D. Strohl and D. Steinborn, Organometallics,

2000, 19, 2829.191. A. C. Cefelas and E. Sarantopoulou,Microelectron. Eng., 2000, 53, 465.192. H. Cottin, M.-C. Gazeau, J.-F. Doussin and F. Raulin, J. Photochem. Photobiol. A,

2000, 135, 53.

Photochemistry336

Part III

Polymer Photochemistry

By Norman S. Allen

Polymer Photochemistry

BY NORMAN S. ALLEN

1 Introduction

The field of polymer photochemistry remains an active area in applied photo-chemistry with many topics growing in industrial development. Photopolymer-ization and photocuring science and technologies as always continue to bedeveloped particularly with regard toward designing novel and specific initiatorsand materials for specialist applications. Interest in active ionic initiators andradical/ionic processes continues while the photocrosslinking of polymers isattractive in terms of enhancing the physical and mechanical properties ofelectronic materials and the development of liquid crystalline materials. Theoptical properties of polymers remains an active area of strong development witha continued growth in photochromic and liquid crystalline materials. Last yearsaw a major literature explosion in LEDs (light emitting diodes). In this year’sreview it represents one of the largest specialized topics in photochemistry andphotophysics.The photooxidation of polymers on the other hand continues to remain at a

low profile. Bio and photodegradable plastics are important for agriculturalusage although interest here is againminimal. The same applies again to polymerstabilization where commercial applications dominate with emphasis on thepractical use of stabilizers. For dyes and pigments stability continues to be amajor issue.

2 Photopolymerization

Over twenty review articles or papers of topical interest have appeared in the lastyear on all aspects of this major subject area. A number of reviews have appearedon the function of different types of cationic photoinitiators and their futuredevelopment and applications1—4. A number of articles have targeted interest inphotosensitive systems5,6, pressure sensitive adhesives and coatings7—10, modellingand general photoinitiators11—13, photoinitiators for visible light14, maleimides15,nitro-aromatic compounds16, urethane resins17, drying and curing control18,photocurable paints19, polymeric photobased systems20, problems in photocur-ing acrylics21, wood coatings22, dye based initiators and electron-transfer pro-cesses23 and the current state of the art and problem developments24.


339

2.1 Photoinitiated Addition Polymerization. — Many new photoinitiator sys-tems continue to be developed for photopolymerization. A number of water-soluble methacrylate copolymers with pendant benzil groups have been syn-thesized and characterised25. These initiators were found to bemuch less sensitiveto self-quenching reactions and exhibited greater efficiency than non-polymericderivatives. The benzil ketyl radical was determined to be the active initiatingentity in radical polymerization. Using ESR other photofragmenting initiatorsbased on [Z]-sulfonyl-2-oximinoketones give �-ketoiminyl radicals associatedwithN—Ocleavage reactions26. These systems have the advantage of inducing theacid-catalysed polymerization of melamine resins. Although many studies tendto concentrate on the primary initiator other workers have developed novelco-synergisticN,N-dimethylaminobenzoates and benzamides27. The esters werefound to be more effective cosynergists than the corresponding amides. Theactivity of the triplet-exciplex formed with the ketone initiator was found to behighly dependent on many factors including structure, electron donation, ab-sorption and photolytic stability. A number of water-soluble anthraquinonecopolymers have been synthesized based on sulfonic acid and trimethyl-ammonium salts28 and found to exhibit activities equivalent to the model sys-tems. Photoreduction quantum yields were found to correlate well with photo-polymerization rates. Polystyrenemacroinitiators with acylphosphine oxide endgroups have also been found to be effective29 as have acrylated photofragmentinginitiators based on acetophenone30. In the case of poly(styrene peroxide) effectivephotopolymerization was observed for various vinyl monomers31. In the case ofacrylamide and acrylonitrile the styrene peroxide was found to be catalytic andnot attach itself to the polymer chain. However, in the case of methyl methac-rylate polystyrene blocks were found in the final polymer. Acrylic polymers withpyrimidinyl moieties have been found to be effective water-soluble initiators32.They will also enter the final polymer product in the chain giving products withenhanced molecular weights.For a range of thioxanthone initiators photoactivity has been found to be

highly dependent upon the ketone structure with competition betweenmonomerand amine cosynergist quenching playing a major role33. Methyl substitution hasbeen found to influence significantly the photochemistry of 2-(2-hydroxy-3-[bis(2-hydroxyethyl)amino]propoxy)thioxanthone34 while a range of novelwater-soluble thioxanthones have been prepared and the activities found tocorrelate well with structure/photochemical activities35—37. Trithianes have beenreported to accelerate the benzophenone-initiated photopolymerization of vinylmonomers38. However, the rates did not correlate with derived radical formationfrom laser flash photolysis. Quenching effects may account for this as well as theformation of derived radicals from the trithianes. Astramol polypropyleneiminedendrimers are highly effective co-synergists when compared with simplealiphatic tertiary amines39. Such molecules have low volatility and graft into thepolymer network. From a series of novel benzoin ether initiators, photoinitiationactivity has been related to their ability to generate free radicals via cleavagerather than being related to their absorption properties in the near UV-visibleregions40. In the case of p-nitroaniline, photoinitiation occurs through the forma-

Photochemistry340

tion of nitro and amino radicals41 formed by proton transfer from the amine tothe nitro group. Photoinitiationwas found to bemore active in non-polarmedia.Similar reactions have been found whereN-acetyl-4-nitro-1-naphthylamine is apowerful sensitizer coupled with the use ofN,N-dimethylaniline42. Other organicnon-ketonic type initiators include poly(dialkyl or alkylphenylsilanes)43 whichhave been found to exhibit high quantum yields of conversion for vinyl andacrylated monomers. Sulfur-containing carboxylic acids synergize effectively inthe photoinduced polymerization of acrylamide using 4-carboxybenzophenoneas an initiator44. The yield of secondary processes is considered important herefollowing the initial step of electron transfer. Decarboxylation is importantespecially in the case of aromatic carboxylic acids where this process is facile.Molecules that do not undergo facile decarboxylation were found to be poorinitiators. Exciplex formation between 3-amino-9-ethylcarbazole and acrylo-nitrile gives rise to polymerization45 while for 1-phenyl-3-sulfonyloxy-1,2-pro-panediones sulfonic acid is formed46. Various chromophoric groups attached toTEMPO have been found to operate as effective systems for forming livingpolymers47. Intramolecular quenching within the TEMPO structure was con-sidered to be important in controlling the initiator triplet lifetime and efficiency.Monochloroacetic acid with dimethylaniline is also claimed to be an effectiveinitiator complex48. Non-ideal kinetics on the polymerization rate indicatedinitiator termination steps and/or degradative initiator transfer with solventplaying a major role. Halomethyl aromatic compounds operate in a similar wayin accelerating the efficiency of benzophenone or anthraquinone initiators49. Inthis case oxygen remains an effective inhibitor with photolysis of the initiatorcomplex palying a role in controlling the escape of radicals from the ‘complex-cage’.Dye complexes continue to show high efficiency in specialised applications.

Cyanine-butyltriphenylborate salts have been found to undergo efficient elec-tron transfer to give sec-butyl radicals50. Dye bleaching during polymerizationdid not influence the overall rate of reaction. Coumarin dyes in conjunction withiodonium salts effectively initiate the polymerization of acrylated monomers51.This reaction is found to proceed via the singlet state of the coumarin complexdue to its oxygen insensitivity. The only problem with this complex was thepotential role of coumarin radicals in acting as chain terminators. Similarcomplexes have been found between Methylene Blue dye and diethanolaminewith iodonium salts52,53. The iodonium salt operates as an effective oxidizingagent to convert the dye back to its original state allowing it to re-enter theprimary process. Eventually, the iodonium salt will photolyse to give initiatingphenyl radicals. Squarylium dyes with iodonium salts are likewise effectiveelectron-transfer initiators giving rise to effective radical formation and dyebleaching54. Coumarin or ketocoumarin have been found to interact with othersensitizers such as bisimidazole55. Here the coumarin derivatives form radicalsvia electron transfer while ketocoumarin undergoes energy transfer. Such sys-tems had applicability in laser imaging. The presence of 1-naphthol with iod-onium salts also undergo electron transfer56. Other highly active compositionsinclude benzothiazoles and aminostyryl dyes with 3,3�4,4�-tetrakis(tert-butyl-

III: Polymer Photochemistry 341

peroxycarbonyl)benzophenone57,58, quinoxalines with amines59, dyes with hexa-arylbiimidazole60 and xanthene dyes with61,62 and without amines63.Metal-based initiators continue to have specialized applications. Poly(ethyl

methacrylate) has been prepared using bis(cyclopentadienyl)titanium dichlorideas initiator to give a polymer that has high acetone insolubility64. Pentacarbonyl-rhenium(I) halides have been found to effectively ring open cyclohexene oxide65.Removal of the carbonyl ligand deactivates the initiator. Tungsten hexacarbonylhas been found to polymerize alkynes and strained cyclic olefins66 as doesdirhenium decacarbonyl67. Zinc chloride on the other hand polymerizes acrylo-nitrile to give an unusually insoluble polymer, which decomposes at only 160 °Cto give the cyclic tetrahydronaphthyridine ring chains68. Ruthenium bipyridylwill polymerize dimercapto-1,3,4-thiadiazole on irradiation69. The polymer isalso able to be removed upon electrochemical reduction. A radical mechanismoperates in the polymerization of styrene with triphenylbismuthonium ylide70

while a series of trialkyl derivatives of Si, Ge and Sn have been found suitable forproducing ‘living polymer systems’71. Benzoyl-substituted ferrocenes have beenshown to be effective anionic initiators72,73. Irradiation gives rise to ring—metalcleavage to give a benzoyl-substituted cyclopentadienide carbanion species. Thisprocess occurs with apparently high efficiency for the dibenzoyl derivatives.Platinum(II) diketonates have been found to ring-open 1,1,3,3-tetramethyl-1,3-disilacyclobutane74.Biorenewable monomers have been discussed which can easily be photo-

polymerized via cationic initiators75. Epoxide—vinyl ether mixtures apparentlyundergo photoinduced cationic polymerizations without copolymerization76.Although interactions take place this is highly dependent upon the nature of theepoxide monomer. In general, the vinyl ether polymerization is slower andusually completes only after the epoxide polymerization has ceased. A mechan-ism involving an equilibrium between alkoxy-carbenium and oxonium ions wasproposed to account for the rates. The presence ofN-vinylcarbazole proved to bea sensitizer77. A series of novel sulfonium salts have been prepared where thepresence of an indanonyl group proved to be highly effective78. Apparently,sulfonium salts possessing polycyclic aromatic structures were the least effective.A series of triphenylphosphonium salts on the other hand only operate aseffective initiators for oxiranes when co-radical generating initiators are pres-ent79. It is claimed that the addition of free radicals to a double bond causesfragmentation of an adduct giving rise to reactive onium radical cations. Thepresence of polyols has been found to enhance the rate of photoinduced polymer-ization of cyclohexene oxide using sulfonium salts80 while onium borates can besensitized by anthracene81. The rate of polymerizationwas found to increase witha corresponding decrease in the free energy change from the excited singlet stateof anthracene to the onium cation of the onium borates. Diphenyliodonium saltsare also effective with dimethylaminobenzophenone82. The enhancement ofphotoinduced cationic initiators with free radical types has also been demon-strated by the use of pyridinium type salts83. The free radicals are oxidized by thepyridinium ions while at the same time the free radicals induce decomposition ofthe pyridinium ions. Novel block copolymers can be made in this way. The

Photochemistry342

cationic polymerization of 2,3-dihydrofuran by sulfonium salts is very rapidgiving a good film forming material84. Cobalt(III) salts of azidopentaamine areeffective in inducing the polymerization of 2-hydroxyethyl methacrylate85. Inwater the reaction is autoaccelerating giving a gel at high monomer concentra-tions. A star shaped polymer of THF has been made by the photoinducedcationic polymerization of THF in the presence of pentaerythritol tetrakis(3,4-epoxybutanoate)86. Epichlorohydrin gave the same effect and appeared to oper-ate by stabilization of the growing cationic chain through ion-pair formation.The molar ratio of the two systems controlled the arm length of the star.Diaryiodonium salts have been shown to be effective near-IR initiators87 andtriarylsulfonium salts induce the ring opening of 1,3-dioxepane88.A number of novel polymer materials have been prepared. Bis(silanes) have

been found to photocopolymerize with methyl methacrylate (MMA)89. Thepresence of the silane functionality apparently accelerated the reaction. Adiblock copolymer has been made from styrene and vinyl acetate, which wasthen hydrolysed to give an amphiphilic diblock copolymer90. Nanostructuredpolymers have also been prepared through hydrogen bonding with nano-liquidcrystalline materials91. Polyacrylamide nanocomposites have been made withvarious metal ions such as Cd, Zn and Pb92. Polyesters containing conjugateddiacetylenes have been photopolymerized and monitored by DSC93 while aphotopolymerizable hydrogel based on an acrylated poly(vinyl alcohol) has beendeveloped for skin implants94. Long chain oligomeric amines have been found toplay an important role in the photosensitized polymerization of oligocarbonatemethacrylates95 via complexation while an alternating copolymer of alkylsorbateswith peroxides has been prepared by photopolymerizationof the mono-mer with oxygen96. The polymeric tributylstannyl ester of silicic acid has beenfound to be a useful intermediate in the preparation of a polysiloxane derivative,which possesses methacryloyloxypropyl groups97. When MMA is photo-polymerized with 2,3-diphenylbutadiene in the presence of a template polymer,poly(N-isopropylacrylamide), using benzoin ether initiators, globular nanopar-ticles are obtained98. The template polymer was not significantly adsorbed intothe particles. A new method for the synthesis of C60-polyfullerenes has beendeveloped in aqueous media99 while other workers have photopolymerizedaerosol particles of mixtures of benzyl chloride with acrolein100. Monomers of1,1,2,2-tetrahydroperfluorodecyl acrylate have been photopolymerized in low-pressure microwave plasmas101 whereas the presence of polyethylene oxide as amacromonomer has been found to decrease the emulsion polymerization of alkylmethacrylates102. The particle size distribution was found to increase with in-creasing size of the alkyl group on the monomer while polymer molecularweights were inversely proportional to the particle size.A few studies have been undertaken on the photopolymerization of maleate

systems. The triplet excited state of maleimides is known to initiate the polymer-ization of acrylate monomers through their ability to abstract hydrogen atoms.By use of laser flash photolysis studies, the rate of quenching of triplet maleim-ides by vinyl ethers has been shown to be independent of the presence of labilehydrogens on the C-atom attached to the central O of the vinyl ether103,104. Using


RTIR the monomer feed composition has been shown to play a decisive role onthe polymerization kinetics of such mixtures105. Thus, when the vinyl ether is inexcess, the two monomers disappear at equivalent rates to yield an alternatingcopolymer. When the maleimide (MI) is in excess, the copolymerization andhomopolymerization of MI occur simultaneously to give copolymers with iso-lated vinyl ether units. Apparently vinyl ether radicals act as the main propagat-ing species. Computer simulationmethods have been developed to monitor suchpolymerizations using Quantum Monte Carlo theory106. Using fluorescenceanalysis electron-donor complexes have been identified between vinylether—maleimide mixtures107,108. Here polymerization rates were also found todepend upon several factors such as light intensity, initiator concentration andoxygen while temperature did not play a significant role. Hybrid monomers ofisopropenyl ether and epoxy-cycloalkane functionalities have been synthesizedthat are capable of cationic polymerization109.A few studies have appeared on the use of photoiniferters. N,N-Diethyl-

dithiocarbamate has been actively studied. The polydispersity of styrene andmethyl methacrylate polymers was found to be very wide using this carbamate asiniferter indicating the formation of a living polymer110,111. Polytetrahydrofuranson the other hand were found to be narrow in their molecular weight distribu-tion112. Copolymers could be made with methyl methacrylate. A macro iniferterhas been made by copolymerizing styrene with an acrylated 2-N,N-diethyl-dithiocarbamyl acetate monomer113. Hypervalent iodine iniferters have beeninvestigated based on 10-I-3-iodanes114. They were found to regulate effectivelythe polymerization of styrene and acrylate monomers especially when used inconjunction with Cu(I) salts or complex forming agents such as dipyridyl. Theinteresting feature of the results in this workwas the observation that the iodanesbehaved as iniferters only under visible light irradiation. UV light initiationsimply initiated radical polymerization.Propagation rate coeficients have been measured using pulsed laser polymer-

izations115,116. The activation energy for the polymerization of 3-[tris(trimethyl-silyloxy)silyl]propyl methacrylate has been found to be significantly less thanthat for lower alkyl methacrylates but similar to dodecyl methacrylate115. Asimilar study has been undertaken on N-vinylcarbazole116. Quenching rate con-stants have also been measured for a number of monomers on various triplet-excited ketones using laser flash photolysis117. Using a semi-empirical calculationthe reactivity of excited ketones could be predicted. From this work it was foundthat the bimolecular quenching depended on the free enthalpy of formation ofthe regioselective favoured 1,4-biradical between the ketone/monomer. In an-other study stilbene probes have been utilized to measure the polymerizationstages for methyl methacrylate118. It was found that coreactive probes were morefundamental to the rate changes rather than free probes. Butyl acrylate polymer-ization has been assessed by the spinning disk method119 while the release ofTEMPO from a benzoyloxystyrene initiator has been measured by laser flashspectroscopy120.The gelation processes in the polymerization of acrylic acid have been meas-

ured by interferometry121. This was found to be a valuable non-destructive

Photochemistry344

method. TheUV-induced decomposition of azo groups attached to the surface ofsilica has been monitored in the photopolymerization of acrylate monomers.122

The effect of monomer hydrophobicity has been measured on the rate of emul-sion polymerization123. For 2-ethylhexyl methacrylate, initiation was associatedwith radicals generated within the microaggregates. One third of the radicalswere actually found not to recombine. C60 fullerene photopolymer has beenprepared that can be converted to a piezopolymer that is as hard as diamond124.C60 has also been used as a supported iniferter125 while 2,5-dimethoxyphenyl andquinone substituted octa-3,5-diynes have been photopolymerized to give blueand then red products126. The insertion of an ester or sulfonyl group into thehydrophobic part of a diyne molecule apparently increases its activity fortopochemical polymerization127. Pulsed irradiation of diyne crystals led to theformation of dimer, trimer and tetramer radicals that have been implicated in thetopochemical polymerization128.

2.2 Photocrosslinking. — The role of various initiators for photocuring hasbeen discussed in a number of articles. Camphorquinone/amine systems havebeen used to photocure mixtures of acrylic acid with triethyleneglycol dimeth-acrylate129. The formation of a product with two cure rates was observed.General mechanistic processes of this system have also been considered130.Benzoin ethers have been grafted to urethane resins via a reactive hydroxylfunctionality131 as have silicon containing oligomers onto 2-hydroxyethylacryl-ate132. High temperature curing of resins has been accelerated by the use of UVphotointiators133 while quinolyl sulfides have been successfully photocured in thepresence of vinyl ethers using visible light134. This process was proposed as beingvaluable for the development of UV curable powder coatings. Poly(furfurylalcohol) with varying amounts of oxymethylene bridges has been synthesizedusing trifluoroacetic acid and p-toluenesulfonic acid135. These polymers had atendency to retain acids and became insoluble upon storage. With maleic an-hydride they were useful for the preparation of negative photoresists. TheMichael addition reaction of a secondary amine with an acrylate resin is anestablished patented technology in the field. However, a recent publication hasincorrectly claimed novelty in this regard136. Microwave dielectrometry graftedbenzoin methyl ethers have been found to be less effective in UV curing than themodel non-grafted system137. A new bis(methylethylamino) derivative of benzo-phenone has been synthesized and claimed to be non-carcinogenic with equival-ent photoactivity to that of Michler’s ketone138. Aminoketones have been foundto be effective for photocuring epoxy-based resins139 in base-catalysed imagingsystems. On irradiation the benzoyl moiety is cleaved and an active tertiaryamine base is liberated. A novel photosensitive polyimide/silica hybrid has beenprepared by a sol—gel route to give a product with high tensile and thermalstability140. Also, a new method for sol—gel analysis data treatment has beenverified using experimental data on the photocrosslinking of polyolefins141. Thedynamics of photofabricationprocesses during surface relief gratings (SRG) havebeen monitored with azobenzene functionalized polymers142. The writing behav-iour of photofabricated SRGs was found to depend upon the irradiated light


intensity and not the spacing of the interference light pattern.Failure modes have been assessed in adhesion joints using a combination of

IR-ATR and fluorescence reflection techniques143 while gelation in free radicalcopolymerization has been measured by a transient fluorescence method144.Excimer fluorescence has been found valuable for on-line monitoring of the cureof silicone release liners145 whereas two photon visible chromophores generatelight capable of activating photoinitiators for laser induced polymerizations146.Charge recombination luminescence (CRL) from epoxy resins produced duringcure has been correlated with the extent of reaction of epoxy groups147. It wasfound that for CRL to be observed the resin must contain enough OH groups tostabilize the electron traps by solvation and be sufficiently vitreous to preventimmediate recombination of electron—cation pairs. FTIR emission spectroscopyhas been found successful for monitoring the cure of photocatalysed dicyanateester resins148. Complexes between the manganese carbonyl catalyst and thedicyanate groups were found to give rise to three different photoproducts.Temperature effects on the kinetics of the photocuring of a diacrylate systemhave been monitored by RTFTIR spectroscopy149. For an epoxy diacrylate therate was found to increase with temperature due to a concurrent decrease in resinviscosity. On the other hand for a glycol diacrylate no such effect was observed.In fact, at high temperatures certain initiators resulted in a decrease in the rate ofconversion. An improved kinetic model has been developed to account forradical trapping during the photocuring of multifunctional monomers such asdiacrylates150. In this model the trapping rate constant is assumed to increaseexponentially with the inverse of the free volume. New predictions using thismodel are that the active radical concentrations pass through a maximum whilethe trapped radicals increase monotonically. Also, higher light intensities lead toa higher fraction of trapped radicals at a given conversion of functional groups atthe end of the reaction as well as correctly predicting the effect of light intensityon reaction rate. The rate of photocuring of acrylates onto wood surfaces isshown to be reduced due to retardation by phenolic groups present in thewood151.With benzophenone for example, laser flash spectroscopy indicated thatthe reduction in rate was associated with triplet quenching by the phenol. Usingpulsed laser polymerization the propoagation rate contstant for N-isopropyl-acrylamide below its critical solution temperature was found to be dependentupon monomer and initiator concentrations152. Significant amounts of dimerwere found to be present as well as complexation processes with propagatingchain ends. The influence of oxygen continues to be examined on the rate ofconsumption of Methylene Blue during photocuring reactions153 with an amineand diphenyliodonium chloride. Using laser flash photolysis it was found thatapart from conventional triplet quenching of the dye by oxygen the initiallyformed alkylamino radicals also scavenge oxygen. Benzoin ethers are effective inthe photocuring of silica filled resins154 while a visible light initiator has beenutilized for photo-orientated polymerizations on silicon waveguides155. One-dimensional models of wave photochemical reactions have been developed156

where monomer conversion profiles coincide with initiator conversion. Studieshave been underatekn on the influence of photoinitiator concentrations on the

Photochemistry346

photocuring of dental materials157 and emulsions158. Kinetic models for 3Dcuring have been developed159,160 while the significance of chain length has beenmeasured on the termination rates of multifunctional monomers161. The resultsof this work showed that chain length dependent termination is important incrosslinked methacrylate systems before the onset of reaction diffusion control-led termination. The thermo-mechanical properties of polyesters with vinyl ethergroups were improved by side-chain photocrosslinking162.There are many new methodologies associated with curing processes and

techniques. 3D-Photocuring has been modelled to include initiator absorptioncoefficient, quantum yield of initiator photoreaction and rate constants of homeand heterophase polymerizations163,164. A novel method based on measurementof the stiffness of a drop of resin laid on the surface of a drum transducer has beenfound to correlate well with the thermodynamic measurements based on photo-DSC165. The application of a magnetic field has been found to significantlyenhance the photocuring rates of resins166 while a novel method on the sub-micrometre scale has been developed for the curing of nanometric polymerdots167. Kraton liquid polymers have been shown to give high adhesion strengthon curing168 while phase cured blends have been developed based on a bisphenol-A dicarylate modified with a poly(ethylene oxide)/poly(sulfone) copolymer169.The glass transition region breadth has been found to be critical for UV curablepressure sensitive adhesives170 and machine washable creases have been incor-porated into wool fibres using water reducible oligomers171. The change inelectrical conductivity of UV curable inks has been found valuable for determin-ing rates of propagation172 while several studies have utilized lasers in differentways; plasmas for poly(methylphenylsilane)173; 3D hardening by carbon dioxidelasers174; submicrotome 3D patterns by lasers175 and photonic crystal structureswith femtosecond lasers176. Multifunctional promoters have been developedusing resins with combined amine synergists and silicone defoamers177 as haveliquid photopolymerizable encapsulants178. Microgels have been developed inorder to enhance the cure rates of hydrogels179 while oxygen has been found toinfluence the UV curing rates of silicone acrylates180.Cycloaddition reactions continue to attract interest. The charge resonance

absorption band due to dimer radical cations formed by electronic interactionbetween styrylpyridinium cations and photogenrated styrylpyridinyl radicalshas been observed in the IR region at 941 nm181. Z,Z and also E,E forms ofmuconic acid have been found to polymerize upon irradiation in the solidstate182,183. Crystal structure analysis indicated the formation of a meso-diisotac-tic-trans-2,5-structure. Organic—inorganic polymer hybrids have been syn-thesized through the photodimerization of thymine184. The reverse action ofthymine in the hybrids could easily be measured by UV absorption spectro-scopy.Maleic anhydride undergoes photocycloaddition to halobenzenes185 whileC60 undergoes cycloaddition to form a 2D rhombohedral structure that can beeasily applied to semiconductor surfaces186. Polymers with cinnamate groupscontinue to be highlighted. Ethylene-co-vinyl cinnamate copolymer has beenfound to undergo rapid crosslinking even at 5 mole% of cinnamate groups187 asdo polyamide-imides with cinnamic acid groups188. Other similar cinnamate


based polymers include polyvinylamines and siloxanes189, oligophenols190,poly(N-2-hydroxypropylmethacrylamide)191 and triazine polyesters192. In the lat-ter case selective photoexcitation can result in separate crosslinking of thecinnamate and triazine groups.Cationic systems continue to attract interest. Dialkylphenacylsulfonium salts

initiate directly the photopolymerization of epoxy/vinyl ethers193—195. They com-pare favourably with conventional di- and tri-aryl sulfonium salts and display amarked induction period consistent with the termination of growing chains byreaction with photogenerated ylides. Also of value is the ability of these types ofinitiators to induce the thermal cure of cationic ring-opening of epoxides. Inhydroxy substituted epoxides the presence of the hydroxyl group has been foundto accelerate markedly the cationic curing of the resins to give hyperbranchedpolymers196. Novel cationically curable octafunctional monomers with cubicsilsesquioxane cores have been developed197. A series of novel polyfluorinatedepoxides have been synthesized to give, after cationic cure, a segregated surfacewith low free energy198. A ternary complex based on a mixture of p-tert-butyl-phenol formaldehyde resin, sodium dodecyl sulfate and diphenylamine-4-dia-zonium salt has been developed as an effective photoresist199. Novel oxetaneshave also been made with good surface cure properties200 as have nano sizedhollow particles made from polysilane shells201. A poly(phenyl ether) coupledwith a photoacid generator has been found to give an effective negative resistwith high thermal stability202 while carbazoles have been found to enhance thephotocationic ring-opening of epoxides203,204. Polysiloxanes with cationic photo-polymerizable groups have been made205 and iron—arene complexes have beenfound to be more effective initiators than sulfonium salts206. An overview articlehas appeared on the photocationic curing of oxetanes207.Photopolymerizable LC polymer materials continue to be developed. A

copolymer composed of PMMA with 2-indolylfulgimide has been made withgood thermal stability208 while phase separations in LC curable resins has shownthat whilst large spheres grow at low nuclei densities, dentrites form at highnuclei densities209. A Pockels effect has been observed in photopolymers withchiral smectic LCs210 while different phases have been developed in other poly-mer systems211. Other experiments have shown that an increase in light intensityand decrease in monomer viscosity improves photo-induced orientation of LCfilms212. Likewise gel stability of a dicholesteryl ester containing a diyne groupshas been enhanced on photocuring213. The effects of artificially introduced mic-ron sized periodic structures have been examined on the growth of spherulites inprepolymer/LC systems214. Using a holographic grating setup the spherulites arefound to be elliptically deformed with an orientation where the long axis is in thedirection of the grating.Major striations tend to be either parallel or perpendicu-lar to the grating wall. From this work a suitable model was developed to predictgrowth processes of spherulites in grating environments. In a similar way LCmethacrylate copolymer films generatemesogenic groups that are orientated in adirection parallel to the electric vector of linear polarized light215. Iso-tropic—cholosteric interfaces and fingerprint patterns have been ascertainedduringUV curing of LC droplets216. OrientatedLC films with different degrees of

Photochemistry348

crosslinking have also been obtained by in situ photopolymerization of variousmesogenic samples at different temperatures217. For naphthalene-basedmonoac-rylates with a diacrylate crosslinking agent the dichroism increased with anincrease in diacrylate content. Morphological changes during the photo-polymerization of single crystals of diacetylene have been measured by atomicforce microscopy218. Here nodule like structures were formed on the surface thatwere aligned along the direction of the b-axis of the crystal and are associatedwith a mechanical slip effect. For methacrylate polymer films with 2-cinna-mmoylethoxybiphenyl mesogenic side groups the degree of orientation on irra-diation was found to depend upon the methylene spacer length on the polymerbackbone as well as the thermotropic nature of the polymers219. Thus longerirradiation times were required to achieve a homogeneous alignment for poly-mer films with long spacers. Lyotropic LC fluoroalkoxymethylmethacrylic acidderivatives have been shown to possess a lamellarmorphology at certain concen-trations and when polymerized yield anisotropic properties that are ideal forrepairing retinal tears220. This fluorinated amphiphile was found to exhibit avarying phase morphology ranging from an isotropic micellar phase to a discon-tinuous cubic and lamellar liquid crystalline phase with increasing concentrationand variation in the percent neutralization of the acidic moiety. The polymeriz-ation kinetics were found to follow a trend of decreasing order with increasingneutralization. The rate on the other hand decreases to to a minimum forsamples with cubic morphology with lower overall degrees of order. Higherpolymerization rates in the lamellar phase are due to a decrease in the termina-tions rate. The use of a self-processing dry photopolymer layer capable ofmemorizing optical information as a local change in thickness has been pro-posed for holograms and gratings221. Contrary to conventional lithographictechniques that require wet chemical post-treatments to remove parts of theresist material, the fully self-processing character of this technique makes therecord available in situ and immediately after exposure.Several novel photocurablematerials have appeared covering various applica-

tions. These include solid polysulfide elastomers222, curable natural rubbers223,zero VOC coatings224, electrical adhesives225, new polyesters226, electronic encap-sulants227—229, novel acrylic adhesives230, biostable composites231, polyimide coat-ings232, phenolic-epoxy coatings233—235, superabsorbent acrylic acid—sodiumacryl-ate copolymers236, 3D polymerization237, carbazole containing acrylics238, self-adhesive labels239, epoxy-acrylates240, fluorinated monomers241, powder coat-ings242, oligomeric esters of 2,5-benzophenonedicarboxylic acid243, poly(4-meth-acryloyloxyphenyl-4�-chlorostyryl ketone)244, poly(N-aminoalkyl tartramide)245,PDMS with benzyl acrylate end-groups246, silicone-epoxies247, silicone-acryl-ates248, stabilized clearcoats249, polycarbodiimides250, polyurethane acrylates251—253

and polyimides254. Hyperbranched polyamine-esters undergo rapid polymeriz-ation in the presence of a photofragmenting initiator255. Methacrylic anhydridesystems are claimed to be more reactive than glycidyl methacrylate and competewell with traditional linear polymers. Photocurable biodegradable polymershave been prepared through the ring-opening of caprolactone256,257. In this casecuring rates were enhanced through higher coumarin functionalities. Covalently


attachedmultiplayer assemblies based on photoreactive diazo-polyaniline resinshave also been prepared258. Adjacent surfaces in the multilayers were found tocrosslink maintaining their electroactive properties. Photopolymer efficiencieshave been improved through base-catalysed transformations259. Thus, forexample, carbamate N-(9-fluorenylmethyloxycarbonyl)piperidine givespiperidine upon irradiation. The kinetics of photocalorimetric devices have beenassessed260 as has the crystallization of poly(ethylene oxide) during the photocur-ing of a dimethacrylate monomer261. Here the application of an electric fieldenhanced separation of phases and crystallization. The physical properties ofphotocured resins have been related to their functionalization262 while functionalpolymers with phenacyl ester groups have been made that photocleave to givecarboxylic acid groups263. Block copolymers with caprolactone groups andperfluoroethers give two amorphous phases after UV curing264. The poly(capro-lactone) phase was found to be partially crystalline while at the surface a highfluorine content was obtained. The photocuring rates of a polybutadiene hyd-roxyl acrylate have been studied and found to depend strongly on light intensityand initiator concentration265 while for UV curing of polysiloxanes the nature ofthe initiator was found to be crucial266. Nanochannels in thin self-assemblingdiblock copolymers of poly(t-butyl acrylate) and poly(2-cinnamoylethyl meth-acrylate) have been formed267. These channels could be controlled and highlyselective for pH dependent devices. Conversion simulations have been developedfor a dimethacrylate resin268 while for the same resin types heterocyclic thiocompounds have been found to exhibit both acceleration and retardation ofcure269. Degradable poly(ether anhydrides) have also been made270 with highthermal instability whereas divinyl end-capped PDMS systems have value inintraocular lense applications271. Various linear alternating copolymers of vinylspiro-orthoesters have been made by a ring-opening mechanism272,273. Iodoniumsalts were found to be highly effective for inducing the reaction with the ratebeing dependent upon their ionic strength.With conventional epoxy acrylates ortriacrylates good alkali developable resists can be obtained.A number of articles have appeared on photocrosslinking of thermoplastic

materials. A thiol—ene system has been found to be highly effective for thephotocrosslinking of SBS274,275. At high vinyl contents the crosslinked networkswere useful as hot-melt adhesives. Photofragmenting initiators have also beenused to photocrosslink SBS276. The reactivity of the radicals toward ethene bondsfollowed the order vinyl�cis�trans. Diffusion analysis indicated a diphasicmorphology which slowly changed to a monophase system on enhanced cross-linking. Rubbers bearing pendant acrylate groups have been prepared by reac-ting acrylic acid with epoxidized rubbers277,278. Rapid crosslinking takes placeupon irradiation with a radical initiator. Cyclic rubbers do not crosslink aseffectively as linear systems due to a reduction in chain mobility. Luminescencehas been used to determine the extent of crosslinking in 3D polysilane net-works279 while a new class of gels has been obtained based on hydroxypropylcellulosemethacrylate280. Photocrosslinkable fluorinated PDMS has been devel-oped281 while the polycondensation of furan derivatives by singlet oxygen, gener-ated by fullerene C60, has been useful for crosslinking polymers282. The photo-

Photochemistry350

crosslinking of polyethylene by benzophenone has been investigated where it isproposed, rather surprisingly, that, for the first time ever, the excited-triplet stateof the benzophenone abstracts a hydrogen atom from the polymer to give ketylradicals283. These workers claim to be the first to identify the ketyl radical by ESRand also the benzpinnacol photoproducts. Polymers with pendant chalconegroups photocrosslink effectively using peroxide initiators284. They are claimedto be useful resist materials and will also crosslink in the absence of an initiator,albeit more slowly. Benzoylated polystyrene also undergoes effective photocros-slinking to give an unusual porous network285. Interestingly, polyesters dopedwith 1,4-phenylene bis(acrylic acid) have been found to undergo effective 2�2cycloaddition to give photochemical thermosetts286.

