Semiclassical Truncated-Wigner-Approximation Theory of Molecular Exciton-Polariton Dynamics in Optical Cavities.

Molecular exciton polaritons, hybrid states formed through the strong coupling of molecular electronic excitations with optical cavity modes, offer a powerful avenue for controlling photophysical and photochemical processes in molecular systems. Here, we present a semiclassical framework for investigating the dynamics of molecular exciton polaritons using the truncated Wigner approximation (TWA). This approach extends the prior TWA method developed for molecular vibration-polariton dynamics ( J. Chem. Theory Comput. 2024, 20, 3019-3027) by incorporating semiclassical treatment of quantum coherence between ground and excited molecular states. To validate the framework, we first apply it to a simplified system of two-level (spin-1/2) molecules without vibronic coupling, demonstrating strong agreement between semiclassical and fully quantum simulations in systems with a large molecular ensemble. We further extend the model to include molecular vibronic coupling, revealing the dynamic polaron decoupling effect, where the quantum coherence between molecular excitations persists under strong light-matter coupling. These findings provide critical insights into the collective behavior and coherence preservation in polaritonic systems with implications for designing cavity-mediated molecular processes.