A One‐Pot Carbonyl‐Functionalization Strategy for Hybrid Multi‐Resonance Thermally Activated Delayed Fluorescence Emitter Towards Highly Efficient Narrowband Blue and Yellow‐Green OLEDs

Abstract The incorporation of fused carbonyl structures into multi‐resonance (MR) molecular frameworks is a promising strategy for precise emission color tuning and spectral narrowing. However, few molecules have been developed through this strategy, primarily because of the harsh reaction conditions required for carbonyl‐related reactions. Herein, a feasible one‐pot synthetic approach is reported for embedding carbonyl groups as lockers in B/N‐based skeletons under mild conditions, yielding BN‐CO, a blue boron/nitrogen/carbonyl hybrid MR emitter. Owing to enhanced molecular planarity and rigidity, BN‐CO exhibits an emission maximum (λ e ) of 462 nm with an ultra‐narrow full width at half maximum (FWHM) of 16 nm. These carbonyl groups also function as versatile modification sites. Subsequent aza‐annulation affords a yellow‐green‐emitting BN‐CN (λ e = 546 nm, FWHM = 26 nm), which uniquely combines imine/amine with B/N MR characteristics while exhibiting a significant 84 nm emission red‐shift. The corresponding organic light‐emitting diodes exhibit high maximum EQEs (33.5% for BN‐CO and 38.0% for BN‐CN). Notably, BN‐CN‐based devices exhibit extremely low efficiency roll‐offs (EQE = 34.2% at 100,000 cd/m 2 ) and a maximum luminance of 5.61×10⁵ cd/m 2 . The proposed approach provides a versatile route for fabricating novel MR architectures and enables the use of carbonyl groups as tunable modification sites facilitating molecular engineering.