Probing the relaxation channels of metalloporphyrin cavity polaritons with ultrafast dynamical spectroscopy

A photochemical reaction involves the reactant moving from its own excited state potential energy surface to the ground state potential energy surface of the product. Control over excited state dynamics remains an unfulfilled goal of the chemical physics community. In this study we examine how the formation of molecular polaritons impacts the molecular dynamics of a ZnTPP molecule strongly coupled to a cavity mode. Cavity polaritons were formed by coupling the Soret transition of ZnTPP to the photons of a Fabry Perot micro cavity. We then proceed to probe the non radiative transition between the S₂ -S₁ excited states using transient spectroscopy measurements as a function of the collective Rabi splitting. We find inverse relationships between both the rate and efficiency of S₂-S₁ internal conversion and the Rabi splitting. We propose that interpolariton decay channels increasingly control the rate of internal conversion as the Rabi splitting approaches the energy of the vibrations involved in non-radiative relaxation of excited state population to the S₁ state. Our research suggests that researchers must carefully understand the photphysics of molecules strongly coupled to cavity photons to enable their application to next generation of photochemical technologies.