2.3 Photografting. — Surface photografting is still widely used for improving ormodifying polymer properties for various applications. Photografting generallyonto polyethylene surfaces is enhanced when the polymer is pretreated in sol-utions of initiators287. Vinyl monomers have been successfully photografted ontoPVC by incorporating pendant N,N-diethyldithiocarbamate groups into thematrix288. Here styrene was found to graft more efficiently than acrylamide. Thioradicals were suspected to be involved in the mechanism. Similarly, otherworkers confirm the use of sequential application methods for enhancing thesurface cure of monomers to polymers where the initiator is first laid down beforegrafting takes place289. Maleic anhydride has been photografted onto polypropy-lene290 via peroxides while acrylamide has been photografted onto cellulose usinganthraquinone-2-sulfonic acid291. Vinyl acetate and other monomers have alsobeen photografted onto polyethylene using benzophenone as initiator292 whilehindered amines have been photografted onto elastomers293. Here anthracenewas used as the photosensitizer in order to generate singlet oxygen. Variouschemical functional groups have been incorporated onto the surface of groundtyre rubber for enhanced properties294 and for cellulose carboxyl values wereenhanced after treatment with organic acids295. Amphiphilic grafted copolymersof poly(phosphazines) have beenmade as drug carriers296 while PEEKfilms havebeen surface functionalized with azide derivatives for microlithographic applica-tions297. Azo groups have also been grafted onto glass fibre surfaces followed bysequential monomer grafting298. Anthraquinone-2-sulfonic acid has been used asan initiator for the photoinduced grafting of acrylamide onto polyethylene299 inorder to reduce the contact angle of water droplets on the surface. CT complexescan be used to photograft methyl methacrylate onto cellulose and polypropy-lene300,301 while in other grafting applications xanthate derivatives have beenfound valuable for copolymer grafting onto polymer surfaces302. PVDF micro-membranes have been plasma grafted with primary amino groups for furtherfunctionalization303.


3 Luminescence and Optical Properties

The optical and luminescence properties of polymer systems continue to attractinterest in specialized fields with LEDs and photochromic materials being themost widely studied areas. The former system has been the subject of over 110articles in the past year. General reviews of interest include water-soluble fluor-escent materials based on poly(acrylonitrile)304, phosphors for polymers305, inter-facial behaviour in water-soluble polymers306, molecular studies on fullerenederivatives307 and triplet exciton energy transfer in poly(vinyl carbazoles)308.Luminescent polymers of general interst include a number of novel materials.

Poly(2-pyridinium hydrochloride—2-pyridylacetylene) is a water soluble poly-mer that is fluorescent with a higher content than expected of protonatedpyridine309. Films of substituted fluorenes have been polymerized310 while excita-tion energy tranfer in polymer under the influence of an electric field has beenexamined311. The polyanilines have also been investigated312 while the electricalconductivity of polymeric five and six membered heterocycles increases withactivation such as iodine313. The birefringence of copolymers of 4-nitroazoben-zene is enhanced with increasing azo content314 as is that of poly(N-vinylcar-bazole) with increasing temperature315. Polymer monolayers of crown etherswith poly(maleic acid hexadecyl monoamide-alt-propylene)undergo fluor-escence shifts on aggregation316 while polyamides with ethidium bromide groupsgive good optical properties317. Water soluble polymeric dyes undergo inter-molecular interactions resulting in aggregate formation318 and conjugated poly-mers with 2,2�-bipyridine and diethynylenebenzene units have been inves-tigated319. Conjugation in these polymers has been shown to be stronger in linearthan angular chains with substitution by alkoxy groups giving high fluorescencequantum yields. Radiationless deactivation in these polymers is associated withchain migration processes.A number of articles have appeared on polyacetylenes. Polyphenylacetylene

has been made using tungsten hexacarbonyl and found to exhibit a strongconcentration dependent fluorescence320. Lower wavelength fluorescenceemission bands were found to disappear at higher concentrations of polymer.Uneven polymer structures were proposed. However, one other possibility is thepresence of ground-state associated dimers or aggregates resulting in monomerquenching.On the other hand phenyl disubstituted polyacetyleneswith attachedbutyl groups give fluorescence with only one exponential decay in solution321.Only in the solid film do they obtain variable decays with emission wavelength.Two long-lived bands are observed, which are associated with polaron transi-tions. Poly(alkylacetylenes) giving strong bluish fluorescence have also beenmade322. The nonyl derivative is claimed to be very highly fluorescent. A newpolymer based on poly[2-(2�-ethylhexyloxy)-1,4-phenylenevinylene] has beenmade by a novel derivatization route323 as have new alkyl substituted polycar-bazolyldiacetylenes324,325. Long-lived photoinduced excitations are observedfrom the latter materials. Whilst charge carriers as well as triplet excitons areformed in the normal unsubstituted blue polymer, triplet excitons dominate thespectrum when long alkyl groups are attached to the aromatic ring. Triplet

Photochemistry352

excitons are normally observed only in the red form of the soluble polydiacety-lenes. Larger interchain separations in the substituted polymers favour thephotogeneration of triplet excitons relative to charged species. Interchain coup-ling in the red form of the polymer is even more reduced. ESR analysis confirmsthe existence of the long-lived polarons rather than charged species. The obser-vation was confirmed further by doping experiments with acceptor fullereneswhere a negative effect was obtained. Other workers concur with these find-ings326,327. Fluorene based diacetylene polymers have also been prepared with LCproperties and good solvent solubility328 as have Langmuir-Blodgett layers ofpoly(2-tetracosyn-1-ol)329, polymers with imidazole rings330 and methyl-coumarin331. Poly(alkenephenylenes) prepared by copolycyclotrimerizationhavehigh thermal stability332.Polythiophenes continue to attract some interest. The luminescence and ab-

sorption of poly[3-(2,5-dioctylphenyl)thiophene] are red shifted upon crystalli-zation333 while that for poly(3-methoxythiophene)-bithiophene is dependentupon the bithiophene concentration334. Partially alkylated and S-oxidizedoligothiophenes have been made and found to be highly emissive335 as ispoly(octylthiophene) doped with gold nanoparticles336. Fluoroalkylthiophenesare also highly fluorescent337 as are a new range of 2-amino-3-cyanophenyl-thiophenes made by electrochemical oxidation338. New polymers of thiopheneand vinylene exhibit thermochromism339 while the luminescence of those basedon a siloxane moiety can be fine tuned340. The emission from polymers with1,3,4-oxadiazole groups can also be fine tuned from 411 to 558 nm341. Thesepolymers also have good charge-injection properties for p- and n-type carriersfor LED applications. Co-oligomers of thiophene and phenylene exhibit concen-tration dependent spectra342. Monomer emission is dominant at low concentra-tions with red emission dominating at high concentrations due to intermolecularinteractions. Intermolecular charge-transfer effects between the thiophene andphenylene groups also dominated spectral shifts.Polymer blend stability has also been probed. 1-(2-Anthryl)-1-phenylethylene

has been found useful as both an initiator and a trapping agent in the synthesis ofanhydride functional fluorescent PMMA and polystyrene343. Good sensitivitywas obtained at high dilution formonitoring polymer—polymer coupling interac-tions. Fluorescence microscopy has been found useful for monitoring blendmiscibility in mixtures of poly(vinyl acetate) with poly(cyclohexyl meth-acrylate)344. Using stilbene and pyrene probes imaging in the different domainscould be readily observed. Apparently, in chloroform smaller domains are foundto be distributed with a 2D hexatic order disrupted by dislocations and disclina-tions. On the other hand for films cast from THF, a larger heterogeneity is foundindicating that there are different solvent effects on evaporation. For poly[1,8-octanedioxy-1,4-phenylenevinylene-2-methoxy-5-(2�-ethyl)hexoxy-1,4-phenyl-enevinylene] and poly[2,5-bis(chloromethyl)-1,4-[methoxy-(2�-ethyl)hexoxyl]benzene] only one maximum emission is observed when they are blended atequal amounts345. At smaller or larger ratios, two emissions are observed fromthe separate phases. Excimer fluorescence has been used to optimize blends ofpoly(N-vinylcarbazole) with poly(oxyethylene)346,347 while depolarized energy


transfer has been found useful for monitoring blends of ultra-high molecularweight polyethylenes348. Phosphorescence quenching has also been found usefulfor monitoring blend miscibility and mixtures of benzophenone (donor) andiodobenzene (acceptor) exhibit optimum quenching in a homogeneous mixtureof polymers349.PPVs (polyphenylene vinylenes) in light emitting diodes represent the greatest

developing area from both an academic and a technological point-of-view.Muchof the direction in this field is to develop luminescent or electroluminescentpolymers with high efficiency in certain specific regions of the electromagneticspectrum. Polymers with methoxy groups are claimed to be more efficient thanthose with N,N-dimethylamino groups350 while those with triphenylamine andalkylcarbazole groups are effective soluble polymers351. Carbazole containingpolymers with deep spacer units emit strong blue light352 whereas those based onpoly(aryl ethers) possess a high glass transition temperature353. PPVs with di-(2-biphenyl)-1,4-phenylene oxadiazole units produce a material with high lumines-cence efficiency and bipolar charge transport ability354. Such materials makepromising single layer LED devices. PPVs undergo chain scission on irradiationshortening their conjugation and shifting the emission to shorter wavelengths355.These authors prepared PPVs under argon and found that their emissionintensity was enhanced by over 70%. It was suggested that encapsulating PPVsfrom oxygen and light would significantly enhance their electroluminescentproperties. Pressure sensitive phosphors have been developed for pressure sensi-tive paints356.Magnetic spin effects have been used to study charge-transfer interactions

between polymer chains in PPVs357 while in other work time dependent configur-ational studies have been undertaken358. Differences between electro- and photo-luminescence of PPVs have been explained by dispersive transport controlledrecombination processes359 while oligo-PPVs with fullerene dyads undergo fastelectron-transfer steps360. Holemobility in PPVs has beenmeasured as a functionof electric field and temperature361. Charge carriers are formed by hoppingamong polymer segments with an almost Gaussian distribution of energies.Using continuous wave absorption ordering in PPVs is associated with thelyotropic liquid crystalline character of the matrix362 whilst electron energymigration in PPV doped with the red emitter poly(perylene-co-diethynylben-zene) has been found to proceed in two steps363. These are firstly migration withinthe host and secondly transfer from the host to the guest. The emissions from thematrix evolve differently with a strong temperature dependence. Singlet energymigration is very evident while triplet excitons show a distinct peak for eachpolymeric component. Triplet—triplet annihilation however, was not evident.PPV containing urethane segments in the chain gives only blue emission, whichis subsequently enhanced upon doping with an oxadiazole—polystyrene364. Triv-ial singlet energy transfer is responsible for the observed intensity enhancement.Polyphenylene has been derived from the anodic oxidation of p-methoxytolueneand is claimed to exhibit good electroluminescencebehaviour365 while PPVswithdendritic side chains can self-organize into highly ordered structures in the solidstate366. Polymers are both thermotropic and lyotropic liquid crystals from

Photochemistry354

which anisotropic films could be made. Several polyphenylenes have been inves-tigated in terms of their emission characteristics and all found to exhibit excellentlaser action except those with m-phenylene groups367. Obviously, interchaininteractions are crucial here. PPVs doped with titania nanocomposites havebeen found to exhibit enhanced emission at equivalent ratios368 whereas PPVswith dendrons give two conformations associated with isolated and aggregatedchains369. Doping of PPVs with transition metal ions apparently reduces theirlaser ablation efficiency except for Fe370 and a novel PPV with 2,5-hexadecyloxyand 2,5-cyano groups has been made with orange luminescence371. These ma-terials had good transport properties especially as double layers. Other cyanosubstituted PPVs have been shown to give emission from both aggregates andisolated chains and when cast under certain conditions give emission frommainly aggregates372. PPVs with cyano modified distyrylbenzene units are alsoclaimed to give higher electroluminescence efficiency373,374 while other workersclaim that no aggregation is observed in cyano substituted PPVs375. A number ofsoluble alkoxy substituted PPVs have been made that give yellow and greenemissions376 and other workers have successfully made a cationic water solubleblue luminescent material, poly[(9,9-dihexyl-2,7-fluorene)-alt-co-(2,5-bis[3-(N,N-dimethyl)-N-ethylammonium]-1-oxapropyl-1,4-phenylene)]dibromide377.The introduction of ether links and aliphatic chains in PPVs enhances solubilityin common organic solvents378. These polymer materials exhibit solvato-chromism and emit primarily in the blue region. PPV blends in other polymershave shown novel spectroscopic effects379. Apparently, in PVC the emissionintensity is enhanced by 15-fold when stretchedwhereas in poly(vinyl acetate) thereverse happens. Compatibility was the main factor accounting for these effects.Oligo-PPVs in solution give electronic transitions with chain-length dependentspectral positions involving exclusively MOs with a prevailing polyene-likecharacter380. Absorption bandswith approximate chain length independent spec-tral positions are associated with transitions between polyene-like MOs as wellas MOs of aromatic character. Multilayered organic super lattices of water-soluble PPVs have been found to exhibit a self-quenching effect on its lumines-cence with increasing concentration381. However, the emission became progress-ively more red shifted due to efficient unidirectional energy transfer. TunableLEDS have been developed based on phenylene—thienyl copolymers382 as havebispyridyl compounds with thiophene units383. Interchain interactions have alsobeen investigated through model system studies in polyethylene384 and PPVswith functionalized 2,6- and 1,5-naphthalene groups emit strongly in the redregion385,386. Novel bipyridine and silicon containing PPVs exhibit differences inemission spectrawith the former emitting in the greenwhile the latter emits in theblue.387,388 Other silyl copolymers give blue—green emission389. A newtriphenylamine based PPV exhibits dual emission in the blue and red re-gions390,391 while other amine-containing PPVs emit green light and possess goodphotoconductivity392. Prior thermal treatment of PPVs gives polymers withdifferent emission spectra393 whereas PPVs complexedwith metal ions exhibit anionchromic effect394, which could have potential for optical switching devices.Dioctylfluorene395 and fluorene396 PPVs, poly(phenyl pyridine)397, fluorinated


tetraphenyl PPVs398, thiophene PPVs399, poly(2-octoxycarbonyl-1,4-phenyl-ene)400, 3-poly(3-dodecylthiophene)401, 2,3-dialkoxy substituted PPVs402, bi-phenyl-oligo-PPVs403 and ion coordinated PPVs404 all give enhanced blue—greenemissions that are capable of fine tuning. Ladder type poly(p-phenylenes) havebeen investigated by phosphorescence spectroscopy405. The emission was intrin-sic to the polymer and gave rise to delayed fluorescence associated with therecombination of geminate electron—hole pairs. Photoluminescence spectralnarrowing in the same type of polymers is consistent with an energetic relaxationof localized excitations406. Transient measurements on PPVs also show thatcharge-carrier generation occurs within 100 fs after excitation407. These carriersare shown to be generated directly and are not formed from exciton annihilation.Furthermore, as above they show a strong dependence upon inter-chain interac-tions. On another note PPVs with tetraalkoxy and triptycene groups have beenmade and found to be specific for DNT and TNT408. Polymers with ethyleneoxide groups were also shown to behave in the same way. PPVs have been madewhereby substitution in the meta position blue shifts the emission409 while PPVswith cyclobutenedione groups give blue emission in solution and red emission inthe solid state410. The vapour deposition of PPVs with N-parylene groups hasbeen utilized to tune the colour of the polymer411 and the ionic conductivity ofpolyethylene oxide copolymers of PPVs has been measured412.Circularly polarized photoluminescence has been studied from chiral nematic

poly(phenylene) films413. The supramolecular structure of a uniaxially alignedfilm showed that the both the polymer backbone and nematic pendants arecollinear and lie predominantly along the buffing direction. These films were alsofound to contain left-handed helical stacks of quasinematic layers with (S)-(�)-1-phenylethanol as a chiral moiety. Oxidation affects the triplet excitons of ladder-type poly(p-phenylenes)414 while ethylene bridges enhance the emission415.Poly(m-phenylenevinylenes) have been made with luminescence efficiencies of upto 52%416 while aggregation effects in PPVs enhances their luminescence417—419

and dendritic side groups cause a reduction due to inter-chain separation420. Awhite light emitting polymer LED has been developed based on a double layerconsisting of a poly(fluorene) and a hexylphenyliminobiphenyl crosslinked poly-mer421. Novel blue light emitting polymers have beenmade based on an adaman-tine moiety422, bispyrroles423, 4�-octyloxybiphenyl groups424, copolymers of PPVswith styrene425 polyketones426 and polyurethanes with stilbene groups427. Whitelight and multicoloured emitting polymers such as the poly(pyridines)are alsoavailable428—430. Poly(quinolines) are totally red emitting polymers431 while alter-nating block copolymerPPVs exhibit high emission quantum yields of�90%432.Photoluminescence in PPV copolymers, however, is quenchedwhen dispersed inan inert poly(ethylene oxide) host433. Other effects on LEDS include oligopheny-lenes with different chain lengths434, twin beam excitation435, pressure effects436,substitution of quinquephenyl groups437, trans-stilbenes438—440, 8-(hydroxyquino-line) aluminium441, oxadiazole groups442, 1,4-dioxo-3,6-diphenylpyrrolo-pyr-roles443 and anionic quenchers444. New approaches have been made via pallad-ium-catalysed oxidation to form PPVs with higher photoluminescence445. PPVswith carbazole and europium acrylates have been shown to give a unique

Photochemistry356

monochromatic red emission associated with sensitization of the Eu3� complexat 614 nm446. Green emission has been observed formPPVswith azobenzene sidechains447,448 whilemultilayer polyelectrolytePPVs have been found to be lamellarin structure449. A number of othermaterials of electroluminescent interest includesingle crystals of a dodecadiyne-urethane polymer450, polymers with phenazineunits451, polyaminonaphthalenes452, poly(pyrrole-2,5-diyl)[p-nitorbenzene]453, o-carborane complexes454, fluorescent gels455, phenylacetylenes456, phospha-phenanthrene dopants457, dioctyl and alkly-PPs458,459 and conjugated bipyridyl-PPVs460.Photoreactions in polymer gels have interesting implications. Metal com-

plexes of Au and Pd in gels of diallyldimethylammonium chloride produce smallmetallic particles on irradiation which slowly convert back to the complex461.Apparently at water contents of 30% thermoadaptive gels are formed. Thehydrophilic nature of the environment in poly(ethylene glycol) gels allows foroptimum study of the mobility in different solvent environments through atagged probe (dimethylaminonaphthylsulfonate)462. Similar work has beenundertaken on polyacrylamide gels463 and a general overview has been providedon these materials464. The size of micelle aggregates has been determined inpolymers tagged with 1-ethylpyrene as a molecular probe465 while other workershave tagged PEEK with pyrene molecules466. The microenvironment has beenmeasured in chitosan gels using pyrene as a probe467 as have phase transitions inPVA gels with fluorescein468. Large spectral shifts were observed in hydrogelswith temperature change due to strong intermolecular bonding with watermolecules. Photoswitching behaviour in poly(ethylene glycol) gels has beenmonitored by using cinnamoyl tags469. Here the degree of swelling of the hydro-gels was modulated by alternating the wavelength of light exposure. Thus, withlight above 300 nm there was a decrease in swellability while with light below 254nm more gel was formed. The latter also resulted in (2��2�) cycloaddition.Resin cure temperatures can be monitored by fluorescent probes470 while euro-pium complexes in silicate microspheres show intense red emission471. Changesin swellability of poly(ethylene glycol) gels using a naphthalene probe can bealtered by the addition of salts such as NaCI472. This reveals the actual poorswellability properties of water for polymers due to their stronger preference forsalts. Deuterium isotope effects also influence the swellability of poly(N-iso-propylacrylamide) gels473 and diffusion coefficients have been measured inPMMA gels using pyrene lifetimes as a molecular probe474—476. The clustering ofsilica particles has been measured in hydrogel polymerizations using fluor-escence anisotropy of a bound dye477.Chemiluminescence continues to attract widespread interest in studying the

properties and oxidation of polymers. Correlations between chemiluminescenceand chain termination reactions in polypropylene oxidation have been estab-lished478—480. The decay kinetics comply with the termination of peroxy radicalswith plasticizers accelerating the effect. Chemiluminescence has been used tofollow temperature cycling oxidation in polypropylene with rates that follow thebimolecular decomposition of hydroperoxides of differing stability481. Selenium,triazine and HALS compounds are all found to influence the chemiluminescence


of polypropylene during oxidation through their ability to scavenge peroxyradicals482—486. Different wood pulps have been found to exhibit differentchemiluminescence spectra487 while other workers have characterized three typesof chemiluminescence in cellulose488,489. At low temperatures the emission isassociated with that of irradiated cellulose and attributed to the decay ofoxygen-hydroxyl/ether charge-transfer complexes. The second type at 135 °C isassociated with the decomposition of peroxides in the cellulose while the third at200 °C is due to chain scission processes. Chemiluminescence has been foundvaluable for assessing the extent of oxidation in polypropylene that has under-gone multi extrusions490. Stress oxidation associated with adiabatic heatingcausing hydroperoxide decomposition has been measured491—493. The presence ofbenzophenone in polyamides has been shown to have no effect on itschemiluminescence confirming its relationship with hydroperoxide reaction kin-etics494. Chemiluminescence lasting up to 12 hours has been observed fromcarbazole and fluorine polymers495 while irradiated PTFE gives an unusuallyhigh chemiluminescence496. Diffusion limited oxidation processes have also beeninvestigated in hydroxy-terminated poly(butadiene)497. Here a decrease in theoxygen diffusion coefficient was obtained during oxidation, which is consistentwith reduced oxygen permeability due to crosslinking of the rubber duringoxidation. The use of digital electronic imaging is reported for monitoringchemiluminescence498. Radiothermoluminescence from pyrene-doped poly-ethylene is associated with an electron-solute radical cation and solute radicalion recombination process499. Electroluminescence is observed at longerwavelengths from J-aggregates of cyanine dyes in a polyimides500. N-Carbazolylsubstituted polysilanes generate deep traps for carriers and give two thermo-luminescence peaks due to monomeric emission at low temperatures and ex-cimeric emission at high temperatures501. Relaxation processes in PVDF havealso been identified at three temperatures by using thermoluminescence502,503.Rare earth doped polymers have considerable interest in terms of probes and

photonic devices. Co-ordination complexes of Eu3� with cellulose have beenmade that fluoresce504 as have compexes with acrylic acid polymerized on thesurface of LDPE505. In the latter case energy transfer is claimed to be observedfrom the polymer to the Eu3� ions. Temperature has been found to enhance theemission intensity from Eu3� and Tb3� ions506 and a metal chelating poly-urethane urea based on 2,6-diaminopyridine and 1,6-diisocyanatohexane hasbeen chain extended with poly(ethylene oxide)507,508. In the latter case multilayerfilms were assembled with a Tb3� salt to give initial globular deposits whichincrease in both the lateral and vertical directions to form diffuse islands thateventually fuse into a more coherent structure. These layers give strong greenemission that could have potential applications in, for example, electrolumines-cent devices. Europium PMMA complexes have also been made509,510 that emitenhanced red light associated with energy-transfer processes within the polymermatrix. Such complexes have also been found to be highly stable511 while Tb3�

ions bound to sodium poly(acrylate—dedritic-polyethers) give enhanced emissiondue to the formation of aggregates512. Pressure sensitive paints have been devel-oped based on the use of Ru3� ions where the diffusion of oxygen quenches the

Photochemistry358

emission513. Eu3� and Ru2� ions have been grafted to aromatic polymers as sidechains and shown to be useful devices for LEDs514. PMMA modified with Nb3�

ions gives homogeneous composites515 and charge-transfer quenching interac-tions have been investigated between -tyrosine esters and Ru(II) based poly-mers516. Cu and Zn complexes of vinyl porphyrin have been made andcopolymerized with styrene517. Long wavelength fluorescence is observed fromthe Zn complex, which depends strongly on the copolymer ratio. Other dopingstudies include Ru(II) complexes in poly(3,4-ethylenedioxythiophene)518, Eu(II)complexeswith �-diketones in PMMA519, polymers with crown ethers of alkalineearth metals520 and siloxane copolymers with 1,4-bis(5�-acetyl-2�-thienyl)ben-zene521.Dendritic polymer materials have expanded in interest in terms of optical

properties. Penta- and hepta-thiophene systems have been developed withcoumarin chromophores on the periphery522. These molecules undergo energytranfer from the coumarin to the thiophene cores to provide excellent lightharvesting properties. Orientation and end-group functionalization had littleeffect on the energy transfer rate. Similar structures have been developed basedon coumarin labelled poly(aryl ethers)523 and terpyridine-functionalized poly-ethers on a polyhedral silsesquioxane core524. In the latter case co-reaction withRu(II) ions gives effective metallodendrimers. Porphyrin cores with coumarindendrimers have also been synthesized525 as have Sn and Zn porphyrins wherestructural collapse is determined by the core size526. Dansyl cores with carboxylicacid peripheries have been developed and investigated with cyclodextrin andpolyclonal anti-dansyl antibodies527. The dansyl residues are shown to be pro-gressively shielded as the dendrimer generation increases. In turn this significant-ly influences the spectroscopic properties of the molecule. Amphiphilic den-drimers have been made through attaching 10,12-pentacosadiynoic acid to apoly(amidoamine) core528, poly(ethylene glycol) hydrophilic blocks withpoly(benzyl ether) hydrophobic blocks529,530, poly(ethylene oxide)-carbo-silanes531,532 pyrene tagged PMMA533 and benzo-15-crown-5 with 3,4-bis(dodecyloxy)benzyl groups coupled via azobenzene bridges534—536.Poly(amidoamine) dendrimers have been made with a cinnamoyl shell thatundergo effective cycloaddition causing, in this case, an increase in fluorescenceintensity537. In a similar way poly(propylene imine) dendrimers have been madewith pyrene peripheries538. In this case, an increase in the generation of pyrenetentacles resulted in an enhancement of pyrene excimer emission. Star likedendrimers have been made of C60 with poly(acrylonitrile)539 as have dendriticpoly(-lysines) with Zn(II) phorphyrins540 and azobenzene groups541. Co(II) ionshave ben found to quench the fluorescence of dansyl functionalities onpoly(propylene amine) dendrimers542. An unusual pH dependence has beenobserved on PAMAMdendrimers using polarity responsive 5-(dimethylamino)-1-naphthalenesulfonic acid probe543. At all basic pHs inward folding of thedendritic termini is observed while as the pH is reduced the amino groupsbecome protonated causing molecular repulsion and hence molecular expan-sion. Other hyperbranched dendrimers cover fluorescent quinoxaline containingpolyethers544, polyuracils545, N,N-diethylaminodithiocarbamoylmethylstyrene


inimers546, benzylaryl ethers547 and spyropyrans548.In doped polymers fullerene fluorescence has been found to be much broader

than when examined alone549 while fluorine doped poly(vinyltoluene) givesemission under electron beam irradiation550. An applied electric field reduces theemission from dyes doped in PVK551 whereas Rhodamine B in poly(N-iso-propylacrylamide) gels gives anti-Stokes fluorescence552 while in PVC it isbroadened553. Polystyrene beads in PVA containing adsorbed Methylene Bluedye gives non-exponential fluorescence decays due to non-homogeneously ad-sorbed dye554. Diffusion processes in poly(N-isopropylacrylamide-co-acryl-amide) have been measured and found to depend upon the ratio of acrylamide inthe polymer555. Higher amounts of the latter give a looser structure. The distribu-tion of dye fluorescence has been used to measure the coating efficiency ofsilicones on textile fibres556 whereas optical excitation of stilbene and dyes inPVC and PVA causes localized heating effects557. A photobleaching techniquehas been used to monitor the rotational dynamics of rubrene dispersed inthermosetting resins558. Apparently, at temperatures below the glass transitionprobe rotational correlation times were found to be shorter and showed a weaktemperature dependence compared with those in glassy polymers. Annealingeffects have been monitored in pressure sensitive paint systems through dopingwith platinum tetra(penta-fluorophenyl)porphine559—561. Heating of the polymerabove its Tg is found to be more important than drying at room temperature inorder to obtain a pressure sensitive film. Bilayers with a sub-coating influence theresponse time of the sensor with less permeable polymers and increase theresponse time. The addition of a pigment is found to have a large effect on thefrequency factor and the activation energy of the diffusion of oxygen in thepolymer film. Aluminium oxide was found to be an ideal pigment in this regardwith useful applications in wind tunnel research. fluorescence anisotropy hasbeen used to monitor orientation effects in polymers when undergoing process-ing562 as well as during polymerization563.Fluorescence tagging continues to be used as a molecular probe. Polyesters

with norbornadiene groups have been made and shown to yield one of thehighest recorded energy releases564 while the fluorescence of C60 end bondedpolystyrene is quenched by triethylamine565 as is that from anthracene labelledpoly(methacrylic acid)566. Fluorescent labelled polystyrene with anhydride ter-minated PMMMA have been examined in order to measure their degree ofcoupling567 whereas an amine functionalized polystyrene has beenmade throughwhich transition metal complexes can be attached, such as ruthenium-poly-pyridine568. The latter system is claimed to be a unique photosynthetic moleculecapable of harnessing light energy effectively through electron transfer. Polymersof PVK tagged with 4-amino-1,8-naphthalimide groups exhibit the same fluor-escence as their monomeric counterparts569 and have potential applications inelectroluminescence. Helical polysilanes tagged with dye molecules have beenmade where exciton transfer occurs over 100 monomer units570. These materialswere considered for the fabrication of luminescent tunable devices. Highlysoluble polyamides and polyesters with biphenylanthracene segments give deepbroad blue fluorescence emission571 as does poly(4-hydroxystilbene)572 while

