Construction of Concentration Quenching‐Resistant Multi‐Resonance TADF Emitters via Positional Isomerization for OLEDs

Multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters are promising for high‐definition organic light‐emitting diodes (OLEDs) due to their high exciton utilization and color purity. However, strong interchromophore interactions cause most MR‐TADF emitters with planar structures to aggregate at high doping concentrations, leading to degraded efficiencies. Herein, using benzenesulfonyl‐functionalized dibenzothiophene sulfoximine with steric effects, three MR‐TADF emitters (2SBN, 3SBN, and 4SBN) are synthesized by coupling the classic DtBuCzB skeleton at different sites. Three emitters exhibit green or blue‐green emission with full width at half maximum (FWHM) values less than 29 nm and photoluminescence quantum yields exceeding 90%. OLEDs based on 2SBN, 3SBN, and 4SBN achieve high maximum external quantum efficiency (EQE max ) values of 30.1%, 27%, and 33.8%, respectively, at a 5 wt.% doping concentration. Notably, due to the distorted conformation of 4SBN and suppressed intermolecular interaction, the OLED remains high EQE max of 28.9% at a doping concentration of 20 wt.%. These results demonstrate the feasibility of molecular design to modulate spatial conformations via positional isomerism to develop MR‐TADF emitters with reduced concentration quenching.