Rational Design of High-Efficiency Deep-Blue Multi-Resonance Thermally Activated Delayed Fluorescence Materials with CIEy < 0.06 and Narrowband Emission

The development of deep-blue emitters for organic light-emitting diodes (OLEDs) faces challenges in achieving high color purity and efficiency. Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials, known for narrowband emission and high photoluminescence quantum yields (PLQYs), offer a promising solution. We propose a molecular design strategy by incorporating rigid carbazole derivatives into the MR framework, yielding deep-blue emitters, DPABNO and DPABNS. These materials exhibited emission peaks at 445 and 448 nm in toluene, with narrow fwhm values of 26 and 25 nm, respectively. Their rigid structures suppress vibronic coupling, achieving PLQYs > 90% in the mCBP host matrix and remarkably short delayed fluorescence lifetimes (32.5 and 31.2 μs), reducing exciton annihilation. Sensitized OLEDs achieved external quantum efficiencies of 21.1% and 23.6%, with CIE coordinates matching the European Broadcast Union deep-blue standard. This work provides a robust strategy for high-performance deep-blue MR-TADF materials, advancing next-generation OLED displays.