Photoinduced electron-transfer from mono-/oligo-1,4-phenylenevinylenes containing aromatic amines to C-60/C-70 and electron-mediating process to viologen dication in polar solution

Photoinduced electron-transfer processes of C-60 and C-70 from alternating oligomers of phenylenevinylene derivatives (oligo(PV) derivatives) containi ng triphenylamine (TPA) or carbazole (Cz) and their monomer models (mono(PV ) derivatives) in polar solvent have been investigated by nanosecond laser photolysis method with the observation of the transient absorption bands in the visible and near-IR regions. The transient species relating to the ele ctron-transfer processes such as the triplet states Of C-60/C-70 (C-3(60)*/ C-3(70)*), radical anions of C-60/C-70 (C-60(.-)/C70(.-)), and the radical cations of oligo(PV) derivatives and mono(PV) derivatives were detected in the region of 400-1600 nm. From their decays and rises, it is revealed that the electron-transfer process takes place via C-3(60).-/C-3(70).- in polar solvent. The transient absorption bands of the radical cations of the PV d erivatives revealed the delocalization of the radical-cation center (hole) along the PV backbone containing aromatic an-dries. In longer time scale, b ack electron transfer takes place from C-60(.-)/C-70(.-) to the radical cat ions of mono(PV)/oligo(PV) derivatives; the back electron-transfer rate con stants for oligo(PV) derivatives were smaller than those for mono(PV) deriv atives. In the presence of octyl viologen dication (OV2+), the electron Of C-60(.-) further transfers to OV2+, yielding the viologen radical cation (O V.+), which prolongs the lifetimes of the cation radicals of mono(PV) and o ligo(PV) derivatives. Although an accumulation of OV.+ was observed for the C60/mono(pV)/OV2+ system, an almost completely reversible photosensitized electron-transfer/electronmediating cycle was observed for C-60/oligo(pV)/O V2+.