Generation of long-lived radical ions through enhanced photoinduced electron transfer processes between [60]fullerene and phenothiazine derivatives

Photoinduced electron transfer processes between fullerenes (C ₆₀) and four phenothiazine derivatives (PTZs) in the absence and presence of hexylviologen dication (HV²⁺) have been studied by the transient absorption method in the visible and near-IR regions. Electron-transfer takes place from PTZs to the triplet states of fullerenes (³C₆₀*) giving the radical anion of fullerenes (C₆₀^•-) and the radical cations of PTZs (PTZ ^•+). The rate constants and efficiencies of electron transfer are quite high, because of the high electron-donor abilities of PTZs as elucidated by their low oxidation potentials. On addition of HV²⁺ to the C₆₀ and PTZ systems, the electron-mediating process occurs from C₆₀^•- to HV²⁺, yielding the viologen radical cation (HV^•+). In the presence of a sacrificial donor, HV^•+ persisted for a long time.