Boron‐Locked Diaza‐Octagon Strategy for Constructing Multi‐Resonance Emitters Enabling Anti‐Quenching Narrowband OLEDs With High Efficiency and Low Efficiency Roll‐Off

ABSTRACT Developing multi‐resonance (MR) emitters to simultaneously achieve high external quantum efficiency (EQE), low efficiency roll‐off, and suppressed aggregation‐caused quenching and spectral broadening is critically important and challenging for advancing narrowband organic light‐emitting diodes. Herein, two emitters, 8NN‐1B and 8NN‐2B, are developed based on diaza‐octagon–containing emitting core (8NN) through the incorporation of multiple boron/nitrogen (B/N) units. Building upon the inherent MR characteristics and saddle‐shaped configuration of the 8NN matrix, the boron‐locked derivatives exhibit a markedly enhanced MR effect along with attractive aggregation‐induced emission and aggregation‐narrowed emission properties. Through rational regulation of electronic effects, their singlet‐triplet energy splitting values are significantly reduced, while the spatially twisted conformation for the diaza‐octagon heterocycle enhances spin–orbit coupling. Consequently, the reverse intersystem crossing rate in 8NN‐2B is boosted up to 7.7 × 10 5 s −1 , and its sensitizer‐free device achieves a high maximum EQE of 32.20% with negligible efficiency roll‐off at 1000 cd m −2 luminance. Notably, such high efficiency is well maintained even at a high doping concentration of 10 wt%, owing to suppressed molecular packing induced by the 8NN matrix. These results highlight a mutual modification strategy that exploits the complementary strengths of the diaza‐octagon core and BN framework for high‐performance narrowband emitters.