Jankunas Dissertation Award (Finalists)Unveiling the photochemistry and photophysics of organic molecules in optical cavities

Molecular polaritons are hybrid light-matter states that emerge when the collective coupling between a large ensemble of molecules and a confined electromagnetic mode of an optical cavity exceeds all dissipation rates. Organic exciton polaritons are particularly interesting systems since strong coupling between electronic and vibrational degrees of freedom (DoF) gives rise to intricate relaxation processes that allow for population transfer between dark and polariton states, a feature which plays a central role in polariton-assisted remote energy transfer, modifications in photochemistry, polariton transport, and polariton condensation.

Despite recent advancements, the field features contradictory findings: some studies report no changes due to formation of polaritons, or provide alternative, non-polaritonic explanations for the observed modifications. A crucial step towards solving these inconsistencies is to have a tractable theoretical and computational framework that can describe the myriads of molecules in the ensemble, and the complex internal vibrational structure of each molecule. To address these issues, we recently introduced a formalism called collective dynamics using truncated equations (CUT-E). First, it exploits permutational symmetry for an efficient representation of the system. Second, it provides a simple solution to the problem for large N by deriving an exact solution in the N → ∞ limit and subsequently carrying out systematic 1/N corrections.

In previous works we showed how this formalism can be used to elucidate collective polaritonic effects on chemical dynamics in the N → ∞ limit and made formal connections with classical linear optics treatments. In this talk, I will focus on 1/N corrections and describe novel photophysical phenomena allowed by collective strong couplings. More specifically, we characterize two main mechanisms: (1) Radiative pumping, where fluorescence into polariton modes can either escape the cavity or be reabsorbed by the molecules (photon recycling); and (2) Polariton-assisted Raman scattering, which involves the virtual emission of a photon followed by Raman scattering off a second molecule.