Direct Evidence of Bimolecular Proton-Coupled Energy Transfer at Room Temperature

A new elementary reaction, denoted proton-coupled energy transfer (PCEnT), has been recently reported in a series of donor-acceptor molecules. In this reaction, excited state energy transfer is made possible by a simultaneous transfer of a proton on the energy acceptor. This type of elementary reaction could have, by analogy to proton-coupled electron transfer, an important role in photochemistry and energy transportation of biological systems. In the previously reported case, the reaction is shown to occur intramolecularly in a covalently linked system in a 77 K glass. In this work, we identify a suitable bimolecular system for PCEnT and provide direct evidence for PCEnT in a room temperature solution using fluorescence spectroscopy. Based on these results, we discuss some simple design principles for PCEnT, including some of the current obstacles in designing a successful system.