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Synthesis and Optoelectronic Propertiesof Some New ThiahelicenesSouad Moussa a , Faouzi Aloui a & Béchir Ben Hassine aa Laboratoire de Synthèse Organique Asymétrique et CatalyseHomogène, Faculté des Sciences , Monastir , TunisiaPublished online: 03 Mar 2011.

To cite this article: Souad Moussa , Faouzi Aloui & Béchir Ben Hassine (2011) Synthesis andOptoelectronic Properties of Some New Thiahelicenes, Synthetic Communications: An InternationalJournal for Rapid Communication of Synthetic Organic Chemistry, 41:7, 1006-1016, DOI:10.1080/00397911003707220

To link to this article: http://dx.doi.org/10.1080/00397911003707220

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SYNTHESIS AND OPTOELECTRONIC PROPERTIES OFSOME NEW THIAHELICENES

Souad Moussa, Faouzi Aloui, and Bechir Ben HassineLaboratoire de Synthese Organique Asymetrique et Catalyse Homogene,Faculte des Sciences, Monastir, Tunisia

GRAPHICAL ABSTRACT

Abstract New symmetrical helically chiral penta- and heptacyclic aromatic systems con-

taining two thiophene rings have been prepared, in good yields, under mild conditions using

a photochemical route. Optoelectronic properties of these helically aromatic thia-systems

were determined and exhibit interesting behavior.

Keywords Helicenes; optoelectronic properties; photodehydrocyclization; thiahelicenes;

Wittig reaction

INTRODUCTION

Helicenes represent a class of helically chiral aromatic molecules in which theextra ortho-condensed rings give rise to a regular cylindrical helix because of therepulsive steric overlap of the terminal aromatic nuclei. These shaped molecules havegained considerable interest thanks to their chiroptical and nonlinear optical proper-ties.[1,2] They have been considered as new, potentially useful systems in chiral disco-tic liquid-crystalline materials,[3] as building blocks for helical conjugatedpolymers,[4,5] and as rotors.[6,7] Furthermore, enantiomerically enriched helicenes

Received January 30, 2010.

Address correspondence to Bechir Ben Hassine, Laboratoire de Synthese Organique Asymetrique

et Catalyse Homogene (01UR1201), Faculte des Sciences, Avenue de l’environnement, 5019 Monastir,

Tunisia. E-mail: bechirbenhassine@yahoo.fr

Synthetic Communications1, 41: 1006–1016, 2011

Copyright # Taylor & Francis Group, LLC

ISSN: 0039-7911 print=1532-2432 online

DOI: 10.1080/00397911003707220

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have been used as helical ligands,[8,9] structures that act as catalysts[10] for enantio-selective transformations, and asymmetric inducers.[11,12]

Heterohelicenes,[13–15] in particular, are very interesting helical-shaped aro-matic systems that possess great potential to develop new materials. They are suit-able building blocks for organic materials with extraordinarily strong chiropticaland optoelectronic properties.[16] Thiahelicenes, for example, combine the electronicproperties afforded by their extensive p-conjugated system with the chiropticalproperties associated with their helical structure,[17] resulting from the ortho-conden-sation of benzene and thiophene rings. These helically chiral molecules exhibit a highelectron affinity and a high thermal stability and could serve as promisingelectron-transport (n-type) materials for organic light-emitting diodes (OLEDs). Inthis context, the development of new hetero-helicenes and the further study of theunderlying structure–property relationships presented an interesting challenge.

In this article, we report the synthesis and characterization of new thiahelicenessuch as 2,11-dithiapentahelicene, 3,10-dithiapentahelicene, 2,15-dithiaheptahelicene,and 3,14-dithiaheptahelicene. The optoelectronic properties[18] of these compoundswere also investigated.

RESULTS AND DISCUSSION

The synthetic route followed to obtain the thiahelicenes started from the syn-thesis of 1,2-disubstituted alkenes, which are obtained through the Wittig reactionfrom the appropriate thiophene carbaldehyde and the suitable bisphosphonium salt.The resulting alkene is then converted into the corresponding helically chiralthia-system by photolysis.

Scheme 1 shows our general synthetic strategy to prepare the helical pentacyc-lic thia-system 1a, which is based on a three-step reaction sequence. The synthesisstarted from the bisphosphonium salt 2, which was easily prepared on a large scalefrom a,a0-dichloro-p-xylene and triphenylphosphine in refluxing dimethylformanide(DMF). The bis(triphenylphosnium) salt 2 was smoothly produced by a doublenucleophilic reaction. The latter compound and 3-thiophene carbaldehyde were

Scheme 1. Synthetic strategy for the synthesis of helically chiral pentacyclic systems 1a and 1b.

