The C ₆₀-photosermitized reductioan of methyl viologen through the intermediary of O ₂

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.