Triphenylene-Involved π-Extension Combining With Phenyl-Blocking Enhances the Stability of MR-TADF Emitter:...

The realization of ultrahigh definition displays necessitates pure-green organic light-emitting diodes (OLEDs) with simultaneously exceptional efficiency, high color purity, and long-term operational stability. Herein, we develop a series of pure-green multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters based on the boron/nitrogen-embedded polycyclic aromatic hydrocarbon (BN-PAH), designed through a rational moderate π-extension and peripheral phenyl blocking strategy. The molecular designs afford narrowband pure-green emission with a full-width at half-maximum (FWHM) of nearly 20 nm and high photoluminescence quantum yields (Φ_PLs, up to 95%). By systematically blocking the redox-active positions with phenyl groups, the emitters exhibit significantly enhanced electrochemical and photochemical stability. In bottom-emitting OLEDs, the optimized emitter BN-Tpl-Ph achieves a maximum external quantum efficiency (EQE_max) of 33.8% and long operational lifetime (LT80 = 4012 h at 1000 cd m^-2). Notably, in a top-emitting OLED configuration, BN-Tpl-Ph delivers a pure-green emission with a Commission Internationale de l'Eclairage (CIE) y-coordinate of 0.78, a high EQE_max up to 59.2%, and an LT80 of 409 h at 5000 cd m^-2. This work reveals the effectiveness of molecular design strategies that combine moderate π-extension with peripheral phenyl blocking for developing high-performance pure-green MR-TADF emitters.