Triplet properties and photoinduced electron-transfer reactions of C120, the [2+2] dimer of fullerene C60

Photophysical and photochemical properties of a [2+2] fullerene dimer, C-120, have been characterized by laser flash photolysis. By laser irradiation to C-120, a triplet-triplet absorption band appeared at 700 nm. From triplet energy-transfer reactions with some energy accepters, photophysical properties of C-120, including triplet energy, extinction coefficient, and quantum yield of the intersystem crossing process, were estimated. Reduction of C-120 in the ground state by tetrakis(dimethylamino)ethylene resulted in decomposition into C-60(.-) and C-60. Photoinduced electron transfer from N,N,N',N'-tetramethyl-1,4-phenylenediamine to triplet-excited C-120 was confirmed by the observation of a transient absorption band due to the radical anion of C-120 at 1020 nm. Electron-transfer rates between triplet-excited C-120 and various electron-donors were explained by the semiempirical Rehm-Weller relation. Oxidation of triplet-excited C-120 was also observed by employing tetracyanoethylene as an electron-acceptor.