Communication between polaritonic and excitonic manifolds in an electronically strong coupled system

Optically dark states, which arise from intermolecular exciton coupling, are a crucial component in understanding the optical properties of natural and artificial light harvesters. Dark states also constitute a major density of states in the energy manifold of a strong-coupled system, which is generated from the interaction between a cavity photon and molecular excitons. Unlike optically bright upper and lower polariton states, dark state wavefunctions contain no photonic excitation and therefore have been considered to retain molecular character. In this framework, dark states not only serve as a deactivation pathway but also can participate in excitation energy exchange to states that are not coupled to cavity photons. We test this view by following the excited-state dynamics of bright to dark state interconversion in an electronically strong-coupled cavity composed of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). We show that dark states have a lifetime longer than that of uncoupled molecules indicating a significant change in the state character. Discussion on the communication between the dark states and the exciton manifold of uncoupled 4CzIPN triplet states will be presented.