Photoinduced electron transfer reactions of highly twisted 1-donor-substituted 2,4,6-triphenylpyridinium cations

Primary processes of photoelectron transfer reactions of highly twisted 1-mesityl- (1a), 1-(2,5-dimethoxyphenyl)- (1b), and 1-(2,3,5,6-tetramethoxyphenyl)- 2,4,6-triphenylpyridinium (1c) tetrafluoroborates in butyronitrile were investigated. The charge-shift states were observed in all cases. Irradiation of 1a generated the charge-shift state (360, 475, and 550 nm), which was converted with a lifetime of 21 ns into the long-lived triplet state (τ = 2.2 μs) localized on the pyridinium moiety. On the other hand, compounds 1b and 1c generated the charge-shift states (λmax = 440 and 540 and λmax = ca. 550 nm as a broad absorption) of short lifetimes, 35 and 16 ps, respectively, decaying exclusively to the singlet ground states.