Boron–Oxygen Lewis Pairs Integrated Multi‐Resonant Thermally Activated Delayed Fluorescence Emitter for High‐Performance BT.2020 Deep‐Blue OLEDs

Abstract The quest for deep‐blue emitters meeting the stringent BT.2020 color standard—requiring an ideal peak, narrow full‐width‐at‐half‐maximum (FWHM), and minimal singlet‐triplet energy splitting (ΔEST)—is often hampered by the complex synthesis of multi‐resonant thermally activated delayed fluorescence (MR‐TADF) molecules. This work introduces a novel, selective strategy: incorporating B–O Lewis pairs into an MR‐TADF system via intramolecular electrophilic borylation. By carefully controlling a tandem bora‐Friedel–Crafts reaction, we synthesized the saddle‐shaped molecule 3BON , despite the typical vulnerability of annulated boron structures to retro‐bora‐Friedel–Crafts reactions. 3BON exhibits highly efficient deep‐blue TADF emission, with a peak at 440 nm, a narrow FWHM of 18 nm, and a low ΔEST of 0.12 eV. Compared to its parent emitter, DABNA‐1, 3BON achieves a simultaneous blue‐shift, narrowed FWHM, and reduced ΔEST. Principal Interacting Orbital (PIO) analysis indicates that unique orbital interactions involving the B–O Lewis pairs destabilize energy levels, causing the blue‐shifted emission. Organic light‐emitting diodes (OLEDs) utilizing 3BON demonstrated state‐of‐the‐art performance. The device achieves a maximum external quantum efficiency (EQE max ) of 24.8% (at 9 wt.%) with ultra‐deep blue narrowband emission (443 nm peak, 24 nm FWHM; CIE: 0.1554, 0.0454), fully satisfying the BT.2020 standard. Furthermore, 3BON's unique saddle‐shaped architecture imparts remarkable doping tolerance, with EQE max climbing up to 26.3% across a wide 0.520 wt.% doping range. A hyperfluorescent (HF) device also showed excellent performance (EQE max = 23.8%, 441 nm peak, 19 nm FWHM). These results represent one of the best BT.2020‐compliant OLED performances reported to date.