Laser photolysis studies of endoergonic triplet energy transfer in solution by observing the carbon–sulfur bond cleavage of triplet-sensitized naphthylmethyl phenyl sulfide

A bimolecular rate constant (kq) and an efficiency (αTET) of an endoergonic triplet energy transfer from triplet α-naphthyl phenyl ketone (NPK) to α-naphthylmethyl phenyl sulfide (NMPS) in solution, where the energy difference (ΔET) is 1.7 kcal mol−1, have been determined by means of nanosecond laser flash photolysis. Base on the Arrhenius plots of the kq value for the NPK–NMPS system, an activation energy (ΔEa) for the endoergonic triplet energy transfer is found to be 2.6 kcal mol−1, which is larger than the endothermic energy gap (ΔET=1.7 kcal mol−1). The endoergonic triplet energy transfer in solution is demonstrated to proceed with the aid of thermal activation for the first time.