Engineering room‐temperature phosphorescence in purely organic materials through isomeric molecular packing and intermolecular interactions

Abstract Achieving control over room‐temperature phosphorescence (RTP) performance through delicate molecular engineering and intermolecular interactions is of great significance for advancing RTP research. In this study, a series of isomers containing up to four compounds were synthesized by integrating a tetrahydroquinoline substituent at different positions of a phenoxathiine core. All compounds exhibit afterglow RTP emission in the crystalline state, attributed to diverse intermolecular interactions that stabilize triplet excitons. Notably, the variation in substitution positions leads to distinct intermolecular interactions, enabling fine‐tuned RTP properties through strategic molecular engineering. Among them, the isomer 2,1‐PXTACR, which exhibits robust intermolecular interactions, achieves an exceptional afterglow duration exceeding 5 s and an average phosphorescence lifetime of 310 ms. Furthermore, the specific role of the solid‐state environment in stabilizing triplet excitons is systematically elucidated in this work. The molecular modulation strategy established herein provides valuable insights into the structure‐property relationships governing RTP materials and offers a rational approach for developing high‐performance purely organic phosphorescent systems.