The strong coupling of cavity photons to the electrons in frontier orbitals of molecular ensembles leads to the formation of cavity polariton states delocalized over many chromophores. Many researchers propose these delocalized, hybrid light-matter excitations can enable novel mechanisms to control energy and charge transfer in addition to ground state chemistry in the dark. While most of the focus on polariton formation deals with mechanistic understanding of how strong light-molecule coupling leverages photonic character to affect chemical processes, much less effort has been put into understanding how molecular properties can impact polaritonic behavior. We present results indicating the non-Condon vibronic coupling of the B and Q states in copper (II) tetraphenyl porphyrin (CuTPP) molecules leads to the formation of a dispersive band significantly below the energy of the cavity photons under strong light-matter coupling. Beginning with a simple three level, Tavis-Cummings model, we show vibronic coupling between the B and Q states of a molecule like CuTPP drives formation of a weakly dispersive, Q-like state that always lie below the energies of dark molecular Q states. To test these theoretical predictions, we fabricated and characterized single and multilayer cavity polariton samples using CuTPP. We find the PL spectra of these samples in the region contains light emission peaks consistent with the predictions of the simple theory. We propose changes in the polariton potential energy surfaces as a function of the energy detuning between cavity photons and the Soret resonance of CuTPP help explain variations in the peak characteristics in different multilayer samples. Our results demonstrate how one can use the intrinsic properties of molecules to enable the formation of novel, light-like states in cavity polariton samples.

Evidence of polaritonic intensity borrowing in a strongly coupled metalloporphyin-cavity system

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.