STUDY ON SPECIFIC INTERACTION AND PHOTOFUNCTIONALITY OF STABLE RADICALS FORMED BY PHOTOINDUCED ELECTRON TRANSFER REACTION

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1) Tetraphenyl salts of styrylpyridinium ions with strong electron-withdrawing groups such as nitro and dicyanovinyl groups were prepared.They formed ion-pair charge-transfer (IPCT) complexes in less polar organic solvents like 1,2-dimethoxyethane (DME).Upon excitation of an IPCT band in degassed conditions, electron transfer reaction occurred resulting in the formation of styrylpyridinyl radical with an absorption spectrum in the visible region. At the same time a broad absorption spectrum was observed in the near infrared region, which was assigned to the charge-resonance (CR) band due to the electronic interaction between a photogenerated styrylpyridinyl radical with a parent styrylpyridinium cation. The CR-band spectrum depended on the substituents and the stabilization energy was slightly higher in nitro-derivative than dicyanavinyl-derivative.2) The Electron Spin Resonance (ESR) spectrum of photoinduced radicals in dicyanovinyl-derivative was a broad singlet due to exchange broad … More ening. Hyperfine structure appeared upon mixing it with unirradiated DME solution of dicyanovinyl-derivateve, which was assigned to dimer radical cations formed by interaction of photogenerated styrylpyridinyl radicals with parent styrylpyridinium cations.3) Kinetic studies were made on these salts using a nano-second (ns) pulsed laser. The CR-band absorption rose within a ns pulse in a similar manner as the visible absorption of styrylpyridinyl radicals, strongly suggested diffusionlness formation of dimer radical cations.4) A mixture of amphipathic nitrostyrylpyridinium tetraphenylborate and arachidic acid showed a solid condensed phase at the air-water interface. Y-type Langmuir-Blodgett films were deposited on a quartz plate with deposition ratio of unity. Microcrystalline films were also prepared by evaporation. Photoexcitation of these solid films at the same condition as in solutions caused some spectral chantes. It was, however, not possible to observe the formation of styrylpyridinyl radicals and dimer radical cations in these solid films. Less