Electronic Strong Coupling Modifies the Ground-state Intermolecular Interactions in Chlorin Thin Films

The electronic strong coupling (ESC) of a molecular transition with cavity modes can result in modified excited state photophysics compared to its uncoupled counterparts. Often, such changes are attributed to kinetics effects, overlooking the possible modifications to ground-state intermolecular interactions. The spin-coated films of Chlorin e6 trimethyl ester (Ce6T) provide a platform for studying the role of ESC in dictating photophysics and intermolecular interactions. The preorganization of Ce6T molecules in thin films facilitates intermolecular excitonic interaction, leading to an intense excimer-like emission upon photoexcitation. Interestingly, the ESC of the Ce6T Q-band results in modified luminescence characteristics, where the polaritonic emission dominates over the excimer-like emission. Remarkably, our steady-state, time-resolved emission and the excitation spectral analysis reveal that ESC suppresses the ground-state intermolecular excitonic interactions that otherwise exist in the preorganized Ce6T thin films. These findings will provide valuable insights into the fundamentals of quantum light-matter interactions and coherent energy transport processes.