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/C70–AA systems, the electron-mediating process from C60˙− and C70˙− to OV2+ occurs yielding the viologen radical cation (OV˙+) with longer lifetime.