Photoinduced Electron Transfer from Tetrathienylethylenes to Fullerenes (C_(60)/C_(70)): Tetrathienylethylene-Dendrimer Effect

摘要

Photoinduced electron-transfer processes between C_(60)/C_(70) and tetrathienylethylenes (TTE's) in benzonitrile have been studied by measuring the transient absorption spectra in the Vis/NIR regions using nanosecond laser photolysis.The absorption bands of the radical anions of C_(60)/C_(70) (C_(60)~(.-)/C_(70)~(.-) and radical cations of TTE's (TTE's~(.+)) were observed with the decay of the triplet states of C_(60)/C_(70) (~3C_(60)~*/~3C_(70)~*),indicating that electron transfer takes place via ~3C_(60)~*/~3C_(70)~*.In addition,formation of the dication of TTE (TTE~(2+)) was confirmed by its characteristic absorption band at 680 nm.The TTE~(2+) is formed by the stepwise collision of TTE with ~3C_(60)~*/~3C_(70)~*.By the substitutions with the MeS groups at the thienyl rings of TTE,the efficiencies and rates of the electron-transfer processes became higher than those of TTE with the PhS groups.For dendrimer TTE's,the photoinduced electron-transfer processes also took place via ~3C_(60)~*/~3C_(70)~*,although the efficiencies and rates were decreased with an increase in the dendrimer generation.After forward electron transfer,the back electron transfer processes were observed between separately solvated C_(60)~(.-) /C_(70)~(.-) and TTE's~(.+) even for the dendrimer TTE's,which suggest that outer-sphere back electron-transfer took place in the backward processes.