Late-stage direct double borylation of B/N-based multi-resonance framework enables high-performance ultra-narrowband...

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are promising for organic light-emitting diodes (OLEDs) owing to their narrowband emission and efficient triplet utilization. However, realizing stable deep-blue emission with high practical efficiency remains challenging, largely due to limited strategies for hypsochromic shifts without compromising photophysical properties. Here, we report a late-stage direct double borylation strategy for B/N-based MR frameworks, which extends π-conjugation resonance, increases transition energy, enhances transition dipole moment, and reduces the S₁-T₁ energy gap. The proof-of-concept emitter, ν-DABNA-M-B-Mes, exhibits blue-shifted emission compared to its parent molecule while maintaining excellent TADF characteristics, including high photoluminescence quantum yield (93%), narrowband emission (16 nm), and fast reverse intersystem crossing rate (2.05 × 10⁵s^-1). OLEDs employing ν-DABNA-M-B-Mes achieve outstanding performance with >30% external quantum efficiency, high luminous efficacy, and near NTSC color purity. Furthermore, phosphor-sensitized fluorescence device display a minimal efficiency roll-off and long operational lifetime (LT₈₀ > 1000 h at 100 cd m^-2), establishing a new benchmark for blue OLEDs.