Photoinduced charge-separation and charge-recombination processes of oligo(thienyleneethynyl)-fullerene dyad molecules

Photoinduced charge-separation and -recombination processes in two series of oligo(thienyleneethynyl)-fullerene dyads (abbreviated as nTE-C-60), in which the nTE moiety has a linear (n alpha TE) or zigzag structure (n beta TE), have been investigated by using transient absorption spectroscopy with sub-picosecond laser flash photolysis. Based on the transient absorption spectra, charge separation occurs in nTE-C-60 with the rate constants on the order of 10(11) s(-1), indicating almost quantitative charge separation. For all nTE-C60 dyads, the charge-separation rate-ccnstants in toluene were larger than those in benzonitrile, suggesting that the charge-separation process is a solvent-controlled adiabatic process. On the other hand, the charge-recombination processes going back to the ground state occurred with the rate constants on the order of 10(8)-10(9) s(-1). The charge-recombination rate of n alpha TE-C-60 was faster than that in n beta TE-C-60 with a zigzag structure, in spite of similar free energy change for the charge recombination.