Photoinduced electron transfer processes of a fused C60–TTF–C60dumbbell triad

Abstract

Intramolecular photoinduced charge-separation and charge-recombination processes in a fused C60–TTF–C60 dumbbell triad molecule, which has been designed to be soluble in organic solvents thanks to the substitution of C60 with polyalcoxy ester groups, have been investigated in various solvents by time-resolved absorption and fluorescence techniques. Appreciable interaction between the C60-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 C60–TTF–C60 compared with methanofullerene in toluene, THF, and benzonitrile indicate that the charge-separation takes place via the singlet excited state of the C60-moiety, producing the ion-pair (C60–TTF˙+–C60˙−), which was confirmed with picosecond transient absorption spectra. The nanosecond transient absorption spectra at 1000 nm indicate the formation of C60–TTF˙+–C60˙−, which decays with a lifetime of 20 ns as an upper limit in benzonitrile. In THF and toluene, clear transient absorption bands of C60–TTF˙+–C60˙− were not observed within nanosecond laser pulse of ca. 6 ns duration, suggesting that C60–TTF˙+–C60˙− state presents a lifetime within 10 ns. These observations were compared with the reported data for C60–TTF dyads.