Photoinduced Electron Transfer and Charge-Recombination in 2-Ureido-4[1H]-Pyrimidinone Quadruple Hydrogen-Bonded Porphyrin–Fullerene Assemblies

Abstract

2-Ureido-4[1H]-pyrimidinone-bridged porphyrin–fullerene dyad assemblies I–II were designed and synthesized to investigate the intra-assembly photoinduced electron transfer (PET) via the quadruple complementary hydrogen bonds. Steady-state and time-resolved spectroscopy demonstrate that upon excitation of the porphyrin, electron transfer to the fullerene occurs with rate constants (quantum efficiency) of 1.6 × 108 s–1 (60%) and 4.2 × 108 s–1 (44%) for assembly I and II, respectively, in a CH2Cl2 solution at room temperature. More importantly, the rate of charge recombination was found to be rather slow with a lifetime of charge separation (CS) up to 9.8 μs for assembly I and 4.0 μs for assembly II. Because the relatively rigid assemblies prevent the porphyrin and fullerene from any intra-assembly collisions either through solvent or through space mechanisms, the quadruple complementary hydrogen bonds play crucial roles in mediating the intra-assembly PET process. This is, to the best of our knowledge, the first direct evidence for the PET process via 2-ureido-4[1H]-pyrimidinone complementary quadruple hydrogen-bonded systems.