Photoinduced Electron-Transfer and Electron-Mediating Processes of Fullerenes and Phenothiazine Oligomers in a Polar Solvent

Abstract

Abstract Photoinduced electron transfer between fullerenes (C60 and C70) and three phenothiazine oligomers ((PTZ)ns; n=1, 2, and 3) was studied by using a transient absorption method in the visible and near-IR regions. Electron transfer took place from (PTZ)ns to the triplet states of fullerenes (3C60∗ and 3C70∗), giving the radical anions of fullerenes (C60•− and C70•−) and the radical cations of (PTZ)ns, which exhibited strong absorptions in visible and near-IR region for n=2 and 3. From these absorptions, positions of the radical cation in (PTZ)2•+ and (PTZ)3•+ generated by electron donation were also determined. Rate constants and quantum efficiencies of the electron transfer were found to be quite high, because of the strong electron-donating abilities of (PTZ)ns; the order of the rates of electron transfer to 3C60∗ and 3C70∗ is (PTZ)1 > (PTZ)2 = (PTZ)3, which corresponds to the decreasing order of their oxidation potentials. Upon addition of hexylviologen dication (HV2+), an electron-mediating process occurred from C60•− to HV2+, yielding the viologen radical cation (HV•+). In the presence of a sacrificial donor, HV•+ persisted for a long time.