COG as photosensitizing electron-transfer mediator for ion-pair charge-transfer complexes between borate anions and methyl viologen dication

Photochemical reactions between the excited triplet state of C₆₀ and the ion-pair charge-transfer complex which consists of electron-acceptor cation (methyl viologen (MV²)) and electron-donor anion (organo borates (~BPh3R, where R = Ph or Bu)) have been investigated by both steady-state and laser-flash photolysis. By photoirradiation of CM in the presence of MV²(-BPh3R)2 in organic solvents, the amount of MV⁺ increases with irradiation time, and persists for a long time even in the dark. From the laser-flash photolysis, it is found that electron transfer proceeds via ³C₆₀ from ^-BPh₃R in the complex, yielding ·BPh₃R and C₆₀^-. Although generated Cr does not decay in the absence of MV²⁺ because of the rapid dissociation of BPh₃R, in the presence of MV²⁺, C₆₀^- decays quickly by transferring an electron to MV²⁺ yielding MV⁺. Thus, it is proved that Ceo acts as a photosensitizer for pumping up an electron from ^-BPh₃R as well as an electron mediator to MV²⁺. In these systems, MV⁺ persists even in air-saturated solution for more than an hour, suggesting that the electron transfer from MV⁺ to O₂ is retarded.