Engineering Nitrogen/Carbonyl MR‐TADF Emitters: Spiro‐Lock and Tert ‐Butyl Synergy in Narrowband Blue Emission

Abstract Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters with rigid planar structures are promising for their exceptional color purity and outstanding device efficiency. However, as an important MR unit, rigidly interlocked nitrogen/carbonyl‐based blue materials often face challenges like spectral broadening, red‐shifting, and reduced efficiency compared to nitrogen/boron system. Herein, a peripheral modification strategy incorporating tert ‐butyl groups via a spiro‐lock framework is used to synthesize four molecules: QAO‐TF, TQAO‐TF, TQAO‐F, and TSOQ. The spiro‐lock structure solidifies the molecular framework, narrows the emission bandwidth, and elevates the photoluminescence quantum yield to over 96%. Meanwhile, the peripheral tert ‐butyl groups introduce steric hindrance, isolating the luminescent core and suppressing intermolecular interactions in the solid state, thereby improving device efficiency while maintaining narrowband emission. Notably, TQAO‐F shows an electroluminescence peak at 476 nm with a 25 nm full width at half maximum (FWHM) and an external quantum efficiency (EQE) of 31.7%. TSOQ, with its oxygen‐induced charge effect, achieves narrowband pure blue emission with an FWHM of 20 nm, surpassing 30% EQE without sensitizers. This overall performance suggests its potential to rival the classic nitrogen/boron system.