Photochemistry360

dansyl labelled polymers with 2-acrylamido-2-methylpropanesulfonic acid givetwo emission peaks at 336 and 533 nm573. The latter are associated with proto-nated and unprotonated species. Complex methacrylate copolymers have beenmade giving red-shifted fluorescence spectra based on 3-phenyl-7-meth-acryloyloxyethoxy-1-methyl-1H-pyrazolo[3,4-b]quinoline574 as have porphyrinbased poly(N-isopropylacrylamides)575. Copolyesters with pendant carbazolegroups give fluorescence emissions up to 600 nm and when doped with p-chloranil became photoconductive576. Perylene has been used as a molecularprobe for the dynamics in crosslinked polysiloxanes577. The thermal fluctuationsof the perylene molecules caused by the Si—O—Si chain flexibility becomes weakwith decreasing temperature in the uncured prepolymer and coupled with achange in packing and dense aggregation around the perylenemolecules causes agradual increase in restriction against rotation of the perylene from roomtemperature to 90 K. In the cured resin there is a fixation of the perylene and itssurrounding space. Of particular interest is a study on the behaviour of slip-flowin a die wall through the use of a dye tagged polyethylene coating578. Theobserved presence of adsorbed polymer chains following slip flow supports thepreviously proposed ‘cohesive’mechanism for the ‘stick-slip transistion’ of PE onhighly adsorbing surfaces. Other tagging processes include homodimeric mono-methine dyes to nucleic acids579, PMMA with aminoanthracene580, benzazolyl-vinylene copolymerized with MMA581, C60 grafted PVK582, polyamides andpolyesters with 2,6-bisphenyl-4-anthracenyl-N-hexadecylpyridinium tetra-fluoroborate ligands583, polyesters with m-terphenyl segments584, PMMA withbenzanilide groups585, benzothiozanthene labelled ethylene-butene copolymer586,polystyrene functionalized with anthracene587, polyisoprene-b-polystyrene withfluorescent dyes588, perylene on PVK589, 4-dicyanomethylene-2,6-dimethyl-4H-pyran on poly(amic acid)590, polystyrene grafted nanospheres of CdS and silica591

and fluoroalkylated end-capped oligomers containing 5-chloro-8-quinonyl seg-ments592.A number of studies have appeared on pyrene binding. Pyrene forms a dimer

complex with �-cyclodextrin, which is stabilized in the crystal state by hydrogenbonding between the OH groups on the rims of adjacent chains593. The coilglobule transition in pyrene labelled poly(�-caprolactone) has been identified inTHF solvent by cooling down to 0 oC594. At lower temperatures the fluorescencespectra and associated decays were invariant with time for more than 50 hours.This proved that the coil globule transition had no aggregation interference.However, below 30 °C aggregation begins to set-in. The diffusion of oxygen hasbeen investigated in pyrene labelled PMMA particles595,596 at different tempera-tures. Diffusion rates were found to increase with increasing film thickness withno temperature effect. Aggregated structures have been observed in pyrenelabelled polyelectrolytes597 while 1-pyrenesulfonyl chloride has been used toinvestigate the microstructure of polysiloxane layers on glass fibres598,599. The pHinduced expansion of poly(acrylic acid) and cationic cellulose has beenmonitored through the use of pyrene and naphthalene probes600 and the swellingof PMMA crosslinked gels with a dimethacrylate monomer has been measuredusing a pyrene probe601. Here pyrene lifetimes in the gel decreased as swelling


increased and using the Li-Tanaka equation mutual and cooperative diffusioncoefficients were found to be around 10�5 and 10�7 cm2 s�1 respectively. Ananosensor system has also been developed based on pyrene tagged poly(acrylicacid) with perfluorinated functionalities602. In this case a change of pH from basicto acidic media induces a collapse of the structure and a concurrent suppressionof preformed excimer sites. Luminescent oxygen sensor paint films have beendeveloped based on Ru(II)-pyrene linked acrylic copolymer systems603. Usingpyrene as a molecular probe the thermally induced smartness of poly(N-iso-propylacrylamide) microgels has been demonstrated and shown to involve atwo-stage mechanism: shrinkage of the nanoparticles followed by aggregationinducing phase separation604. Pyrene-labelled polyelectrolytes have been pro-duced with sulfonate groups605. Hydrophobic aggregation is shown to existthrough local electrostatic attraction in polar solvents. Other studies includepyrene tagged polystyrene latexes606 and poly(methacrylic acid-g-ethyleneglycol) copolymers607.Photochromic polymeric systems continue to increase in interest second to

that of LED polymers with over 50 papers on the topic. Methacrylate, methyl-styrene and itaconate copolymers have been made with side-chain amino-nitroazobenzene groups608. Here geometrical effects of the side chains wereexamined on the dynamics of photoinduced birefringence. Anisotropy in severalazo-dye tagged polymers has also been examined with Tg playing a key role onoptical activity609. Several workers have made methacrylate polymers andcopolymers with azobenzene chromophores610—615. Photoinduced birefringence ismore important in tagged molecules than doped610,611 while in other work relax-ation effects depend highly on temperature effects612. Intra- and intermolecularhydrogen bonding effects are also important between chain side-chains613 whilethermal decay reactions depend upon the alkyl chain lengths in the copolymer614.In ester methacrylates fluctuations in local free volume observed in cis—transisomerism of azobenzene chromophores have been related to local structuralrelaxations615. Macroconformations in polystyrene have been controlledthrough the use of azobenzene side-chains616 while a series of azobenzene modi-fied poly(amides) fitted with spirobi-indane and chiral binaphthyl chromophoreshave been found suitable for high performance applications617. trans—cis Isomer-ization was induced through UV irradiation and reversed using thermal orvisible light. Irradiation of the polymer samples to drive the trans—cis isomeriz-ation reaction resulted in an immediate chiroptical response, with CD bandintensities and optical rotations significantly reduced. These effects were fullyreversible and were attributed to the presence of putative one-handed helicalconformations in the trans-azobenzene-modified polymers that were severelydisrupted following trans—cis isomerization. Poly(azoaromatic viologens) havebeen prepared618 that undergo a reversible photoinduced supramolecular assem-bly and also form complexes with the dye Eosin that have enhanced conductivityon irradiation. Such complexes are considered to be photoswitchable. Photo-dynamic properties of azo-modified polymers are found to depend upon thedegree of functionalization619 while photochromism in tungstophosphate acidacrylamide polymer is related to the presence and diffusion of oxygen620. Transi-

Photochemistry362

ent diradical species are observed in polyene sequences621 while photochromicdyes have been developed that can photoswitch to bind and release metal ions622.Here spiropyrans can be used to control environmental pollution. A novelmechanism has been proposed for the observed fast relaxation of photoinducedanisotropy in a poly(malonic ester) with p-cyanoazobenzene groups623. Theseworkers observed an increase in the induced birefringence in the decay processjust after the pumping beam polarized perpendicularly to the recording beamwas illuminated in the relaxation process. They considered a newmodel based onan elastic force between the side-chain and the backbone of the polymeric film.Here the backbone could be reorientated together with the side-chain with fastrelaxation being associated with the elastic force. Photochromicdihetarylethenes have beenmade and shown to undergo photocyclization whichdecreases in the order of substituents COOH�COOMe�CONHAr624. Photo-chromic organic—inorganic hybrids have been made through a sol—gel reactionof tetramethoxysilane in the presence of spiropyran modified poly(N,N-dimethylacrylamide)625. Exposure to UV light gave a new absorption at 557 nmthat was little affected by the presence of the silica. The photochemical andphotodynamic behaviour of E/Z isomerization of an azobenzene side-chainpolymer have been related through UV and dielectric spectroscopy626. Poly(3,4-ethylenedioxypyrrole) undergoes electrochromic switching from red to blueforms627 while a new photochromic spirothiopyranobenzenopyrylium dyeundergoes very rapid reversible ring opening on irradiation-dark reaction628. Animprovement has been made on the theory of all-optical poling629 whereasmonolayers of PVA with azobenzene spacers undergo reversible expansion andcontraction processes on irradiation630. An increase in the length of the spacersgave a non-linear response in the reversible process whereas short chain spacersgave a linear response. The non-linear behaviour is associated with co-operat-ivity stemming from the self-assembling nature of the trans-azobenzene side-chains. Photochromic poly(tetramethylene oxide)/tungsten trioxide hybrid ma-terials have been developed that undergo yellow—blue reversible changes631.Long chain organomercury(II) dithionate complexes undergo similar changes632.Ion-selective amphiphilic crown ether dyes in monolayer form collapse in thepresence of Na(I), Ca(II) and Mg(II) ions but this is reversed in the presence ofK(I) ions633. Here dye—cation complexes are formed in the monolayers, whichinfluences its expansion.With K� ions photodimerization takes place. Local freevolume has been investigated for poly(methylsilsesquioxane) probed withazobenzene chromophores634 where the final cis fraction in uncured PMSQdecreased markedly below 250 K, which is claimed to be unusual for linearpolysiloxanes. Polyurethane cationomers undergo reduced isomerism with in-creasing azo group concentration635 while multilayers have been developed ofazopolyelectrolytes636,637 that also exhibit a photochromic dependence on the azogroup concentration. Photochromic liquid crystalline copolymers containing aphotochromic liquid crystalline monomeric unit showed only a smectic phasewhile those with non-LC monomeric units show a chiral nematic phase638.Photochromic inks have been made based on bacteriorhodopsin639 while poly(4-polyphenylazophenol) has been synthesized using an enzymatic method640. This


polymer has a long relaxation time and behaves as a glassy macromolecular dye.An LC polymer has been made based on 4,4�-dialkoxystilbene tagged meth-acrylate641 as has a 6-[4-(4-ethylphenyl)diazenylphenyloxy]hexyl methacrylatecopolymer642. Azobenzene multilayer assemblies of poly(vinyl sulfate) undergorapid isomerism without fatigue643 as do cationic and anionic bolaamphiphilesbased on azobenzene derivatives644. In the latter case photoswitching can becontrolled by the nature of the counterion. Other photochromic systems ofinterest include polymers with 2-phenyl-1,3-indandione moieties645, imidazol-one azopolycyanurates646, 2-[[4-(4-cyanophenylcarbamoyl)phenyl]ethyl]ethylmethacrylate647, dimethyl-6-aryl-2,2-dimethyl-2H-chromene-7,8-dicarboxy-lates648, azo-tagged polyacetylenes649, composites650, spiropyrans651, azo-taggedcyclodextrins652, benzofurans653, azo-tagged polystyrene654, dithienylethene655,poly(dihexylsilane)656 and articles on general topics657—659.Over twenty articles have been published relevant to LC polymer materials.

Photo-orientation effects of poly(methacrylates) with azobenzene side-chainshave been investigated660. The polymer exhibits excellent thermal stability andhigh optical anisotropy with a well-ordered domain. In-plane orientation wasgenerated in the glassy state as well as above the Tg and irradiation at 90 °C gaverise to a distinct transformation from in-plane orientation at the early stage tosuccessive out-of-plane orientation, which was also accompanied by H-aggrega-tion. Such systems are claimed to be valuable for recording optical images on thebasis of the differential in birefringences between the two orientational modes.Two fluorescence bands are observed from LC polyesters with naphthoatemesogen units at 410 and 430 nm661. The former band is due to partiallyoverlapping naphthoate units while the latter is due to ground-state fully over-lapping complexes. The latter assignment is confirmed by the observation thatincreasing viscosity increases the 430 nm peak intensity. Non-LC and LC basedpolymer blends have been mixed to give systems in which the former reduces theemission at 420 nm but generates a new band at 480 nm662. Prior thermaltreatment of the blends and casting onto rubbed polyimide film increased thenew emission by over an order of magnitude. On the other hand blends com-posed of cholesteric copolymer and a chiral monomer give rise to a thermo-dynamically incompatible matrix giving rise to a separate amorphous phase663.This causes a decrease in the concentration of the chiral component in choles-teric phase and, as a result, leads to untwisting of the helix bringing about a shiftin the maximum of the selective light reflection to longer wavelengths. Suchmaterials may also be used for optical data storage. The thermal quenching andoptical bleaching of the luminescence from polyacrylates with cyanoterphenylside groups is dependent upon the composition of the matrix664. However, thereis no dependence upon the degree of crosslinking of the polymer. The chainpacking in polyesters with biphenyl side groups influences their luminescenceproperties665. Here the rotational diffusion coefficient was found to increasegradually with temperature showing a sudden jump at the liquid crystal—iso-tropic transition temperature. In another area a modified stereolithographicprocess was developed using a magnetic field to align the liquid crystal mono-mers in each layer of a multiplayer part666. Thus, multilayered photopolymerized

Photochemistry364

parts with various layer alignments were obtained. In this way it was possible toachieve any desired in-plane coefficient of thermal expansion values between 0and 90 °C for unidirectional alignments. A new chiral menthone-based acrylicpolymer has been made that is capable of cis—trans isomerization coupled with anematogenic monomer667. On irradiation the step of the helix is changed with aplanar orientation. A new crosslinked LC network has also been made contain-ing a fluorescent probe668. From birefringence measurements no appreciable lossin alignment was found up to 200 °C. However, it was found that the fluorescentchromophore was less well ordered than the liquid crystal. The thermoreversiblegelation of rod-like poly(�-stearyl-�-l-glutamate) has been investigated and itwas found that its long-range features such as a cholesteric twist remain frozenby gelation669. The nano- and meso-scale morphologies of polymer films ofvarying LC concentration have been examined670. These polymers, photocross-linked and based primarily on a penta-acrylatematrix with an LC dopant, revealincreasing nanocale heterogeneity with increasing LC content. In this type ofmatrix an increase in LC content causes a coalescent regime of aggregated beadsof LC polymer the size and uniformity of which increase with increasing LCconcentration. Phase separation has also been investigated theoretically using atime-coupled dependent Ginzburg-Landau equation671. Here the simulations onthe spatio-temporal evolution of the coupled LC concentration and orientationorder parameter initially lag behind those of the concentration order parameter.The polymer-induced phase separation is characterized only by the late stage ofphase separation. Also, the growth behaviour and simulated morphology con-sisting of LC droplets dispersed in a matrix of polymer appears the same for allcompositions, the only exception being that the size increases with increasing LCconcentration. Of particular interest with this model is that the simulationcaptures the observed domain topologies. LC systems containing azobenzeneside-groups become translucent on irradiation due to the isomerism672. The lightscattering is associated with a biphasic morphology produced transiently due toa partial photochemical transition. The topochemical polymerization of 1,3-dienemuconic and sorbic acids with naphthylammonium salt counterions formsstereoregularmeso- or erythro-diisotactic-trans-2,5-polymers irrespective of theirstarting configuration673. Microscopic mechanisms of LC photoalignment havebeen considered for poly(methylphenylsilanes)674 and polarization in meth-acrylate polymers with azobenzene side-groups675. Novel photocrosslinkablepolymers with biphenyl or naphthalene groups have been prepared with anchor-ing and tilt angles676 whereas new photochromic spiropyrane acrylic monomerswith varying methylene spacers give ternary cholesteric copolymers when reac-ted with hematogenic and chiral monomers677. The latter exhibit selective lightreflection in the visible region of the spectrum while under UV light irradiationthey form a merocyanine form of dye, the absorption maximum of whichcorresponds to the maximum of light reflection. Other studies of interest includediscotic materials coated onto polyimides678, bismaleimides with divinyl com-pounds679, poly(3,7-di-tert-butylnaphthyleneethynylene)680, chiral diacrylates681,discotic epoxy systems682, polymers with chiral tails683, PMMA with azo-sidegroups684 and polythiophenes with ionic viologen mesogenic side-chains685. In


one study using Langmuir-Blodgett films it was shown that intermolecularinteractions decrease the efficiency of photochromic transformations686.Several articles have appeared dealing specifically with excimer formation in

polymers. Novel photoactive heterocyclic polyimides containing naphthalenegroups have been synthesized and found to give rise to excimer emission687, as docopolymers of methacrylates with carbazole and naphthalene groups688. Elec-tronic energy migration and excimer dissociation control the fluorescence kin-etics in copolymers of 1-vinylnaphthalene andMMA689. A similar study has alsoshown that excimer formation between naphthalene goups in related copolymerscannot be inhibited690. The emission spectra of diblock and triblock sphericalvesicles of polyquinoline—polystyrene have features that are characteristic oftheir supramolecular morphology691. Strong excimer emission was observed dueto J-like aggregation with the potential of developing photonic materials. Sul-fonated polystyrene gives692 excimer emission in concentrated solutions of above2.0 g L�1 while macrocyclic polystyrene shows significant enhancement of ex-cimer emission with decreasing molecular weight693. Copolymers of sodium2-(acrylamido)-2-methylpropanesulfonate and N-oleylmethacrylamide havebeen tagged with naphthalene groups in order to monitor the formation ofhydrophobic domains and their self-association behaviour694. cis-Ethene bondsin the oleyl group were found to form clusters in the hydrophobic domainscoupled with a strong tendency to undergo intramolecular association. Orienta-tion of PMMA chains tagged with naphthalene groups results in an enhance-ment of excimer formation due to chain alignment and close intermolecularpacking695 and indene—PMMA also gives excimer emission696. Naphthalenegroups undergo energy tranfer in polyrotaxane molecules697 while in poly(di-octylfluorene), excimers are formed with only a small change in intermolecularseparation698. In this polymer the exciton diffusion constant was found to be twoorders of magnitude larger than the excimer diffusion constant thus accountingfor strong quenching effect of excitonic luminescence by quenching sites. Herethe excitonic emission exhibits a significant polarization anisotropy, which isconsistent with the migration of excitons between regions of different orientationof the polymer chains. This is in contrast to excimer formation between suchdomains, which will be inhibited by the fact that excimers experience the domainborders as potential barriers. Excimer formation in poly(ethylene naphthalate) isalso enhanced by elongation due to chain chromophore alignment699 while frontface geometry is claimed to be better for observing excimer emission than aright-angled arrangement as it corrects for re-absorption700. Excimer formationof methylphenylsiloxanes has been associated with diad conformations in thechains where distances between the C atoms were 4.2 A� with an angle of rotationof 110o in DS to angles between phenyl rings of 15o coupled with a staggering ofthe aromatic groups and angles between the Si—C bonds between neighbouringrings of below 45o 701. It is claimed that the conformation of excimer forming sitesin these polymers is significantly different from those in normal hydrocarbonanalogues with large movements being necessary to form the excimer sites.Energymigration continues to be investigated in a variety of polymer systems.

Vinyloxy monomers with 1,8-naphthalimide groups have been synthesized and

Photochemistry366

fluoresce with intensities which are dependent upon the spacer lengths betweenthe naphthalimide groups702. Self-quenching occurs by intramolecular charge-transfer interactions between the electron-donating vinyloxy and electron ac-cepting naphthalimide groups. Molecular dynamics of polystyrene with anthrylend groups have been studied by fluorescence depolarization703 while theluminescence from cation-doped poly(fluorene) is observed to depend upon thecation layer thicknesses704. Highly fluorescent poly(cyclodiboranes) have beensynthesized705 and photoinduced electron transfer observed between pyrene anda xanthene dye706. Long-range energy transfer has been observed between layersof PVK on poly(9,9�-di-n-hexyl-2,7-fluorenylvinylene)707 while poly(fluorene)copolymers exhibit exciton migration and trapping to the copolymer cyanostil-bene units708. The copolymer exhibits red-shifted emission and enhanced colourstability. Stern-Volmer quenching analysis has been undertaken on polysilanesusing different halogenated solvents709 and steady-state triplet exciton densitieshave been measured in poly(2,5-diheptyl-1,4-phenylene-alt-2,5-thienylene)710.Polymers of 3-methyl-acrylamide-9-carbazole have been found to exhibit higherfluorescence intensities than the corresponding monomer analogues711 and elec-tron—hole generation has been examined for poly(N-epoxypropylcarabzole)712.In carbazole-methacrylate copolymers there is little interaction between theethene bonds of the methacrylate groups and the carbazole chromophores713.Self-quenching was found to be highly dependent upon the polarity of thesolvent, high polarity inducing intramolecular association and hence quenching.Meso-linked zinc porphyrins doped in PMMA exhibit photoinduced chargetransfer across the arrays714 while other studies of interest have concentrated ondichromophoric copolymers with 1,8-naphthalimide groups715, poly[oxy-1,4-phenylenecarbonyl-1,4-phenyleneoxy-1,4-phenylene[(2-carboxyphenyl)methyl-idyne]-1,4-phenylene] doped with TCNQ716 and aggregation effects in watersoluble polymers717.Polymers in micellar media continue to attract significant interest. Pyrene

solubilised in poly(N-isopropylacrylamide) shows unusual fluorescence aniso-tropy behaviour718. Rather than decay to zero, as might be expected for a freelyrotating species in solution, the emission attains a minimum finite value. After100s of nanoseconds the anisotropy increases and becomes more polarized withtime. This behaviour reflects the heterogeneous nature of the medium in whichthe probe is dispersed; that is to say whether it is free or occluded in the polymerhost. The latter will evidently give rise to the unusually longer-lived growth inanisotropy. The Gemini surfactant 1,4-bis-(2�-(N-dodecylpyridinio-4-yl)-ethenyl)benzene dibromide exhibits a large fluorescence enhancement and shiftin maxima in alcoholic solvents719. This polymer effectively solubilizes pyreneand totally quenches its emission. Pyrene has also been used as a probe to studythe effect of pH on viscosity of acrylamide copolymers in solution720. Hereviscosity increases with pH due to the polymer changing from a compact (lesssoluble state) to an expanded state (more soluble). The critical solution tempera-ture of poly(N,N-dimethylmethacrylamidophenylammonium propane sul-tone)has been found to be less than 0 °C721. Pyrenylacrylic acid has been used as aprobe and found to give varying emission spectra depending upon the solvent


polarity722. The probe also shows two stages of protonation (i.e. of the negativecarboxylic group and carbonyl oxygen) and this is claimed to be useful foridentifying vicinal versus geminal OH groups on silica particles. Polyurethaneionomers tagged with fluorescent dyes form aggregates and give rise to UVfluorescence723. The intermolecular interactions between the hydrophilic groupsof the fluorescent dye become stronger with increasing concentration causing anincrease in average particle size. For polystyrene-graft-polyoxyethylenes thehigher the temperature and shorter the side-chain lengths the lower is the CMCvalue724. Double diene lipids with spacer lengths greater than six show enhancedstability toward surfactants while solubility in organic solvents is decreased725.Thus, heterobifunctional amphiphiles with long spacer lengths tend to favourcrosslinking. Amphiphilic block copolymers of poly(2-methyl-2-oxazoline) showgood solubility in aqueous media with an aggregation dependent on molecularweight726 while cationic fluorophores on methacrylate copolymers are quenchedby halide ions727. For a series of acrylic terpolymers increasing the hydrophobicchain lengths increases their viscosity in solution728. Low levels of baterial growthhave been detected in polymeric detergents729 while the fluorescence quenchingbehaviour of an anionic conjugated polymer towards small amounts of quen-chers can be modulated by complexation with a countercharged detergent730.For example, upon adding dodecyltrimethylammonium bromide to a con-jugated polymer, cationic quenchers such as methylviologen become less effec-tive while the quenching by neutral agents, most notably nitoraromatics, isenhanced. Such polymer—detergent complexes provide a new method for sensingchemical agents. Crosslinked gelatin gives strong inherent blue fluorescence dueto dimeric tyrosine731 and this is enhanced in non-solvents due to increasedintramolecular associations. Complexation between poly(acrylamide) andpoly(methacrylic acid) is influenced by pH732 and the emission from poly(2,5-methoxypropyloxysulfonate) is enhanced by a cationic surfactant733. Other stu-dies of interest include those investigating phosphor containing acrylic acids734,quinoline—styrene—quinoline triblock copolymers735, pyrene in mixed surfac-tants736, aminocoumarin dyes in restricted media737, diazo resins with sodiumdodecyl sulfonate738, pyrene with amphiphilic polymer aggregates739, bis(2-ethyl-hexyl)sodium sulfosuccinate) with polymer surfactants740, ketocyanine dyes inmicellar media741, hydrophobically modified polyacids742, perylene dyes743 andeffects of urea and thiourea on Safraninine T dye emission in micelles744.Fluorescence has been used to measure the degree of bonding in adhesive

joints for polyester/polyethylene materials745,746 while fluorescence from recycledpaper has been removed using chlorine dioxide747. Thermally stimulatedluminescence from a poly(ester urethane) has been found to vary with filmthickness748 which is assumed to be due to the diffusion effect of oxygen. Poly(4-vinylpyridine) exhibits variable emissions depending upon the degree andwavelength of irradiation749. This effect is due to a photoinduced directionalordering of the polymer chains in a special quasi-crystal formation and orig-inates from protonation of the side-chain pyridine groups after solvation. Thissol—gel transformation process is reversible. PPMA beads with coumarin dyeshave been synthesized as photonic crystals750 Poly(cyclophane) and its poly([2]-

Photochemistry368

catenane) have been made and the latter is found to require a higher oxidationpotential to reach its conductive state than that of the former751. The emissionfrom cellulose was found to depend upon heating and cooling cycles752. Attemperatures above 145 °C degradation sets in and yields different products.Polyerythrosin has been made electrochemically753 and the thermoluminescenceof polystyrene sulfonic acid examined754. Polycarbonate luminescence has beenobserved following irradiation with uranium ions755 and a theoretical investiga-tion has been undertaken on the redox behaviour of p-n diblock conjugatedpolymers756. The fluorescence form LDPE has been found to depend uponradiation dosage757 while the permeability of oxygen in alkylaminothionylphos-phazine films has been monitored by phosphorescence analysis758. Depolariz-ation of the fluorescence of labelled macromolecules has been determined bysecond rank time orientational correlation functions (OCFs) of the absorptionand emission components759. The OCFs under certain conditions exhibit anoscillatory behaviour, which is irreproducible within the studied diffusion equa-tion. Other studies of interest include those of aromatic polyesters760, failure ofadhesive joints761, relaxation in density gratings762, spectroscopic behaviour ofnovel poly(pyridine-2,5-diyl)763, fluorescence of Schiff-base polymers764, aromaticand aliphatic copolyamides765, polysilylenes766,767 and metal containing poly-mers768.

4 Photodegradation and Photooxidation Processes in Polymers

As discussed in the last report interest in polymer photodegradation/oxidationhas remained at a steady but low level of activity in the published journalscompared with what was at one time a highly prolific field of interest. Reviews ofthis topic include a comparative assessment of weathering devices769, degradablepolymer materials770, photooxidation of rubbers771, bio- and photodegradabil-ity772 and dehydrohalogenation773.

4.1 Polyolefins. — This class of polymers tends to be one of the most widelystudied. Photooxidation of polypropylene has been described in terms of threekinetic parameters774. This involves a typical induction period and autoacceler-ation build-up of hydroperoxides, an intermediate slower hydroperoxide growthand finally a very slow hydroperoxide growth. The early stages also appear tooscillate strongly, possibly due to heterogeneous oxidation sites. Polyethylenehas been studied in great detail. Ethylene carbon monoxide copolymers disinte-grate rapidly on irradiation and give substantial amounts of ether products775.Norrish Type I is the primary reaction with the formation of acyl and alkylterminal radicals776 together with water and carbon dioxide as the major volatileproducts. Irradiation of isotactic polypropylene in a mixture of 32O2 and 36O2

generates 34O2 due to a pseudo-termination reaction through the recombinationof peroxy radicals to give tetroxides777. The latter then decompose to givemolecular oxygen and alkoxy radicals. Several agents can speed up the photooxi-dation of polyethylene such as grafted methylenebutandioic acid778, iron diethyl


dithiocarbamate779,780 and ferric salts781. In the latter case the presence of starchacts as a synergist for photosensitization. Polyethylene and polyethylene waxesare biodegradable when the molecular weight is less than 5000782 and theactivation energy of thermal oxidation of polyethylene is sensitive to all pro-cesses resulting from the exposure to UV light783. Surface cracking in polyethyl-ene has beenmodelled by percolation784. Here the geometric characteristics of thegenerated Voroni decompositions and simulated clusters do not affect the de-pendence of the characteristic size of clusters on their capacity. At the same timethe rate of surface cracking is characterized by the presence of a strong size effect.Surprisingly, the use of compatibilizers such as anthraquinone enhances themechanical performance of polyolefin blends after irradiation785. Differences innatural and artifical ageing of LDPE have been measured and shed some doubton the issue of hydroperoxides as key intermediates in the photooxidationkinetics786. For recyclability in pipe applications it has been formulated that onlyup to 50% by weight of recycled material should be used with fresh virginpolymer787 and metallocene polyethylene has been studied788. In the latter casefor two grades of polymer metallocene material has been found to be morephotostable that conventional Ziegler-Natta polymer.

4.2 Polystyrenes. — Poly(styrene peroxides) undergo a chain unzipping mech-anism with stability being dependent upon the bialkoxy radicals789. Polystyrenecopolymerswith benzil and benzoyl peroxide undergo the same rates of degrada-tion790. UV exposure dose enhances the surface wettability of polystyrene791. Thisis due to the formation of low molecular mass products at the surface of thepolymer material increasing hydrophilization. Poly(methyl vinyl ether) andpolystyrene blends exhibit strong interactions on photooxidation792 whereaspolystyrene irradiated with fluorescent tubes undergoes random scission pro-cesses with crosslinking playing a more important role on the surface rather thanthe bulk793. The latter is associated with the usual oxygen starvation effect in thebulk of the material. The presence of sensitizers such as benzophenone hampersthe crosslinking reaction in polystyrene794. Diketonic groups have been co-reac-ted into polystyrene to enhance reactivity795 while post-reactions have beenobserved in the photooxidation of butadiene—styrene copolymers doped withdiphenylethanedione796. For SIS triblock copolymers the isoprene units onlyundergo oxidation resulting eventually in phase demixing797. Multivariate analy-sis procedures have been used to measure the photooxidation of ABS798.

4.3 Poly(acrylates) and Poly(alkyl acrylates). — Of a range of poly(alkyl meth-acrylates), PMMA has been found to be the slowest for photooxidation butfastest for photodegradation799. Flexibility and mobility of the free radicalsaccount for this differential in reactivity. For another range of acrylate andmethacrylate polymers the former were found to be more reactive800. Thus, withshorter alkyl side groups, chain scissions prevailed over crosslinking reactions inboth acrylate and methacrylate samples. Only the butyl methacrylate undergoesrapid crosslinking and fragmentation.With 248 nm radiation, side-chain scissionpredominates coupled with some main chain scisson801. There is a strong

Photochemistry370

stereochemical influence on the methacrylate spectra, which manifests itselfthrough changes in time-resolved EPR analysis as a function of tacticity andtemperature. Similar studies have been undertaken on a range of acrylate coat-ings and the side-chain length again appears to be important in controlling thereaction rates802. Polymers with long ester groups undergo fast and extensivecrosslinking reactions while methyl and ethyl groups are relatively stable.

4.4 Polyesters. — Polyethylene terephthalate and its copolymer with 1,4-cyclo-hexanedimethanol have been photolysed under different conditions803. Undervacuum pure photoytic processes occur involving Norrish Type I and II reac-tions with hydroxylated and carbonyl products being enhanced in the case of thecopolymer. This effect is associated with the labile hydrogen atom on the tertiarycarbon atom of the cyclohexane units. Under oxidation conditions the aliphaticportions of the molecular chains also undergo attack forming hydroperoxidesthat eventually result in formic and acetic acid production. Hydroxylation of thearomatic rings also occurs as well as the formation of terephthalic acid. In thephotooxidation of poly(butylenes terephthalate) anhydride formation has beenconfirmed through reaction with tetramethylammonium hydroxide to givemethyl-4-methoxybutyrate804.

