Photoinduced electron transfer and electron-mediating systems from aromatic amines to triplet states of C₆₀ and C₇₀ in the presence of a viologen dication

Photoinduced electron transfer between fullerenes (C₆₀ and C₇₀) and various aromatic amines (AA's) in the absence and presence of a viologen dication has been studied by the transient absorption method in the visible and near-IR regions. Electron-transfer takes place from AA's to the triplet states of fullerenes (³C₆₀* and ³C₇₀*) giving the anion radicals of fullerenes (C₆₀^.- and C₇₀^.-) and the radical cations of AA's (AA^.+). The rate constants and efficiencies of electron transfer are quite high, because of the high electron-donor abilities of AA's as their low oxidation potentials indicate. The absorption bands of AA^.+ appeared also in the near-IR region indicating that the radical-cation center (hole) delocalizes over the entire region of each AA. On addition of an octylviologen dication (OV²⁺) to C₆₀/C ₇₀-AA systems, the electron-mediating process from C ₆₀^.- and C₇₀^.- to OV²⁺ occurs yielding the viologen radical cation (OV^.+) with longer lifetime.