Basic study of photochemistry of photochromic molecules

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1. Photochromic reactions of diarylethenesPhotochromic reactions of diarylethenes, cis-1,2-dicyano-1,2-bis (2,4,5-trimethyl-3-thienyl) ethene (Compound 1) and 2,3-bis (2,4,5-trimethyl-3-thienyl) maleic anhydride (Compound 2) were studied. (1) Photochromic reaction with high efficiency was confirmed for compound 1 in mixed LB films of arachidic acid and methyl arachidate on the basis o UV-visible absorption spectra before and after UV irradiation. (2) Conformations of the ground states and excited states of diarylethenes were optimized by a semiempirical molecular orbital method, MOPAC.Barrier heights between conformeres and charge distributions were also calculated. The dependence of photochromic reaction efficiency on polymer (or solvent) polarity was explained in terms of large dipolemoment in the S_1 state. (3) It was found that photochromic reaction efficiency of Compound 2 is high in a polymer matrix with low polarity and low glass-transformation temperature. Photochromic reaction … More efficiency of Compound 1 was not significantly affected by the kind of polymer. (4) Colloidal solutions and amorphous films of diarylethenes were formed and their efficiency of photochromic reactions was studied. Colloidal solution of Compound 1 has an efficiency as high as its hexane solution. However the efficiency was dropped soon after UV irradiation started, because energy transfer from ring-opened form to ring-closed form occurs in solid phase. No photochromic reactions were observed for polycrystal or colloidal solution of Compound 2. On the other hand, a little part of amorphous films of Comopund 2 was colored by UV irradiation.2. Photochromic reactins of cyanine dyesCounterions in a non-polar solvent affect lifetimes of photoisomer of cyanine dyes. The Influence was large for some kinds of dyes. Wavelengths of visible absorption and fluorescence maxima also were affected by counterions. Semiempirical molecular orbital calculations clarified the mechanism of the counterion effects. Less