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 state of C 60 and the ion-pair charge-transfer complex which consists of electron-acceptor cation (methyl viologen (MV 2+ )) and electron-donor anion (organo borates ( - BPh 3 R, 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 MV 2+ ( - BPh 3 R) 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 3 C 60 * from - BPh 3 R in the complex, yielding • BPh 3 R and C 60 -• . Although generated C 60 -• does not decay in the absence of MV 2+ because of the rapid dissociation of • BPh 3 R, in the presence of MV 2+, C 60 -• decays quickly by transferring an electron to MV 2+ yielding MV +• . Thus, it is proved that C 60 acts as a photosensitizer for pumping up an electron from - BPh 3 R as well as an electron mediator to MV 2+ . 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.