Photoinduced Electron-Transfer from Mono-/Oligo-1,4-phenylenevinylenes Containing Aromatic Amines to C60/C70 and Electron-Mediating Process to Viologen Dication in Polar Solution

Photoinduced electron-transfer processes of C60 and C70 from alternating oligomers of phenylenevinylene derivatives (oligo(PV) derivatives) containing 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 electron-transfer processes such as the triplet states of C60/C70 (3C60*/3C70*), radical anions of C60/C70 (C60 •-/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 3C60*/3C70* in polar solvent. The transient absorption bands of the radical cations of the PV derivatives revealed the delocalization of the radical-cation center (hole) along the PV backbone containing aromatic amines. In longer time scale, back electron transfer takes place from C60 •-/C70 •- to the radical cations of mono(PV)/oligo(PV) derivatives; the back electron-transfer rate constants for oligo(PV) derivatives were smaller than those for mono(PV) derivatives. In the presence of octyl viologen dication (OV2+), the electron of C60 •- further transfers to OV2+, yielding the viologen radical cation (OV•+), which prolongs the lifetimes of the cation radicals of mono(PV) and oligo(PV) derivatives. Although an accumulation of OV•+ was observed for the C60/mono(PV)/OV2+ system, an almost completely reversible photosensitized electron-transfer/electron-mediating cycle was observed for C60/oligo(PV)/OV2+.