Photoinduced electron transfer processes of a fused C_(60)-TTF-C_(60) dumbbel triad

摘要

Intramolecular photoinduced charge-separation and charge-recombination processes in a fused C_(60)-TTF-C_(60) dumbbell triad molecule,which has been designed to be soluble in organic solvents thanks to the substitution of C_(60) with polyalcoxy ester groups,have been investigated in various solvents by time-resolved absorption and fluorescence techniques.Appreciable interaction between the C_(60)-moiety and TTF-moiety in the ground state has been suggested by steady-state absorption spectra.The fluorescence spectra suggest also considerable interaction in the singlet excited state.The observed short fluorescence lifetimes of C_(60)-TTF-C_(60) compared with methanofullerene in toluene,THF,and benzonitrile indicate that the charge-separation takes place via the singlet excited state of the C_(60)-moiety,producing the ion-pair (C_(60)-TTF~(·+)-C_(60)~(·-)),which was confirmed with picosecond transient absorption spectra.The nanosecond transient absorption spectra at 1000 nm indicate the formation of C_(60)-TTF~(·+)-C_(60)~(·-),which decays with a lifetime of 20 ns as an upper limit in benzonitrile,In THF and toluene,clear transient absorption bands of C_(60)-TTF~(·+)-C_(60)~(·-) were not observed within nanosecond laser pulse of ca.6 ns duration,suggesting that C_(60)-TTF~(·+)-C_(60)~(·-) state presents a lifetime within 10 ns.These observations were compared with the reported data for C_(60)-TTF dyads.