Quantitative Modeling of Polaritonic Emission Using the Source Term Method.

Strong exciton-photon coupling leads to the formation of hybrid states, polaritons, with properties different from those of their constituents, making it a valuable tool for modifying the physical and chemical properties of organic and inorganic materials. Despite its potential, the field lacks a fundamental understanding of the photophysics involved and the ability to model experimental data effectively. In this study, we quantitatively simulate polaritonic emission using the source term method. This model assumes that each molecular dipole in the exciton reservoir emits as it would in free space, into the optical environment formed by the polaritons. To benchmark theory with experiments, a BODIPY derivative containing a suitable amount of steric bulk was synthesized. Neat films of this molecule exhibited close to unperturbed absorption and emission envelopes compared to dilute solution. When placed in an optical cavity, the ultrastrong coupling regime was reached, and a collapse of the polaritonic line width was observed. Such a collapse is an indication of an ideal polariton, and it allowed for the emission in the transverse electric and magnetic polarizations to be spectrally resolved and thus successfully compared to the simulated emission. This work hence describes an effective model that fits experimental data, which is crucial for advancing the field and for optimizing applications.