Reaction-Diffusion Dynamics Simulations of Bimolecular Quenching in Solution

A computational method to simulate bimolecular quenching reactions using coarse-grained reaction-diffusion dynamics is presented and applied to the quenching of molecular photosensitizers in solution. The simulations describe photoinduced reactions involving explicit excited states of light-harvesting species together with intrinsic deactivation, as well as collision quenching from separate quencher species. The simulation methodology is applied to time-resolved quenching of light-harvesting Fe(III) complexes in electron-donating solvents as a prototype system for reaction-diffusion dynamics of experimental interest over a wide range of quencher concentrations. The results show clear signatures for the transition from classical diffusion-limited Stern-Volmer dynamics to close-contact quencher-photosensitizer interactions at high quencher concentrations, and the simulations are used to elucidate physically realistic photosensitizer-quenching collision interaction parameters for photoinduced dynamics beyond the classical Stern-Volmer model. The simulation method provides the means to directly model and analyze system kinetics and dynamics beyond standard theoretical equations, opening up significant opportunities to simulate a broad range of reactions in solutions.