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subjected to a double Wittig olefination procedure leading to the bis(stilbene)-typederivative 3a in 74% yield. The mixture gave rise to a violet fluorescent aspect in sol-ution. To complete the synthesis of the helicene skeleton, alkenes 3a underwent adouble photocyclization, in dilute solution, in the presence of a stoichiometricamount of iodine and an excess of propylene oxide.[19] The photolysis was performedon a 200-mg scale per run in a 1-L reactor for about 5 h, to afford the expected2,11-dithiapentahelicene 1a in 44% yield after purification by column chromato-graphy. The relatively moderate yield of 44% for 1a is perhaps a consequence ofthe unfavorable solubility properties of alkenes 3a in toluene, necessitating theiruse as suspensions. No other isomer was isolated from the reaction mixture, indicat-ing that the ring closure of 3a had occurred from the opposite side of the benzenering (Scheme 1).

Utilizing similar conditions to those described for the preparation of 1a, thesynthesis of compound 1b was attempted by the reaction of bisphosphonium salt2 with 2-thiophene carbaldehyde followed by a photocylization reaction(Scheme 1). However, 1b was isolated in 60% yield after column chromatographyand fully characterized by NMR and mass spectrometry. This result can beexplained by the higher solubility of alkenes 3b compared to alkenes 3a.

Following this synthetic approach, it was possible to prepare two thiahelicenederivatives, namely 2,15- and 3,14-dithiaheptahelicenes. The second syntheticapproach may appear longer, because it was necessary to prepare the startingbisphosphonium salt 4 (Scheme 2) on a gram scale in a four-step sequence involvinga Wittig reaction between p-methylbenzaldehyde and the phosphonium salt derivedfrom p-methylbenzyl chloride, leading to 4,40-dimethylstilbene 5 in 94% yield.Alkenes 5 were then irradiated using a 500-W high-pressure mercury immersionlamp on a 800-mg scale to afford 3,6-dimethylphenanthrene 6 in 90% yield. Thephenanthrene derivative was converted into its dibromide 7 through a doublebenzylic bromination with N-bromosuccinimide (NBS) followed by a treatment withtriphenylphosphine in refluxing acetonitrile, which provided the bisphosphoniumsalt 4, as a white solid, in 96% yield and an overall 64% yield.

Scheme 2. Synthetic pathway of bisphosphonium salt 4.

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The salt 4 was subjected to a double Wittig reaction with either 3- or 2-thiophene carbaldehyde leading to the corresponding bis(stilbene)-type derivatives8a and 8b in 75% and 65% yields, respectively (Scheme 3). The last step of the wholesynthetic strategy is the formation of the chiral heptacyclic systems. Thus, the pho-tolysis of 8a carried out in toluene for about 7 h, on a 200-mg scale, afforded theexpected 2,15-dithiaheptahelicene 9a in 60% yield and an overall 26% yield over

Scheme 3. Synthetic strategy for the synthesis of helically chiral heptacyclic systems 9a and 9b.

Figure 1. (a) 1H NMR and (b) 13C NMR spectra of 9b in CDCl3.

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six steps. On the other hand, the photocyclization of alkenes 8b conducted in thesame conditions gave only 40% yield of 3,14-dithiaheptahelicene 9b.

3,14-Dithiaheptahelicene 9b is a light yellow solid. It shows a violet fluores-cence when dissolved. It is characterized by 1H and 13C NMR spectroscopy.Figure 1 shows the two NMR spectra.

Optical Properties

The ultraviolet (UV)–visible absorption spectra of the four dithia-helicallychiral systems 1a, 1b, 9a, and 9b have been recorded with a Hach-Lang-DR50000spectrometer, in chloroform (10�5M). The lowest energy absorption bands belongto the p–p� transitions.

Dithiapentaheicenes 1a and 1b have different absorption maxima (kAbsmax) at 246

and 263 nm, respectively. However, in the case of 2,15-dithiaheptahelicene 9a and3,14-dithiaheptahelicene 9b, the absorption kAbs

max corresponds to 267 and 271 nm,respectively.

