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

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/m²) and a maximum luminance of 5.61×10⁵ cd/m². 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.