4.5 Polyamides and Polyimides. — Very little published work has appeared onthese materials. Nylon 6,6 has been shown to exhibit an increase in crystallinityupon irradiation although this fact is already well-established805. What is new isthe observation that there is no change in X-ray diffraction, indicating a new typeof crystalline morphology. Crack formation was observed at the centre ofspherulitic structures, which increased with irradiation time.

4.6 Poly(alkyl and aromatic ethers). — Poly(oxyhexylenoxy-4,4�-benzilylene)undergoes rapid degradation on irradiationwith crosslinking and fragmentationdepending upon the source intensity806. Crosslinked epoxy resins undergo rapidsurface photooxidation developing a growth in hydroxy absorption807 whilelaminates have also been found to exhibit growths in ester and carboxylic acid808.Photoageing has also been found to influence the mechanical properties of epoxysystems809. Multifunctional polymers with phenacyl ester and vinyl ether groupsundergo direct cleavage of the ester groups upon irradiation to give pendantcarboxylic acid groups810. The latter, in turn, react with the vinyl ether groups togive acetal linkages. Degradation products of poly(ethylene oxide) have beenanalysed by pyrolysis/GC811. Poly(ether ether ketone) has been investigated andfound to undergo pinacolization, photo-Claisen and direct chain scission pro-cesses812. Intra- and intermolecular phenylation reactions also occur coupledwith discoloration.

4.7 Silicone Polymers. — Irradiation of C60 and a polysilane in solution af-forded an adduct of the two molecules with unique electronic properties813. Avariety of linear and crosslinked polysilanes have been converted into silicon


oxides by ozone/UV treatment processes814. Under this type of treatment all ofthe organics are removed as volatiles.

4.8 Polyurethanes and Rubbers. — The physical properties of EPDM rubberseals for automobiles have been examined under weathering conditions815 whileimpurities in raw natural rubber can sensitize its photooxidation816. The erosionresistance of protective elastomeric coatings during UV exposure has beenexamined817 as has the degradation of polyurethanes based on 4,4�-dibenzyldiisocyanate818 and 4,4�-methylene bis(4-phenylisocyanate)819. The extent ofphotolysis is greater for soft segments resulting eventually in phase separationfrom the hard-aromatic segments.

4.9 Poly(vinyl halides). — PVC has been examined by depth profiling on irradi-ation820 and conjugated double bonds generated by UV irradiation821. Dehyd-rochlorination is associated with C—Cl bond cleavage and using a KrF laserconjugation sequences of up to 30 C atoms can be made822. Iron pigments havebeen used in PVC laminates and, as might be expected, this affects the degrada-tion rate823.

4.10 Photoablation of Polymers. — Excimer lasers (UV) have been used to in-duce the reaction between phenylsilane and methylphenylsilane824 while thesame lasers used for ablating polypropylene show that photochemical andthermal effects are co-operative825. Water repellant fabrics have been madethrough plasma irradiation of vinylidene fluoride and 1,1,1,2-tetrafluorethyl-ene826 while self-assembled organo-silane layers undergo direct C—C and C—Sibond scissions from 172 nm radiation827. Using a nitrogen laser polyimide filmshave been shown to generate surface carbonyl groups828. PTFE has been ablatedwith pulsed nano- and femto-second lasers829 and experimental uncertainties inthe processes have been discussed. The products of degradation under 157 and248 nm irradiation from typical lithographic materials have been examined830.Hydroxystyrene polymers were found to undergo crosslinking while acrylatesand methacrylates undergo chain scission. The latter show film loss on irradi-ation while hydroxystyrenes do not. Consideration of these processes was felt tobe important during laser curing reactions at 157 nm. Halonaphthalene dopantsin PMMA undergo significant degradation on 248 nm excimer laser ablation831

while for a triazeno polyether only neutral products were identified using thesame irradiation at fluences below 1.3 J cm�2 832,833. The irreversible increase inhole width and decrease in hole area for polysiloxane matrixes has been inves-tigated and found to be due to local relaxation of the siloxane chains834. Surfaceinteractions of radical species have been examined during plasma irradiation ofpolymer surfaces by fluorocarbon plasmas835. Three types of surface interactionswere seen, namely generation of CF2 (S�1), surface loss of CF2(S�1) and unitscattering (S�1). The difference in these systems is believed to be due to differ-ence in overall surface interactions. For example, NH2 can be generated onirradiation of PTFE substrates but consumed on polyimide surfaces. Formulaefor determining themechanisms for ablation of polymers have been developed836.

Photochemistry372

4.11 Natural Polymers. — Aside from polyolefins, cellulose and wood remainone of the most highly active fields of study in light-induced degradation pro-cesses. It has been found that denaturation temperature of collagen due to waterloss is reduced on irradiation837 while wood panels treated with different anhyd-rides have been found to be more resistant to photoyellowing838. The wavelengthdistribution of the irradiation source strongly influences the photochemicalreactions839. Thus, with broadband UV light photochemical reactions wereinduced with products at 370 and 415 nm while with fluorescence narrow bandUV sources photobleaching was observed. Again acetylation was shown tostabilize the processes. Hydrogenation of the aromatic lignin products alsoimparts stability toward yellowing840 as do hindered nitroxide molecules841. Thestabilizing effect of o-hydroxybenzophenone screeners has been enhancedthrough increasing their water solubility by the well-known Mannich reactionintroducing dialkylamino groups into the 3-position of the phenyl rings842. Othereffective stabilizer treatments include the use of borates and boric acid843 andsodium borohydride/sulfite treatment followed by acetylation as reportedabove844. A more severe process of inhibiting the yellowing involved protectingthe OH groups on the phenolic compounds in paper and wood as triflates andthen catalytic hydrogen atom transfer845. Stilbene—hydroquinone chromophoreshave been analysed in photobleaching of paper pulps846 and in other workhydroxyl radicals have been considered to be the major species causing thedegradation of carbohydrates847. On a different front cotton knitwear has beenfound to yellow on storage and this was considered to be due to contaminationthrough lubricating oils848. On irradiation, chitosan undergoes significant oxida-tion at the glucosidic linkages with a conversion of the amide to amine groups849.Cr(VI) is released and quantified on irradiating leather materials850.

4.12 Miscellaneous Polymers. — Positron annihilation measurements have beenused to measure the effects of irradiation on the microstructure of ABS andpolycarbonate851. Initially, chain scission predominates followed by crosslinkingin the later stages. In fluorinated urethanes both ether and urethane sites havebeen found to exhibit similar reactivity on irradiation852 and crosslinked poly-ethylene has been shown to give rise to the usual carbonyl and hydroperoxideoxidation products853. The photooxidation of poly(benzoxazines) generates p-benzoquinone854—856 and the nature and type of para-substituent on the phenylring plays an important role in controlling the oxidation rate. Poly(chloro andp-xylylenes) have been photooxidized and shown to undergo oxidation of themethylene groups as well as the aromatic rings857,858. The products were found tobe predominantly low molecular weight in nature while for the chloro derivativeadditionally C—Cl bond scission was prevalent. The mechanisms and kinetics ofthe keto—enol tautomerism in poly(acryloylacetone) and poly(ethyl acrylo-acetate) have been investigated for monolayers859. There is an increase in area perunit during the conversion process followed by a slow interfacial reorganizationof the products to a more favourable state. Using laser flash photolysis, fullereneadducts have been identified to PMMA when doped with N-methylfulleropyr-rolidine860. The new product is claimed to exist in a trans-3-trans-3-trans-3


adduct form. The photostabilities of poly(pyridinium salts) have been found todecrease with decreasing backbone conjugation861. The authors suggest that theinductive effect of one pyridinium ring upon the other is important in photodeg-radation. The evolution of viscoelastic properties upon the photoageing ofpoly(octenamer) shows that the average molecular weight of the polymer in-creasing from the onset of irradiation involving rapid crosslinking reactions862.Unusually, no chemical changes were evident in the polymer at this stage of thereaction indicating the high sensitivity of the methodology. Lyocell fibres exhibitopen pores upon UV exposure863 while in Shellac inter-etherification reactionsoccur with farUV light864. Other studies of interest include ultra-high weatheringdevices865, performance of thermosetts on weathering866,867, a novel tool fordestructive depth profiling868, biodegradable hydrophobic—hydrophilic hydro-gels869, oxidation processes in oil based varnishes870, ageing of papers871 andyellowing of polycarbonates872.

5 Photostabilization of Polymers

There has been very little academic research in this field. Much of the publishedliterature relates to commercial reviews of topical articles of interest such asimprovements in stability of urethane foams873, new stabilizers for polycarbon-ates874, polypropylene875, powder coatings876, polycarbonate-styrenics877, newHALS878, fabrics879, polycarbonate sheets880, polyolefins881, clearcoats882, multi-functional monomers883, engineering polymers884 and new calixarenes885. Numer-ous reviews have appeared on HALS stabiliers and their latest develop-ments886—896 and monitoring methods for weathering have been assessed897.Benzotriazole stabiliers have been reviewed898 and glucoside derivatives havebeen found to be good stabilizers for PVC899 and HALS for oriental laquers900.Substitution of benzotriazoles in the 5-position with electron withdrawinggroups significantly improves their performance901,902.Several studies have appeared on different aspects of hindered piperidine light

stabilizers (HALS). One interesting feature has been the encapsulation of lightstabilizers into silica matting agents for copoly(methyl methacrylate/butyl acryl-ate) paints903. Here encapsulation rather than straight addition of the stabilizershad a significant improvement on the light stabilizing ability of the coatings.Pyrene grafted to HALS molecules undergoes rapid photolysis on irradiation904

and oligomeric HALS are as good as stabilizers in poly(octenamer) as they are inpoly(propylene)905. HALS inhibit the crosslinking reactions in acrylic-melamineclear-coats906 while in pre-oxidized ABS a series of HALS exhibits the stabilizingorder tert-amine�sec-amine�amino ether groups907. HALS are antagonized bythe presence of fire retardants in light stabilization of polyolefins908. Halogenatedfire retardants are the main problem giving rise to chlorine or bromine radicalsthat form amine salts with the HALS N—H functionality. Chemiluminescence ofHALS stabilized polypropylene has been undertaken909 while polymeric HALSperform well in styrene—butadiene rubber910. New HALS blends have beenfound to be effective for automotive articles.911 New HALS based on urethane

Photochemistry374

linkages912 and terpene resins913 have been synthesized, and copolymerized inpolyolefins by metallocene catalysts914.

6 Photochemistry of Dyed and Pigmented Polymers

A number of reviews and articles of interest have appeared. These includephotofading of organic dyes915,916, photocatalysts in textiles917, coatings918 andrubber919.Two isomers of a cyanine dye have been reported to be photostable920 and the

fading of Rhodamine 6G in PMMA appears to have mutual effect921,922. For arange of cyanine dyes stability increases in the order benzoxazole�benzo-selenazole�benzothiazole923 while Rhodamine dyes are photostabilized by thepresence of thioureas924. Bridging in styryl dyes has an important stabilizingeffect on the excited state of the dye925 as does aggregation for squarylium dyes926.Mordanting dyes with iron has been found to seriously influence the stability ofthe fibre927 as iron is a well-known photocatalyst whereas nickel complexes of4-benzoyloxybenzenesulfonic acid have been found to photoprotect acid dyes928.In both nylon and polyester a series of monoazo dyes have been shown toundergo reductive photofading except when the reaction was controlled throughthe generation of singlet oxygen using copper phthalocyanine as a sensitizer929.Carbon black pigments have been shown for the first time to behave as triplet

quenchers930. They effectively quench the excited triplet phosphorescent speciesin polyethylene as well as the triplet lifetime of benzophenone. In terms ofstability there was also an unusual synergy between carbon black pigments andbenzophenone in the light stabilization of the polymer. Titania pigment filledaliphatic polyester coatings are found to be more light stable than aromaticbased polyesters931. Although there were no changes in gloss, FTIR showedchemical group changes. Nanocrystalline titanium dioxide pigments are photo-catalysts in PVC932,933 but can also photocatalyse the polymerization of diacety-lenemonomers934. In acrylic titania pigmented paint films, carbon dioxide gener-ation on photooxidation is proportional to the square root of the lightintensity935. With light at 405 nm anatase is reported to act as a light stabilizer.Other studies of interest on pigments include the titania sensitized degradationof bacteria936, leather dyes937 and surfactants938. Zinc oxide is also a photocatalystfor leather dyes939 and reactive dyes940. Free radical generation on irradiatedtitania pigments has also been monitored941.

7 References

1. Y. Yagci, NATO Sci. Ser., Ser. E., 1999, 359, 205.2. K. Morio, Setchaku no Gijutsu, 1999, 19, 22.3. J. V. Crivello, W. A. Mowers and S. K. Rajaraman, Rad. Tech. Res., 2000, 14, 34.4. J. V. Crivello,NATO Sci. Ser., Ser. E., 1999, 359, 45.5. J. P. Fouassier, Trends Photochem. Photobiol., 1999, 5, 1.


6. J. P. Fouassier, Photosensitive Systems for Photopolymerization Reactions, in[Trends in Photochem. Photobiol.], Research Trends, Trivandrum, India, 1999, 201pp.

7. A. J. Berejka, Adhes. Age, 2000, 43, S17.8. B. Quirk, Adhes. Age, 2000, 43, S5.9. C. Bachmann and S. Cantor, Adhes. Age, 2000, 43, S20.10. M. Kakuoka, Setchaku no Gijutsu, 1999, 19, 1.11. Y. Takaimoto,Kobunshi Tenkazai no Kaitatsu Gijutsu, 1998, 34, 107.12. J. Jakubiak and J. F. Rabek, Polimery, 2000, 45, 485.13. J. Jakubiak and J. F. Rabek, Polimery, 2000, 45, 659.14. J. Jakubiak and J. F. Rabek, Polimery, 1999, 44, 447.15. C. E. Hoyle, C. W.Miller and S. E. Jonsson, Trends Photochem. Photobiol., 1999, 5,

149.16. A. Costela, I. Garcia-Moreno, O. Garcia and R. Sastre, Recent Res. Dev. Phys.

Chem., 1999, 3, 111.17. K. D. Suh, J. W. Kim and J. Y. Kim,Kobunja Kwahak Kwa Kisul, 1999, 10, 629.18. V. Verkholantsev, Eur. Coat. J., 2000, 1, 44.19. O. Maruyama, Setachaku no Gijutsu, 1999, 19, 56.20. H. Tate and M. Kakuoka,Kobunshi Kako, 2000, 49, 2.21. T. Motoyama, Setchaku, 1999, 43, 529.22. S. Tang, Shanghai Tuliao, 1999, 1, 30.23. J. Paczkowski, Z. Kucybala, F. Scigalski and A. Wrzysczynski, Trends Photochem.

Photobiol., 1999, 5, 79.24. H. Strub, Actual. Chim., 2000, 2, 5.25. F. Catalina, C. Peinado, M. Blanco, A. Alonso and N. S. Allen, J. Photochem.

Photobiol., 2000, 131, 141.26. H. J. Hageman, P. Oosterhoff and J. Verbeek, J. Photochem. Photobiol., Chem. Ed.,

1999, 121, 207.27. N. S. Allen, M. Edge, S. Sethi, F. Catalina, T. Corrales and A. Green, J. Photochem.

Photobiol., Chem. Ed., 1998, 137, 169.28. F. Catalina, C. Peinado, T. Corrales and N. S. Allen, Polymer, 2000, 42, 1825.29. K. Subramanian,Polym.Prepr. (Am.Chem. Soc.,Div.Polym.Chem.), 1999, 40, 1028.30. S. Y. Yang and M. M. Green, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.),

2000, 41, 948.31. K. Subramanian, Eur. Polym. J., 2000, 37, 55.32. F. M. Li, Q. U. Gao, F. S. Du, G. X. Yang, F. L. Zhang, J. X. Zhang and Z. C. Li, J.

Appl. Polym. Sci., 2000, 76, 19.33. T. Corrales, C. Peinado, F. Catalina, M. G. Neumann, N. S. Allen, A. M. Rufs and

M. V. Encinas, Polymer, 1999, 41, 9103.34. J. W. Yang, X. M. Yang and Y. L. Chen, Gaodeng Xuexiao Huaxue Xuebao, 1999,

20, 1965.35. Yi Lin, Jin Wang and Guo Qi,Huadong Ligong Daxue Xuebao, 2000, 26, 212.36. Z. Qian and J. D. Wang, Gongneng Gaofenzi Xuebao, 2000, 13, 154.37. Y. Lin, J. Wang and G. Qi, Jingyong Huaxue, 1999, 16, 25.38. E. Andrzejewska, G. L. Hug, M. Andrzejewska and B. Marciniak, Nukleonika,

2000, 45, 83.39. J. F. G. A. Jansen, A. A. Dias, H. Hartwig and R.A. J. Janssen, Surf.Coat. Int., 2000,

83, 119.40. V. Lemee, D. Burget, J. P. Fouassier and H. Tomioka, Eur. Polym. J., 2000, 36,

1221.

Photochemistry376

41. M.V. Encinas, A.M. Rufs, E. Norambuena and C. Giannotti, J.Polym. Sci.,Part A:Polym. Chem. Ed., 2000, 38, 2269.

42. A. Costela, I. Garcia-Moreno and R. Sastre, Polymer, 2000, 41, 8017.43. C. Peinado, A. Alonso, F. Catalina andW. Schnabel,Makromol.Chem.Phys., 2000,

201, 1156.44. A.Wrzyszczynski, P. Filipiak, G. L. Hug, B. Marciniak and J. Paczkowski,Macro-

molecules, 2000, 33, 1577.45. C. Liu, Y. Cui, C. Chen and Q. Gao, Huaxue Yanjiu, 1999, 10, 23.46. J. Hageman and P. Oosterhoff,Macromol. Chem. Phys., 2000, 20, 1687.47. S. Hu, J. H. Malpert, X. Yang and D. C. Neckers, Polymer, 2000, 41, 445.48. P. Ghosh and G. S. Mukherjee, Polym. Adv. Technol., 1999, 10, 687.49. V. B. Ivanov and E. Yu. Khavina,Vysokomol. Soedin., Ser.A, Ser.B., 1999, 41, 1116.50. J. Kabatc, B. Jedrzejewska and J. Paczkowski, J. Polym. Sci., Part A: Polym. Chem.

Ed., 2000, 38, 2365.51. G. Gso and Y. Yang, Gaofenzi Xuebao, 2000, 1, 125.52. K. S. Padon and A. B. Scranton, Polym.Mater. Eng. Sci., 2000, 82, 27.53. K. S. Padon and A. B. Scranton, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38,

2057.54. H. Yong, W. Zhou, G. Liu, M. L. Zhen and E. Wang, J. Photopolym. Sci. Technol.,

2000, 13, 253.55. X. Allonas, J. P. Fouassier, M. Kaji andM.Miyasaka, J. Photopolym. Sci. Technol.,

2000, 13, 237.56. H. Gu, W. Zhang and D. C. Neckers, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 2000, 41, 1266.57. T. Urano and E. Hino, J. Photopolym. Sci. Technol., 2000, 13, 97.58. T. Urano, Y. Tsurutani, M. Ishikawa and H. Itoh, J. Photopolym. Sci. Technol.,

2000, 13, 83.59. N. Arsu and M. Aydin, Angew.Makromol. Chem., 1999, 270, 1.60. F. Gao, J. Q. Xu, Y. X. Song, D. L. Li, Y. Y. Yang and S. J. Feng, Chin. J. Chem.,

2000, 18, 280.61. D. Burget, J. P. Fouassier, F. Amat-Guerri, R. Mallavia and R. Sastre,Acta Polym.,

1999, 50, 337.62. F. Amat-Guerri, R. Mallavia and R. Sastre, Trends Photochem. Photobiol., 1999, 5,

103.63. P. J. Campagnola, D.M. Delguidice, G. A. Epling, K. D. Hoffacker, A. R. Howell, J.

D. Pitts and S. L. Goodman,Macromolecules, 2000, 33, 1511.64. T. Sato, T. Katayose and M. Seno, J. Appl. Polym. Sci., 2000, 79, 166.65. I. I. Abu-Abdoun, Des.Monomers Polym., 2000, 3, 171.66. G. Bhukta, R. Manivannan and G. Sundararajan, J. Organomet. Chem., 2000, 60,

16.67. I. I. Abu-Abdoun, Polym. Int., 1999, 48, 1197.68. S. Mah, S. Park, H. Nam and C. Seoul, J. Appl. Polym. Sci., 2000, 77, 2588.69. K. Yamada, H. Tabe and H. Hamano,Nippon Shashin Gakkaishi, 2000, 63, 152.70. M. Kaur and A. K. Srivastava,Macromol. Rapid Commun., 2000, 21, 291.71. W. G. Skene, T. J. Connolly and J. C. Scaiano, Int. J. Chem.Kinet., 2000, 32, 238.72. Y. Yamaguchi and C. Kutal,Macromolecules, 2000, 33, 1152.73. Y. Yamaguchi and C. Kutal, Monogr. Ser. Int. Conf. Coordination Chem., 1999, 4,

209.74. X.Wu and D. C. Neckers, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000,

41, 494.


75. J. V. Crivello, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 1849.76. S. K. Rajaraman, W. A. Mowers and J. V. Crivello, J. Polym. Sci., Part A: Polym.

Chem. Ed., 1999, 37, 4007.77. Y. Hua and J. V. Crivello, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38,

3697.78. J. V. Crivello and S. Kong, J. Polym. Sci., Part A: Polym.Chem. Ed., 2000, 38, 1433.79. L. Atmaca, I. Kayihan and Y. Yagci, Polymer, 2000, 41, 6035.80. Y. Yagci and W. Schnabel, Angew.Makromol. Chem., 1999, 270, 38.81. Y. Toba, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38, 982.82. Q. Gao, R. Li, G. Yang and H. Guan,Haxue Yanjiu, 2000, 11, 20.83. W. Schnabel,Makromol. Rapid Commun., 2000, 21, 628.84. O. Nuyken and M. Ruile,NATO Sci. Ses., Ser. E, 1999, 359, 117.85. C. Billaud, M. Sarakha and M. Bolte, Eur. Polym. J., 2000, 36, 1401.86. S. Mah, H. Hwang and J. H. Shin, J. Appl. Polym. Sci., 1999, 74, 2637.87. K. D. Belfield, K. J. Schafer and J. Liu, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 2000, 41, 578.88. D. M. Vuluga, M. Pantiru and M. J. M. Abadie, Eur. Polym. J., 1999, 35, 2193.89. H. G.Woo, E.M. Oh, J. H. Park, B. H. Kim, Y. N. Kim,H. C. Yoon andH. S. Ham,

Bull.Korean Chem. Soc., 2000, 21, 291.90. X. Huang, Z. Huang and J. Huang, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000,

38, 914.91. W. J. Zhou and D. L. Gin, Polym. Prepr. (Am. Chem. Soc.,Div. Polym.Chem.), 2000,

41, 1330.92. Y. Zhou, L. Hao, Y. Hu, Y. Zhu and Z. Chen, Chem. Lett., 2000, 11, 1308.93. Y. W. Bai, X. F. Chen, D. Zhang, X. H. Wan and Q. F. Zhou, Chin. J. Polym. Sci.,

2000, 18, 351.94. S. Bryant, P. Martens, J. Elisseeff, M. Randolf, R. Langer and K. S. Anseth, Wiley

Polym.Networks Group Rev. Ser., 1999, 2, 395.95. A. F. Maslyuk, V. V. Ageeva, G. K. Bereznitskii, V. A. Khranovskii, I. M. Sopina

and S. F. Kercha, Vysokomol. Soedin. Ser. A, Ser. B., 1998, 40, 209.96. A. Matsumoto and H. Higashi,Macromolecules, 2000, 33, 1651.97. T. Sugizaki, Y. Sasaki, O. Moriya, Y. Nakamura, T. Endo and T. Kageyama, J.

Polym. Sci., Part A: Polym. Chem. Ed., 1999, 37, 4226.98. M. R. Pokhrel, K. Janik and S. H. Bossmann,Macromolecules, 2000, 33, 3577.99. V. V. Lavrov, I. V. Arkhangel’skii, E. V. Skokan, Yu. A. Velikodney, L. N. Sidorov,

V. V. Pryadyun and V. A. Davydov, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. C,1998, 11, 13.

100. H. Morita and K. Kokuryo, J. Photopolym. Sci. Technol., 2000, 13, 159.101. F. Hochart, J. Levalois-Mitjaville and R. DeJaeger, Polymer, 2000, 41, 3159.102. I. Capek, Eur. Polym. J., 1999, 36, 255.103. C. E. Hoyle, D. Yang, K. Viswanathan, S. Jonsson and C. Hasselgren,Polym.Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 934.104. S. Jonsson,K. Viswanathan, C. E.Hoyle, S. C. Clark, C.Miller, C. Nguyen, L. Shao,

F. Morel and C. Decker, J. Photopolym. Sci. Technol., 2000, 13, 125.105. C. Decker, C. Bianichi, F. Morel, S. Jonsson and C. E. Hoyle, Macromol. Chem.

Phys., 2000, 201, 1493.106. R. B. Pandey, D. Yang, Y. Liu, S. Jonsson, J. B. Whitehead and C. E. Hoyle, Polym.

Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 932.107. L. Zhang, L. Liu and Y. Chen, J. Appl. Polym. Sci., 1999, 74, 3541.108. L. Liu and Y. Chen, Zhanjie, 2000, 21, 1.

Photochemistry378

109. S. K. Rajaraman, W. A. Mowers and J. V. Crivello, Polym.Mater. Sci. Eng., 1999,81, 116.

110. Q. Wu, W. Gao and Y. Li, Suliao Gongye, 2000, 28, 1.111. Q. Wu, W. Gao and Y. Li, Qingdao Huagong Xueyuan Xuebao, 2000, 21, 95.112. M. H. Acar, A. Gulkanat, S. Seyren and G. Hizal, Polymer, 2000, 41, 6709.113. S. H. Qin and K. Y. Qiu, J. Appl. Polym. Sci., 2000, 75, 1350.114. G. S. Georgiev, N. V. Tsarevsky, E. B. Kamenska and L. K. Christov, Polym.Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 385.115. L. M. Muratore, M. L. Coote and T. P. Davis, Polymer, 1999, 41, 1441.116. M. Ohoka, S. Misumi and M. Yamamoto, Polym. J. (Tokyo), 1999, 31, 878.117. V. Lemee, D. Burget, P. Jacques and J. P. Fouassier, J. Polym. Sci., Part A: Polym.

Chem. Ed., 2000, 38, 1785.118. W. F. Jager, A. M. Sarker and D. C. Neckers,Macromolecules, 1999, 32, 8791.119. J.Dalglish, R. Jachuck andC. Ramshaw,BHRGroupConf. Ser.Publ., 1999, 38, 209.120. W. G. Skene and J. C. Scaiano, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.),

1999, 41, 163.121. Y. Guang, Q. Chen, X. Zhang, Y. Peng and J. Xu,Macromol.Rapid.Commun., 2000,

21, 998.122. M. J. M. Abadie, M. Popa, M. Zaharia-Arnautu, V. Bulacovski and A. A. Popa ,

Eur. Polym. J., 2000, 36, 571.123. M. V. Encinas, E. A. Lissi and A. M. Rufs, Bol. Soc. Chil. Quim., 2000, 45, 409.124. F. Cataldo, Eur. Polym. J., 2000, 36, 653.125. J. He and J. Wang, Qingdao Daxue Xuebao, Gongcheng Jishuban, 2000, 15, 17.126. H. Irngartinger and M. Skipinski, Tetrahedron, 2000, 56, 6781.127. A. Alexander, I. Domnin, H. Lemmetyinen and A. Nikitenko, Macromol. Chem.

Phys., 2000, 20, 1317.128. C. Ito, Int. J. Photoenergy, 1999, 1, 147.129. J. Jakubiak, J. Nie, L. A. Linden and J. F. Rabek, J. Polym. Sci., Part A: Polym.

Chem. Ed., 2000, 38, 876.130. J. F. Rabek, J. P. Fouassier, L. A. Linden, J. Nie, E. Andrzejewska, J. Jakubiak, J.

Paczkowski, A. Wrzyszczynski and A. Sionkowska, Trends Photochem. Photobiol.,1999, 5, 51.

131. D.W. Davies, F. D. Jones, J. Garrett, I. Hutchinson andG.Walton, Surf.Coat. Int.,2000, 83, 72.

132. F. Sun, Yu. Li. Huang, A. Korigodski, G. Popova and V. Kireev, Ganguang KexueYu Guang Huaxue, 2000, 18, 229.

133. J. Stejny, J. Carrell and M. J. Palmer, Radiat.Meas., 2000, 32, 299.134. K. Suyama, K. Honma, M. Shirai and M. Tsunooka, J. Photopolym. Sci. Technol.,

2000, 13, 113.135. M. Principe, R. Martinez, P. Ortiz and J. Rieumont, Polim.: Cienc. Technol., 2000,

10, 8.136. W. Xiong, J. S. Liu and J. Y. Wen,Hecheng Huaxue, 1999, 7, 202.137. L. Angiolini, D. Caretti, C. Carlini, E. Corelli and E. Salatelli, Polymer, 1999, 40,

7197.138. R. Nagarajan, J. S. Bowers, H. Cui, A. J. Muller, J. R. I. Eubanks, Z. Wu and C. C.

Geiger, Surf. Coat. Int., 2000, 83, 181.139. H. Kura, H. Oka, J. L. Birbaum and T. Kikuchi, J. Photopolym. Sci. Technol., 2000,

13, 145.140. F. Cao, Z. Zhu and J. Yin, Gongneng Gaofenzi Xuebao, 2000, 13, 325.141. A. V. Shichuk and G. V. Korol,Ukr.Khim. Zh., 2000, 66, 61.


142. T. Fukuda, K. Sumaru, T. Yamanaka and H. Matsuda,Mol. Cryst. Liq. Cryst. Sci.Technol., Sect. A., 2000, 345, 263.

143. C. N. Jeong, N. J. Kim, M. Weir, C. S. P. Sung, B. Kilhenny, S. Connelly and N. H.Sung, Proc. Annu.Meet. Adhes. Soc., 2000, 23rd, 553.

144. O. Peckan, D. Kaya and M. Erdogan, Polymer, 2000, 42, 645.145. E. P. Chang, Y. F. Wang and M. Ziemelis, Proc. Annu. Meet. Adhes. Soc., 1999,

22nd, 421.146. L. R. Denny, J. W. Baur, M. D. Alexander, S. M. Kirkpatrick and S. J. Clarson,

Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 71, 3.147. G. J. Sewell, N. C. Billingham,K. A. Kozielski and G. A. George,Polymer, 1999, 41,

2113.148. H. Liu and G. A. George, Polym. Int., 2000, 49, 1505.149. T. Sherzer and U. Decker, Polymer, 2000, 41, 7681.150. M. Wen and A. V. McCormick,Macromolecules, 2000, 33, 9247.151. M. Dossot, M. Sylla, X. Allonas, A. Merlin, P. Jacques and J. P. Fouassier, J. Appl.

Polym. Sci., 2000, 78, 2061.152. F. Ganachaud, R. Balic, M. J. Monteiro and R. G. Gilbert,Macromolecules, 2000,

33, 8589.153. K. Padon and A. B. Scranton, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38,

3336.154. H. Inoue, Y. Matsuura, K. Matsukawa, Y. Otani, N. Higashi and M. Niwa, J.

Photopolym. Sci. Technol., 2000, 13, 109.155. K. Saravanamuttu and M. P. Andrews, Polym.Mater. Sci. Eng., 1999, 81, 477.156. V. V. Ivanov, B. L. Rytov and V. B. Ivanov,Vysokomol. Soedin., Ser.A, Ser. B, 1998,

40, 5.157. D. L. Starokadomskii and T. N. Solov’eva, Zh. Prikl.Khim., 2000, 73, 825.158. N. Pietschamann, Eur. Coat. J., 1999, 9, 60.159. Yu. G. Medvedevskikh, E. A. Zaglad’ko, A. A. Turovskii and G. E. Zaikov, Khim.

