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

Abstract A bimolecular rate constant ( k q ) and an efficiency ( α TET ) 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 (Δ E T ) is 1.7 kcal mol −1 , have been determined by means of nanosecond laser flash photolysis. Base on the Arrhenius plots of the k q value for the NPK–NMPS system, an activation energy (Δ E a ) for the endoergonic triplet energy transfer is found to be 2.6 kcal mol −1 , which is larger than the endothermic energy gap ( Δ E T =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.