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

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.