Photoinduced Charge Separation and Charge Recombination in [60]Fullerene-(Benzothiadiazole-Triphenylamine) Based Dyad in Polar Solvents

Abstract

The molecular dyad C60-(BTD-TPA) consisting of an electron donor triphenylamine-appended 2,1,3-benzothiadiazole chromophore (BTD-TPA) unit covalently linked to an electron acceptor [60]fullerene has been synthesized. The photoinduced electron transfer in C60-(BTD-TPA) has been studied in polar and nonpolar solvents using time-resolved transient absorption and fluorescence measurements. By fluorescence lifetime measurements in picosecond time regions, the excitation of the C60 moiety leads to the formation of C60•--(BTD-TPA)•+ efficiently via the singlet excited state of the C60 moiety. Excitation of the BTD-TPA moiety leads to initial energy transfer to 1C60*- (BTD-TPA), from which electron transfer occurs to form C60•--(BTD-TPA)•+. In the nanosecond time region, C60•--(BTD-TPA)•+ in which the radical cation (hole) delocalizes in the BTD-TPA moiety is persistent for 690 ns in DMF at room temperature. From the temperature dependence of the charge-recombination rate constants, which gave the Marcus parameters, we attempted to reveal the origins of long persistent C60•--(BTD-TPA)•+ in DMF.