Dual-Core Engineering for Efficient Deep-Blue Multiple Resonance Thermally Activated Delayed Fluorescent Materials

Developing narrowband blue multiple resonance (MR) organic emitters with Commission Internationale de L'Eclairage (CIE) y coordinates <0.1 is essential for advanced display technologies. This study proposes a deep-blue thermally activated delayed fluorescence (TADF) emitter, named 2BNO, which integrates two independent MR cores. Unlike many TADF materials with single-bonded dual emitting cores, 2BNO utilizes a steric hindrance-assisted fluorene bridge to achieve an orthorhombic molecular structure. The dual-core MR-TADF emitter shows enhanced light absorption and a high photoluminescence quantum yield. Notably, the emission of 2BNO is not significantly redshifted compared to single-core compounds and maintains a narrow full width at half-maximum (FWHM) of 24 nm with CIE coordinates of (0.147, 0.041) in 2Me-THF solution, nearing the BT.2020 blue standard. Organic light-emitting diodes (OLEDs) incorporating 2BNO as the emitter exhibit deep-blue emission at 460 nm with a narrow FWHM of 29 nm and CIE coordinates of (0.14, 0.09). The dual emitting core design significantly improves device efficiency, achieving a high external quantum efficiency (EQE) of 19.8%. The dual-core molecular design strategy in this work is demonstrated to be effective in promoting the efficiency of the TADF emitters while preserving deep-blue color purity.