Fullerene derivatives functionalized with diethylamino-substituted conjugated oligomers: synthesis and photoinduced electron transfer.

Diethylamino-substituted oligophenylenevinylene (OPV) building blocks have been prepared and used for the synthesis of two [60]fullerene-OPV dyads, F-D1 and F-D2, which exhibit different conjugation length of the OPV fragments. The electrochemical properties of these acceptor-donor dyads have been studied by cyclic voltammetry. The first reduction is always assigned to the fullerene moiety and the first oxidation centered on the diethylaniline groups of the OPV rods, thus making these systems suitable candidates for photoinduced electron transfer. Both the OPV and the fullerene-centered fluorescence bands are quenched in toluene and benzonitrile, which suggests the occurrence of photoinduced electron transfer from the amino-substituted OPVs to the carbon sphere in the dyads in both solvents. By means of bimolecular quenching experiments, transient absorption spectral fingerprints of the radical cationic species are detected in the visible (670 nm) and near-IR (1300-1500 nm) regions, along with the much weaker fullerene anion band at lambda(max)=1030 nm. Definitive evidence for photoinduced electron transfer in F-D1 and F-D2 comes from transient absorption measurements. A charge-separated state is formed within 100 ps and decays in less than 5 ns.