Fiz., 1999, 18, 39.160. Yu. G. Medvedevskikh, E. A. Zaglad’ko, A. A. Turovskii and G. E. Zaikov, Plast.

Massy., 1999, 9, 129161. J. Nie, L. G. Lovell and C. N. Bowman, Polym. Prepr. (Am. Chem. Soc., Div.Polym.

Sci.), 1999, 40, 1332.162. D. E. Nikles, T. Woo and J. Y. Huh, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 2000, 41, 1845.163. A. N. Bratus, A. A. Turovskii, Yu. G. Medvedevskikh, I. V. Semenyuk and G. E.

Zaikov, Plast.Massy, 2000, 1, 20.164. A. N. Bratus, A. A. Turovskii, Yu. G. Medvedevskikh, I. V. Semenyuk and G. E.

Zaikov, Int. J. Polym.Mater., 1999, 43, 157.165. P. Dolez, B. J. Love and C. Holten, Proc. Annu.Meet. Adhes. Soc., 2000, 23rd, 243.166. I. V. Khudyakov, J. C. Legg, M. B. Purvis and J. B. Overton, Proc. SPIE-Int. Soc.

Soc. Opt. Eng., 1999, 3848, 151.167. G.Wurtz, R. Bachelot, F. H’Dhili, P. Royer, C. Triger, C. Ecoffet and J.D. Lougnot,

Jpn. J. Appl. Phys. Part 2, 2000, 39, L98.168. J. R. Erickson and P. A. Mancinelli, Adhes. Age, 2000, 43, S11.169. K. Murata, H. Etori, T. Fujisawa and T. Anazawa, Polymer (Korea), 2000, 32, 375.170. C. Glotfelter, Adhes. Age, 2000, 43, S24.171. J. Jang, W. R. Kennon and C. M. Carr, J. Text. Inst., Part I, 1999, 90, 616.172. S. Yamada, Y. Takahashi, S. Nisibu and N. Adachi, Nippon Insatsu Gakkaishi,

1999, 36, 315.

Photochemistry380

173. V. Cech, P. Horvath, J. Jancar, F. Schauer and S. Nespurek,Macromol.Symp., 1999,148, 321.

174. Y. Katano and M. Wakaki, J. Adv. Sci., 1999, 11, 140.175. H. B. Sun, T. Kawakami, Y. Xu, J. Yu. Ye, S. Matsuo, H. Misawa, M. Miwa and R.

Kaneko, Opt. Lett., 1999, 25, 1110.176. H. B. Sun, Y. Yu, M. Miwa, S. Matsuo and H. Misawa, Proc. SPIE-Int. Soc. Soc.

Opt. Eng., 2000, 3888, 122.177. Y. Sun and Q. Pan, Tuliao Gongye, 1999, 29, 8.178. K. K. Baikerikar and A. B. Scranton, Polym.Mater. Sci. Eng., 2000, 82, 39.179. D. Kuckling, I. G. Ivanova, H. J. P. Adler, F. K. Arndt and T. Wolff, Polym. Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 714.180. U. Muller, Organosilicon Chem. IV.Muenchner Silicontage 4th, 1998, 663.181. M. Ishikawa, H. Kawai, I. Petkov and T. Namura, Kenkyusho Kenkyu Hokoku,

1999, 34, 33.182. K. Tashiro, A. N. Zadorin, S. Saragi, T. Kamae, A. Matsumoto, K. Yokoi and S.

Aoki,Macromolecules, 1999, 32, 7946.183. T. Odani and A. Matsumoto,Macromol. Rapid Commun., 2000, 21, 40.184. Y. Imai, T. Ogoshi, K. Naka and Y. Chujo, Polym. Bull. (Berlin), 2000, 45, 9.185. B. A. Zhubanov and V. D. Kravtsova, Izv.Minist.Nauki Vyssh. Obraz. Resp.Kaz.,

Nats. Akad.Nauk Resp.Kaz., Ser.Khim., 1999, 6, 64.186. J. Onoe, T. Nakayama, A. Nakao, Y. Hashi, K. Esfarjani, Y. Kawazoe, M. Aono

and K. Takeuchi,Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A, 2000, 340, 689.187. M. M. Coleman, Y. Hu, M. Sobkowiak and P. C. Painter,Macromol. Symp., 1999,

141, 197.188. M. Onciu, C. I. Chiriac, D. Timpu, C. Ioan and G. Grigoriu, Rev. Roum. Chim.,

2000, 44, 265.189. X. Coqueret, J. Phys. IV, 1999, 9, 105.190. M. H. Reihmann and H. Ritter,Macromol. Chem. Phys., 2000, 201, 1593.191. A. Laschewsky and E. D. Rekai,Macromol. Rapid Commun., 2000, 21, 937.192. N.Hoogen andO.Nyuken, J.Polym. Sci.,Part A:Polym.Chem.Ed., 2000, 32, 1903.193. J. V. Crivello and S. Kong,Macromolecules, 2000, 33, 833.194. S. Kong and J. V. Crivello,Polym.Prepr. (Am.Chem. Soc.,Div. Polym.Chem.), 1999,

40, 569.195. J. V. Crivello and S. Kong,Macromolecules, 2000, 33, 825.196. J. V. Crivello and S. Liu, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38, 389.197. J. V. Crivello and R. Malik, ACS Symp. Ser., 2000, 729, 284.198. S. Matuszczak and W. J. Feast, J. Fluorine Chem., 2000, 102, 269.199. Y. Zhang and W. Cao, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38, 2566.200. H. Sasaki, J. Photopolym. Sci. Technol., 2000, 13, 119.201. T. Sanji, Y. Nakatsuka, S. Ohnishi andH. Sakurai,Macromolecules, 2000, 33, 8524.202. K. Takeshi, K. Okuyama, Y. Ohba and M. Ueda, Polym. Prepr. (Am. Chem. Soc.,

Div. Polym. Chem.), 2000, 41, 365.203. Y. Chen, T. Yamamura and K. Igarashi, J. Polym. Sci., Part A: Polym. Chem. Ed.,

2000, 38, 90.204. T. Yamamura, T. tanabe and T. Ukachi, J. Photopolym. Sci.Technol., 2000, 13, 117.205. B. Youssef, L. Lecamp, S. Garina and C. Bunel, Nucl. Instrumen. Methods Phys.

Res., Sect. B, 1999, 151, 313.206. R. Lazauskaite, R. Budreckiene, J. V. Grazulevicius and M. J. M. Abadie, J. Prakt.

Chem., 2000, 342, 569.207. H. Sasaki,Nippon Setachaku Gaikkaishi, 1999, 35, 360.


208. Y. Liang, A. S. Dvornikov and P. M. Rentzepis, Polym. Int., 2000, 17, 1641.209. K. Mimura and K. Sumiyoshi,Mol. Cryst. Liq. Cryst., Sci. Technol., Sect. A, 1999,

330, 1267.210. N. Pereda, J. Etxebarria, C. L. Folcia, J. Ortega, C. Artal, M. B. Ros and J. L.

Serrano, J. Appl. Phys., 2000, 87, 217.211. D. Nwabunma and T. Kyu, Polymer, 2000, 42, 801.212. L. Sun and S. Wang, Proc. SPIE-Int. Soc. Opt. Eng., 2000, 4079, 201.213. N. Tamaoki, S. Shimada, Y. Okada, A. Belaissaoui, G. Kyuk, K. Yase and H.

Matsuda, Langmuir, 2000, 16, 7545.214. T. Karasawa and Y. Taketomi, J. Appl. Phys., 2000, 88, 5071.215. N. Kawatsuki, K. Matsuyoshi and T. Yamamoto, Macromolecules, 2000, 33,

1698.216. C. Binet, M. Mitov, A. Boudet, M. Mauzac and P. Sopena, Liq. Cryst., 1999, 26,

1735.217. C. Sanchez, B. Villacampa, R. Cases, R. Alcala, C. Martinez, L. Oriol andM. Pinol,

J. Appl. Phys., 2000, 87, 274.218. T. Yaji, S. Isoda, N. Kwase, T. Kobayashi and K. Takeda,Mol. Cryst. Liq. Cryst.

Sci. Technol. Sect. A, 2000, 349, 107.219. N. Kawatsuki, K. Matsuyoshi, H. Takatsuki and T. Yamamoto, Chem. Mater.,

2000, 12, 1549.220. C. L. Lester and C. A. Guymon,Macromolecules, 2000, 33, 5448.221. S. Calixto, C. Croutxe-Barghorn and D. L. Lougnot, Eur. Phys. J., 1999, 31, 717.222. M. Caddy and T. J. Kemp, Polym.Prepr. (Am.Chem. Soc.,Div.Polym.Chem.), 2000,

41, 22.223. P. Phynocheep and S. Duangthong, J. Appl. Polym. Sci., 2000, 78, 1478.224. H. Zhang, J. L. Massingill and J. T. Woo, J. Coat. Technol., 2000, 72, 77.225. H. Yamada, Setachu no Gijutsu, 1999, 19, 21.226. P. Penczek, Z. Boncza-Tomaszewski, Polimery, 1999, 44, 709.227. K. K. Baikerikar and A. B. Scranton, Polym. Compos., 2000, 21, 297.228. A. Bratoy, C. Dominguez and M. Bourray, Adv. Sci. Technol. (Faenza, Italy), 1999,

26 287.229. K. K. Baikerikar and A. B. Scranton, Polymer, 2000, 42, 431.230. S. Trenor and B. Love, Proc. Annu.Meet. Adhes. Soc., 2000, 23rd, 237.231. N. Davidenko, R. Sastre, M. A. Villegas and R. G. Carrodeguas, Rev. CENIC,

Cienc. Quim., 1999, 30, 187.232. M. Tomikawa, M. Suwa, S. Yoshida, R. Okuda and G. Ohbayashi, J. Photopolym.

Sci. Technol., 2000, 13, 357.233. S. Li, K. Yu and S. Guan,Xiandai Huagong, 2000, 20, 46.234. C. C. Chappelow, C. S. Pinzino, L. Jeang, C. D. Harris, A. J. Holder and J. D. Eick,

J. Appl. Polym. Sci., 2000, 76, 1715.235. S. Li, S. Guan and L. Wu, Tuliao Gongye, 2000, 30, 6.236. J. Lin and Y. Huang, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41,

950.237. Yu. G. Medvedevskikh, E. A. Zagladko, A. A. Turovskiy and G. E. Zaikov, Polym.

Yearb., 2000, 17, 311.238. J. E. McGrath, L. Rasmussen, H. Shobha, M. Sankarapandian and K. E. Uhrich,

Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 1363.239. M. H. Lenedic, S. Rousseau, L. Jorissen, G. Marchetti, J. C. Ciza, M. Descroix and

D. C. Rich, Am. Ink Maker, 2000, 78, 89.240. S. wang, R. Cao and Y. Duan,Huaxue Gongcheng, 1999, 27, 44.

Photochemistry382

241. C. E. Hoyle, L. J. Mathias, C. Jariwala, D. Sheng and P. E. Sundell,ACS Symp. Ser.,2000, 755, 54.

242. B. E. Russ and J. B. Talbot, J. Adhes., 1998, 68, 257.243. S. S. Skorokhodov, S. S. Bogolyubova, N. V. Klimova, L. I. Rudaya and T. A.

Yurre, Zh. Prikl. Khim., 2000, 73, 268.244. K. Subramanian, V. Krishnasamy, S. Nanjundan and R. A. V. Reddy, Polym. Int.,

2000, 49, 579.245. E. R. Nagarajan, N. Rajeswari and S. Viswanathan, Process. Fabr. Adv.Mater. VI

Proc. Symp., 6th, 1998, 2, 1615.246. C. Iojoiu, M. J. M. Abadie, V. Harabagiu, M. Pineteala and B. C. Simionescu, Eur.

Polym. J., 2000, 36, 2115.247. M. D. Soucek, S. Wu and S. Chakrapani, ACS Symp. Ser., 2000, 729, 516.248. J. M. Jethmalani, J. A. Kornfield, R. H. Grubbs and D. M. Schwartz, Polym. Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 234.249. A. Valet, Prog. Org. Coat., 1999, 35, 223.250. A. Mochizuki, M. Sakamoto, M. Yoshioka, T. Fukuoka, K. Takeshi andM. Ueda,

J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38, 329.251. J. Ledru, J. M. Saiter, J. Grenet, B. Youssef, F. Burel and C. Bunel, J. Thermal Anal.

Calor., 1999, 58, 13.252. X. Yang, J. Yang, Y. Chen andW. Xiong,Gongneng Gaofenzi Xuebao, 1999, 12, 285.253. P. Dolez and B. Love, Polym.Mater. Sci. Eng., 1999, 81, 407.254. L. Liu, Z. Wang, Z. Zhu and L. Sun, Shanghai Jiaotong Daxue Xuebao, 1999, 33,

1233.255. H. Kou and W. Shi, Goafenzi Xuebao, 2000, 5, 554.256. T. Matsuda, M. Mizutani and S. C. Arnold,Macromolecules, 2000, 33, 795.257. T. Matsuda and M. Mizutani,Macromolecules, 2000, 33, 791.258. J. Sun, L. Cheng, F. Liu, S. Dong, Z. Wang and S. J. Zhang, Colloids Surf. Sci. A,

2000, 169, 209.259. K. Arimitsu, M. Miyamoto and K. Ichimura, Polym.Mater. Sci. Eng., 1999, 81, 93.260. G. Gozzelino, G. Malucelli and V. Lambertini, J. Appl. Polym. Sci., 2000, 78, 458.261. C. Park and R. E. Robertson, Polymer, 2000, 42, 2597.262. C.Wuertz, A. Bismarck, J. Springer andR. Koniger,Prog.Org.Coat., 1999, 37, 117.263. K. Inomata, S. Kawasaki, A. Kameyama and T. Nishibubo, React. Funct. Polym.,

2000, 45, 1.264. R. Bongiovanni, G. Malucelli, M. Messori, F. Pilati, A. Priola, C. Tonelli and M.

Toselli, J. Appl. Polym. Sci., 2000, 75, 651.265. C. Li, J. Huang, H. Chen, D. Zhu, Y. Li and J. Shi, Gaofenzi Cailiao Kexue Yu

Gongcheng, 1999, 15, 141.266. F. Catalina, A. Alonso and C. Peinado, Rev. Plast.Mod., 1999, 78, 258.267. G. Liu,Mat. Sci. Eng., 1999, C10, 159.268. L. Lecamp, P. Lebaudy, B. Youssef and C. Bunel,Macromol. Symp., 1999, 148, 77.269. E. Andrzejewski, D. Zych-Tomkowiak and M. Andrzejewski, Polymery, 2000, 45,

639.270. B. S. Kim, J. S. Hrkach and R. Langer, J. Polym. Sci., Part A: Polym. Chem. Ed.,

2000, 38, 1277.271. J. M. Jethmalani, J. A. Kornfield, R. H. Grubbs and D. M. Schwartz, Polym. Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 271.272. Z. S. Zheng, M. Z. Li and E. J. Wang, Gongneng Gaofenzi Xuebao, 2000, 13, 15.273. Z. S. Zheng,M. Z. Li and E. J. Wang,GanguangKexueYu Guang Huaxue, 2000, 18,

25.


274. C. Decker, T. Viet and T. Nguyen, J. Appl. Polym. Sci., 2000, 77, 1902.275. C. Decker, T. Viet and T. Nguyen, Polymer, 2000, 41, 3905.276. J. L. Mateo, P. Bosch, J. Serrano and M. Calvo, Eur. Polym. J., 2000, 36, 1903.277. C. Decker, T. Viet and T. Nguyen, Eur. Polym. J., 1996, 32, 559278. C. Decker, T. Viet and T. Nguyen, Eur. Polym. J., 1996, 32, 549.279. F. Schauer, S. Nespurek, P. Horvath, J. Zemek and V. Fidler, Synthet.Met., 2000,

109, 321.280. E. Marsano, S. Gagliardi, F. Ghioni and E. Bianchi, Polymer, 2000, 41, 7691.281. B. Boutevin, F. Guidapietrasanta and A. Ratsimihety,Macromol. Rapid Commun.,

2000, 38, 3722.282. Y. Tajima, H. Arai and K. Takeuchi,Kagaku Kogaku Ronbunshu, 1999, 25, 873.283. B. Qu, Y. Xu, L. Ding and B. Ranby, J. Polym. Sci., Part A: Polym.Chem., 2000, 38,

999.284. K. Subramanian, V. Krishnasamy, S. Nanjundan and A. V. Rami Reddy, Eur.

Polym. J., 2000, 36, 2343.285. B. George, M. J. Nasrullah and R. Dhamodharan, J. Macromol. Sci., Pure Appl.

Chem., 1999, A36, 1923.286. M. Vargas, D. M. Collard, C. L. Liotta and D. A. Schiraldi, J. Polym. Sci., Part A:

Polym. Chem., 2000, 38, 2167.287. H. Zeng, J. Li, X. Wang and P. Wen, Zhongguo Suliao, 1999, 13, 34.288. J. Guan and W. Yang, J. Appl. Polym. Sci., 2000, 77, 2569.289. H. Ma, R. H. Davis and C. N. Bowman,Macromolecules, 2000, 33, 331.290. B. Pan and R. B. Moore, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999,

40, 764.291. S. Chen, S. Wakayama, H. yamazaki, Y. Tsubakiyama, S. Hashiya and S. Ohoya,

Sen’I Kogyo Kenkyu Kyokai Hokoku, 2000, 10, 33.292. J. P. Deng, W. T. Yang and B. Ranby, J. Appl. Polym. Sci., 2000, 77, 1513.293. J. Lacoste, S. Chmela, J. F. Pilichovski and I. Lukac,Gummi Fasern,Kunstst., 2000,

53, 644.294. I. Fuhrmann and J. Karger-Kocsis, Plast. Rubb. Compos., 1999, 28, 500.295. P. Ghosh and P. Gangopadhyay, Eur. Polym. J., 2000, 36, 625.296. J. I. Chang, P. J. Park and M. J. Han,Macromolecules, 2000, 33, 321.297. B. C. Henneuse-Boxus, E. Duliere and J. Marchand-Brynaert,Eur. Polym. J., 2000,

37, 9.298. K. Fujiki and M. Sakamoto, Polym. Polym. Compos., 1999, 7, 453.299. G. Geuskens, A. Etoc and P. Di Michele, Eur. Polym. J., 1999, 36, 265.300. J. L. Garnett, L. Ng and V. Viengkhou, Rad. Phys. Chem., 1999, 56, 387.301. J. L. Garnett, L. T. Ng, V. Viengkou, I. W. Hennessy and E. F. Zilic, Polym. Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 134.302. R. Francis and A. Ajayaghosh,Macromolecules, 2000, 33, 4699.303. M. Muller and C. Oehr, Surf. Coat. Technol., 1999, 116, 802.304. X. Ma and D. Fang, Guangzhou Huagong, 1999, 27, 65.305. Y. Murayama, Purasuchikkusu, 2000, 51, 63.306. Y. Fang and D. Hu, Gaoefenzi Tongbao, 2000, 2, 58.307. G. B. Adams and J. B. Page, Springer Ser.Mat. Sci., 2000, 38, 185.308. V. M. Yashchuk, Polimery, 1999, 44, 475.309. R. P. Millen, M. L. Temperini, D. L. A. De Faria and D. N. Batchelder, J. Raman

Spectrosc., 1999, 30, 1027.310. C. Lee, Y. Kang, S. Lee, J. Hee, S. H. Jung and J. S. Kim,Mol.Cryst. Liq.Cryst. Sci.

Technol., Sect. A, 2000, 349, 503.

Photochemistry384

311. H. Jiang, X. H. Xu, X. Sun, R. L. Fu and J. H. Chu, Wuli Xuebao, 1999, 48, 2327.312. W. Li, B. Berry, T. Viswanathan and W. Zhao, Poly. Prep. (Am. Chem. Soc., Div.

Polym. Chem.), 2000, 41, 345.313. O. P. Studzinskii, R. P. Ponomareva and T. V. Proskuryalova,Russ. J.Gen.Chem.,

1999, 69, 1651.314. G. Iftime, L. Fischer, A. Natansohn and P. Rochon, Can. J. Chem., 2000, 78,

409.315. P. A. Blanche, Ph. C. Lemaire, C. Maertens, P. Dubois and R. Jerome, J. Opt. Soc.

Am. B, 2000, 17, 729.316. E. A. Baryshnikova, T. I. Sergeeva, U. Oertel, J. Nagel and S. Yu. Zaitsev,Macro-

mol. Rapid Commun., 2000, 21, 45.317. Y. Fukushima, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38, 123.318. O. Varnavski and T. Goodson, Chem. Phys. Lett., 2000, 320, 686.319. U. W. Grummt, E. Birckner, E. Klemm, D. A. M. Egbe and B. Heise, J. Phys. Org.

Chem., 2000, 13, 112.320. S. Guang, H. Xu, S. Zhang, B. Tong, S. Yin and Q. Yu, Jinxi Huagong, 2000, 17,

467.321. T. L. Gustafson, E. M. Kyllo, T. L. Frost, R. G. Sun, H. Lim, D. K. Wang, A. J.

Epstein, C. Lefumeux, G. Burdzinski, G. Buntinx and O. Poizat, Synth.Met., 2000,116, 31.

322. Y.M. Huang, J. Wing Yip Lam, K. Ka Lweung Cheuk,W. Ge and B. Z. Tang, ThinSolid Films, 2000, 363, 146.

323. S. Lo, A. K. Sheridan, I. D. W. Samuels and P. L. Burns, J. Mat. Chem., 2000, 10,275.

324. G. Dellepiane, D. Comoretto and C. Cuniberti, J.Mol. Struct., 2000, 521, 157.325. C. J. Brabec, H. Johansson, A. Cravino, N. S. Sariciftci, D. Comoretto, G. De-

llepiane and I. Moggio, J. Chem. Phys., 1999, 11, 10354.326. D. T. McQuade, J. Kim and T. M. Swager, Polym.Mater. Sci. Eng., 2000, 83, 529.327. M. Yoshizawa, A. Kubo and S. Saikan,Phys.Rev.B:Condens.MatterMater.Phys.,

1999, 60, 15632.328. H. N. Cho, J. M. Hong, D. K. Moon and C. Y. Kim, Synth.Met., 2000, 111, 429.329. F. N. Dultsev, S. M. Repinsky and L. L. Sveshnikova, Thin Solid Films, 2000, 359,

239.330. C. Wang, J. H. Wang, Ya. A. Cao, C. S. Cao and J. N. Yao, Poly. Prep. (Am. Chem.

Soc., Div. Polym. Chem.), 2000, 41, 246.331. H. Balcar, P. Kubat, M. Pacovska and V. Blechta, Polym. J., 2000, 32, 370.332. K. Xu, H. Peng, P. P. S. Lee, Y. Dong and B. Z. Tang, Poly. Prep. (Am. Chem. Soc.,

Div. Polym. Chem.), 2000, 41, 1318.333. T. Granlund, L. A. A. Pettersson, M. R. Anderson and O. Inganas, J. Appl. Phys.,

2000, 87, 8549.334. M. Fall, J. J. Aron and D. Gningue-Sall, J. Fluoresc., 2000, 10, 107.335. G. Barbarella, L. Favaretto, G. Satgiu, M. Zambianchi, V. Fattori, M. Cocchi, F.

Cacialli, G. Gigli and R. Cingolani, Adv.Mater., 1999, 11, 1375.336. S. K. Vijaya, K. S. Narayan, J. Kim and J. O. White, Chem. Phys. Lett., 2000, 318,

543.337. R. L. Pilston and R. D. McCullough, Synth.Met., 2000, 111, 433.338. D. Ekinci, N. Horasan, R. Altundas and U. Demir, J.Electroanal.Chem., 2000, 484,

101.339. F. Goldoni, R. A. J. Janssen and E. W. Meijer, J. Polym. Sci., Part A: Polym. Chem.

Ed., 1999, 37, 4629.


340. T. H. Tong andL. C. Chien, J.Polym. Sci.,Part A:Polym.Chem.Ed., 2000, 38, 1450.341. H. Meng andW. Huang, J. Org. Chem., 2000, 65, 3894.342. S. A. Lee, S. Hotta and F. Nakanishi, J. Phys. Chem., 2000, 104, 1827.343. T. R. Hoye, B. Moon and C. W. Macosko, Polym. Prepr. (Am. Chem. Soc., Div.

Polym. Chem.), 1999, 40, 1074.344. B. Serrano, J. Baselga, J. Bravo, F. Mikes, L. Sese, I. Esteban and I. F. Pierola, J.

Fluoresc., 2000, 10, 135.345. J. H. Han, Y. S. Lee, K. S. Nahm, E. H. Cho, S. B. Ko, C. J. Kim, I. C. Jeon, W. H.

Lee, E. K. Suh and Y. H. Lee, Bull.Korean Chem. Soc., 1999, 20, 1093.346. F. Ishizaki, S. Machida and K. Horie, Polym. Bull., 2000, 44, 417.347. F. Ishizaki, S. Machida and K. Horie, Polym. Bull., 2000, 32, 62.348. A.Montali, A. R. A. Palmans, J. Bras, B. Pepin-Donat, S. Guillerez, P. Smith andC.

Weder, Synth.Met., 2000, 115, 41.349. L. Qiao and A. Langner, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999,

40, 667.350. X. H. Zhang, Y. C. Jiang, S. K. Wu, Z. Q. Gao, Z. S. Li, C. S. Lee, S. T. Li and S. T.

Lee, Ganguang Kexue Yu Guang Huaxue, 2000, 18, 160.351. F. Bai, M. Zheng, G. Yu and D. Zhu, Thin Solid Films, 2000, 363, 118.352. L. Pui-Sze, Y. Geng, H.S. Kwok and B. Z. Wang, Thin Solid Films, 2000, 149,

149.353. S. W. Hwang and Y. Chen, Polymer, 2000, 41, 6581.354. Z. Peng, Y. Pan, B. Xu and J. Zhang,Macromol. Symp., 2000, 154, 245.355. S. M. Lipson, D. F. O’Brien, H. J. Byrne, A. P. Davey and W. J. Blau, Thin Solid

Films, 2000, 370, 262.356. S. W. Alison, M. R. Cates and D. L. Beshears, Proc. Int. Instrument. Symp., 2000,

46th, 29.357. E. L. Frankevich, G. E. Zorinyants, M. M. Tribel, A. N. Chaban, S. Blyumshtengel

and V. M. Bobryanskii,Khim. Fiz., 1999, 18, 27.358. E. Arici, A. Greiner, F. Raubacher and J. H. Wendorff, Macromol. Chem. Phys.,

2000, 201, 1679.359. W. L. Wang and S. X. Wang, React. Funct. Polym., 2000, 45, 183.360. E. Peeters, P. A. Van Hal, J. Knol, C. J. Brabec, N. S. Sariciftci, J. C. Hummelen and

R. A. J. Janssen, J. Phys. Chem. B., 2000, 104, 10174.361. C. Im, H. Bassler, H. Rost and H. H. Horgold, J. Chem. Phys., 2000, 113, 3802.362. C. Gadermaier, E. J. W. List, P. Markart, W. Graupner, J. Partee, J. Shinar, R.

Smith, D. Gin and G. Leising, Synth.Met., 2000, 111, 523.363. E. J. W. List, J. Partee, J. Shinar, C. Gadermaier, G. Leising and W. Graupner,

Synth.Met., 2000, 116, 185.364. C. H. Cho, Y. S. Lee, K. S. Nahm, Y. B. Hahn and S. C. Yu, Synth.Met., 2000, 114,

331.365. A. J. Said, C. Dridi, S. Roudesli and F. M. Mhalla, Bulg. Chem. Commun., 2000, 36,

909.366. X. L. Chen, Z. Bao, A. J. Lovinger,M.Meier, A. Dodabalapur, K. R. Amundsun, R.

Jakubiak and L. J. Rothberg, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.),1999, 40, 1204.

367. N. I. Nijegorodov, W. S. Downey and M. B. Danailov, Spectrochim. Acta, Part A,2000, 56, 783.

368. J. Zhang, X. C. Ai, Q. S. Li, B.W. Zhang andB. J.Wang,GaoedengXuexiaoHuaxueXuebao, 2000, 21, 1530.

369. R. Jakubiak, Z. Bao and L. J. Rothberg, Synth.Met., 2000, 116, 41.

Photochemistry386

370. A. Talaie, Y. K. Lee, J. Jang, D. J. Choo, S. M. Park, S. H. Park, G. Huh, I. H. Leeand J. Y. Lee, Thin Solid Films, 2000, 363, 282.

371. M. R. Pinto, B. Hu, F. E. Karasz and L. Akelrud, Polymer, 2000, 41, 8095.372. G. Rumbles, P. F.Miller,M.M.DeSouza, I. R. Gould, H. Amer, D. L. Russell, A. B.

Holmes, S. C. Moratti and I. D. W. Samuels, Proc. SPIE-Int. Soc. Opt. Eng., 1999,3797, 101.

373. M. R. Pinto, B. Hu, F. E. Karaz and L. Akcelrud, Polymer, 1999, 41, 2603.374. Y. Xiao, W. L. Yu, Z. K. Chen, N. H. S. Lee, Y. H. Lai and W. Huang, Thin Solid

Films, 2000, 363, 102.375. G. Rumbles, C. J. Collinson, D. L. Russell, L. A. Magnani, A. B. Holmes, S. C.

Moratti and I. D. W. Samuels, Synth.Met., 2000, 11, 501.376. D. M. Johansson, G. Srdanov, G. Yu, M. Theander, O. Inganaes and M. R.

Andersson,Macromolecules, 2000, 33, 2525.377. B. Liu, Y. H. lai, W. L. Yu and W. Huang, Chem. Commun., 2000, 551.378. S. W. Hwang and Y. Chen, J. Polym. Sci., Part A: Polym.Chem. Ed., 2000, 38, 1311.379. G. Yang, Y. Li, A. Zhu, J. O.White andH.G. Drickamer,Macromolecules, 2000, 33,

3173.380. H. J. Egelhaaf, L. Luer, A. Tompert, P. Bauerle, K. Mullen and D. Oelkrug, Synth.

Met., 2000, 115, 63.381. H. L. Wang, D.W.McBranch, V. I. Klimov, R. Helgeson and F.Wudl,Chem.Phys.

Lett., 1999, 315, 173.382. H. Sarker, I. W. Ong, P. C. Searson and T. O. Poehler, Synth.Met., 2000, 113, 151.383. C. W. Co and H. C. Lin, Thin Solid Films, 2000, 363, 81.384. N. Verdal, J. T. Godbout, T. L. Perkins, G. P. Bartholomew,G. C. Bazan and A.M.

Kelley, Chem. Phys. Lett., 2000, 320, 95.385. P. Martinez-Ruiz, B. Behnisch, K. H. Schweikart, M. Hanack, L. Luer and D.

Oelkrug, Chem. Eur. J., 2000, 6, 1294.386. B. Behnisch, P. Martinez-Ruiz, K. H. Schweikart and M. Hanack, Eur. J. Org.

Chem., 2000, 14, 2541.387. S. Y. Liu, Z. K. Chen, L. H. Wang, E. T. Kang, Y. H. Lai, S. J. Chua andW. Huang,

Synth.Met., 2000, 114, 101.388. Z. K. Chen, W. Huang, L. H. Wang, E. T. Kang, B. J. Chen, C. S. Lee and S. T. Lee,

Macromolecules, 2000, 33, 9015.389. T. Ahn, S. Y. Song and H. K. Shim,Macromolecules, 2000, 33, 6764.390. Y. J. Pu,M. Soma, E. Tsuchida andH.Nishide, J.Polym. Sci.,Part A:Polym.Chem.

Ed., 2000, 38, 4119.391. W. L. Yu, J. Pu, W. Huang and A. J. Heeger, Chem. Commun., 2000, 681.392. S. Pfeiffer, H. Rost and H. H. Horhold,Macromol. Chem. Phys., 1999, 200, 2471.393. Y. Mo, D. Jia, H. Hezhou and X. Zheng, Gongneng Cailiao, 2000, 31, 546.394. C. Huang, W. Huang, J. Guo and C. Z. Yang, Polym. Prepr. (Am. Chem. Soc., Div.

Polym. Chem.), 2000, 41, 1271.395. R. C. Advincula, C. Chuanjuan and S. Inaoka, Polym. Prepr. (Am. Chem. Soc., Div.

