Photoinduced Triplet-Triplet Energy Transfer in a 2-Ureido-4(1H)-Pyrimidinone-Bridged, Quadruply Hydrogen-Bonded Ferrocene-Fullerene Assembly

2-Ureido-4(1H)-pyrimidinone-bridged ferrocenefullerene assembly I is designed and synthesized for elaborating the photoinduced electron-transfer processes in self-complementary quadruply hydrogen-bonded modules. Unexpectedly, steady-state and time-resolved spectroscopy reveal an inefficient electron-transfer process from the ferrocene to the singlet or triplet excited state of the fullerene, although the electron-transfer reactions are thermodynamically feasible. Instead, an effective intra-assembly triplettriplet energy-transfer process is found to be operative in assembly I with a rate constant of 9.2 x 105 s(-1) and an efficiency of 73% in CH2Cl2 at room temperature.