Aromaticity-Localized Square Tetraboron-Extended Multiple-Resonance Emitters With B‒N Covalent Bonds for Highly...

Polycyclic aromatic hydrocarbons with multiple-resonance (MR) effect are emerging as leading candidates for wide-color-gamut displays. However, it remains a significant challenge to red-shift their emissions to long wavelengths without sacrificing the spectral full width at half maximum (FWHM). Herein, a synergistic strategy of aromaticity localization and tetraboron extension is newly proposed, in which a B‒N covalent-bond-fused MR core is fused with 5,10-dihydro-5,10-diphenylphenazine (DPPA) to afford two yellow-emitting narrowband tetraboron emitters. By integrating multiple local B-π-B motifs into a rigid square-like tetraboron MR framework, DPA-4B and DMAC-4B achieve a pronounced red shift from violet-blue DPA-1B to yellow emission. The antiaromatic N₂C₄ ring and surrounding nonaromatic 1,2-BN/1,4-BN heterocycles promote aromaticity localization and suppress excited-state relaxation, affording narrow emissions at 544-559 nm with FWHMs of 20-21 nm. The DPA-4B and DMAC-4B-based sensitized OLEDs further achieve narrowband yellow electroluminescence with maximum EQE values of 36.7% and 30.1%, respectively. These results demonstrate that the combination of aromaticity localization and tetraboron extension is a promising molecular design rule for simultaneously realizing emission red-shifting, spectral narrowing, and device efficiency in B‒N covalent-bond-containing MR emitters.