Efficient narrowband organic light-emitting diodes based on B,O embedded multi-resonance emitters containing B-N covalent bonds

Multi-resonance (MR) thermally activated delayed fluorescence (TADF) materials emerge rapidly in recent years, and are expected to be an effective solution for ultra-high-resolution displays. Solving the main issues of low yield and dangerous lithium reagent for synthesis, extending the material diversity and figuring out the structure–activity relationship would all be beneficial to promote their commercialization. Herein, two easy-to-access MR-TADF emitters, BO-N1 and BO-N2, are constructed by integrating B,O-based MR polycyclic aromatic with B-N covalent bonds. The B-N covalent bonds are formed through simple amine-directed borylation with high yield over 90 %, which significantly improves yield, simplifies procedure and effectively avoids hazardous lithiation compared to the traditional methods. Two emitters exhibit bright green emissions in doped films with full width at half maximum (FWHM) of 28 and 24 nm, and high photoluminescence quantum yields (PLQY) of 85 % and 90 %. The green electroluminescent device of BO-N2 achieves narrow-band spectrum with FWHM of 29 nm, maximum brightness of 10480 cd m−2 and external quantum efficiency (EQE) of 20.1 %.