Polym. Chem.), 2000, 41, 859.396. A. Donat-Bouillud, I. Levesque, Y. Tao, M. D’Iorio, S. Beaupre, P. Blondin, M.

Ranger, J. Bouchard and M. Leclerc, Chem.Mater., 2000, 12, 1931.397. A. Fujii, R. Ootake, T. Fujisawa, M. Ozaki, Y. Ohmori, T. Laga, K. Yoshino, H. F.

Lu, H. S. O. Chan and S. C. Ng, Appl. Phys. Lett., 2000, 77, 660.398. D. H. Hwang, S. Y. Song, T. Ahn, H. Y. Chu, L. M. Do, S. H. Kim, and T. Zyung,

Synth.Met., 2000, 111, 485.399. S. Y. Song and H. K. Shim, Synth.Met., 2000, 111, 437.


400. R. P. Quirk andW. Yu,Polym.Prepr. (Am.Chem. Soc.,Div.Polym.Chem.), 2000, 41,837.

401. K. Tada and M. Onoda, Thin Solid Films, 2000, 363, 195.402. R. E.Martin, F. Geneste, B. S. Chuah, A. B. Holmes, R. Riehn, F. Cacialli and R. H.

Friend, Chem. Commun., 2000, 291.403. B. Xu, J. Zhang and Z. Peng, Synth.Met., 2000, 113, 35.404. J. Morgado, R. H. Friend, F. Cacialli, B. S. Chuah, S. C. Maratti and A. B. Holmes,

J. Appl. Phys., 1999, 86, 6392.405. Yu. V. Romanovskii, A. Gerhard, B. Sweitzer, U. Scherf, R. I. Personov and H.

Bassler, Phys. Rev. Letts., 2000, 84, 1027; Chem. Phys. Lett., 2000, 326, 51.406. G. Wegmann, B. Schweitzer, D. Hertel, H. Giessen, M. Oestreich, U. Scherf, K.

Mullen and R. F. Mart, Chem. Phys. Lett., 1999, 312, 376.407. D. Moses, A. Dagariu and A. J. Heeger, Chem. Phys. Lett., 2000, 316, 356.408. Y. J. Miao, J. Kim and T. M. Swager , Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 1999, 40, 825.409. F. Cacialli, R. Daik, J. W. Feast and R. H. Friend, Opt.Mat., 1999, 12, 315.410. N. C. yang, J. K. Jeong, S. J. Choi, T. H. Rhee and D. H. Suh, Macromol. Rapid

Commun., 1999, 20, 586.411. K. Vaeth and K. F. Jensen,Macromolecules, 2000, 33, 5336.412. C. Yang, G. He, R. Wang and Y. Li, Mol. Cryst. Liq. Crsyt. Sci. Technol. Sect. A,

1999, 337, 473.413. D. Katsis, H.M. P. Chen, S. H. Chen and T. Tsutsui,Proc. SPIE-Int. Soc.Opt.Eng.,

2000, 4107, 77; H. P. Chen, D. Katsis, J. C. Mastangelo, K. L. Marshall, S. H. Chenand T. H. Mourey, Chem.Mater., 2000, 12, 2275.

414. E. J. W. List, J. Partee, J. Shinar, U. Scherf, K. Mullen, E. Zojer, K. Petritsch, G.Leising and W. Graupner, Phys. Revs. B: Condens.Matter. Phys., 2000, 61, 10807.

415. M. Forster and U. Scherf,Macromol. Rapid. Commun., 2000, 21, 810.416. H. Schlick, F. Stelzer, S. Tasch and G. Leising, J.Mol. Catal. A: Chem., 2000, 160,

71.417. R. Deans, J. Kim, M. R. Machacek and T. M. Swager, J. Am.Chem. Soc., 2000, 122,

8565.418. S. Yokojima, X. J. Wang, D. H. Zhou and G. H. Chen, Chem. Phys., 1999, 111,

10444.419. R. Chang, J. H. Hsu, W. S. Fann, J. Hu, S. H. Lin, Y. Z. Lee and S. A. Chen, Chem.

Phys. Lett., 2000, 317, 153.420. R. Jakubiak, Z. Bao and L. Rothberg, Synth.Met., 2000, 114, 61.421. J. P. Chen, V. Y. Lee, S. Swanson, J. Salem, R. D. Miller and J. C. Scott, Polym.

Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 835.422. S. Zheng, J. Shi and R. Mateu, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.),

2000, 41, 822.423. J. Eldo, E. Arunkumar and A. Ajayaghosh, Tetrahedron Lett., 2000, 41, 6241.424. J. L. Kim, J. K. Kim, H. N. Cho, D. Y. Kim and S. Hong,Macromol. Chem. Phys.,

2000, 20, 768.425. H. Lim, J. Y. Noh, G. H. Lee, S. E. Lee, H. Jeong, K. Lee, M. Cha, H. Suh and C. S.

Ha, Thin Solid Films, 2000, 363, 152.426. S. H. Jung, J. H. Choi, S. K. Kwon, W. J. Cho and C. S. Ha, Thin Solid Films, 2000,

363, 161.427. D. Wang, P. Wei and Z. Wu,Macromolecules, 2000, 33, 6896.428. A. P.Monkman, L. E.Horsburgh,M. E. Vascetto, H. D. Burrows,W. Brown andL.

Pettersson, Annu. Techn. Conf.-Soc. Plast. Eng., 1999, 57th, 1510.

Photochemistry388

429. E. Vaganova, M. Rozenberg and S. Yitzchaik, Chem.Mater., 2000, 12, 261.430. F. Feller and A. P. Monkman, Appl. Phys. Lett., 2000, 76, 664.431. D. W. Chang, S. Kim, S. Y. Park, H. Yu and D. J. Jang,Macromolecules, 2000, 33,

151.432. R. G. Sun, Y. Z. Wang, D. K. Wang, Q. B. Zheng, E. M. Kyllo, T. L. Gustafson, F.

Wang and A. J. Epstein, Chem. Lett., 2000, 111, 595.433. X. Chen, Z. Wang, Y. Hou, Z. Xu and X. Xu, Displays, 2000, 21, 55.434. J. Z. Sun, F.Wu,W. J. Tian, Y. G.Ma, Y. Chen and J. C. Shen,Chin. J.Chem., 2000,

17, 495.435. S. V. Frolov, Appl. Phys. Lett., 2000, 77, 833.436. S. C. Yang,W.Graupner, S. Guha, P. Puscnig, C.Martin, H. R. Chandrasekhar,M.

Chandrasekhar, G. Leising, C. Ambrosch-Draxl and U. Scherf, Phys. Rev. Lett.,2000, 85, 2388.

437. V. Deimed, K. S. Andikopulos, G. A. Voyiatzis, F. Konstandakopoulou and J. K.Kallitis,Macromolecules, 1999, 32, 8848.

438. C. Zhan, Z. Cheng, Q. I, J. Hu, J. Zhen, X. Yang and J. Qin, Chem. Lett., 2000, 11,1326.

439. C. B. Yoon and H. K. Shim, Synth.Met., 2000, 111, 469.440. C. Zhan, Z. Cheng, H. Xiao, Z. Li, X. Yang and J. Qin, Macromolecules, 2000, 33,

5455.441. S. H. Jin, W. H. Kim, I. S. Song, S. K. Kwon, K. S. Lee and E. M. Han, Thin Solid

Films, 2000, 363, 255.442. Z. Wang, X. Yang, X. Chen, Z. Xu and X. Xu, Thin Solid Films, 2000, 363, 94.443. T. Beyerlin and B. Tieke,Macromol. Rapid Commun., 2000, 21, 182.444. B. Harrison, M. B. Ramey, J. R. Reynolds and K. S. Schanze, J. Am. Chem. Soc.,

2000, 122, 8561.445. D. Wang, Z. Wu, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 809.446. M. Yang, Q. Ling, M. Hiller, X. Fun, X. Liu, L. ang and W. Zhang, J. Polym. Sci.,

Part A: Polym. Chem. Ed., 2000, 38, 3045.447. G. J. Wang, M. Li, X. F. Chen, F. Wu, W. J. Tian and J. C. Shen,Macromol. Rapid

Commun., 1999, 20, 591.448. A. Izumi,M. Teraguchi, R. Nomura and T.Masuda,Holzforschung, 2000, 33, 5347.449. A. F. Thuenemann and D. Ruppelt, Langmuir, 2000, 16, 3221.450. S.Moller,G.Weiser, R. Lecuiller andC. Lapersonne-Meyer,Synth.Met., 2000, 116,

153.451. A. Izumi, R. Nomura and T. Masuda,Macromolecules, 2000, 33, 8918.452. S. Atkinson, H. S. O. Chan, A. J. Neuendorf, S. C. Ng, T. T. Ong and D. J. Young,

Chem. Lett., 2000, 3, 276.453. W. Yi, W. Yan, L. Wang, M. Wang and L. Zhang, Xi’an Jiaotong Daxue Xuebao,

2000, 34, 5.454. E. Hong, Y. Han, M. H. Lee, H. Jang and Y. Do, Spec. Publ. Roy. Soc. Chem., 2000,

253, 20.455. R. F. Harris, A. J. Nation, G. T. Copeland and S. J. Miller, J. Am. Chem. Soc., 2000,

122, 11270.456. H. Ghosh, A. Shukla and S. Mazumdar, Phys. Rev. B: Condens. Matter. Mater.

Phys., 2000, 62, 12763.457. Y. M. Sun and C. S. Wang, Polymer, 2000, 42, 1035.458. S. J. Liu, D. Zeng and H. Wang, Yingyong Huaxue, 2000, 17, 512.459. J. Zheng, G. He, C. Yang, R. Wang, L. Huang and Y. Li, Gaofenzi Xuebao, 2000, 5,

644.


460. D. Wang, J. Wang, D. Moses, G. C. Bazan and A. J. Heeger, Langmuir, 2001, ACSASAP.

461. K.Malone, S.Weaver, D. Taylor, G.Mills andW.Gale,Adv.Sci.Technol., 1999, 25,55.

462. H. J. Egelhaaf, B. Lehr, M. Hof, A. Hafner, H. Fritz, F. W. Schneider, E. Bayer andD. Oelkrug, J. Fluoresc., 2000, 10, 383.

463. G. Geuskens and A. Soukrati, Eur. Polym. J., 2000, 36, 1537.464. K. Iwai,Kobunshi Kako, 1999, 48, 248.465. O. Vorobyova and M. A. Winnik, ACS Symp., 2000, 765, 143.466. C. Henneuse-Boxus, A. De Ro, P. Bertrand and J. Marchand-Brynaert, Polymer,

1999, 41, 2339.467. J. C. Qiang, M. Z. Wang, Yu. Fang, D. D. Hu, Y. L. Cui and Y. Q. Wang,Huaxue

Xuebao, 2000, 58, 627.468. D. Dibbern-Brunelli and T. D. Z. Atvars, J. Appl. Polym. Sci., 2000, 75, 815.469. F. M. Andreopoulos, E. J. Beckman and A. J. Russell, J. Polym. Sci., Part A: Polym.

Chem. Ed., 2000, 38, 1466.470. A. J. Bur and S. C. Roth, Annu. Techn. Conf.-Soc. Plast. Eng., 2000, 59th, 2058.471. H. Li, K. Machida and G. Ya. Adachi,Kidorui, 2000, 36, 260.472. G. V. Rakova and K. S. Kazanskii, Vysokomol. Soedin., Ser. A, Ser. B, 1998, 40,

498.473. H. Shirota, K. Ohkawa, N. Kuwabara, N. Endo and K. Horie, Macromol. Chem.

Phys., 2000, 201, 2210.474. O. Peckan and M. Erdogan, Polymer, 2000, 41, 4921.475. O. Peckan and M. Erdogan, Polym. Int., 2000, 49, 1641.476. O. Peckan, D. Kaya and M. Erdogan, J. Appl. Polym. Sci., 2000, 76, 1494.477. D. J. S. Birch and C. D. Geddes, Phys. Rev. E: Stat. Phys., Plasmas, Fluids Relat.

Interdisc. Top., 2000, 62, 2977.478. A. L. Margolin and V. Ya. Shlyapintokh, Russ. Polym.News, 2000, 5, 13.479. A. L. Margolin and V. Ya. Shlyapintokh, Int. J. Polym.Mat., 2000, 47, 443.480. A. L. Margolin and V. Ya. Shlyapintokh, Vysokomol. Soedin., Ser. A, Ser. B., 2000,

42, 366.481. J. Rychly, L. Matisova-Rychla and D. Jurcak, Polym. Degrad. Stab., 2000, 68, 239.482. S. Jipa, T. Zaharescu, R. Setnescu, T. Setnescu, D. Wurm and M. Dumitru,Mater.

Plast., 2000, 37, 29.483. S. Jipa, R. Setnescu, T. Zaharescu and I. Mihalcea,Mat. Plast., 1999, 36, 211.484. S. Jipa, T. Zaharescu, R. Setnescu, T. Setnescu, M. Giurginca and D. Wurm,Mat.

Plast., 2000, 37, 63.485. S. Jipa, T. Zaharescu, R. Setnescu and T. Setnescu, Polym. Degrad. Stab., 2000, 68,

159.486. S. Jipa, T. Zaharescu, R. Setnescu and T. Setnescu, Polym. Degrad. Stab., 2000, 68,

165.487. F. Konoma, X. Cai, Y. Okada and Z. Osawa,Materiaru Raifu., 2000, 12, 150.488. J. Rychly, L. Rychla and M. Strlic, Polym. Int., 2000, 49, 981.489. M. Strlic, J. Kolar, B. Pihlar, J. Rychly and L. Matisova-Rychla, Eur. Polym. J.,

2000, 36, 2351.490. P. K. Fearon, N. Marshall, N. C. Billingham and S. W. Bigger, J. Appl. Polym. Sci.,

2000, 79, 733.491. K. Jacobsen, B. Stenberg, B. Terselius and T. Reitberger, Prog. Rubber Plast.

Technol., 2000, 16, 135.

Photochemistry390

492. K. Jacobsen, B. Stenberg, B. Terselius and T. Reitberger, Polym. Degrad. Stab.,2000, 68, 53.

493. K. Jacobsen, B. Stenberg, B. Terselius and T. Reitberger, Polym. Int., 2000, 49, 654.494. L.M. Postnikov andA. V. Vinogradov, Vysokomol. Soedin., Ser.A, Ser.B, 2000, 42,

764.495. C. W. Lee, H. W. Rhee, C. Kim andM. S. Gong, Bull.Korean Chem. Soc., 2000, 21,

701.496. X. Zhong, J. Sun, Y. Fumio, S. Takashi andM.Keizo, JAERI-Conf. 2000, 2000, 8th,

255.497. C. Sinturel and N. C. Billingham, Polym. Int., 2000, 49, 937.498. L. Woo, C. Sandford, H. Blom, M. T. K. Ling and S. Y. Ding, Proc.NATAS Annu.

Conf. Therm. Anal. Appl., 2000, 28th, 246.499. M. Szadkowska-Nicze and J. Mayer, J. Polym. Sci.,Part A:Polym.Chem.Ed., 2000,

38, 3378.500. E. I. Malt’sev, D. A. Lypenko, B. I. Shapiro, M. A. Brusentseva, E. V. Lunina, V. I.

Berendyaev, B. V. Kotov and A. V. Vannikov, Vysokomol. Soedin., Ser. A, Ser. B,1999, 41, 1480.

501. I. Glowacki, E. Dobruchowska and J. Urbanski, Synth.Met., 2000, 109, 139.502. Yu. Gorokhovatsky, P. Kunze,W. Stark andD. Temnov,Proc-Int. Symp.Electrets,

1999, 10th, 403.503. Yu. Gorokhovatsky, P. Kunze,W. Stark andD. Temnov,Proc-Int. Symp.Electrets,

1999, 10th, 399.504. Y. Jun, X. Jian, L. Wenzhi and F. Peiming, Emerging Techn. Pulp. Papermak.

Fast-Grow. Wood, Proc. Int. Symp., 1998, 109.505. S. Araujo, J. Maria, O. A. Serra and G. Gomes de Barros, J.Appl.Polym. Sci., 2000,

78, 919.506. A. G. Mirochnik, N. V. Petrochenkova and V. E. Karasev, Vysokomol. Soedin., Ser.

A, Ser. B, 1999, 41, 1642.507. J. K.Mwaura,D. L. Thomsen, T. Phely-Bobin, S. Theodoropoulos and F. Padimit-

rakopoulos, J. Am. Chem. Soc., 2000, 122, 2647.508. J. K. Mwaura, D. L. Thomsen, T. Phely-Bobin, S. Theodoropoulos and F. Padi-

mitrakopoulos, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41,842.

509. Y. Zhao, L. Yang, L. Zhang, W. Zhou, J. Wu, C. Bao, D.Wang andD. Xu,GaofenziXuebao, 2000, 4, 393.

510. L. H. Wang, W. Wang, W. G. Zhang, E. T. Kang and W. Huang, Chem. Res., 2000,12, 2212.

511. A. G. Mirochnik, N. V. Petrochenkova, V. E. Karasev and A. N. Pyatkina,Vysokomol. Soedin. Ser. A, Ser. B, 1998, 40, 369.

512. L. Y. Zhu, X. F. Tong, M. Z. Li and E. J. Wang, Ganguang Kexue Guang Huaxue,2000, 18, 188.

513. F. Jiang, R. Xu, D. Wang, X. Dong and G. Li, Ganguang Kexue Guang Huaxue,1999, 17, 309.

514. J. Kim, Y. G. Kim, K. G. Chittibabu, M. J. Cazeca, D. Y. Kim, J. Kumar and S. K.Tripathy, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 1237.

515. A. V. Byanov, R. A. Mayer, G. M. Mokrousov and V. P. Smagin, Vysokomol.Soedin., Ser. A, Ser. B, 1999, 41, 1675.

516. M. Susuki,M. Sano,M.Kimura, K. Hanabusa andH. Shirai, J. Polym. Sci.,Part A:Polym. Chem. Ed., 1999, 37, 4360.


517. A. D. Pomogailo, V. F. Razumov and I. S. Voloshanovskii, J. PorphyrinsPhthalocyanines, 2000, 4, 45.

518. L. Hermans and E. W. Jones, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.),2000, 41, 409.

519. S. B. Meshkova, Z. M. Topilova, N. A. Nazarenko, I. S. Voloshanovskii and E. V.Malinka, J. Anal. Chem., 2000, 55, 676.

520. S. H. Chan, S. M. lam, W. T. Wong and W. K. Chan,Macromol. Rapid Commun.,2000, 21, 1075.

521. D. Huang, J. Yang and W. P. Weber, Polym. Bull. (Berlin), 2000, 43, 465.522. A. Adronov, P. R. L. Malenfant and J. M. J. Frechet, Chem.Mater., 2000, 12, 1463.523. J. M. J. Frechet, A. Adronov andD. R. Robello,Polym. Prepr. (Am.Chem. Soc.,Div.

Polym. Chem.), 2000, 41, 851.524. H. J. Murfee and B. Hong, Polym. Prepr. (Am.Chem. Soc.,Div. Polym.Chem.), 2000,

41, 431.525. S. Hecht, H. Ihre and J. M. J. Frechet, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 2000, 41, 791.526. M. S. Matos, J. Hofkens,W. Verheijen, F. C. DeSchryver, S. Hecht, K.W. Pollak, J.

M. J. Frechet, B. Forier and W. Dehaen,Macromolecules, 2000, 33, 2967.527. C.M. Cardona, J. Alvarez, A. E. Kaifer, T. D.McCarley, S. Pandey, G. A. Baker, N.

J. Banzagni and F. V. Bright, J. Am. Chem. Soc., 2000, 122, 6319.528. G. Sui, M. Micic, Q. Huo and R. M. Leblanc, Colloids Surf., 2000, 168, 193.529. I. Gitsov, ACS Symp. Ser., 2000, 765, 72.530. I. Gitsov, K. R. Lambrych, V. A. Remnant and R. Pracitto, J. Polym. Sci., Part A :

Polym. Chem. Ed., 2000, 38, 12711.531. Y. Chang, Y. C. Kwon, S. C. Lee and C. Kim, Polym. Prepr. (Am. Chem. Soc., Div.

Polym. Chem.), 1999, 40, 269.532. Y. Chang, Y. C. Kwon, S. C. Lee and C. Kim,Macromolecules, 2000, 33, 4496.533. M. Yoo, C. W. Frank, A. Heise, J. L. Hedrick and R. D. Miller, Polym. Prepr. (Am.

Chem. Soc., Div. Polym. Chem.), 2000, 41, 979.534. S. Li and D. V. McGrath, J. Am. Chem. Soc., 2000, 122, 6795.535. S. Li, S. Sikder and D. V. McGrath, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 1999, 40, 267.536. S Li. and D. V. McGrath, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000,

41, 861.537. J. Wang, X. Jia, H. Zhong, H. Wu, Y. Li, X. Xu, M. Li and Y. Wei, J. Polym. Sci.,

Part A: Polym. Chem. Ed., 2000, 38, 4147.538. L. A. Baker and R. M. Crooks,Macromolecules,2000, 33, 9034.539. G. Ma, S. Qian, Y. Chen, R. Cai, T. Zhao and X. Ye, Synth.Met., 2000, 20, 270.540. T. Kato, M. Uchiyama, N. Maruo, T. Arai and N. Nishino, Chem. Lett., 2000, 2,

144.541. T. Nagasaki, K. Atarashi, K. Makino, A. Noguchi and S. Tamagaki, Mol. Cryst.

Liq. Cryst. Sci. Technol., Sect A., 2000, 345, 227.542. F. Voegtle, S. Gestermann, C. Kauffmann, P. Ceroni, V. Vicinelli and V. Balzani, J.

Am. Chem. Soc., 2000, 122, 10398.543. W. Chen, D. A. Tomalia and J. L. Thomas,Macromolecules, 2000, 33, 9169.544. J. B. Baek and L. C. Chien,Polym.Prepr. (Am.Chem. Soc.,Div. Polym.Chem.), 1999,

40, 607.545. M. Tominaga, K. Konishi and T. Aida, Chem. Lett., 2000, 4, 374.546. K. Ishizu and A. Mori,Macromol. Rapid Commun., 2000, 21, 665.

Photochemistry392

547. M. Smet, L. X. Liao, W. Dehaen and D. V. McGrath, Org. Lett., 2000, 2, 511.548. U. Radhakrishnan and D. V. McGrath, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 2000, 41, 883.549. G. Z. Li and N. Minami, Chem. Phys. Lett., 2000, 331, 26.550. L. Torrisi, A. Desiderio and G. Foti, Nucl. Instrumen.Methods Phys. Res., Sect B.,

2000, 166, 664.551. Y. Hou, X. Yang, Y. Li and X. Xu, Thin Solid Films, 2000, 363, 248.552. E. Kato and T. Murakami, Wiley Polym.Networks Group Rev. Ser., 1999, 2, 169.553. M. Abdel, M. Hussein, L. Z. Ismail, F. G. Abdel and Z. A. Zohdy, Polym. Test.,

2000, 20, 135.554. R. Meallet-Renault, H. Yoshikawa, Y. Tamaki, T. Asahi, R. B. Pansu and H.

Masuhara, Polym. Adv. Techn., 2000, 11, 772.555. J. Li, X. Shi and S. Wu, Ganguang Kexue Yu Guang Huaxue, 2000, 18, 208.556. W. Schindler and P. Drescher,Melliand Int., 1999, 1, 85.557. A. Kawski, P. Bojarski and B. Kuklinski, Z. Naturforsch., A: Phys. Sci., 2000, 55,

444.558. C. Y. Wang and M. D. Ediger, J. Polym. Sci., Part A: Polym. Phys. Ed., 2000, 38,

2233.559. S. Gouin and M. Gouterman, J. Appl. Polym. Sci., 2000, 77, 2805; E. Pulkin, B.

Carlson, S. Gouin, C. Costin, E. Green, S. Ponamorev, H. Tanji and M. Gouter-man, J. Appl. Polym. Sci., 2000, 77, 2795.

560. S. Gouin and M. Gouterman, J. Appl. Polym. Sci., 2000, 77, 2815.561. S. Gouin and M. Gouterman, J. Appl. Polym. Sci., 2000, 77, 2824.562. A. J. Bur, S. C. Roth and C. L. Thomas, Rev. Sci. Instrument., 2000, 71, 1516.563. J. Gimez, M. Boudris, Ph. Cassagnau and A. Michel, Synth.Met., 2000, 8, 135.564. M. Sampei, K. Hiramatu, A. Kameyama andT.Nishikuboto,Kobunshi Ronbunshu,

2000, 57, 569.565. P. Zhou, G. Q. Chen, H. Hong, F. S. Du, Z. C. Li and F. M. Li, Macromolecules,

2000, 33, 1948.566. J.H. Clements and S. E.Webber,Polym.Prepr. (Am.Chem. Soc.,Div.Polym.Chem.),

1999, 40, 228.567. B. Moon, T. R. Hoye and C. W. Macosko, J. Polym. Sci., Part A: Polym.Chem. Ed.,

2000, 38, 2177.568. M. Sykora, K. A. Maxwell, J. M. DeSimone and T. J. Meyer, Proc.Natl. Acad. Sci.

U.S.A., 2000, 97, 7687.569. X. L. Yan, C. C. Xu, M. Xeng and F. L. Bai, Ganguang Kexue Yu Guang Huaxue,

2000, 18, 112.570. H. Tachibana, H. Kishida and Y. Tokura, Appl. Phys. Lett., 2000, 77, 2443.571. J. A. Mikroyannidis, Polymer, 2000, 41, 8193.572. P. Wu, S. Balasubramanian, W. Liu, J. Kumar, L. Samuelson and S. K. Tripathy,

Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 1361.573. B. Ren, Z. Tong, F. Gao, X. Liu and F. Zeng, Polymer, 2000, 42, 2001.574. D. Bogdal, Polimery, 1999, 44, 555.575. Y. S. Yuri, T. A. Chevtchouk, V. N. Knyushto, O. G. Kulinkovich and K. N.

Solovyov, J. Porphyrins Phthalocyanines, 2000, 4, 579.576. B. H. Lee, J. Lee and J. L. Jin,Korea Polym. J., 1999, 7, 325.577. K. Yoshii, S. Machida, K. Horie and M. Itoh, Polym. J., 2000, 32, 37.578. J. R. Barone, S. Q. Wang, J. P. S. Farinha and M. A. Winnik, 2000, ACS ASAP.579. T. G. Deligeorgiev, N. I. Gadjev, I. I. Iljana, V. A.Maximova, H. E. Katerinopoulos

and E. Foukaraki, Dyes Pigments, 1999, 44, 131.


580. J. M. Kim, T. E. Chan, D. K. Han and K. D. Ahn, J. Photopolym. Sci and Technol.,2000, 13, 273.

581. L. F. Campo, D. S. Correa, M. A. De Araujo and V. Stefani, Macromol. RapidCommun., 2000, 21, 832.

582. L. Li, Z. H. Tao, C. C. Wang, W. L. Yang and S. K. Fu, Gaodeng Xuexiao HuxaueXuebao, 2000, 21, 816.

583. J. A. Mikroyannidis, J. Polym. Sci., Part A: Polym., Chem. Ed., 2000, 38, 2492.584. J. A. Mikroyannidis, J. Polym. Sci., Part A: Polym., Chem. Ed., 2000, 38, 2381.585. S. Lucht and J. Stumpe, J. Lumin., 2000, 91, 203.586. J. D. Tong, M. Moffitt, X. Huang, M. A. Winnik and R. A. Ryntz, J. Polym. Sci.,

Part A: Polym., Chem. Ed., 2000, 39, 239.587. R. Porouchani, L. Garamszegi, T. Q. Nguyen and J. Hilborn, Macromol. Rapid

Commun., 2000, 21, 837.588. J. D. Tong, S. Ni and M. A. Winnik,Macromolecules, 2000, 33, 1482.589. D. Liu, Y. Xiao, Y. Li and W. Li, Dyes Pigments, 2000, 46, 63.590. J. H. Wang and Y. Q. Shen, Adv.Mater. Opt. Electron., 2000, 9, 129.591. S. C. Farmer and T. E. Patten, Polym.Mater. Sci. Eng., 2000, 82, 237.592. H. Sawada, T. Kawase and T. Tomita, J. Fluorine Chem., 2000, 103, 31.593. T. C. Werner, K. J. Forrestall, S. L. McIntosh and J. Pitha, Appl. Spectrosc., 2000,

54, 560.594. S. Picarra, P. T. Gomes and J. M. G. Martinho,Macromolecules, 2000, 33, 3947.595. S. Ugur and O. Peckan, J. Appl. Polym. Sci., 2000, 77, 1087.596. O. Peckan and S. Ugur, Polymer, 2000, 41, 7531.597. F. Gao, B. Ren, Yu Yan and Z. Tong, Wuli Huaxue Xuebao, 2000, 16, 450.598. J. Gonzalez-Benito, A. J. Aznar, A. Macanita and J. Baselga, Bol. Soc. Esp. Ceram.

Vidrio, 2000, 39, 396.599. J. Gonzalez-Benito, A. J. Aznar, J. Lima, A. Macanita and J. Baselga, J. Fluoresc.,

2000, 10, 141.600. F. Winnik, T. A. S. Regismond and D. F. Anghel, ACS Symp. Ser, 2000, 765, 286.601. M. Erdogan and O. Peckan , J. Polym. Sci., Part B: Polym. Phys. Ed., 2000, 38, 739.602. M. R. Pokhrel and S. H. Bossmann, J. Phys. Chem. B., 2000, 104, 2215.603. H. F. Ji, Y. Shen, J. P. Hubner, B. F. Carroll, R. H. Schmehl, J. A. Simon and K. S.

Schanze, Appl. Spectrosc., 2000, 54, 856.604. N. J. Flint, S. Gardebrecht, I. Soutar and L. Swanson, Polym. Prepr. (Am. Chem.

Soc., Div. Polym. Chem.), 1999, 40, 230.605. F. Gao, Y. Yan, B. Y. Ren and Z. Tong, Gaodeng Xuexiao Huaxue Xuebao, 2000,

21, 976.606. K. Nakashima, Polym.Mater. Sci. Eng., 2000, 82, 375.607. A. M. Mathur, R. Drescher and A. B. Scranton, Spectroscopy, 2000, 15, 36.608. D. H. Choi and H. S. Kang, Bull. Korean Chem. Soc., 2000, 20, 1186.609. P. A. Blanche, Ph. C. Lemaire, M. Dumont and M. Fischer, Opt. Lett., 1999, 24,

1349.610. C. Maerns, P. Dubois, R. Jerome, P. Blanche and Ph. C. Lemaire, J. Polym. Sci.,

Part B: Polym. Phys. Ed., 2000, 38, 205.611. C. Carlini, A. Fissi, A. Galletti, R. Maria and G. Sbrana,Macromol. Chem. Phys.,

2000, 20, 1161.612. Y. Imamura, Y. Yamaguchi and Q. Tran-Cong, J. Polym. Sci., Part B: Polym. Phys.

Ed., 2000, 38, 682.613. C. Carlini, A. G. Fissi, M. R. Anna and G. Sbrana, Macromol. Chem. Phys., 2000,

201, 1540.

Photochemistry394

614. M. Hirai, T. Yuzawa, Y. Haramoto and M. Nansawa, React. Funct. Polym., 2000,45, 175.

615. K. Yoshii, S. Machida and K. Horie, J. Polym. Sci., Part B: Polym. Phys. Ed., 2000,38, 3098.

616. G. Clavier, F. Ilhan and V. M. Rotello,Macromolecules, 2000, 33, 9173.617. G. J. Everlof and G. D. Jaycox, Polymer, 2000, 41, 6527.618. Q. Guo and Z. Zhong,Mat. Sci. Eng., 2000, C7, 91.619. Y. He, H. Yang, X. Wang and Q. Zhou, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 2000, 41, 1358.620. W. Feng, T. R. Zhang, Y. Liu, R. Lu, Y. Y. Zhao and J. N. Yao, Gaodeng Xuexiao

Huaxue Xuebao, 2000, 21, 1563.621. M.Garavelli, B. R. Smith, M. J. Bearpark, F. Bernadi,M. Olivucci andM. A. Robb,

J. Am. Chem. Soc., 2000, 122, 5568.622. M. R. Nimlos, J. Filley, M. A. Ibrahim, A. S. Watt and D. M. Blake, Proc.

Renewable Adv. Energy Syst. 21st Century, 1999, 392.623. W. J. Joo, H. D. Shin, C. H. Oh, S. H. Song, P. S. Kim, B. S. Ko and Y. K. Han, J.

