Synthesis and photoelectrochemical properties of a fullerene-azothiophene dyad

In this paper we describe the synthesis, electrochemistry and photophysical behavior of a fullerene-based donor-acceptor dyad (2) in which the donor u nit is an azothiophene dye. Dyad 2, prepared in one step starting from C-60 , commercially available N-methylglycine and thienylazobenzeneamine 1, can be selectively excited in the visible region where the dye has an absorptio n maximum at 567 nm. Implementation of electrochemical and photophysical da ta reveals that both intramolecular energy- and electron-transfer are therm odynamically feasible processes. Steady-state luminescence of dyad 2 in CH2 Cl2 shows a quenching of the dye singlet excited state ((1)dye*) and eviden ce of the fullerene singlet excited state (C-1(60)*) emission. Flash-photol ytic experiments, on the other hand, exhibit characteristic differential ab sorption changes attributed to the C-60(.-)-dye(.+) charge-separated state. Interestingly, it has been estimated that the energy difference between C- 1(60)* and the charge separated state is very small, leading to the hypothe sis that a rapid exchange between the two states occurs. Sensitization of T iO2 with dyad 2 and model compound 3 is also reported and discussed.