41‐4: Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters for Pure Blue OLEDs with Suppressed Efficiency Roll‐Off

Herein, we demonstrate versatile narrowband deep blue MR‐TADF emitters (KHU 1 and KHU 2) featuring enlarged ring‐fused structurally increased steric hindrance rigidity accessed by incorporating meta‐xylene rotors. In comparison to 1, tri substituted emitter exhibits a substantial shift (12 nm) while maintaining characteristics with high color purity (FWHM = 27 nm). Further, the solid‐state investigations conclude that they possibly suppress non‐radiative energy loss thus improve fast reverse intersystem crossing rate (kRISC ~ 2.8 x 10 5 S ‐1 ) photoluminescence quantum yield > 90%. Fabricated HF‐ OLEDs these show excellent external efficiency of over 26% ultra‐low roll‐off.