Synergistic π-Extension and Peripheral-Locking of B/N-Based Multi-Resonance Framework Enables High-Performance Pure-Green Organic Light-Emitting Diodes.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters offer natural advantages for creating power-efficient, wide-color-gamut OLEDs. However, current green MR-TADF emitters face challenges in simultaneously achieving high color purity and efficient reverse inter-system crossing (RISC), leading to suboptimal device performance. In this study, we propose a synergistic molecular design approach that combines π-extension and peripheral locking to address these challenges. This approach allows for the construction of quadruple borylated MR-TADF emitters that not only deliver precisely tuned pure-green emission with a narrow full width at half maximum (FWHM) of 15 nm, but also exhibit close-to-unity quantum yield, rapid RISC, and optimal horizontal dipole orientation. The resulting sensitizer-free OLED approaches the BT.2020 standard with CIE coordinates of (0.18, 0.74) and demonstrates impressive external quantum efficiency (EQE) of 36.6 % at maximum and 31.8 % at 1000 cd m. Additionally, the device shows good operational stability, with a lifetime (LT) of 485 hours at an initial luminance of 1000 cd m. This study hence offers a promising molecular design strategy that effectively enhances the comprehensive OLED performance.