Cavity Polaritons formed from Spatially Separated Quasi-degenerate Porphyrin Excitons: Energetics and Structures of Bright and Dark States

In this study, we assess the properties of cavity polaritons formed from the strong coupling of photons to nearly degenerate molecular excitons located in separate layers of multi-layer Fabry-Perot resonators. By embedding copper (II) tetraphenyl porphyrin (CuTPP) and free base tetraphenyl porphyrin (H2TPP) in separate layers of the intracavity region, we present evidence of cavity polariton formation using angularly resolved transmission spectra. Multi- chromophore models enable our characterization of the polariton state consistent with our experimental results. The results show the existence of a middle polariton state whose photonic content does exceed 5% for any fabricated sample, which makes these states spectroscopically dark. We use models of the excited state potential energy surfaces (PESs) of each porphyrin molecular species to computed and characterize multipolariton PESs. These calculations indicate modulations of each molecule’s structure lead to different changes in the composition and energy of the multipolariton states. In particular, by modulating the structure of H2TPP, which possesses a lower energy Soret transition, we can drive excitonic resonance that cause the photonic content of the MP state to oscillate between zero and non-zero values. Our results and analysis suggest multipolariton formation from quasi-degenerate molecular excitons could provide means to optoelectronic device such as THz-rate light modulators useful for classical and quantum information processing protocols.