Photoinduced Electron Transfer from Tetrathienylethylenes to Fullerenes (C60/C70): Tetrathienylethylene-Dendrimer Effect

Photoinduced electron-transfer processes between C60/C70 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 C60/C70 (C60•-/C70•-) and radical cations of TTE’s (TTE’s•+) were observed with the decay of the triplet states of C60/C70 (3C60/3C70), indicating that electron transfer takes place via 3C60/3C70. 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 3C60/3C70. 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 3C60/3C70, 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 C60•-/C70•- and TTE’s•+ even for the dendrimer TTE’s, which suggest that outer-sphere back electron-transfer took place in the backward processes.