Boron-Oxygen Lewis Pairs Integrated Multi-Resonant Thermally Activated Delayed Fluorescence Emitter for...

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.