C60 as photosensitizing electron-transfer mediator for ion-pair charge-transfer complexes between borate anions and methyl viologen dication

Photochemical reactions between the excited triplet stale of C-60 and the ion-pair charge-transfer complex which consists of electron-acceptor cation (methyl viologen (MV2+)) and electron-donor anion (organo berates (-BPh3R, where R = Ph or Bu)) have been investigated by both steady-state and laser-flash photolysis. By photoirradiation of C-60 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 C-3(60)* from -BPh3R in the complex, yielding (BPh3R)-B-. and C-60(-.). Although generated C-60(-.) does not decay in the absence of MV2+ because of the rapid dissociation of (BPh3R)-B-., in the presence of MV2+, C-60(-.) decays quickly by transferring an electron to MV2+ yielding MV+.. Thus, it is proved that C-60 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 O-2 is retarded.