Structural Influence on Exciton Formation and the Critical Role of Dark Excitons in Polymeric Carbon Nitrides

Abstract: Polymeric carbon nitrides (PCNs) exhibit intriguing optical properties and exceptional performance in (photo)catalysis, optoelectronics, and energy storage. Nevertheless, the intricate phenomena involving light absorption extending to the visible range, long-lived excitons, photo-charging, and photochemical processes observed in PCN derivatives remain poorly understood. Our theoretical investigation elucidates the origin of distinct dark and bright excitons, their stability and lifetimes, and their correlation with the microstructural attributes of PCNs. Furthermore, we identify the decisive role of dark excitons in catalytic reactivity, which underlies the differences in the photocatalytic performance of different PCN derivatives.