Prolongation of the Lifetime of the Charge-Separated State at Low Temperatures in a Photoinduced Electron-Transfer System of [60]Fullerene and Ferrocene Moieties Tethered by Rotaxane Structures
作者:G. Abraham Rajkumar、Atula S. D. Sandanayaka、Kei-ichiro Ikeshita、Yasuyuki Araki、Yoshio Furusho、Toshikazu Takata、Osamu Ito
DOI:10.1021/jp056699i
日期:2006.4.1
A rotaxane tethering both fullerene (C-60) and ferrocene (Fc) moieties (abbreviated as (C-60;Fc)(rotax+)) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ether-secondary amine motif. In (C-60;Fc)(rotax+), the C-60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C-60 and Fc in (C-60;Fc)(rotax+) have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Nanosecond transient absorption measurements of the rotaxane demonstrated that the charge-separated state (C60(center dot-);Fc(center dot+))(rotax+) is formed mainly via the excited triplet state of C-60 in polar solvents. The lifetime of (C60(center dot-);Fc(center dot+))(rotax+) was evaluated to be 20 ns in dimethylfortnamide (DMF) at room temperature. With lowing temperature, the lifetime of (C-60(center dot-);Fc(center dot+))(rotax+) extends to 270 ns in DMF at -65 degrees C, due to the structural changes leaving C-60(center dot-) and Fc(center dot+) at a relatively long distance in the low-temperature region.