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, formation of long‐lived excitons, photo‐charging, and photochemical processes observed in PCNs remain poorly understood. This theoretical investigation elucidates the origin of distinct dark and bright excitons, their stability and lifetimes, and their correlation with the microstructural attributes of PCNs. Based on these results, the decisive role of dark excitons in photocatalytic reactivity is proposed, which underlies the experimentally observed differences in the photocatalytic performance of various PCN derivatives. This study thus establishes novel insights into the factors governing the light‐driven processes in PCNs that can provide essential guidelines for rational design of PCNs with enhanced performance.