Boron‐Nitrogen Multi‐Resonance Framework With Heptagon‐Fused Carbazole and Spiro‐Locking Units Enables Extremely Long‐Lifetime Narrowband Green OLEDs

Achieving high efficiency, narrow emission bandwidth, and long operational stability simultaneously remains a major challenge for organic light-emitting diodes (OLEDs) in ultra-high-definition (UHD) displays. Herein, we report a synergistic molecular design integrating boron-nitrogen-based multiple resonance (MR) frameworks with π-extended heptagon-fused carbazole (HpCz) and dibenzo-carbazole (DBCz) units, reinforced by a spiro-locking architecture. This dual strategy enhances molecular rigidity, suppresses vibronic coupling, and improves chemical stability. The resulting emitters, DBCzB-Fl and HpCzB-Fl, exhibit narrow green emission with full-widths at half-maximum of 26 (0.114 eV) and 22 nm (0.080 eV), respectively. OLEDs based on HpCzB-Fl achieve an external quantum efficiency of 27.7%, a current efficiency of 113.0 cd·A^-1, a power efficiency of 126.8 lm·W^-1, and an operational lifetime (LT₉₀ at 1000 cd·m^-2) of 17811 h, which is 2.3 times longer than its DBCz analogue. The superior performance and stability arise from the HpCz-spiro synergy, offering a robust design paradigm for stabilizing MR frameworks while maintaining spectral precision for next-generation UHD display technologies.