Study on Electron-Transfer Systems of Colloidal TiO_2 Sensitized by Fullerenes Pending Carboxylic Acid Groups in the Presence of Methyl Viologen and Amines

摘要

The electron-transfer systems of colloidal TiO2 sensitized by fullerenes pending the carboxylic acid groups (C60R), which were adsorbed on TiO2, have been studied by steady-state visible-light irradiation and laser flash photolysis methods. Accumulation of MV"+ was observed in the course of the visible light irradiation exciting QoR in the system containing a donor amine (p-anisidine; PAD), C60R, TiO2, methyl viologen (MV2+), and a sacrificial amine (triethanolamine; TEOA). In the transient absorption spectra measured by nanosecond laser flash photolysis, the absorption peaks of 3C6oR*, CeoR"" and MV"h were successively observed. From the absorption time-profiles, it was confirmed that initial electron transfer takes place from PAD to ~3C_(60)R~*, producing C_60R~* and PAD'+. In the presence of TiO_2, the electron injection takes place from C60R*" into TiO2, giving TiO_2(e~-), when the reduction potential (Erai) of C60R was more negative than that of TiO_2. MV2t accepts the electron from TiO2(e~) giving MV~(2+). For CboR with less negative Ereii value than that of TiO_2, the back electron transfer from C_(60)R~(·-) to PAD' was retarded by TiO2; thus, the electron mediating from C60R"" to MV2+ may competitively become predominant, accumulating MV"+. Back electron transfer from MV(·+) to PAD(·+) was further retarded by TEOA via the rapid consumption of PAD~(·+).