Electron-Transfer Reactions between Fullerenes (C60 and C70) and Tetrakis(dimethylamino)ethylene in the Ground and Excited States

Electron-transfer reactions between tetrakis(dimethylamino)ethylene (TDAE) and fullerenes (C 60 and C 70 ) in solution have been studied in the ground and excited states. Analyses of the thermal equilibria indicate that the radical ions are present as free radical ions in appropriate polar solvents, while the radical ion pairs are predominant in less polar solvents. On the laser excitation of C 60 /C 70 in the presence of TDAE, the concentration of the radical anions (C 60 •- /C 70 •- ) was increased by photoinduced electron transfer via the triplet state of C 60 /C 70 . The photochemically generated C 60 •- /C 70 •- decayed rapidly by the back-electron transfer returning to the thermal equilibrium. In polar solvents the back-electron-transfer reactions obey bimolecular kinetics, suggesting that radical ions are separately solvated. In less polar solvents, on the other hand, first-order kinetics of the decay of C 60 •- /C 70 •- indicates that the back-electron transfer occurs within the ion pairs. On combination of the rate constants of the back-electron transfer with the equilibrium constants, the rate constants of the electron transfer in the ground states were evaluated, which are 1 / 3 to 1 / 45 of those in the excited triplet states.