Anionically Stabilized B‐N Emitting Frameworks via Asymmetric N‐fusion: A Route to Long‐Lived Blue Multi‐Resonance Emitters

Abstract Stable multi‐resonance thermally activated delayed fluorescence (MR‐TADF) blue emitters are an effective choice for organic light‐emitting diodes (OLEDs), offering high colour purity and efficiency. Here, a stable B─N emitting core is developed through an asymmetric N‐fusion strategy. This involved constructing a B─N emitting core on a robust carbazole backbone, which enhances structural rigidity and reduces the number of weak sp ³ C─N bonds relative to typical DABNA emitters, thereby increasing the bond‐dissociation energies of the anionic state. Additionally, the peripherally fused carbazoles yielded two emitters, namely, pCz‐BN2 and mCz‐BN2, exhibiting pure blue emissions at 457 and 459 nm in a toluene solution, with corresponding CIEx,y of (0.13, 0.07), and achieved high photoluminescence quantum yields over 95% for the emitters, respectively. The fabricated fluorescence OLEDs produce pure blue emissions at 459 and 463 nm, with maximum EQEs of 8.67% and 6.90% for pCz‐BN2 and mCz‐BN2 , respectively, demonstrating minimal efficiency roll‐off. Furthermore, the PSF‐OLEDs emit blue light with high EQEs of 25.8% and 23.6%, respectively, with reduced roll‐off. Significantly, the pCz‐BN2 ‐based Fl‐OLED has attained a remarkable operational lifetime (LT ₉₅ ) of 95 h at an initial luminance of 1000 cd m ^{− 2} , the longest reported among single‐boron MR emitters to date.