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.
Synthesis of [60]fullerene-functionalized rotaxanes
Synthesis of [60]fullerene (C60)-functionalized rotaxanes via Diels–Alder reactions with C60 is described. Diels–Alder reaction of C60 and sulfolene moiety as masked diene attached on the wheels of rotaxanes results in high yields of C60 incorporation. Rotaxanes are prepared by tin-catalyzed urethane-forming end-capping reaction with isocyanate of pseudorotaxane having the wheel carrying C60 functionality