Photoinduced electron-transfer processes in C60-tetrathiafulvalene dyads containing a short or long flexible spacer

Intramolecular photoinduced charge-separation and charge-recombination processes in two C-60-spacer-TTF dyads, in which C-60 and TTF (tetrathiafulvalene) are connected through a flexible spacer of different lengths, have been investigated in polar solvents by time-resolved absorption and fluorescence techniques. Weak interaction between the C-60-moiety and TTF-moiety in the ground state was suggested by the steady-state absorption spectra; the dyad with the shorter spacer shows slightly stronger interaction than that with the longer spacer. The observed short fluorescence lifetimes of these dyads, compared with that of their precursor fullerene derivative in THF and benzonitrile indicate that the charge separation takes place via the singlet excited state of the C-60-moiety, producing the ion pairs (C-60(.-)-spacer- TTF.+) as shown from the transient absorption spectra in the 800-1100 nm region. In polar benzonitrile solvent, the ion-pair state with the long flexible chain shows longer lifetime than that with the short chain, suggesting that weaker interaction between C-60 and TTF moieties is preferred to the long ion-pair lifetime. These observations were compared with other reported data for C-60-TTF dyads.