Synthesis and photoelectrochemical properties of a fullerene–azothiophene dyad

Abstract

In this paper we describe the synthesis, electrochemistry and photophysical behavior of a fullerene-based donor–acceptor dyad (2) in which the donor unit is an azothiophene dye. Dyad 2, prepared in one step starting from C₆₀, commercially available N-methylglycine and thienylazobenzeneamine 1, can be selectively excited in the visible region where the dye has an absorption maximum at 567 nm. Implementation of electrochemical and photophysical data reveals that both intramolecular energy- and electron-transfer are thermodynamically feasible processes. Steady-state luminescence of dyad 2 in CH₂Cl₂ shows a quenching of the dye singlet excited state (¹dye*) and evidence of the fullerene singlet excited state (¹C₆₀*) emission. Flash-photolytic experiments, on the other hand, exhibit characteristic differential absorption changes attributed to the C₆₀^·––dye^·+ charge-separated state. Interestingly, it has been estimated that the energy difference between ¹C₆₀* and the charge separated state is very small, leading to the hypothesis that a rapid exchange between the two states occurs. Sensitization of TiO₂ with dyad 2 and model compound 3 is also reported and discussed.