cis – trans Isomerism Enables Visible Light‐Excited Room‐Temperature Phosphorescence and Dynamic Afterglow

Isomerism serves as a powerful strategy for modulating organic room‐temperature phosphorescence (RTP), which is crucial for developing novel RTP materials and elucidating structure‐property relationships. However, cis – trans isomerism that is widespread in organic compounds has not been deeply explored in terms of its influence on RTP properties. In this study, the cis – trans isomers of two 9,10‐dihydrophenanthrene‐9,10‐dicarbonitriles, DPCN‐H and DPCN‐O (with OMe group), are designed and synthesized. Significant differences in luminous behavior are observed between the cis‐ and trans ‐isomers. The trans ‐DPCNs exhibit notably superior RTP and afterglow performance compared to cis ‐DPCNs for their better structural planarity and tighter packing. Among them, trans ‐DPCN‐O achieves an afterglow quantum yield as high as 43% upon visible‐light excitation. Additionally, trans ‐DPCN‐H displays excitation‐power‐dependent and temperature‐dependent afterglow color modulation, while the nanoparticles of trans ‐DPCN‐O demonstrates efficient visible‐light‐excited afterglow in aqueous solution. The excellent RTP properties of the trans‐ DPCNs enable their successful application in complex anti‐counterfeiting with four dimensions, and in vivo imaging in mice under white LED excitation with a signal‐to‐noise ratio of up to 228. This work presents the first investigation into how cis – trans isomerism affects organic RTP and provides new insights into designing high‐performance RTP materials.