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J. Phys. Chem. A 1997, 101, 1056-1061
Photochemical Generation of Radical Cations of Dithienothiophenes, Condensed Thiophene Trimers, Studied by Laser Flash Photolysis Mamoru Fujitsuka,*,† Tadatake Sato,‡ Takeo Shimidzu,‡ Akira Watanabe,† and Osamu Ito*,† Institute for Chemical Reaction Science, Tohoku UniVersity, Katahira, Aoba-ku, Sendai 980-77, Japan, and DiVision of Molecular Engineering, Graduate School of Engineering, Kyoto UniVersity, Sakyo-ku, Kyoto 606-01, Japan ReceiVed: October 1, 1996; In Final Form: NoVember 23, 1996X
Photoinduced electron-transfer reactions between dithienothiophene (DTT) and the electron acceptors, p-dinitrobenzene (DNB) and CCl4, have been investigated using nanosecond laser flash photolysis and timeresolved fluoresence spectroscopy. Generation of the radical cations of DTTs and radical anion of DNB in acetonitrile solution was confirmed by transient absorption spectra in the visible and near-IR regions. Observed transient absorption bands corresponded to those of radical ions generated by γ irradiation in a frozen matrix. Electron transfer occurred both from the singlet and triplet excited states of DTT to DNB at the diffusioncontrolled rate, ∼1010 M-1 s-1. When CCl4 was used as an acceptor, electron transfer from the singlet excited state occurred at the diffusion-controlled rate, while the reaction from the triplet excited state occurred at
