The C60-Photosensitized Reduction of Methyl Viologen Through the Intermediary of O2

C60-photosensitized reduction system of methyl viologen (1,1′-dimethyl-4,4′-bipyridinium) electron-mediated by O2 in organic solvents was demonstrated. By steady-state photoirradiation of C60 in the presence of electron donors such as triethanolamine (2,2′,2′′-nitrilotriethanol) and tetraphenylborate (-BPh4), the absorption-band of C60•- increased with irradiation time, and persisted for a long time. On introduction of O2, followed by the irradiation, C60•- disappeared and superoxide anion (O2•-) was generated. The photochemical reaction mechanisms were investigated by the transient-absorption method. The rate constant for electron transfer from C60•- to O2 was estimated to be (3.7 ± 0.2) × 102 mol-1 dm3 s-1. On addition of MV2+, electron transfer from O2•- to MV2+ was observed in aprotic solvents such as benzonitrile, yielding blue methyl viologen cation radical (MV•+). By irradiation of the system of C60/electron donor/O2/MV2+, MV•+ was also generated. In these systems, MV•+ accumulated and remained even in air-saturated solution for more than 1 h, because electron transfer from O2•- to MV2+ is an exothermic process in aprotic solvents.