Chem. Phys., 2000, 113, 8848.624. M. M. Krayushkin, M. A. Kalik, D. L. Dzhavadov, L. G. Vorontsova, Z. A.

Starikova, A. Yu. Martynkin, V. L. Ivanov and B. M. Uzhinov, Russ. Chem. Bull.,2000, 49, 1757.

625. Y. Imai, K. Adachi, K. Naka and Y. Chujo, Polym. Bull., 2000, 44, 9.626. A. Fritz, A. Schonhals, M. Rutloh and J. Stumpe,Macromol. Symp., 2000, 154, 127.627. C. L. Gaupp, K. Zong, P. Schottland, B. C. Thompson, C. A. Thomas and J. R.

Reynolds,Macromolecules, 2000, 33, 1132.628. S. Yagi, K. Maeda and H. Nakazumi, Synthesis, 2000, 2, 247.629. G. Xu, X. Liu, J. Si, P. Ye, Z. Li and Y. Shen, Opt. Lett., 2000, 25, 329.630. T. Seki, H. Sekizawa and K. Ichimura, Polym. J., 1999, 31, 1079.631. H. Ikake, W. Hashimoto, T. Obara, K. Kurita and S. Yano, Kobunshi Ronbunshu,

2000, 57, 376.632. N. L. Cromhout and A. T. Hutton, Appl. Organomet. Chem., 2000, 14, 66.633. S. Yu. Zaitsev, T. I. Sergeeva, E. A. Baryshnikova, W. Zeiss, D. Mobius, O. V.

Yescheulova, S. P. Gromov, O. A. Fedorova and M. V. Alfimov,Mater. Sci. Eng.,1999, C8, 469.

634. T. Kondo, K. Yoshii, K. Horie and M. Itoh,Macromolecules, 2000, 33, 3650.635. T. Buruiana, E. C. Buruiana, A. Airinei and I. Grecu, Chin. J. Polym. Sci., 2000, 37,

343.636. X. Tuo, Z. Chen, L. Wu, X. Wang and D. Liu, Polym. Prepr. (Am. Chem. Soc., Div.

Polym. Chem.), 2000, 41, 1405.637. X. G. Wang, L. F. Wu, X. Zhou, L. Li, S. Balasubraminian, J. Kumar and S. K.

Tripathy, Chin. J. Polym. Sci., 2000, 18, 337.638. H. Hattori and T. Uryu, J. Polym. Sci., Part A: Polym. Chem. Ed., 2000, 38, 887.639. N. A. Hampp, M. Neebe and A. Seitz, Proc. SPIE-Int. Soc. Opt. Eng., 2000, 3973,

118.640. W. Liu, S. Bian, L. Li, L. Samuelson, J. Kumar and S. Tripathy,Chem.Mater., 2000,

12, 1577.641. A. M. Peeler, S. Mahadevan, C. E. Hoyle and D. Creed, Polym. Prepr. (Am. Chem.

Soc., Div. Polym. Chem.), 2000, 40, 540.642. Y. Wu, J. mamiya, A. Kanazawa, T. Shiono, T. Ikeda and Q. Zhang, Macro-

molecules, 1999, 32, 8829.643. A. L. Park and J. D. Hong,Macromol. Symp., 1999, 142, 121.


644. A. Toutianoush, F. Saremi and B. Tieke,Mater. Sci. Eng., 1999, C8, 343.645. C. I. Bratschkov, S. Minchev and I. D. Schopov, Bulg. Chem. Commun., 2000, 32,

24.646. S. M. Bhalakia and R. G. Patel, Int. J. Polym.Mater., 1999, 43, 63.647. A. Fritz, A. Schonhals, B. Sapich, M. Ruthloh and J. Stumpe, Proc.-Int. Symp.

Electrets, 10th, 1999, 693.648. A. Maggiani, A. Tubul and P. Brun,Helv. Chim. Acta, 2000, 83, 650.649. M. Teraguchi and T. Masuda,Macromolecules, 2000, 33, 240.650. T. Nagata, M. Ozaki, K. Yoshino and F. Kajzar,Denki Zairyo Gijitsu Zasshi, 1999,

8, 46.651. A. Yu. Bobrovsky, N. I. Boiko and V. P. Shibaev, Liq. Cryst., 2000, 27, 219.652. I. Yamaguchi, K. Osakada and T. Yamamoto, Chem. Commun., 2000, 1335.653. H. G. Heller, D. S. Hughes, M. B. Hursthouse and N. G. Rowles, Chem. Commun.,

2000, 1397.654. S. Yu. Grebenkin and B. V. Bol’shakov, Vysokomol. Soedin., Ser. A, Ser. B, 2000, 42,

857.655. M. Fukudome, K. Kamiyama, T. Kawai and M. Irie, Chem. Lett., 2001, 1, 70.656. K. Fukuda, T. Seki and K. Ichimura,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect A,

2000, 345, 137.657. T. J. Homola,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 2000, 344, 63.658. Q. Chen and Z. Wang,Hecheng Shuzhi Ji Suliao, 1999, 16, 55.659. V. Shibaev, A. Bobrovsky, N. Boiko andK. Schaumburg,Polym. Int., 2000, 49, 931.660. M. Han, S. Morino and K. Ichimura,Macromolecules, 2000, 33, 6360.661. Y. Uchida, H. H. Huang, K. Horie, L. Y. Qing, H. Tuchiya and J. Watanabe, J.

Polym. Sci., Part B: Polym. Phys. Ed., 2000, 38, 2922.662. Y. C. Kim, H. N. Cho, D. Y. Kim, J. M. Hong, W. N. Song, D. Kim and C. Y. Kim,

Polymer (Korea), 2000, 24, 211.663. A. Yu. Bobrovskii, N. I. Boiko and V. P. Shibaev,Vysokomol. Soedin., Ser.A, Ser.B,

2000, 42, 50.664. C. Sanchez, R. Alcala, R. Cases, L. Oriol and M. Pinol, J. Appl. Phys., 2000, 88,

7124.665. K. Horie, H. W. Huang and M. Shimada, Pol. Int. Time-Space Organ. Macromol.

Syst., Proc. OUMS’98, 1999, 55.666. R. P. Chartoff, J. S. Ullett and J. W. Schultz, Polym.Mater. Sci. Eng., 2000, 82, 361.667. A. Yu. Bobrovskii, N. I. Boiko and V. P. Shibaev,Vysokomol. Soedin. Ser.A, Ser. B,

1998, 40, 410.668. A. P. Davey, R. G. Howard, W. J. Blau and H. J. Byrne, Int. J. Polym.Mater., 1999,

44, 241.669. S. Schmidtke, P. Russo, J. Nakamatsu, E. Buyuktanir, B. Turfan, E. Temyanko and

I. Negulescu,Macromolecules, 2000, 33, 4427.670. R. A. Vaia, D. W. Tomlin, M. D. Schultze and T. J. Bunning, Polymer, 2001, 42,

1055.671. D. Nwabunma, H. W. Chiu and T. Kyu, J. Chem. Phys., 2000, 113, 6429.672. S. Kurihara, Y. Natkatake, K. Masumoto and T. Nonaka, Polym. Adv. Technol.,

2000, 11th, 434.673. A. Matsumoto, S. Nagahama and T. Odani, J. Am. Chem. Soc., 2000, 122, 9109.674. O. Yaroshchuk and A. Kadashchuk, Appl. Surf. Sci., 2000, 158, 357.675. R. MacDonald, R. Schultz and C. Schreiber, Proc. SPIE-Int. Soc. Opt. Eng., 1999,

3800, 2.676. S. Perney, P. Le Barny, J. Delaire, I. Dozov, S. Forget and P. Auroy, Liq. Cryst.,

2000, 27, 349.

Photochemistry396

677. A. Yu. Bobrovskii, N. I. Boiko and V. P. Shibaev,Vysokomol. Soedin., Ser.A, Ser. B,2000, 42, 56.

678. M. M. Sonpatki, T. Sergan, J. Kelly and L. C. Chien,Macromol. Symp., 2000, 154,83.

679. C. E.Hoyle, J. B.Whitehead,N. L.Gill, M. L. Hladik andW.Kuang,Polym.Mater.Sci. Eng., 2000, 82, 336.

680. N. G. Pschirer and U. H. F. Bunz, Polym. Prepr. (Am. Chem. Soc., Div. Polym.Chem.), 2000, 41, 460.

681. B. C. Baxter, R. V. Talroze and D. L. Gin, Polym.Mater. Sci. Eng., 2000, 82, 338.682. M.M. Sonpatki, T. Sergan, J. Kelly and L. C. Chien,Polym.Prepr. (Am.Chem. Soc.,

Div. Polym. Chem.), 1999, 40, 1165.683. S. N. Shah, C. E. Hoyle and D. Creed, Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.), 1999, 40, 494.684. M. H. Li, P. Auroy and P. Keller, Liq. Cryst., 2000, 27, 1497.685. M. Kijima, K. Setoh and H. Shirkawa, Chem. Lett., 2000, 8, 936.686. V. Barachevsky and G. Chudinova,Mater. Sci. Eng. C, 1999, 8, 73.687. S. E. Mallakpour, A. R. Hajipour and A. R. Mahdavian, J. Appl. Polym. Sci., 2000,

78, 527.688. X. Yuan, Z. Chen, J. Qiao and J. Chai, Spectrochim. Acta, Part A, 2000, 56, 1869.689. M. J. Carey and D. Phillips, Eur. Polym. J., 2000, 36, 619.690. Y. Itoh and M. Inoue, Eur. Polym. J., 2000, 36, 2605.691. S. A. Jenekhe and X. L. Chen, J. Phys. Chem. B, 2000, 104, 6332.692. Z. Liao, J. Zhao, J. Shen and X. Chen,Hencheng Xiangjiao Gongye, 2000, 23, 52.693. Y. Gan, D. Dong, S. Carlotti and T. E. Hogen-Esch, J. Am. Chem. Soc., 2000, 122,

2130.694. H. Yamamoto, A. Hashidzume and Y. Morishima, Polym. J., 2000, 32, 737.695. J. Yang, G. Wang, H. Li, L. Chen and B. He, J. Appl. Polym. Sci., 2000, 78, 1869.696. M. I. Esteban, M. R. Vigil, V. Moreno-Montes and C. S. Renamayor, Polym. Int.,

2000, 49, 663.697. M. Tamura and A. Ueno, Bull. Chem. Soc. Jpn., 2000, 73, 147.698. L.M.Herz andR. T. Phillips,Phys.Rev.B:Condens.Matter.Mater.Phys., 2000, 61,

13691.699. J. Davenas, G. Boiteux, G. Seytre and C. Jardin, Synth.Met., 2000, 115, 83.700. X. G. Jin, Z. Jiang, M. Ni, F. L. Bai and R. Y. Qian, Polymer, 2000, 18, 465.701. A. Horta, I. F. Pierola and A. L. Macanita,Macromolecules, 2000, 33, 1213.702. F. S. Du, Y. Zhou, Z. C. Li and F. M. Li, Polym. Adv. Technol., 2000, 11, 798.703. J. Horinaka, M. Yamamoto and T. Matsuda, Comput. Theoret. Polym. Sci., 2000,

10, 365.704. M. Stoessel, G. Wittmann, J. Staudigel, F. Steuber, J. Blassing, W. Roth, H.

Klausmann, W. Rogler, J. Simmerer, A. Winnacker, M. Inbasekaran and E. P.Woo, J. Appl. Phys., 2000, 87, 4467.

705. N. Matsumi, T. Umeyama and Y. Chujo,Macromolecules, 2000, 33, 3956.706. D. Pevenage, M. Van der Auweraer and F. C. DeSchryver,Chem. Phys. Lett., 2000,

319, 512.707. J. W. Yu, J. K. Kim, H. N. Cho, D. Y. Kim, C. Y. Kim, N. W. Song and D. Kim,

Macromolecules, 2000, 33, 5443.708. J. I. Lee, T. Zyung, R. D. Miller, Y. H. Kim, S. C. Jeoung and D. Kim, J. Mater.

Chem., 2000, 10, 1547.709. G. Li, J. Tan, H. Fu, H. Ma, D. Chen and Z. Zhou, J. Appl. Polym. Sci., 2000, 78,

133.710. M. A. Loi, C. Gadermaier, E. J. W. List, G. Leising, W. Graupner, G. Bongiovanni,


A. Mura, J. J. Pireaux and K. Kaeriyama, Phys. Rev. B: Condens. Mater. Phys.,2000, 61, 1859.

711. Y. Cui, C. Liu and Q. Gao, Polym. Adv. Technol., 2000, 11, 172.712. N. A. Davidenko, N. G. Kuvshinsky and V. G. Syromiatnikov, Fiz.Napivprovidn.,

Kvantova Optoelektron., 2000, 3, 39.713. F. S. Du, Z. C. Chen, W. Hong, Q. Yu. Gao and F. M. Li, J. Polym. Sci., Part A:

Polym. Chem. Ed., 2000, 38, 679.714. N. Ohta, Y. Iwaki, T. Ito, I. Yamazaki and A. Osuka, J. Phys. Chem. B, 1999, 103,

11242.715. Y. He and H. Te, Huadong Ligong Daxue Xuebao, 2000, 26, 434.716. N. Lu, C. Wang, H. Zhou, W. Song, D. Wang and T. Li, Polym. Prepr. (Am. Chem.

Soc., Div. Polym. Chem.), 1999, 40, 632.717. Z. Wang and Z. Ton, Huaxue Tongbao, 2000, 11, 1.718. C. K. Chee, K. P. Ghiggino, T. A. Smith, S. Rimmer, I. Soutar and L. Swanson,

Polymer, 2000, 42, 2235.719. E. Stathatos, P. Lianos, R. H. Rakotoaly, A. Lashewsky and R. Zana, J. Colloid

Interf. Sci., 2000, 227, 476.720. L. Zhu, Z. Chang, M. Li and E. Wang, Ganguang Kexue Yu Guang Huaxue, 2000,

18, 12.721. D. J. Liauw, C. C. Huang, H. C. Sang and E. T. Kang, Chin. Chem. Lett., 2001, 42,

209.722. S. Pankasem, M. Biscoglio and J. K. Thomas, Langmuir, 2000, 16, 3620.723. C. L. Wang, Y. M. Kuo and D. Y. Chao, Polym. Adv. Technol., 2000, 11, 127.724. Z. Xu, S. Cheng andG. Song,Hubei DaxueXuebao,Ziran Kexueban, 2000, 22, 171.725. S. Liu and D. F. O’Brien, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 2000,

41, 760.726. W. H. Binder and H. Gruber,Macrom. Chem. Phys., 2000, 20, 949.727. C. D. Geddes and P. Douglas, J. Appl. Polym. Sci., 2000, 76, 603.728. G. L. Smith and C. L. McCormick,Macromolecules, 2001, 34, 918.729. X. Gonzalez, I. Cid, P. Castan and A. Prat,Commun. Jorn. Com. Esp.Deterg., 2000,

30, 93.730. L. Chen, D. McBranch, R. Wang and D. Whitten, Chem. Phys. Lett., 2000, 330, 27.731. W. G. Liu, K. De Yao, G. C. Wang and H. X. Li, Polymer, 2000, 41, 7589.732. S. Liu, Yu. Fang, D. Hu and H. Lu, Wuli Huaxue Xuebao, 2000, 16, 214.733. L. Chen, S. Xu, D. McBranch and D. Whitten, J. Am. Chem. Soc., 2000, 122, 9302.734. Q. Lu, H. He, X. Ran, X. Zhang, S. Zhan, Y. Wang and Q. Xu, Jingxi Huagong,

2000, 17, 456.735. X. L. Chen and S. A. Jenekhe,Macromolecules, 2000, 33, 4610.736. H. Li, F. Gao, C. H. Tung and L. Z. Wu,Macromolecules, 2000, 18, 506.737. B. B. Raju and S. M. B. Costa, Spectrochim. Acta, Part A, 2000, 56, 1703.738. X. Liu, C. Yang, R. He and Y. Wang, Wuxi Qinggong Daxue Xuebao, 2000, 19, 365.739. C. Frochot, C. Muller, A. Brembilla, M. C. Carre, P. Lochon and M. L. Viriot, Int.

J. Polym. Anal. Charact., 2000, 6, 109.740. X. Fu, J. Li, F. Wang, D. B. Wang and Z. S. Hu, Yingyong Huaxue, 2000, 17, 146.741. R. Pramanik, D. Kumar and S. Bagchi, Phys. Chem. Chem. Phys., 2000, 2, 4307.742. N. J. Flint, I. Soutar, L. Swanson and S. C. Yu, Polym. Prepr. (Am. Chem. Soc., Div.

Plym. Chem.), 1999, 40, 289.743. H. Langhals, R. Ismael and O. Yuruk, Tetrahedron, 2000, 56, 5435.744. K. R. Acharya, S. C. Bhattacharya and S. P. Subbash, J.Mol. Liq., 2000, 87, 85.745. C. N. Jeong and C. S. P. Sung, Proc. Annu.Meet. Adhes., 2000, 23rd, 2559.

Photochemistry398

746. C. N. Cheong, C. S. P. Sung and N. H. Sung, Proc. Annu.Meet. Adhes. Soc, 1999,22nd, 195.

747. P. F. Earl and T. Znajewski, Pulp. Paper Can., 2000, 101, 62.748. D. W. Cooke, B. L. Bennett, R. E. Muenchausen, E. B. Orler and D. A. Wrobleski,

Radiat. Phys. Chem., 2000, 58, 29.749. E. Vaganova,G.Meshulam, Z.Kotler,M. Rozenberg and S. Yitzchaik, J.Fluoresc.,

2000, 10, 81.750. M. Muller, R. Zentel, T. Maka, S. G. Romanov and C. M. S. Torres, Polym. Prepr.

(Am. Chem. Soc., Div. Polym. Chem.), 2000, 41, 810.751. D. L. Simone and T. M. Swager, J. Am. Chem. Soc., 2000, 122, 9300.752. H. Tylli, I. Forsskahl and C. Olkkonen, Cellulose (Neth.), 2000, 7, 133.753. H. Zhu and S. Mu, Dianhuaxue, 2000, 6, 311.754. P. Amareshwar, P. K. Kumar andM. R. K.Murthy, J.Polym.Mater. Sci., 2000, 17,

77.755. O. Puglisi, M. Chipara, W. Enge, G. Compagnini, J. Reyes-Romero, U. Bacmeister

andM. D. Chipara,Nucl. Instr.Methods Phys. Res., Sect B, 2000, 166, 944.756. J. F. Pan, S. J. Chua and W. Huang, Synth.Meth., 2000, 110, 85.757. H. M. Banford, S. Wysocki and R. A. Fouracre, Annu. Rep.-Conf. Insul. Dielectric

Phenom., 1999, 2, 512.758. C. N. Jayarajah, A. Yekta, I. Manners andM. A.Winnik,Macromolecules, 2000, 33,

5693.759. A. P. Blokhin, M. F. Gelin and A. V. Uvarov, Proc. SPIE-Int. Soc. Opt. Eng., 2000,

4002, 255.760. C. E. Hoyle, M. D. Ziemer, B. Rufus, K. Viswanathan, D. Hill, D. Hunter and P.

Pomery, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 758.761. N. J. Kim, C. N. Chang, S. P. Chong andN.H. Sung,Polym.Mat. Sci.Eng, 1999, 81,

387.762. R. A. Rupp, C. Pruner, F. S. Havermeyer, D. W. Schubert and J. Vollbrandt, OSA

Trends Opt. Photonics Ser., 1999, 27, 191.763. T. Yamamoto, M. Takeuchi and K. Kubota, J. Polym. Sci., Part B: Polym. Phys.

Ed., 2000, 38, 1348.764. H. Ren, Z. Lei, H. Zhang and Y. Wang, Xibei Shifan Daxue Xuebao, Ziran

Kexueban, 2000, 36, 36.765. Z. Lei, H. Ren and Y.Wang,Xibei Shifan DaxueXuebao,ZiranKexueban, 2000, 36,

91.766. P. Horvath, F. Schauer, O. Salyk. I. Kuritka, S. Nespurek, J. Zemek and V. Fidler,

J.Non-Cryst. Solids, 2000, 266, 989.767. T. Itoh, J. Inorg. Organomet. Polym., 1999, 9, 245.768. V. P. Smagin, R. A. Maier, G. M. Makrousov, V. M. Belov and V. V. Evstigneev,

Perspekt Mater., 1998, 6, 38.769. N. Urabe, Porima Daijesuto, 2000, 52, 81.770. L. Zhang and Y. Xu, Huanan Shifan Daxue Xuebao, Ziran Kexueban, 1999, 3,

108.771. N. Urabe, Porima Daijesuto, 2000, 52, 81.772. M. Tsnooka,Kobunshi Tenkazai no Kaihatsu Gijutsu, 1998, 317.773. S. E. Evsyukov, Phys. Chem.Mater. Low-Dimens. Struct., 1999, 21, 55.774. M. L. Castejon, P. Tiemblo and J.M.Gomez-Elvira,Polym.Degrad. Stab., 2000, 70,

357.775. F. Severini, R. Gallo, L. Brambilla, C. Castiglioni and S. Ipsale, Polym. Degrad.

Stab., 2000, 69, 133.


776. S. I. Kuzina, A. P. Pivovarov, A. I. Mikhailov and G. P. Belov, Eur. Polym. J., 2000,36, 975.

777. J. L. Philippart and J. L. Gardette, Polym. Degrad. Stab., 2000, 71, 189.778. S. S. Pesetskii, Yu.M. Krivoguz andA. I. Kuzavkov,Zh.Prikl.Khim., 2000, 73, 272.779. X. Li, Zhongguo Suliao, 1999, 13, 70.780. Q. Chen, Q. Qian and Z. Huaji, Zhongguo Suliao, 1999, 13, 50.781. J. P. Gao, S. M. Wang, J. G. Yu, T. Lin and X. D. Wang, Macromol. Symp., 1999,

144, 323.782. F. Kawai,M. Shibata, S. Yokoyama, S.Maeda,K. Tada and S. Hayashi,Macromol.

Symp., 1999, 144, 73.783. O. Ya. Tolkach and N. R. Prokopczuk, Vestsi Nats. Akad. Navuk Belarusi, Ser.

Fiz.-Tekh.Navuk., 1999, 3, 14.784. I. D. Skrypnyk and J. L. Spoormaker,Mater. Sci., 1999, 35, 527.785. O. V. Shibirin, O. P. Mityukhin, Z. O. Streltsova and P. V. Zamoatev, Katal.

Neftekhim., 2000, 4, 58.786. A. Tidjani, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 601.787. R. Sciamanna, C. Albano, A. Ramos, A. Silveira and L. Espejo,Rev. Fac. Ing.Univ.

Cent. Venez., 1999, 14, 123.788. S. H. Hamid, J. Appl. Polym. Sci., 2000, 78, 1591.789. J. Jayaseharan, A. K. Nanda and K. Kishore, Polymer, 2000, 41, 5721.790. C. Kosa, I. Lukac and R. G. Weiss,Macromolecules, 2000, 33, 4015.791. V. M. Rudoi, I. V. Yaminskii and V. A. Ogarev, Vysokomol. Soedin. Ser. A, Ser. B,

1999, 41, 1671.792. B. Mailhot, S. Morlat and J. L. Gardette, Polymer, 1999, 41, 1981.793. A. V. Shyichuk and J. R. White, J. Appl. Polym. Sci., 2000, 77, 3015.794. H. Kaczmarek, A. Kaminska, M. Swiatek and S. Sanyal, Eur. Polym. J., 2000, 36,

1167.795. A. Mansri and K. Guemra, Eur. Polym. J., 2000, 36, 751.796. A. V. Ivanov and E. Yu. Khavina, Vysokomol. Soedin., Ser.A, Ser. B., 1998, 40, 255.797. L. Gonon and J. L. Gardette, Polymer, 1999, 41, 1669.798. M. S. Sanchez,M.M.C. Ferreira andM. I. Felisberti,Polim.:Cienc.Tecnol., 1999, 9,

116.799. H. Kaczmarek, A. Kaminska and A. Van Herk, Eur. Polym. J., 2000, 36, 767.800. O. Chiantore, L. Trossarelli and M. Lazzari, Polymer, 1999, 41, 1657.801. E. J. Harbron, V. P.McCaffrey, R. Xu andM.D. E. Forbes, J.Am.Chem. Soc., 2000,

122, 9182.802. O. Chiantore and M. Lazzari, Polymer, 2000, 42, 17.803. T. Grossetete, A. Rivaton, J. L. Gardette, C. E. Hoyle, M. Ziemer, D. R. Fagerburg

and H. Clauberg, Polymer, 2000, 41, 3541.804. N. Manabe and Y. Yokota, Polym. Degrad. Stab., 2000, 69, 183.805. P. N. Thanki, C. Ramesh and R. P. Singh, Polymer, 2001, 42, 535.806. H. Simburger, K. Hummel and C. Hagg, Polymer, 2000, 41, 7883.807. L.Monney, C. Dubois and A. Chambaudet,Angew.Makromol.Chem., 1999, 273, 6.808. B. S. Lee and D. C. Lee, IEEE Trans. Dielectric Electrical Insul., 1999, 6, 907.809. D. Kotnarowska, Prog. Org. Coat., 1999, 37, 149.810. K. Inomata, S. Kawasaki, A. Kameyama and T. Nishikubo, Kobunshi Ronbunshu,

2000, 57, 457.811. K. Kaczmarek, J. Kowalonek, H. Janssen and H. P. M. Lieshout, Polimery, 2000,

45, 433.812. S. Giancaterina,A. Rossi, A. Rivaton and J. L.Gardette,Polym.Degrad.Stab., 2000,

68, 133.

Photochemistry400

813. T. Wakahara, T. Kondo, M. Okamura, T. Akasaka, Y. Hamada, T. Suzuki, M.Kako and Y. Nakadaira, J. Organomet. Chem., 2000, 611, 785

814. M. Ouyang, C. Yuan, R. J. Muisener, A. Boulares and J. T. Koberstein, Chem.Mater., 2000, ACS ASAP.

815. M. Ginic-Markovic, N. R. Choudhury,M. Dimopoulos and J. G.Matisons, Polym.Degrad. Stab., 2000, 69, 157.

816. Z. A. Maidunny, J. Rubb. Res., 1999, 2, 223.817. P. J. Slikerveer, M. H. A. van Dongen and F. J. Touwslager, Wear, 1999, 236,

189.818. M. Palamaru, A. Iordan, C. Ciobanu, A. L. Cecal and N. Niga, An. Stiint.Univ. ‘Al.

I. Cuza’ Iasi, Chim., 1999, 7, 39.819. L. Irusta and M. J. Fernandez-Berridi, Polymer, 2000, 41, 3297.820. J. F. Power, O. V. Nepotchatykh and S. W. Fu, Appl. Spectrosc., 2000, 54, 1782.821. L. Sheu, K. Imen and S. D. Allen, J. Appl. Polym. Sci., 2000, 77, 59.822. A. Yabe, Polym. Chem.Mater., 1999, 21, 75.823. S. Girois, J. Vinyl Addit. Technol., 1999, 5, 218.824. M. Susuki, O. Nishimura, H. Nagai, Y. Nakata and T. Okutani, Appl. Organomet.

Chem., 2000, 14, 325.825. Y. Feng, Z. Q. Liu and X. S. Yi, Appl. Surf. Sci., 2000, 156, 177.826. T. Yajima, T. Domon, T. Suzuki, N. Harada, H. Kurihara, K. Miyawaki, K.

Sugiyama and Y. Okabe, J. Photopolym. Sci. Technol., 2000, 13, 21.827. H. Sugimura, T. Shimizu and O. Takai, J. Photopolym. Sci. Technol., 2000, 13, 69.828. Z. Qin, J. Zhang, H. Zhou, Y. Song and T. He, Nucl. Instrum.Methods Phys. Res.,

Sect B, 2000, 170, 406.829. A. Ya. Temkin, Laser Eng., 1999, 9, 239.830. T. H. Fedynyshyn, R. R. Kunz, R. F. Sinta, R. B. Goodman and S. P. Doran, J. Vac.

Sci. Technol. B, 2000, 18, 3332.831. A. Athanassiou, M. Lassithiotaki, D. Anglos, S. Georgiou and C. Fotakis, Appl.

Surf. Sci., 2000, 154, 89.832. T. Lippert, A. Wokaun, S. C. Langford and J. T. Dickinson, Appl. Phys. A:Mater.

Sci. Proc., 1999, 69, S655.833. T. Lippert, A.Wokaun, S. C. Langford,G. Savas and J. T. Dickinson, J.Appl.Phys.,

1999, 86, 7116.834. K. Yoshii, S. Machida, K. Horie and M. Itoh, J. Non-Cryst. Solids, 2000, 272, 75.835. C. I. Butoi, N. M. Mackie, P. R. McCurdy, R. D. Peers and E. R. Fischer, Plasma

Polym., 1999, 4, 77.836. M. C. Castex, N. Bityurin, C. Livero, S. Muraviov, N. Bronnikova and D. Reidel,

Appl. Surf. Sci., 2000, 168, 175.837. A. Sionkowska, Polym. Degrad. Stab., 2000, 68, 147.838. S. T. Chang and H. T. Chang, Polym. Degrad. Stab., 2001, 71, 261.839. M. Paulson and A. J. Ragauskas, ACS Symp. Ser., 2000, 742, 490.840. T. Q. Hu and B. R. James, J. Pulp. Paper. Sci., 2000, 26, 173.841. P. McGarry, C. Heitner, J. Schmidt, G. Cunkle and J. P. Wolf, J. Pulp. Paper Sci.,

2000, 26, 59.842. D. S. Argyropoulos, P. Halevy and P. Peng, Photochem. Photobiol., 2000, 71, 141.843. J. H. Cameron, Q. Zhou, C. Longcore and R. Aravamuthan, AIChE Symp. Ser.,

1999, 322, 54.844. G. Fang, A. Castellan, J. De Bernard and Z. Shen, Linchan Huaxue Yu Gongye,

2000, 20, 51.845. T. Q. Hu and G. R. Cairns, Holzforschung, 2000, 54, 127.846. B. Ruffin and A. Castellan, Can. J. Chem., 2000, 78, 73.


