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

Abstract

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