Hybrid Multi-Resonance Thermally Activated Delayed Fluorescence Emitters via Carbonyl-Mediated Structural Engineering

Incorporating fused carbonyl structures into multi-resonance (MR) molecular frameworks has become a promising strategy for precise emission color tuning and spectral narrowing. However, only a handful of such molecules have been developed, primarily due to the harsh reaction conditions required for carbonyl-related reactions. Herein, we report a feasible one-pot synthetic approach to embed carbonyl groups as lockers into B/N-skeletons under mild conditions, yielding BN-CO—the first blue boron/nitrogen/carbonyl hybrid MR emitter. Owing to enhanced molecular planarity and rigidity, BN-CO exhibits an emission maximum (λₑₘ) of 462 nm with an ultra-narrow full width at half maximum (FWHM) of merely 16 nm. Notably, these carbonyl groups also serve as versatile modification sites: subsequent iron-catalyzed aza-annulation affords a yellow-green-emitting BN-CN (λₑₘ=546 nm, FWHM=26 nm), which uniquely combines imine/amine and B/N MR characteristics while exhibiting a significant 84 nm emission red-shift. The corresponding OLEDs show remarkable maximum EQEs: 33.5% for BN-CO and 38.0% for BN-CN. Notably, BN-CN-based devices exhibit extremely small efficiency roll-off (EQE=34.2% at 100,000 cd/m²) and a maximum luminance of 5.61×10⁵ cd/m². This approach provides a versatile route to novel MR architectures and enables carbonyl groups as tunable modification sites for advanced molecular engineering.