Singlet-energy transfer in quadruple hydrogen-bonded oligo(p-phenylenevinylene)-fullerene dyads

Two novel supramolecular dyads consisting of an oligo(p-phenylenevinylene) (OPV) donor and fullerence (C-60) acceptor are created via quadruple hydrogen bonding using self-complementary 2-ureido-4[1H]-pyrimidinone units. In the dyads, singlet-energy transfer from the excited OPV unit to the fullerence causes a strong quenching of the OPV fluorescence. The high association constant of the 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonding unit results in high quenching factors (Q(max) greater than or equal to 90). The lower limit obtained for the rate constant for energy transfer (k(EN) greater than or equal to 6 x 10(10) s (1)) is rationalized in terms of the Forster mechanism. Photoinduced electron transfer does not occur in these hydrogen-bonded dimers, even in polar solvents. The absence of charge separation is ascribed to a low electronic coupling between the donor and acceptor in the excited state as result of the long distance between the chromophores.