Syntheses of [60]Fullerene and N,N-Bis(4-biphenyl)aniline-Tethered Rotaxane:Photoinduced Electron-Transfer Processes via Singlet and Triplet States of [60]Fullerene

摘要

A rotaxane containing [60]fullerene (Ceo) and N,N-bis(4-biphenyl)aniline (BBA) moieties was synthesized.In this structure,C_60 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 C_60 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 (C_60~(centre dot-);BBA~(centre dot+))_(rotaxane) was formed via both the excited singlet and triplet states of C_60 (~1C_60* and ~3C_60*,respectively) in polar solvents.The rate constants for charge-separation process were evaluated to be in the range of (3.6-3.7) x 10~8 s~(-1) via ~1C_60* and (5.1-5.6) x 10~7 s~(-1) via ~3C_60* in the ratio of (0.36-0.38):(0.43-0.51).The rate constants of charge recombination were 2.5 x 106 s"1 and 4.4 x 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 ~3C_60* 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.