Photoinduced Electron-Transfer Processes between [C60]Fullerene and Triphenylamine Moieties Tethered by Rotaxane Structures. Through-Space Electron Transfer via Excited Triplet States of [60]Fullerene

Abstract

Two rotaxanes tethering [60]fullerene (C60) and triphenylamine (TPA) moieties were synthesized in good yields by the urethane end-capping method using a crown ether−secondary amine motif. In these rotaxanes, the C60 group serving as electron acceptor is attached to the crown ether wheel through which the axle with a TPA group acting as electron donor on its terminal penetrates. One rotaxane has an ammonium moiety, whereas the other has a neutral amide moiety in the center of the axle. The corresponding reference compounds without rotaxane structures were also prepared. The intra-rotaxane photoinduced electron-transfer processes of C60 and TPA have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity and temperature. Nanosecond transient absorption measurements of these rotaxanes demonstrated that the long-lived charge-separated state (C60•-,TPA•+)rotaxane is formed via the excited triplet state of C60 (3C60*) in polar solvents. The rate const...