A rotaxane containing fullerene (C60) and N,N-bis(4-biphenyl)aniline (BBA) moieties was synthesized. In this structure, C60 acting as an electron acceptor, is attached to the crown-ether ring through which the axle with terminal BBA moieties acting as electron donors on both ends is penetrating. This rotaxane had a neutral amide moiety in the center of the axle in which two BBA moieties act as stoppers. The intra-rotaxane photoinduced electron-transfer processes of the C60 and BBA moieties were investigated by time-resolved transient absorption and fluorescence measurements while changing solvent polarity and temperature. Time-resolved transient absorption measurements of the rotaxanes confirmed that the long-lived charge-separated state (C60.-; BBA.+)rotaxane was formed via both the excited singlet and triplet states of Q60 (1Q60* and 3C60*, respectively) in polar solvents. The rate constants for charge-separation process were evaluated to be in the range of (3.6-3.7) × 108 s-1 via 1Q60* and (5.1-5.6) × 107 s -1 via 3C60* in the ratio of (0.36-0.38):(0.43-0.51). The rate constants of charge recombination were 2.5 × 106 s-1 and 4.4 × 106 s -1, corresponding to the lifetimes of the charge-separated states of 400 ns and 230 ns in THF and benzonitrile, respectively. By the temperature dependences, the activation free-energy changes of charge-separation process via 3Q60* were evaluated to be 0.10 eV, while those of the charge-recombination process were estimated to be 0.03 eV in THF and benzonitrile. These low activation energies are one of the characteristics of through-space electron transfer in the rotaxanes.
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