Bright Reservoir States in Vibrational Strong Coupling

High Resolution Image Download MS PowerPoint Slide Strong coupling hybridizes molecular vibrations with confined photonic modes, forming a pair of polariton states and a large manifold of reservoir states. Molecular polaritons attract interest because of their envisioned potential to alter chemical reactions and energy transport. Although classical electrodynamics satisfactorily describes linear spectroscopic observables in strongly coupled systems, understanding possible changes in reactivity and transport necessitates an adequate quantum mechanical description. Within the latter, from a density-of-states perspective, any macroscopic change in reactivity or transport must be linked to changes in the properties of the reservoir states. In the homogeneous limit, the reservoir is optically dark owing to destructive interference between the transition dipoles of the participating molecules, whereas molecular disorder leads to a nonvanishing reservoir transition strength. However, accounting for the inhomogeneous distribution of molecular transition frequencies alone is insufficient to reproduce the reservoir signals emerging in realistic systems. In open photonic cavity configurations, reservoir states are observed in transmission spectroscopy, whereas in Fabry–Perot cavities, they are observed in reflection measurements. Herein, we demonstrate that when the spatial distribution of the cavity electric field and the isotropic distribution of molecular orientations are accounted for, in addition to inhomogeneous broadening, quantitative modeling of the experimental results can be achieved. This model suggests a significant presence of a photonic component in the reservoir manifold capable of efficiently redistributing the excitation energy.