Dual Multiresonance Core Strategy Enable Efficient Pure Blue Organic Light‐Emitting Devices Based on Fluorene Linkages

Abstract Multiresonance thermally activated delayed fluorescence (MR‐TADF) emitters with high color purity in virtue of their inherent narrowband emission have received great interest in organic light‐emitting diodes (OLEDs). However, it remains a big challenge to develop the ultrapure blue MR‐TADF emitters with high efficiency. In this work, a novel “dual‐MR‐core” strategy is proposed by connecting two parent N‐B‐O‐skeletons with non‐conjugate 9‐position substituted fluorene linkages for high efficient deep‐blue MR‐TADF emitters, namely H‐FOBN and Me‐FOBN, which possess the highly twisted structure with suppressed aggregation. Finally, the vacuum‐deposited deep‐blue OLED exhibits excellent external quantum efficiency (EQE) of 25.1% with small full width at half maximum (FWHM) of 28 nm, as well as CIE of (0.14, 0.08). Furthermore, owing to enhanced solubility, the solution‐processed deep‐blue OLED based on Me‐FOBN shows EQE of 11.3%, with small FWHM of 32 nm and CIE of (0.14,0.09). These outstanding performances confirm that this “dual‐MR‐core” strategy provides a feasible approach to develop high efficient ultrapure blue MR‐TADF emitters.