Katsuki OkunoMiyasaka Laboratory

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IntroductionDefinitionExample of Photochromic MoleculesHistory

Recent researchPhotochromism in single crystalShape change of photochromic crystalFluorescence switching by photochromic reaction

Research with LasersObservation of reaction dynamicsControl chemical reaction by laser

What I am going to study Future Prospects in Photochromism

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Original Definition of PhotochromismPhenomenon that color of material is changed bylight irradiation.

photo(light) + chrom(color) + ism(phenomenon)

Similar phenomena・ Thermochromism color is changed by changing temperature・ Electrochromism color is changed by gain or loss of electron・ Solvatochromism color is changed by changing polarity of

solvent 3

Definition of Molecular PhotochromismReversible isomerization between two isomers having different absorption spectra, which is induced in at least one direction by light irradiation.

A and B have an equal molecular weightbut have different structures.A B

h

h’ or

UV light

Vis. light

Example (diarylethene in solution)

S S

F2

F2 F2

S S

F2

F2 F2

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Azobenzene

Spiropyran / Spirooxazine

Fulgide

DiaryletheneN N

Cl N N

Cl N N

Cl NN

Cl

h

HABI

T-type P-type 5

(Hexaarylbiimidazole)

Application

Basic

Quick property change•Absoption spectra•Refractive indices•Dielectric constants•Redox potential•Structure

etc.

Rewritable paperPhoto-memoriesPhoto-switchesPhoto-driven actuator

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Application

Time origin of reaction is easily determined

time-resolved detection of precise reaction profiles

1867 First discovery of photochromism (M. Fritsche, Comp. Rend. 1867, 69, 1035.)

1905 Discovery of fulgide (H. Stobbe, Ber. 1905, 38, 3673.)

1937 Discovery of azobenzene (G. S. Hartley, Nature 1937, 140, 281.)

1952 Discovery of spiropyran (E. Fischer, Y. Hirshberg, J. Chem. Soc. 1952, 4522.)

1960 Discovery of HABI (Japan) (T. Hayashi, K. Maeda, Bull. Chem. Soc. Jpn. 1960, 33, 565.)

1967 Discovery of spirooxazine (Japan) (Fuji Film)

1988 Discovery of diarylethene (Japan) (M. Irie, M. Mohri, J. Org. Chem. 1988, 53, 803.)

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UV light

Vis. light

Digital switching

T. Fukaminato, M. Irie et al., Nature, 420 (2002) 759.T. Fukaminato, M. Irie et al., J. AM. CHEM. SOC. 126, (2004) 14843.

fluorescent non-fluorescent

8→ Single-molecular photo-memory/switch

S S

F2

F2 F2

S S

F2

F2 F2

UV

Vis.

Open form(colorless)

Closed form (blue)

S. Kobatake and M. Irie, Science, 291 (2001) 1769.

AFM image of surface of diarylethene single crystal

UV Vis

UV Vis

Photochromic reaction occurs in crystalline phase

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S. Kobatake, M. Irie et al, Nature, 446 (2007) 778.10

Changing of crystalline shape isinduced by photochromic reaction

Energy of light is directlyconverted into mechanical energy“Photo-driven mesoscopic actuator”

UV

Vis

Open-form Closed-form

t

sample

photo detectorpump pulse

monitor pulse

Timet=0

pump pulse monitor pulse

observe spectra at various delay time t

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S1

S0

h

isomerization

Excited state(S1) have limited life timeIsomerization occurs in competition with ・ radiative transition (fluorescence and phosphorescence) ・ nonradiative transition (internal conversion and intersystem crossing)

Measurement of reaction dynamicsRevealing reaction mechanismDetermination of rate constantRevealing the factors determining reaction rate

→ Rational principle for development of advanced molecule12

Steady-state Xe lampAt 532 nm0.05 mW

1 mm2

PS 532 nm irradiation4.2 mJ / mm2 2 shots

5 min. 3.75 mJ / mm2 10 min. 7.5 mJ / mm2

20 min. 15 mJ / mm2 5,10,20 min.

in PMMA matrices

S S

F2

F2 F2

S S

F2

F2 F2

UV

Vis.

colorlessblue

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S S

F2

F2 F2

S S

F2

F2 F2

Vis.

OCH3

CH3O CH3O

OCH3

H3C CH3 H3C CH3

Cycloreversion reaction yield : 10-5

When used as optical memory Data writing → UV light Data reading → weak visible light Data deleting → strong visible light

Cycloreversion reaction is more than 2500 times enchanced by 15-ps 532-nm laser pulse excitation.

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Open form

UV one-photonabsorption process

266 nm

×532 nm

Large reaction yield

S1

Sn

532 nm

visible two-photon absorption process

Open form Closed form

J. Am. Chem. Soc., 123 (2001) 753, J. Am. Chem. Soc, 126 (2004) 14764J. Phys. Chem. C, 111 (2007) 2730, J. Phys. Org. Chem., 20 (2007) 953, J. Phys. Chem. C, 112 (2008) 11150.Phys. Chem. Chem. Phys, 11 (2009) 2640, New. J. Chem. 33 (2009) 1409, Photochem. Photobiol. Sci., 9 (2010) 172. 15

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pump pulse

monitor pulse

repump/dump pulse

photo detector

S0

Sn

S1

Property of higherexcited state

Role of excessvibrational energy?

?

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0.0 0.5 1.0 1.5 2.0

0.00

0.01

0.02

0.03

0.04 Probed at 710 nm

Ab

sorb

an

ce

Time / ps

Graund state

S0

Sn

S1

1. Application of molecular photochromic reaction into control of bulk and surface properties.

ex. hydrophilicity/hydrophobility2. More effective and rapid response photo-actuator;

direct change of photo-energy into mechanical force3. New photochromic molecular system with nonlinear

and threshold function.4. Revealing the reaction dynamics; intramolecular

vibration, nonradiative transition and symmetry of electronic state

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