Optical band gaps (EOpt) determined from the absorption edge of the solutionspectra are given in Table 1. The optical band gap varies from 3.05 eV (compound9b) to 3.40 eV (compound 1a, Table 1). The gap energy was evaluated by the extra-polation of the tangent to the first inflexion point in the UV curve.[20]

The UV-visible absorption spectrum of 3,14-dithiaheptahelicene 9b is shown inFig. 2. The sample shows a strong absorption below 400 nm (3.05 eV) with awell-defined absorbance peak at around 271 nm (4.67 eV). The band gap can bedetermined by fitting the absorption data to the direct transition equation by anextrapolation of the linear portions of the curves to absorption equal to zero (Fig. 2):

Eg ¼ hn

where hn is the photon energy and Eg is the direct band gap determined byUV-visible spectroscopy. The estimated band gap of compound 9b is found to be3.05 eV.

It can be seen that the increase in conjugation length and the increased elec-tronic density in hepta systems leads to a large bathochromic shift of an absorptionmaximum, compared to pentacyclic systems.

In summary, four new symmetrical helically chiral aromatic compounds havingbenzothiophene units were synthesized in good overall yields starting from readilyavailable and inexpensive materials. Among these new thiahelicenes, 3,14-dithiahep-tahelicene showed the lowest band gap (3.05 eV) and the largest wavelength

Table 1. Physical properties of helically chiral dithia-helicenes 1a, 1b, 9a, and 9b

Compound kAbsmax (nm) EOpt (eV)

1a 246 3.40

1b 263 3.35

9a 267 3.20

9b 271 3.05

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(271 nm). These new dithiahelicenes may also serve as model systems to investigatethe structure–property relationships with respect to the electronic, electrochemical,photoconductive, and nonlinear optical properties of p-conjugated polymers.

EXPERIMENTAL

All reactions were performed under an argon atmosphere and were monitoredby thin-layer chromatography (TLC) Merck 60F-254 silica-gel plates (layer thick-ness 0.25mm). Column chromatography was performed on silica gel (70–230 mesh)using ethyl acetate and cyclohexane mixture as eluents. Melting temperatures weredetermined on an Electrothermal 9002 apparatus and were reported uncorrected.NMR spectra were recorded on a Bruker AC-300 spectrometer at 300MHz (1H)and 75MHz (13C). All chemical shifts were reported as d values (ppm) relative tointernal tetramethylsilane. Toluene was distilled from sodium prior to use. Photocy-clizations were carried out in a 1.5-L water-cooled quartz photoreactor equippedwith a high-pressure mercury immersion lamp [Heraeus TQ 500]. Mass spectra(MS) were recorded on a Hewlett-Packard HP 5989 instrument. High-resolutionmass spectra (HRMS) were recorded on a matrix-assisted laser desorption=ionization time-of-flight (MALDI-TOF) Perspective Biosystems Voyager DE-STRinstrument.

General Procedure A for Wittig Reaction

Sodium methoxide (1M in methanol) was added over 0.5 h under Ar to arefluxing solution of triphenylphosphonium salt and the corresponding aldehydein dry methanol (25mL). Heating at reflux was continued for 3 h. The reactionmixture was cooled to room temperature and concentrated under vaccum to halfits volume. Water was added, and the solution was extracted many times with a large

Figure 2. Room-temperature optical absorbance spectrum of 3,14-dithiaheptahelicene 9b.

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volume of CH2Cl2. After drying and solvent evacuation, the residue was chromato-graphed on silica gel. Solvents, yield, melting points, and data for individualcompounds are reported for each case.

General Procedure B for the Photocyclodehydrogenation Reaction

A solution (or a suspension in the cases of 3a and 8b) of the respective bis(stil-bene) (1 equiv), iodine (1.2 equiv), and propylene oxide (100 equiv) in toluene (1.5 L)was irradiated for 5–7 h, under Ar, in a photoreactor fitted with a water-cooledimmersion well and a high-pressure Hg lamp. Evaporation of the solvent and col-umn chromatography (SiO2) yielded the pure racemic helicene. Experimental detailsand specific data for individual compounds are given.

