Enhanced Light–Matter Interaction and Polariton Relaxation by the Control of Molecular Orientation

Exciton‐polaritons, in which the electronic state of an excited organic molecule and a photonic state are strongly coupled, can form a Bose–Einstein condensate (BEC) at room temperature. However, so far, the reported thresholds of organic polariton BECs under optical excitation are as high as Pth = 11–500 μJ cm–2. One route toward lowering the condensation threshold is to increase the Rabi energy by aligning the molecular transition dipole moments. In this report, it is demonstrated that control of the orientation of a perylene‐based discotic dye, which is able to self‐organize in mesogenic columnar structures, can significantly enhance exciton–photon interaction and polariton relaxation rate in optical cavities. These results show the importance of the molecular orientation for strong light–matter interactions and provide a promising strategy toward the realization of an organic low threshold polariton BEC system and electrically driven organic polariton BEC. This work demonstrates for the first time experimentally, that the orientation of the transition dipole moments is one of the key factors for the accelerating polariton relaxation. These outcomes show that the in‐plane orientation of dipole moments is a promising strategy for lowering the Bose–Einstein condensate (BEC) threshold mainly related to the polariton relaxation rate.