Integrating Asymmetric O−B−N Unit in Multi-Resonance Thermally Activated Delayed Fluorescence Emitters towards High-Performance Deep-Blue Organic Light-Emitting Diodes

Developing deep-blue thermally activated delayed fluorescence (TADF) emitters with both high efficiency and color purity remains a formidable challenge. Here, we proposed a design strategy by integrating asymmetric oxygen-boron-nitrogen (O−B−N) multi-resonance (MR) unit into traditional N−B−N MR molecules to form a rigid and extended O−B−N−B−N MR π-skeleton. Three deep-blue MR-TADF emitters of OBN, NBN and ODBN featuring asymmetric O−B−N, symmetric N−B−N and extended O−B−N−B−N MR units were synthesized through the regioselective one-shot electrophilic C−H borylation at different positions of the same precursor. The proof-of-concept emitter ODBN exhibited respectable deep-blue emission with Commission International de l′Eclairage coordinate of (0.16, 0.03), high photoluminescence quantum yield of 93 % and narrow full width at half maximum of 26 nm in toluene. Impressively, the simple trilayer OLED employing ODBN as emitter achieved a high external quantum efficiency up to 24.15 % accompanied by a deep blue emission with the corresponding CIE y coordinate below 0.1.