Bisphosphonium Salt (2)

Compound 2 was prepared from a,a0-dichloro-p-xylene (2 g, 11.4mmol) andtriphenylphosphine (6.62 g, 25.21mmol) in boiling dimethylformamide (DMF,35mL). The bisphosphonium salt was precipitated and filtered off at the end ofthe reaction. Compound 2 was obtained as a white solid in 95% yield, mp> 300 �C(decomposed), and was used directly without further purification. 1H NMR(300MHz, CDCl3): d¼ 5.38 (d, JH-P¼ 13.2Hz, 4H, 2 CH2-P), 6.94 (s, 4H),7.66–7.75 (m, 30H) ppm;13C NMR (75MHz, CDCl3): d¼ 29.8 (d, JC-P¼ 46.2Hz,2CH2-P), 117.07–134.99 (21C) ppm; 31P NMR (121.5MHz, CDCl3): d¼ 24.47(s) ppm.

Bis-stilbene-Type Derivatives (3a)

Compounds 3a [(E, Z) isomers] were obtained from the bisphosphonium salt 2(5 g, 6.34mmol) and 3-thiophene carbaldehyde (1mL, 11.4mmol) in 74% yield(2.45 g) according to procedure A. They were purified by column chromatographyusing cyclohexane=ethyl acetate (90:10) as the eluent. 1H NMR (300MHz, CDCl3):d¼ 6.55 (d, J¼ 16.2Hz, 2H); 6.94 (d, J¼ 16.2Hz, 2H), 7.15 (d, J¼ 6.6Hz, 2H), 7.33(d, J¼ 6.6Hz, 2H), 7.34–7.60 (m, 6H) ppm;13C NMR (75MHz, CDCl3): d¼ 122.47,122.88, 124.18, 124.45, 124.94, 125.03, 126.20, 126.29, 128.08, 128.34, 129.20, 129.26,136.31, 136.95, 138.35, 140.17 ppm; MS (EI, 50 ev): m=z¼ 294 ([M]þ, 65%).

2,11-Dithiapentahelicene (1a)

Compound 1a was obtained from alkenes 3a, in 44% yield, according to theprocedure B. It was purified by column chromatography using cyclohexane as theeluent (Rf¼ 0.41) and resulted as a light yellow solid, mp 50–52 �C. 1H NMR(300MHz, CDCl3): d¼ 7.85 (d, J¼ 9Hz, 2H), 7.91 (d, J¼ 8.7Hz, 2H), 8.00–8.13(m, 4H), 8.73 (s, 2H) ppm; 13C NMR (75MHz, CDCl3): d¼ 119.79, 122.03,126.28, 128.40, 129.05, 129.50, 135.53, 136.32, 137.49 ppm; ESI-MS: m=z¼ 313.0[MþNa]þ. HRMS (MALDI-TOF) calcd. for C18H10S2Na [MþNa]þ: 313.0121.Found: 313.0135.

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Bis-stilbene-Type Derivatives (3b)

Compound 3b was obtained from 2 (1 g, 1.26mmol) and 2-thiophene carbalde-hyde (215 mL, 2.30mmol) in 78% yield according to the procedure A. It was purifiedby column chromatography using cyclohexane=ethyl acetate (98:2) as the eluent.White solid, mp 149–151 �C. 1H NMR (300MHz, CDCl3): d¼ 6.58 (d, J¼ 11.7Hz,Hz, 2H), 6.7 (d, J¼ 11.7Hz, 2H), 6.9 (dd, J¼ 4.8 and 3.9Hz, 2H), 7.01 (d, J¼ 3Hz,2H), 7.15 (d, J¼ 4.8Hz, 2H), 7.36 (s, 4H) ppm;13C NMR (75MHz, CDCl3):d¼ 123.48, 125.52, 126.27, 126.56, 129.26, 129.48, 136.65, 139.84 ppm; MS (EI,50 ev): m=z¼ 294 ([M]þ, 70%).

3,10-Dithiapentahelicene (1b)

Compound 1b was obtained from 3b as a light yellow solid, in 60% yield,according to procedure B. It was purified by column chromatography using cyclo-hexane as the eluent (Rf¼ 0.41), mp¼ 25–27 �C. 1H NMR (300MHz, CDCl3):d¼ 7.71 (d, J¼ 8.7Hz, 2H), 7.83 (d, J¼ 8.4Hz, 2H), 7.86 (d, J¼ 5.1Hz, 2H), 7.98(d, J¼ 5.4Hz, 2H), 8.13 (s, 2H) ppm; 13C NMR (75MHz, CDCl3) d¼ 119.79,125.52, 126.90, 127.33, 129.05, 129.50, 135.53, 136.32, 137.49 ppm; ESI-MS: m=z¼313.0 [MþNa]þ, HRMS (MALDI-TOF) calcd. for C18H10S2Na [MþNa]þ:313.0121. Found: 313.0139.

