N─B─N Isomer Induced Room Temperature Phosphorescence: Expression, Mechanistic Insights, and Multi‐Level Anti‐Counterfeiting Applications

Abstract Achieving pure organic room temperature phosphorescence (RTP) materials is of great interest due to their applications in optoelectronics. However, improving RTP in pure organic materials by controlling triplet excitons is challenging due to their complex relaxation processes. Therefore, exploring effective strategies to modulate triplet excitons is crucial. Herein, we propose a N─B─N isomerization strategy to enhance RTP performance. Two isomers containing HN─B─NH units (B 2 {1,2‐(NH) 2 C 6 H 4 } 2 ), namely 1,1‐DB and 1,2‐DB, were synthesized to explore their RTP properties. Intriguingly, 1,1‐DB exhibited excellent RTP, whereas 1,2‐DB displayed negligible phosphorescence. The N─B─N unit in 1,1‐DB optimizes molecular configuration and interactions, enhancing electron delocalization and stabilizing triplet excitons, which improves intersystem crossing (ISC) and spin‐orbit coupling (SOC) while reducing nonradiative decay, thus enabling RTP. Additionally, based on phosphorescence resonance energy transfer, multicolor afterglows were achieved by doping fluorescein into 1,1‐DB. This work not only provides a new class of RTP materials but also offers valuable insights for the discovery and optimization of rational designs in RTP materials, potentially triggering the exploration of new functions and properties within boron‐nitrogen molecular systems.