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

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 × 105 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.