Bisphosphonium Salt (4)

The compound was prepared from 3,6-bis(bromomethyl)phenanthrene 7 (3 g,8.24mmol) and triphenylphosphine (4.75 g, 18.10mmol) in boiling acetonitrile(60mL). The bisphosphonium salt precipitated after cooling at room temperatureand was filtered off. Compound 4 was obtained as a white solid in 96% yield, mp300–302 �C. 1H NMR (300MHz, CD3OD): d¼ 5.24 (d, JH-P¼ 15Hz, 4H, 2CH2-P), 7.11–7.14 (m, 2H), 7.64–7.70 (m, 26H), 7.81–7.91 (m, 8H), 8.32 (s, 2H) ppm;13C NMR (300MHz, CD3OD): d¼ 31.87 (d, JC-P¼ 47.4Hz, 2CH2-P), 119.01,120.15, 127.70, 127.80, 127.92, 128.04, 128.87, 130.34, 130.82, 131.48, 131.78,131.95, 133.74, 135.88, 136.01, 136.88, 136.92, 136.93 ppm;31P NMR (121.5MHz,CD3OD): d¼ 23.70 (s) ppm.

4,4’-Dimethylstilbene (5)

4,40-Dimethylstilbene 5 [(E,Z) isomers] was prepared in 94% yield, fromp-methylbenzaldehyde (2 g, 16.65mmol) and tolylmethyltriphenylphosphoniumchloride (7.37 g, 18.30mmol), according to procedure A. It was purified by columnchromatography using cyclohexane=ethyl acetate (98:2) as the eluent and resultedas a white solid, mp 165–167 �C. 1H NMR (300MHz, CDCl3): d¼ 2.37 (s, 6H,2CH3), 7.05 (s, 2H), 7.17 (m, 4H), 7.42 (m, 4H) ppm; 13C NMR (75MHz, CDCl3):d¼ 21.30, 126.36, 127.68, 129.42, 134.78, 137.33 ppm; MS (EI, 70 ev): m=z¼ 208([M]þ, 78%).

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3,6-Dimethylphenanthrene (6)

The photolysis of 4,40-dimethylstilbene 5 according to procedure B gave3,6-dimethylphenanthrene 6 as a white solid in 60% yield. 1H NMR (300MHz,CDCl3): d¼ 2.63 (s, 6H), 6.97 (d, J¼ 8.1Hz, 2H), 7.65 (s, 2H), 7.77 (d, J¼ 8Hz,2H), 8.48 (s, 2H) ppm; 13C NMR (75MHz, CDCl3): d¼ 22.17, 122.41, 125.82,128.20, 128.68, 129.17, 130.12, 136.06 ppm; MS (EI, 70 ev): m=z¼ 206 ([M]þ, 75%).

3,6-Bis(Bromomethyl)phenanthrene (7)

3,6-Dimethylphenanthrene (5.0 g, 24.27mmol), N-bromosuccinimide (8.64 g,48.54mmol), and benzoylperoxide (0.011 g, 0.48mmol) were dissolved in 20mL ofanhydrous carbon tetrachloride under a nitrogen atmosphere. The mixture wasrefluxed with a vigorous stirring at 80 �C for 24 h under nitrogen and then cooledto room temperature. The succinimide produced was filtered out with suction, andwater (25mL) was added to the filtrate, which was extracted three times with diethylether (60mL). The organic layer was washed successively with saturated aqueoussodium bicarbonate (30mL) and sodium chloride solution (30mL) and dried withanhydrous potassium carbonate. After the evaporation of the solvent, the resultingcrude residue was purified by column chromatography with cyclohexane=ethyl acet-ate (98:2) as the eluent to yield 8.45 g (80% yield) of 7; mp¼ 142–144 �C. 1H NMR(300MHz, CDCl3): d¼ 4.84 (s, 4H, 2CH2-Br), 7.72 (dd, J¼ 8.4 and 1.5Hz, 2H), 7.83(s, 2H), 7.96 (dd, J¼ 8.4 and 1.5Hz, 2H), 8.74 (d, J¼ 1.2Hz, 2H) ppm; 13C NMR(75MHz, CDCl3): d¼ 33.87 (2CH2-Br), 113.85–138.12 (14Carom.) ppm; MS (EI,70 ev): m=z¼ 364 ([M]þ, 68%).

