Vibrational strong coupling (VSC), or the strong interaction between molecular vibrations and an optical cavity photon, gives rise to hybrid light-matter states called polaritons. Experiments find that VSC can drastically alter the kinetics of organic reactions, including nucleophilic substitution, cycloaddition, and enzyme catalysis. However, conventional reaction-rate theories, such as transition-state theory, have been unsuccessful at explaining such “VSC catalysis.” These models all assume that internal thermal equilibrium (i.e., within the states of each chemical species) is maintained throughout the reaction. Here, we explore how VSC affects thermally activated electron transfer in the limit where the equilibrium assumption breaks down. By combining the Marcus-Levich-Jortner theory of electron transfer with the theory of relaxation dynamics for molecular polaritons, we develop a general kinetic framework that treats reactive transitions and dissipative processes on equal footing. We then apply this method to simulate the reaction kinetics of two- and many-molecule systems under VSC. For each case, our calculations reveal a distinct mechanism by which VSC can promote internal thermalization and thereby suppress nonequilibrium effects that influence reactivity.

Nonequilibrium models for thermally activated electron transfer under vibrational strong coupling

ACS Fall 2021

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