Katsuki Okuno Miyasaka Laboratory 1

 Introduction Definition Example of Photochromic Molecules History  Recent research Photochromism in single crystal Shape change of photochromic crystal Fluorescence switching by photochromic reaction  Research with Lasers Observation of reaction dynamics Control chemical reaction by laser  What I am going to study  Future Prospects in Photochromism 2

 Original Definition of Photochromism Phenomenon that color of material is changed by light 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 Photochromism Reversible 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. AB h h ’ or  UV light Vis. light Example (diarylethene in solution) 4

Azobenzene Spiropyran / Spirooxazine Fulgide Diarylethene HABI T-typeP-type 5 (Hexaarylbiimidazole)

 Application  Basic Quick property change Absoption spectra Refractive indices Dielectric constants Redox potential Structure etc. Rewritable paper Photo-memories Photo-switches Photo-driven actuator 6 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.) 7

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) fluorescentnon-fluorescent 8 → Single-molecular photo-memory/switch

S. Kobatake and M. Irie, Science, 291 (2001) AFM image of surface of diarylethene single crystal UVVis UVVis Photochromic reaction occurs in crystalline phase 9

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

tt sample photo detector pump pulse monitor pulse Time t=0 pump pulsemonitor pulse observe spectra at various delay time  t 11

S1S1 S0S0 h isomerization Excited state(S 1 ) 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 12

Steady-state Xe lamp At 532 nm 0.05 mW 1 mm 2 PS 532 nm irradiation 4.2 mJ / mm 2 2 shots 5 min mJ / mm 2 10 min. 7.5 mJ / mm 2 20 min. 15 mJ / mm 2 5,10,20 min. in PMMA matrices 13

Cycloreversion reaction yield : 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. 14

Open form UV one-photon absorption process 266 nm × 532 nm Large reaction yield S1S1 SnSn 532 nm visible two-photon absorption process Open form Closed form J. Am. Chem. Soc., 123 (2001) 753, J. Am. Chem. Soc, 126 (2004) J. Phys. Chem. C, 111 (2007) 2730, J. Phys. Org. Chem., 20 (2007) 953, J. Phys. Chem. C, 112 (2008) Phys. Chem. Chem. Phys, 11 (2009) 2640, New. J. Chem. 33 (2009) 1409, Photochem. Photobiol. Sci., 9 (2010)

16 pump pulse monitor pulse repump/dump pulse photo detector S0S0 SnSn S1S1 Property of higher excited state Role of excess vibrational energy ? ?

17 Graund state S0S0 SnSn S1S1

1. Application of molecular photochromic reaction into control of bulk and surface properties. ex. hydrophilicity/hydrophobility 2. More effective and rapid response photo-actuator; direct change of photo-energy into mechanical force 3. New photochromic molecular system with nonlinear and threshold function. 4. Revealing the reaction dynamics; intramolecular vibration, nonradiative transition and symmetry of electronic state 18