Bis-stilbene-Type Derivatives (8a)

Bis-stilbene-type derivatives 8a [(E,Z) isomers] were prepared frombisphosphonium salt 4 (2 g, 2.24mmol) and 3-thiophene carbaldehyde (360 mL,0.45mmol), in 75% yield, according to procedure A. 1H NMR (300MHz, CDCl3):d¼ 6.68–7.56 (m, 5H), 7.61–7.91 (m, 9H), 8.47–8.82 (m, 4H) ppm;13C NMR(75MHz, CDCl3): d (ppm): 121.40, 121.52, 122.11, 122.28, 122.46, 122.54, 123.11,123.24, 123.76, 123.88, 124.08, 124.51, 124.61, 125.70, 125.81, 126.33, 126.33,126.53, 126.65, 126.87, 126.93, 127.00, 172.26, 127.47, 127.64, 127.78, 128.48,128.53, 128.74, 128.87, 129.00, 129.26, 130.15, 130.36, 130.57, 131.61, 131.82,134.96, 135.26 ppm; ESI-MS: m=z¼ 417.0 [MþNa]þ.

2,16-Dithiahepthahelicene (9a)

The photolysis of the bis-stilbene-type derivatives 8a according to procedure Bgave 2,16-dithiahepthahelicene 9a as a light yellow solid in 60% yield; mp139–141 �C. 1H NMR (300MHz, CDCl3): d¼ 7.15 (s, 2H), 7.20–7.49 (m, 6H),7.70 (s, 2H), 7.83 (d, J¼ 8.1Hz, 2H), 8.53 (s, 2H) ppm; 13C NMR (75MHz, CDCl3):d¼ 122.81, 126.22, 127.28, 128.33, 128.60, 128.81, 129.17, 129.27, 129.60, 130.43,130.50, 130.57, 136.43 ppm; ESI-MS: m=z¼ 413.0 [MþNa]þ. HRMS(MALDI-TOF) calcd. for C26H14NaS2 [MþNa]þ: 413.04346. Found 413.04487.

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Bis-stilbene-Type Derivatives (8b)

Bis-stilbene-type derivatives 8b were prepared from bisphosphonium salt 4 (1 g,1.12mmol) and 2-thiophene carbaldehyde (200 mL, 1.02mmol) according to pro-cedure A. Workup and purification on column chromatography yielded 65% of ayellow solid [(E,Z) isomers of 8b]. 1H NMR (300MHz, CDCl3): d¼ 6.76–7.28 (m,8H), 7.38–7.88 (m, 8H), 8.39–8.78 (m, 2H) ppm;13C NMR (75MHz, CDCl3):d¼ 121.40, 121.52, 122.11, 122.28, 122.46, 122.54, 123.11, 123.24, 123.76, 123.88,124.09, 142.51, 124.61, 125.70, 125.81, 126.33, 126,53, 126.65, 126.87, 126.93,127.00, 127.26, 127.47, 127.64, 127.78, 128.48, 128.53, 128.74, 128.87, 129.00,129.26, 130.15, 130.36, 130.57, 131.61, 131.82, 134.96, 135.26, 135.58, 136.45 ppm;ESI-MS: m=z¼ 417.0 [MþNa]þ.

3,14-Dithiahepthahelicene (9b)

The photolysis of bis-stilbene-type derivatives 8b according to procedure Bgave 3,14-dithiahepthahelicene 9b as a light yellow solid in 60% yield; mp229–231 �C. 1H NMR (300MHz, CDCl3): d¼ 6.24 (d, J¼ 5.4Hz, 2H); 6.60 (d,J¼ 5.4Hz, 2H), 7.85–7.91 (m, 4H), 7.99 (d, J¼ 8.4Hz, 2H), 8.06 (s, 2H), 8.08 (d,J¼ 8.4Hz, 2H) ppm; 13C NMR (75MHz, CDCl3): d¼ 121.34, 122.93, 124.06,124.56, 125.03, 125,35, 127.00, 127.75, 127.86, 129.79, 132.15, 135.23, 135.90 ppm;ESI-MS: m=z¼ 413.0 [MþNa]þ. HRMS (MALDI-TOF) calcd. for C26H14NaS2[MþNa]þ: 413.04346. Found 413.04479.

ACKNOWLEDGMENT

The authors are grateful to DGRSRT (Direction Generale de la RechercheScientifique et de la Renovation Technologique) of the Tunisian Ministry of HigherEducation, Scientific Research, and Technology for the financial support.

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