C 60-photosensitized reduction system of methyl viologen (1,1′-dimethyl-4,4′-bipyridinium) electron-mediated by O 2 in organic solvents was demonstrated. By steady-state photoirradiation of C 60 in the presence of electron donors such as triethanolamine (2,2′,2″-nitrilotriethanol) and tetraphenylborate ( -BPh 4), the absorption-band of C 60 ·- increased with irradiation time, and persisted for a long time. On introduction of O 2, followed by the irradiation, C 60 ·- disappeared and superoxide anion (O 2 ·-) was generated. The photochemical reaction mechanisms were investigated by the transient-absorption method. The rate constant for electron transfer from C 60 ·- to O 2 was estimated to be 13.7 ± 0.2) x 10 2 mol -1 dm 3 s -1. On addition of MV 2+, electron transfer from O 2 ·- to MV 2+ was observed in aprotic solvents such as benzonitrile, yielding blue methyl viologen cation radical (MV ·+). By irradiation of the system of C 60/electron donor/O 2/ MV 2+, 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 O 2 ·- to MV 2+ is an exothermic process in aprotic solvents.
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