Photochromism in Organic Molecules

1. Photochromism in Organic Molecules Katsuki Okuno Miyasaka Laboratory

2. Contents • IntroductionDefinition Example of Photochromic Molecules History • Recent researchPhotochromism in single crystal Shape change of photochromic crystal Fluorescence switching by photochromic reaction • Research with LasersObservation of reaction dynamics Control chemical reaction by laser • What I am going to study • Future Prospects in Photochromism

3. Definition • 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

4. Definition • 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 weight but have different structures. A B hn Example (diarylethene in solution) hn’ orD UV light Vis. light

5. Example of Photochromic Molecules Azobenzene Fulgide Spiropyran / Spirooxazine Diarylethene HABI (Hexaarylbiimidazole) T-type P-type

6. Application and Basic Aspect of Photochromism • Application Quick property change Application • Absoption spectra • Refractive indices • Dielectric constants • Redox potential • Structureetc. Rewritable paper Photo-memories Photo-switches Photo-driven actuator • Basic Time origin of reaction is easily determined time-resolved detection of precise reaction profiles

7. History of Photochromism • 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, Nature1937, 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.)

8. Single molecular fluorescence switching by photochromic reaction UV light Vis. light fluorescent non-fluorescent 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. →Single-molecular photo-memory/switch

9. Surface morphology changes of diarylethene single crystal Photochromic reaction occurs in crystalline phase UV Vis UV Vis AFM image of surface of diarylethene single crystal S. Kobatake and M. Irie, Science, 291 (2001) 1769.

10. Morphology changes of diarylethene single crystal Changing of crystalline shape is induced by photochromic reaction UV Vis Energy of light is directly converted into mechanical energy “Photo-driven mesoscopic actuator” Open-form Closed-form S. Kobatake, M. Irie et al, Nature, 446 (2007) 778.

11. photo detector pump pulse monitor pulse Dt sample Observation of Reaction Dynamics by Ultrashort Pulsed Laser pump pulse monitor pulse Time t=0 observe spectra at various delay time Dt

12. S1 hn isomerization S0 Mechanism of Photochromic Reaction Excited state(S1) have limited life time Isomerization occurs in competition with ・radiative transition (fluorescence and phosphorescence) ・nonradiative transition (internal conversion and intersystem crossing) Measurement of reaction dynamics Revealing reaction mechanism Determination of rate constant Revealing the factors determining reaction rate → Rational principle for development of advanced molecule

13. 1 mm2 Cycloreversion of diarylethene in PMMA matrix excited 15-ps 532-nm laser pulse in PMMA matrices PS 532 nm irradiation 4.2 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. Steady-state Xe lamp At 532 nm 0.05 mW

14. 15-ps 532-nm laser pulse extremely enhances cycloreversion reaction yield Cycloreversion reaction is more than 2500 times enchanced by 15-ps 532-nm laser pulse excitation. Cycloreversion reaction yield : 10-5 When used as optical memory Data writing → UV light Data reading → weak visible light Data deleting → strong visible light

15. visible two-photon absorption process UV one-photon absorption process Sn Large reaction yield 532 nm × S1 266 nm 532 nm Open form Open form Closed form Multi-photon absorption process J. Am. Chem. Soc., 123 (2001) 753, J. Am. Chem. Soc, 126 (2004) 14764 J. 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.

16. What I am going to study ? Property of higher excited state Sn ? Role of excess vibrational energy photo detector S1 monitor pulse S0 pump pulse repump/dump pulse

17. Sn What I am going to study S1 S0 Graund state

18. Future Prospects • Application of molecular photochromic reaction into control of bulk and surface properties. ex. hydrophilicity/hydrophobility • More effective and rapid response photo-actuator;direct change of photo-energy into mechanical force • New photochromic molecular system with nonlinear and threshold function. • Revealing the reaction dynamics; intramolecular vibration, nonradiative transition and symmetry of electronic state