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 (³C*₆₀/³C*₇₀), 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 ³C*₆₀/³C*₇₀ 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⁺.