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 (nαTE) or zigzag structure (nβTE), 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-C ₆₀ dyads, the charge-separation rate-constants 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 nαTE-C ₆₀ was faster than that in nβTE-C ₆₀ with a zigzag structure, in spite of similar free energy change for the charge recombination.