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 (EQEmax) 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 EQEmax 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. Three efficient multiple resonance thermally activated delayed fluorescence emitters are synthesized through positional isomerization of benzenesulfonyl-functionalized dibenzothiophene sulfinylimide units. The corresponding organic light-emitting diodes show high external quantum efficiencies (EQEmax) of up to 33.8%. Even at a doping concentration of 20 wt.%, the EQEmax remains at 28.9%. image