Intermolecular photochemical proton transfer in solution: new insights and perspectives

Recent theoretical results on the title topic, informed by femtosecond and steady state spectroscopic studies, are reviewed. It is argued that currently employed conceptions of excited state intermolecular proton transfer of the hydroxyarene acid–base type in solution need to be extended or replaced. Among the key features involved are aspects associated with the dynamics—such as the quantum character of the proton nuclear motion and the nature of the reaction coordinate—and the electronic structure description of the reaction process. One example of the latter—the source of the greatly enhanced acidity in the excited state compared to that of the ground state—is given special attention.