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

ABSTRACT 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 (LT 90 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.