Photothermal beam deflection study of energy transfer from excited triplet states in fluid solution

Abstract

Photothermal beam deflection spectroscopy was used to follow the decay of the lowest excited triplet state of benzophenone including energy transfer to biphenyl. Because of the simple step function time response of the beam deflection signal, we were able to extract two exponential functions from the heat accumulation waveform. From the results, we obtained a triplet—triplet energy transfer rate from benzophenone to biphenyl of k q = (4.6 ± 0.8) × 10 8 M −1 s −1. The triplet energy of biphenyl was also extracted from the results: E AT = 67 ± 0.5 kcal mol −1. From an analysis of the calorimetric amplitudes, we report the first photothermal observation of an endothermic energy transfer process from the triplet excited state of biphenyl to ground state benzophenone.