847. D. F. Guay, B. J. W. Cole, R. C. Fort, J. M. Genco and M. C. Hausman, J. Wood.Chem. Technol., 2000, 20, 375.

848. K. Stana-Kleinschek and S. Iskrac, Tekstilec., 2000, 43, 77.849. M.Mucha, M. Bratkowska and D. Woszczalski,Adv. Chitin Sci., 2000, 4, 436.850. J. Font, R. M. Cuadros,M. R. Reyes, J. Costa-Lopez and A.Marsal, J. Soc. Leather

Technol. Chem., 1999, 83, 300.851. R. Ramami and C. Ranganathaiah, Polym. Degrad. Stab., 2000, 69, 347.852. F. Posada and J. L. Gardette, Polym. Degrad. Stab., 2000, 70, 17.853. Q. Wu, B. Qu, Y. Xu and Q. Wu, Polym. Degrad. Stab., 2000, 68, 97.854. J. A. Macko andH.Ishida, Polym. Prepr. (Am. Chem. Soc.,Div. Polym.Chem.), 2000,

41, 68.855. J. A. Macko and H. Ishida, Polymer, 2001, 42, 227.856. J. A. Macko and H. Ishida, J. Polym. Sci. Part A: Polym. Chem. Ed., 2000, 38, 2687.857. M. Bera, A. Rivaton, C. Gandon and J. L. Gardette, Eur. Polym. J., 2000, 36, 1765.858. M. Bera, A. Rivaton, C. Gandon and J. L. Gardette, Eur. Polym. J., 2000, 36, 1753.859. K. Balashev, N. Panchev, I. Petkov and I. Panaiotov,Colloid Polym. Sci., 2000, 278,

301.860. G. Agostini, L. Pasimeni, M. Ruzzi, S. Monti, M. Maggini, M. Prato, I. Lamparth

and A. Hirsch, Chem. Phys., 2000, 253, 105.861. G. B. Wayton and F. W. Harris,Polym. Prepr. (Am. Chem. Soc., Div. Polym.Chem.),

2000, 41, 54.862. S. Commereuc, S. Bonhomme, V. Verney and J. Lacoste, Polymer, 2000, 41, 917.863. F. Dadashian and M. A. Wilding, Text. Res. J., 2001, 71, 7.864. P. C. Sarkar and A. K. Shrivastava, Pigment Resin Technol., 1999, 2, 123.865. Y. Kishima, Purasuchikkusu, 2000, 46, 118.866. C. Decker, K. Zahouily and A. Valet, Polym.Mater. Sci. Eng., 2000, 83, 323.867. T. Nguyen, J. W.Martin, E. Byrd andN. Embree, Polym.Mater. Sci.Eng., 2000, 83,

118.868. O. V. Nepotchatykh and J. F. Power, Polym. Eng. Sci., 2000, 40, 1747.869. Y. Zhang, C. Y. Won and C. C. Chu, J. Polym. Sci., Part A: Polym.Chem.Ed., 2000,

38, 2392.870. J. Mallegol, J. L. Gardette and J. Lemaire, J. Am. Oil. Chem. Soc., 2000, 77, 257.871. J. Dufour, J. B. G. A. Havermans and P. Vink, Afinidad, 2000, 57, 143.872. J. E. Pickett, Polym.Mater. Sci. Eng., 2000, 83, 141.873. B. Anthony and J. Tu, Polyurethanes Expo’98 Proc., 1998, 145.874. J. H. Botkin and A. Schmitter, Tech. Conf.-Soc. Plast. Eng., 1999, 57th, 3101.875. L. Yu. Smolyak, N. R. Prokopchuk and I. A. Klimovstova, Dokl. Nat. Akad. Nauk

Belarusi, 1998, 42, 65.876. A. Valet and D. Rogez, Surf. Coat. Int., 1999, 82, 293.877. S. M. Andrews, Annu. Techn. Conf.-Soc. Plast. Eng., 1999, 57th, 3105.878. D. Horsey, M. Bonora and P. Holbein, Polyolefins XI, Int. Conf., 1999, 541.879. I. Dumitrescu and M. Niculescu, Ind. Text., 1999, 50, 161.880. J. H. Botkin and A. Schmitter, J. Vinyl Addit. Technol., 2000, 6, 53.881. M. Kovalcikova, Plasty Kauc., 2000, 37, 36.882. G. Faoro, Polym. Paint. Col. J., 2000, 190, 22.883. X. Liu and Y. Chen, Gaofenzi Tongbao, 1999, 4, 57.884. G. Xie, Shanghai Huagong, 2000, 25, 83.885. X. Hong, Y. Feng, X. Li, L. Zhou and B. Guo, Zhongguo Suliao, 2000, 14, 71.886. P. Wu, Yu Chen and H. Kang, Zhongguo Suliao, 1999, 13, 70.887. Y. Ohkatsu, Purasuchikkusu Eji, 2000, 46, 101.

Photochemistry402

888. N. Ishihara, Purasuchikkusu Eji, 2000, 46, 106.889. S. Ohkatsu,Kobunshi Tenkazai no Shintenkai, 1998, 98.890. Y. Ohkatsu,Kobunshi Tenkazai no Shintenkai, 1998, 1.891. Anon, Caoutch. Plast., 1999, 76, 59.892. Y. Nakahara,Kobunshi Tenkazai no Shintenkai, 1998, 15.893. I. Vulic, J. M. Eng, S. B. Samuels and A. H. Wagner, Polym. Polym. Compos., 1999,

7, 565.894. S. B. Wagner, J. M. Eng and A. H. Wagner, Polyolefins XI, Int. Conf., 1999, 521.895. D. Bartning, Pop. Plast. Pack., 1995, 40, 67.896. M. McCusker,Met. Finish., 1999, 97, 38.897. J. Tochacek, Plasty Kauc., 2000, 37, 4.898. Z. Ding, C. X. Tian and Z. Guo, Reguxing Shuzi, 1999, 14, 23.899. D. Braun, E. Richter, S. T. Rabie, A. A. Nada, M. A. Abd-El-Ghaffar and A. A.

Yassin, Angew.Makromol. Chem., 1999, 271, 93.900. J. W. Hong,M. Y. Park, H. K. Im and J. O. Choi, Bull.Korean Chem. Soc., 2000, 21,

61.901. J. C. Suhadolnik, A. D. DeBellis, C. Hendricks-Guy, R. Iyengar and M. G. Wood,

Polym.Mater., 2000, 83, 126.902. L. Stoeber, A. Sustic, W. J. Simonsick and O. Vogl, 1998, J. Macromol. Sci., Pure

Appl. Chem., 2000, A37, 943.903. A. M. Morrow, N. S. Allen, M. Edge, D. Aldcroft and H. Jones, Polym. Degrad.

Stab., 2000, 69, 143.904. L. Bucsiova, S. Chemla and P. Hrdlovic, Polym. Degrad. Stab., 2001, 71, 135.905. S. Chmela, P. Lajoie, P. Hrdlovic and J. Lacoste, Polym. Degrad. Stab., 2001, 71,

171.906. M. E. Nichols and J. L. Gerlock, Polym. Degrad. Stab., 2000, 69, 197.907. G. Geuskens and D. M. McFarlane, J. Vinyl Addit. Technol., 1999, 5, 186.908. C. Sinturel, J. Lemaire and J. L. Gardette, Eur. Polym. J., 2000, 36, 1431.909. S. Jipa, T. Zaharescu, R. Setnescu, T. Setnescu,W. J.Wayne and J. Q. Pau,Polymer,

2000, 41, 6949.910. K. H. Chae and J. S. Kim, J. Photosci., 1999, 6, 25.911. T. Yukino and M. Fukushima, Polyolefins XI, Int. Conf., 1999, 505.912. J. Q. Pan, P. W. Quek, N. C. Lau and W. Y. Wayne, J. Appl. Polym. Sci., 2000, 78,

403.913. M. L. Binet, S. Commereuc, P. Lajoie and J. Lacoste, J. Photochem. Photobiol.,

2000, 137, 71.914. C. E.Wilen,M. Auer, J. Stranden, J. H. Naesman, B. Rotzinger, A. Steinmann, R. E.

King, H. Zweifel and R. Drewes,Macromolecules, 2000, 33, 5011.915. X. Yu, S. Zhang and J. Yang, Ganguang Kexue u Guang Huaxue, 2000, 18, 243.916. N. Yamashita, Senshoku Kenkyu, 1999, 43, 97.917. M. Miyazaki, Toso to Toryo, 1999, 597, 21.918. N. Urabe, Porima Daijesuto, 1999, 51, 112.919. D. Gupta, Colourage, 1999, 46, 17.920. J. E. Buston, J. R. Young and H. L. Anderson, Chem. Commun., 2000, 905.921. W. Holzer, H. Gratz, T. Schmitt, A. Penzkofer, A. Costela, I. Garcia-Moreno, R.

Sastre and F. J. Duarte, Chem. Phys., 2000, 256, 125.922. V. N. Serova, V. V. Chirkov, V. I. Morozov, A. V. Arkhireeva and V. P. Arkhireev,

J. Polym. Eng., 1999, 19, 233.923. Z. Qian, P. Chen, S. Sun, D. Zheng and T. Li, Ganguang Kexue Yu Guang Huaxue,

1999, 17, 323.


924. V. N. Serova, O. A. Cherkasova, E. N. Cherezova,Zh. Prikl.Khim., 1999, 72, 1883.925. M. J. Van derMeer, H. Zhang,W. Rettig andM. Glasbeek,Chem.Phys.Lett., 2000,

320, 673.926. S. H. Kim, S. H. Hwang, N. K. Kim, J. W. Kim, C.M. Yoon and S. R. Keum, J. Soc.

Dyers Colourists, 2000, 116, 126.927. N. Kohara, Cellul. Commun., 2000, 7, 121.928. H. Oda, Dyes Pigments, 2001, 48, 151.929. K. Himeno, Y. Okada and Z. Morita, Dyes Pigments, 2000, 45, 109.930. J. M. Pena, N. S. Allen, M. Edge, C. M. Liuaw, I. Roberts and B. Valange, Polym.

Degrad. Stab., 2000, 70, 437.931. A. P. Mast and P. Gijsman, Verfkroniek, 1999, 72, 11.932. U. Gesenhues, Polym. Degrad. Stab., 2000, 68, 185.933. V. N.Mishchenko, N. D. Konovalova and V. M. Ogenko,Ukr.Khim.Zh., 2000, 66,

87.934. D. B. Wolfe, S. J. Oldenburg, S. L. Westcott, J. B. Jackson, M. S. Paley and N. J.

Halas, Proc. SPIE-Int. Soc. Opt. Eng., 1999, 3793, 129.935. P. A. Cristensen, A. Dilks, T. Egerton and J. Temperley, J. Mater. Sci., 2000, 35,

5353.936. T. Yasunaga, E. Iwamura and T. Satou, R&D Res. Dev. (Kobe Steel Ltd.), 2000, 50,

38.937. S. Sakthivel, B. Neppolian, B. Arabindoo, M. Palanichamy and V. Murugesan, J.

Sci. Ind. Res., 2000, 59, 556.938. B. Singhal, G. Patel, J. Vardia and S. C. Ameta, Pollut. Res., 2000, 19, 219.939. S. Sakthivel, B. Neppolian, B. Arabindoo,M. Palanichamy and V.Murugesan, Ind.

J. Eng.Mater. Sci., 2000, 7, 87.940. T. Sivakumar, K. Shanthi, S. P. S. Guru, B. Srividya, P. S. Kiruthiga and R.

Gaghunathan, Asian J.Microbiol. Biotechnol. Environ. Sci., 1999, 1, 167.941. S. Scierka and N. Blough, Polym.Mater. Sci. Eng., 2000, 83, 338.

Photochemistry404

Part IV

Photochemical Aspects of Solar Energy Conversion

By Alan Cox

Photochemical Aspects of Solar EnergyConversion

BY ALAN COX

1 Introduction

Topics which have formed the subjects of reviews this year include productionand utilisation systems for solar chemical energy,1 the conversion of light intochemical energy,2 light harvesting for quantum solar energy conversion,3 solarenergy assisted photocatalysis of water,4 water decomposition to form hydrogenby photocatalysis and mechanocatalysis,5 molecular catalysts for water oxida-tion,6 photocatalytic decomposition of pure water on doped mixed oxides,7 solarenergy conversion by photocatalysts,8 organic solar cells based on photosyn-thesis,9 the prospects of hydrogen production as a result of photobiologicalactivity of enzyme hydrogen generation10 and the use of solar energy for drivingphoto- and thermochemical processes for energetic and environmental pur-poses.11

An investigation of cascade solar elements to determine the conditions ofmaximum use of the solar spectrum energy12 and a general article on solarchemistry at the beginning of the third millennium13 have also appeared.

2 Homogeneous Photosystems

The photoproduction of hydrogen fromwater has been shown to be catalysed bya ruthenium melanoidin, a condensation product of amino acids and carbohyd-rates, using wavelengths �320 nm in the presence of EDTA as electron donorand methylviologen as electron relay.14 The reaction rate has been shown to bediffusion controlled and evidence is offered which suggests that an inefficientelectron transfer occurs between the excited melanoidin and the methylviologen.A study has beenmade of the photophysics of a molecular assembly consisting ofcovalently linked metal mesoporphyrin dimers and light-harvesting (LH)-� and-� polypeptides in n-octyl-�--glucopyranoside micelles.15 Highly efficient intra-molecular excitation energy transfer from Zn porphyrin to Ni porphyrin units inthe hybrid was observed with (LH)-�. Water has been found to be efficientlyphoto-oxidised by visible light in the presence of a photosystem comprisingcolloidal IrO2·xH2O stabilised by solubleNafion, [Ru(bipy)3]2�, and persulfate.16


407

Stimulated by the observation that irradiation of Cp�2MoH2 (Cp��5-C5H4Me)dissolved in 3:5 H2O—MeCN leads to the quantitative formation of Cp�2MoOtogether with two equivalents of molecular hydrogen, the possible use of suchmolybdocene complexes as sensitisers in a photochemical water-splitting schemehas been evaluated.17

3 Heterogeneous Photosystems

A mimic for the light-harvesting and energy-conversion steps of photosynthesis,and based on derivatised styrene-p-chloromethylstyrene copolymer [co-PS-CH2NHCO-(Os3Ru13)](PF6)32,Ru-polypyridine has been described.18 Followingvisible light excitation, both energy- and electron-transfer dynamics have beenexamined quantitatively, and these offer valuable insights into mechanisms ofenergy-transport and electron-transfer processes involved in light-to-chemicalenergy conversion. Dihydrogen evolution has been achieved from aqueoussuspensions of platinised titanium dioxide particles containing [Ru(bpy)3]2�,tris(bipyrimidine)Ru(II), and porphines using visible light in the presence ofEDTA as sacrificial electron donor.19 The evolution of dihydrogen has beenobserved to be a maximum at pH 7, and this is interpreted in terms of theadsorption of the dye on the TiO2. Highly donor-doped (110) layered perovskitesloaded with Ni and of the generic composition AmBmO3m�2 (m�4, 5; A�Ca, Sr,La; B�Nb, Ti) are reported as being highly efficient photocatalysts for splittingwater.20 Their high electron density is thought to create a narrower chargedepletion region in the semiconductor and an increased band bending leading tomore efficient hole separation and higher quantum yields.Water in oil emulsions containing Pt/TiO2 have been found to photodecom-

pose on being irradiated to give hydrogen.21 Based upon the effect of addingwater, the conclusion has been reached that the water in the emulsion containingPt/TiO2 is more active than free water in the decomposition reaction to formhydrogen. Addition of sodium carbonate to Pt/TiO2 appears to be useful inaccelerating the splitting of water over a range of semiconductor photocatalystoxides, and the role of CO3

2� in the acceleration process has been clarified.22 Thesame workers also report that a 3 wt% NiOx/TiO2 photocatalyst is effective indecomposing water efficiently and stoichiometrically to give dihydrogen anddioxygen. Photocatalytic hydrogen generation over Pt/TiO2 has been inves-tigated in the presence of oxalic acid as electron donor, revealing that the organicacid substantially promotes the process.23,24 This studymay have implications forthe degradation of pollutants.Measurements of the photocatalytic activity of metal-loaded TiO2 have been

made for dihydrogen evolution from water containing methanol as sacrificialreagent.25 Using 2 wt% platinum as loading material, hydrogen evolutionreached 16.9 mL min�1, whereas with Ru or Rh yields were considerably lower.An eosin Y fixed Pt-TiO2 (E.Y-TiO2) has been constructed and observed to becapable of causing dihydrogen evolution from aqueous triethanolamine solutionunder visible light irradiation for extended periods.26 The turnover number of the

Photochemistry408

dye molecule fixed on the TiO2 surface exceeds 10 000, and the quantum yield ofthe E.Y-TiO2 at 520 nm is about 10%.In the presence of CN� as hole scavenger, hydrogen has been generated from

water by irradiating over NiO/TiO2, and the quantity of hydrogen produced isfound to be proportional to the total amount of CN� in solution.27 It has beensuggested that [Ni(CN)4]2� arises fromNiO/TiO2 and CN�, and that during thephotolysis the complex decomposes with hydrogen evolution. A study has beenreported of the photocatalytic dehydrogenation of propan-2-ol for use in a solarthermal cell.28 Noble metals (Pt, Ru, Rh and Pd) supported on various forms ofTiO2 have been used as catalyst, and a combination of highest activity has beenidentified. The effects of inorganic sacrificial reducing agents and of irradiationwavelength on the photocatalytic production of hydrogen generated by irradiat-ing suspended crystals of InP have been described,29 and photoevolution ofmolecular hydrogen has been observed from aqueous solutions containingK2SO3 and Na2S, using a Ni-doped ZnS photocatalyst of compositionZn0.999Ni0.001S and visible light.30 This process is still effective in the absence ofco-catalysts such as Pt.Mixed crystal powders consisting of Cd, Fe, and S have been examined as

potential catalysts for photochemical generation of hydrogen from water, butonly those of the form CdS/Pt were found to be effective in aqueous sodiumsulfite.31 This has been rationalised in terms of a shift of the onset potential to thepositive and a decrease in the band gap energy. A mechanism based uponconduction band potential and hydrogen evolution potential has been described.Colloidal CdS, stabilised in 1% copolymer (1:1) styrene/maleic anhydride, andcolloidal Pt, obtained in situ by irradiation of K2PtCl6 as redox catalyst, havebeen used to obtain hydrogen from water.32 The system was optimised and theturnover number of the system was calculated. An examination of the photo-catalytic production of hydrogen using CdS suspensions in aqueous solutioncontaining Na2S—Na2SO3 has revealed that the photocatalytic activity of theCdS is dependent upon the salts from which it has been prepared.33 Addition ofPt, Pd, Ag2S or RuO2 each leads to a maximum hydrogen production at adefinite composition, and an attempt has been made to correlate the photo-chemical activity order of the semiconductors with their luminescence proper-ties.High photocatalytic activity has been observed from a layered mixed metal

oxide of composition AMWO6 (A�H and/or alkali metals; M�V, Nb and/orTa).34 This photocatalyst, which has been found to be useful for the photolysis ofwater, may be clathrated in interlayers of the mixed metal oxide, and smallamounts of Pt, Ru, Rh, Ir or Ni and/or NiO also supported on the mixed metaloxide.Water has been successfully split stoichiometrically intomolecular hydro-gen and oxygen by irradiating over K2LnTa5O15 (Ln�La, Pr, Nd, Sm, Gd, Tb,Dy, and Tm) loaded with NiO co-catalysts.35 The lanthanide ions seem to playthe most significant role, with K2PrTa5O15 and K2SmTa5O15 being the mostactive. A system has been devised consisting of zinc tetraphenylporphine(ZnTPP) incorporated into a Nafion membrane coated on a platinum electrode(Pt/Nf[ZnTPP] and which when irradiated (��390 nm) generates a photocur-

IV: Photochemical Aspects of Solar Energy Conversion 409

rent.36 Studies indicate that the primary photochemical process consists of areductive quenching by electron injection from the Pt electrode to the singletexcited ZnTPP forming ZnTPP�, and that this subsequently produces molecu-lar hydrogen by a bimolecular catalysis of the ZnTPP.An investigation has found no evidence for the photosplitting of D2O using a

thin film of copper(I) oxide grown on a Cu(111) crystal, using radiation in therange 1.55—6.21 eV.37 An upper limit of 2�10�21 cm2 for the cross section of thephotoprocess was required. The copper chloride graphite intercalation com-pound (CuCl2-GIC) in the presence of metallic copper powder causes hydrogenproduction when illuminated in aqueous methanolic solution.38 Mechanisticstudies carried out include illumination time, methanol concentration andCuCl2-GIC concentration dependencies of the reaction.

4 Photoelectrochemical Cells

The new photosynthesis type organic solar cell containing the charge separator(1; R�H, lower mercaptoalkoxy, lower mercaptoalkyl; Ar�(un)substitutedphenyl) which incorporates a fullerene derivative as electron acceptor, an elec-tron donor group and a photosensitiser group such that the compound can beanisotropically oriented, has been described.39 A high degree of efficiency isdisplayed by these solar cells. Photo-spectral sensitive controllable cells havebeen constructed using a multi-layered arrangement of organic dyes, and theirphotoelectrical properties have been investigated.40 These cells show high sensi-tivity in the visible range, and this has been accounted for in terms of thefield-dependent and wavelength-dependent quantum efficiency of the organiclayers. Electronic states of intrinsic layers in n-i-p solar cells near the amorphousto microcrystalline silicon transition have been studied by photoluminescencespectroscopy.41 The conclusion is drawn that photoluminescence spectroscopy is

a sensitive tool for characterising the gradual amorphous-to-microcrystallinestructural transition in thin film solar cells. In a study of the effect on solar cellefficiency of rare earth ion complexes, rare earth doped fluorescent glass wasapplied to a-Si and p-Si solar cells.42 Some small improvementwas observed withconcentrated sunlight. A photo-rechargeable battery having both opto-electricconversion and electrochemical energy storage capabilities has been studied inthe case in which it incorporates TiO2/carbon fibre compounds as electrodes.43

Low temperature photoluminescence spectroscopic examination of thin filmpolycrystalline n-CdTe/n-CdS solar cell structures deposited on tin oxide coated

Photochemistry410

glass have been made.44 These show that, for certain annealing temperatures,illuminated current—voltage measurements indicate that considerable improve-ments occur in short circuit c.d., and these are believed to be associatedwith n- top-type conversion of the CdTe film. The same authors have carried out roomtemperature photoluminescence spectroscopic and decay time measurements onCdTe/CdS solar cells, and have found that excitation via the CdTe free surfaceproduces decay curves which consist of a fast and a slow component.45 Of these,the fast component is attributed to non-radiative recombination at grain bound-aries or at the CdT free surface, whereas the slow component is explained interms of carrier drift and diffusion, and subsequent recombination at theCdTe/CdS interface. Solar cells have been described which consist of a CdS filmand a CdTe film formed successively on one side of a transparent glass substrate,and having a membrane of a fluorescent material on the other.46 A time-resolvedphotoluminescence study of the effect of impurities and heat treatment onCdTe/CdS solar cells has appeared,47 and CdS/CdTe solar cells containingfluorescent acrylic plates fixed to the side proximate to the incident light, andincorporating a fluorescent acrylic plate, have been constructed.48 Such cells arereported to be capable of generating light of wavelength�510 nm by absorbingwavelengths �510 nm attached to the other side.A new structure for Si/Si1�cGec solar cells has appeared and the distribution of

photogenerated carriers in the Si-based region and Si1�cGec gradient region forlong-wave radiation has been solved.49 The possibility of designing photo-receivers and solar cells based upon silicon doped by deep impurities such as NiandZn has been discussed,50 and a study has been reported of photorechargeableair batteries which discharge by reducing oxygen in the air, and which arerecharged by the photochemical reaction that occurs at a metalhydride—semiconductor/electrolyte interface.51 In particular, the capabilities of aSrTiO3—LaNi3.76Al1.24HnKOHO2 cell have been examined. Solar cell moduleshaving a fluorescent coating on the light incident side have been described andare claimed to have increased conversion efficiency.52 Photoinduced electrontransfer from an organic dye to semiconductor nanoparticles is the most import-ant process in the functioning of wet solar cells.53 This has been studied using avisible pump/white light probe in the case of coumarin 343 sensitised TiO2

colloidal solution, and allows simultaneous observation of the relaxation of theexcited dye, the injection process of the electron, cooling of the injected electron,and the charge recombination reaction.A new encapsulant material which includes a layer of metallocene poly-

ethylene disposed between two layers of an acid copolymer of polyethylene hasbeen described.54 This material can be used in solar cell module and laminatedglass applications.

5 Biological Systems

The effect of light—dark cycles on photo-hydrogen production by the photosyn-thetic bacterium Rhodobacter sphaeroides RV has been investigated.55 A study


has also been reported of hydrogen production by the photosynthetic bacterialstrains Rhodopseudomonas sp. and Rhodopseudomonas palustris from differentshort-chain organic acids, and in particular of the effect of light intensity whenacetate is used as electron donor.56 Of these strains, Rhodopseudomonas sp. wasfound to produce the greatest volume of hydrogen. The relationship betweenlight wavelength and hydrogen production has been examined for photosyn-thetic bacteria using selective optical filters. The results showed that forwavelengths in the regions 420—480 and 860—960 nm there was effective releaseof hydrogen.57 Production of hydrogen has also been achieved by adding intactcells of Rhodopseudomonas capsulata as photocatalyst using light of ��400 nmto a slurry of naked or sensitised TiO2 semiconductor containingmethylviologenas an electron relay.58 In this process the catalyst may be the nitrogenase enzymeof the bacterial cells. Sensitisation of the TiO2 gives greater hydrogen productionthan naked TiO2, and such sensitisation has been achieved using organic dyes,Cu(II), or with low-band gap semiconductors such as CdS.A new photobioreactor which incorporates whey diluted with water as sub-

strate has been evaluated for hydrogen production, and on sunny days has beenfound to reach a hydrogen production corresponding to a conversion efficiencyfrom sunlight to hydrogen of �2%.59 The outdoor operation of a bioreactorusing photosynthetic bacteria has been monitored, together with the effect of thedark reaction.60 Maximum efficiency (�1%) was achieved using a plane modulephotoreactor with a 3 cm depth. A closed-cycle power plant for solar energyconversion by photosynthesis to electrical energy has been described.61

References

1 M. Kaneko, Taiyo Enerugi, 2000, 26, 2.2 A. Kudo,Kagaku to Kyoiku, 2000, 48, 6.3. T. Markvart, Prog. Quantum Electron., 2000, 24, 107.4. H. Arakawa and K. Sayama, 21-Seiki no Enerugi Gijutsu to Shinzairyo Kaihatsu,

2001, 346.5. M. Hara and K. Domen, Petrotech (Tokyo), 2001, 24, 90.6. M. Yagi and M. Kaneko, Chem. Rev., 2001, 101, 21.7. T. Ishihara and Y. Takita,Mater. Integr., 2001, 14, 13.8. M. Hara and K. Domen,Mater. Integr., 2001, 14, 7.9. H. Imahori, Oyo Butsuri, 2000, 69, 1192.10. W. M. Lewandowski, Gospod. Paliwami Energ., 2000, 48, 6.11. J. Lede, Entropie, 2000, 36, 6.12. M. Mirzabaev, K. Rasulov and R. D. Yusupov, Geliotekhnika, 1999, 8.13. D. Robert, J.-V. Weber and J. Lede, Entropie, 2000, 36, 2.14. A. Serban and A. Nissenbaum, Int. J.Hydrogen Energy, 2000, 25, 733.15. A. Kashiwada, Y. Takeuchi, H. Watanabe, T. Mizuno, H. Yasue, K. Kitagawa, K.

Iida, Z.-Y. Wang, T. Nozawa, H. Kawai, T. Nagamura, Y. Kurono andM. Nango,Tetrahedron Lett., 2000, 41, 2115.

16. M. Hara and T. E. Mallouk, Chem. Commun., 2000, 1903.

Photochemistry412

17. G. T. Baxley, A. A. Avey, T.M. Aukett andD.R. Tyler, Inorg.Chim.Acta, 2000, 300,102.

18. M. Sykora, K. A. Kimberly, J. M. DeSimone and T. J. Meyer, Proc.Natl.Acad. Sci.U. S. A., 2000, 97, 7687.

19. K. Hirano, E Suzuki, A. Ishikawa, T. Moroi, H. Shiroishi and M. Kaneko, J.Photochem. Photobiol., A, 2000, 136, 157.

20. D. W. Hwang, H. G. Kim, J. Kim, K. Y. Cha, Y. G. Kim and J. S. Lee, J. Catal.,2000, 193, 40.

21. T. Miyao, Y. Suzuki and S. Naito, Catal. Lett., 2000, 66, 197.22. H. Arakawa and K. Sayama, Catal. Surv. Jpn., 2000, 4, 75.23. Y. Li, G. Lu and S. Li, Cuihua Xuebao, 2001, 22, 212.24. Y. Li, G. Lu and S. Li, Appl. Catal., A, 2001, 214, 179.25. K. Tomita, J.-i. Kadokawa,M. Karasu andH. Tagaya,Trans.Mater.Res. Soc. Jpn.,

2000, 25, 1147.26. R. Abe, K. Hara, K. Sayama, K. Domen andH. Arakawa, J.Photochem.Photobiol.,

A, 2000, 137, 63.27. S. G. Lee, S. Lee and H.-I. Lee, Appl. Catal., A, 2001, 207, 173.28. M. Ning, Y. Ando, T. Tanaka and T. Takashima, Proc. Intersoc. Energy Convers.

Eng. Conf., 2000, 35th (Vol 1), 405.29. T. Ohmori, H. Mametsuka and E. Suzuki, Int. J.Hydrogen Energy, 2000, 25, 953.30. A. Kudo and M. Sekizawa, Chem. Commun., 2000, 1371.31. C. Cho, S. Park and H. Kim, Bull. Korean Chem. Soc., 2000, 21, 805.32. T. Oncescu, M. Contineanu and L. Meahcov, Int. J. Photoenergy, 1999, 1, 75.33. G. C. De and A. M. Roy, J. Surf. Sci. Technol., 1999, 15, 147.34. T. Sato and M. Ishizuka, Jpn.Kokai Tokkyo Koho JP 2000 189,806.35. A. Kudo, H. Okutomi and H. Kato, Chem. Lett., 2000, 1212.36. T. Abe, H. Imaya, M. Endo and M. Kaneko, Polym. Adv. Technol., 2000, 11, 167.37. A. V. Walker and T. Yates, J. Phys. Chem. B, 2000, 104, 9038.38. Y. Ohnishi, K. Kuroda, K. Ikeuchi, Y. Hamada, I. Izumi and N. Iwashita, Denki,

Kagakkai Gijutsu, Kyoiku Kenkyu Ronbunshi, 2000, 9, 47.39. H. Imahori, Y. Nakajima, S. Ozawa, S. Sakata and K. Ushida, Jpn.Kokai Tokkyo

Koho JP 2000 261,016.40. M. Iizuka, K. Kudo, S. Kuniyoshi and K. Tanaka, Synth.Met., 2000, 115, 181.41. G. Yue, D. Han, D. L. Williamson, J. Yang, K. Lord and S. Guha,Appl.Phys. Lett.,

2000, 77, 3185.42. K. Yamada, Y. Wada and K. Kawano,Kidorui, 2000, 36, 252.43. X. Zou, N. Maesako, T. Nomiyama, Y. Horie and T. Miyazaki, Sol. Energy Mater.

Sol. Cells, 2000, 62, 133.44. C. J. Bridge, P. Dawson, P. D. Buckle and M. E. Ozsan, Semicond. Sci. Technol.,

2000, 15, 975.45. C. J. Bridge, P. Dawson, P. D. Buckle and M. E. Ozsan, J. Appl. Phys., 2000, 88,

6451.46. Y. Ogawa and T. Maruyama, Jpn.Kokai Tokkyo Koho JP 2001 94,129.47. D. P. Halliday,M.D. G. Potter and P. Dawson,Conf.Rec. IEEEPhotovoltaic Spec.

Conf., 2000, 28th, 521.48. T. Maruyama, Jpn.Kokai Tokkyo Koho JP 2. 001, 111,091.49. C.-h. Li, Y.-w. Zhao, X.-m. Li, F.-y. Wang, Y.-t. Wang, X.-b. Yan and W. Lu,

Bandaoti Xuebao, 2000, 21, 1122.50. B. M. Abdurakhmano, I. V. Drachuk, V. I. Shopen and Sh. K. Akbarov, Uzb. J.

Phys., 2000, 2, 73.


51. K. Akuto and Y. Sakurai, J. Electrochem. Soc., 2001, 148, A121.52. T. Maruyama, Jpn.Kokai Tokkyo Koho JP 2001 07,377.53. J. Wachtveitl, R. Huber, S. Sporlein, J. E. Moser and M. Gratzel, Int. J. Photo-

energy, 1999, 1, 153.54. J. I. Hanoka and P. P. Klemchuk,U.S. US 6,187,448.55. T. Wakayama, A. Toriyama, T. Kawasugi, Y. Asada and J. Miyake, Photosynth.:

Mech. Eff., Proc. Int. Congr. Photosynth., 11th, 1998, 5, 4135, ed. G. Garab, KluwerAcademic Publishers: Dordrecht, Netherlands.

56. M. J. Barbosa, J. M. S. Rocha, J. Tramper and R. H. Wijffels, J. Biotechnol., 2001,85, 25.

57. E. Nakada, S. Nishikata, Y. Asada and J.Miyake,Photosynth.:Mech. Eff.,Proc. Int.Congr. Photosynth., 11th, 1998, 5, 4139, ed. G. Garab, Kluwer Academic Publishers:Dordrecht, Netherlands.

58. K. Gurunathan, J.Mol. Catal. A: Chem., 2000, 156, 59.59. M. Modigell and N. Holle, Hydrogen Energy Prog. XII, Proc. World Hydrogen

Energy Conf., 12th, 1998, 3, 2045, ed. J. C. Bolcich and T. N. Veziroglu.60. Y. Kitajima, S. Otsuka, Y. Ueno, S. Kawasaki andM.Morimoto,Hydrogen Energy

Prog. XII,Proc.WorldHydrogen Energy Conf., 12th, 1998, 3, 2025, ed. J. C. Bolcichand T. N. Veziroglu.

61. E. Yantovsky, PCT Int. Appl. WO 00 57,105.

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