Control and functionalizations of dynamics of radicals and ionic intermediates generated by photocatalysts

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Design and development of photochemical and electron-transfer reactions for novel functionalities have been studied, focusing on unique characteristics of radical and ionic intermediates in organic photochemistry, with three directions as follows: (1) Doping and storage of hole and electron utilizing electron-transfer induced bond formation/cleavage reactions. Generation of electric conductivity of organic thin films was observed upon the irradiation of alternatively layered LB films of a designed sacrificial donor-photo-sensitizer molecule and tetracyanoquinodimethane with long alkyl chain. In addition, electronic acceptors incorporated with a stable radical to form covalent bond by one-electron reduction were prepared which may enable a reversible photochemical doping reaction. (2) Construction of novel reversible systems employing photochemical cyclization of substituted norbornadienes and the electron-transfer valence isomerization of quadricyclanes. (a) Photochromic system designed for recording of repeat counts with quadricyclanes carrying sacrificial electron donors, which undergo bond-cleavage upon reverse reaction by the one-electron oxidation. (b) Flip-flop type photochromic system, which repeats on and off cycles by every pulsed light irradiation, utilizing the acidity change of a norbornadiene-quadricyclae system substituted with carboxylic acid. (3) The development of novel functional interfacial reactions: In addition, formation of electrochromic and conductive thin films by oxidative polymerization of triphenylamine olygomers, electrostatic control of photocatalytic reactions, generation of the high spin states by photodissociation reactions have been studied.