Photoinduced Triplet−Triplet Energy Transfer via the 2-Ureido-4[1H]-pyrimidinone Self-Complementary Quadruple Hydrogen-Bonded Module

Phosphorescence quenching and flash photolysis experiments demonstrate that photoinduced intra-assembly triplet−triplet energy transfer can take place via a 2-ureido-4[1H]-pyrimidinone-bridged benzophenone−naphthalene assembly I with a rate constant of 3.0 × 10⁶ s^-1 and an efficiency of 95% in CH₂Cl₂. This new finding suggests that with high binding strength and directionality, the 2-ureido-4[1H]-pyrimidinone hydrogen-bonded module may serve as a new model to illustrate the fundamental principles governing the triplet−triplet energy-transfer process through hydrogen bonds.