Photoinduced electron transfer and electron-mediating systems of [60]fullerene and triphenylamine derivatives in the presence of viologen dication in polar solvent

Photoinduced electron-transfer processes between fullerenes (C ₆₀) and three triphenylamines (TPA's) including bis(tolylaminophenyl) cyclohexane in the absence and presence of hexylviologen dication (HV ²⁺) and 1-benzyl-1,4-dihydronicotinamide (BNAH) have been studied by the transient absorption method in the visible and near-IR regions. Electron-transfer takes place initially from TPA's to the triplet states of fullerenes (³C₆₀*), giving the radical anions of fullerenes (C₆₀^.-) and the radical cations of TPA's (TPA^.+). The rate constants and efficiencies of electron transfer are quite high, because of the high electron-donor abilities of TPA's as their low oxidation potentials indicate. On addition of HV²⁺ to the C ₆₀ and TPA systems, the electron-mediating process from C ₆₀^.- to HV²⁺ occurs, yielding the viologen radical cation (HV^.+). In the further addition of BNAH, which acts as a sacrificial donor, steady-state concentration of HV^.+ was accumulated during continuous photoirradiation and persisted for a long time.