Helical Multi-Resonance Thermally Activated Delayed Fluorescence Emitters for High-Performance Anti-Quenching Narrowband Blue OLEDs.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) has established a new approach for narrowband blue organic light emitting diodes (OLEDs), yet effectively suppressing intermolecular interactions especially at high doping concentrations while preserving the intrinsic narrowband emission remains a formidable challenge. Herein, a novel designing paradigm is proposed for achieving anti-quenching narrowband emission in MR-TADF molecules by embedding the indeno[2,1-b]carbazole unit into the polycyclic aromatic hydrocarbon skeleton. The proof-of-concept emitter DT-BON1 reveals a favorable twist angle of 31.8°, manifesting formation of helical architecture within MR core. As a result, the emission peaks and full width at half maximum show virtually no variation with changing doping concentration from 1 wt% to 20 wt%. Moreover, the photoluminance quantum yields exceed 90% even at 20 wt% doping concentration endowed by the outstanding anti-quenching characteristics. The DT-BON1 based OLEDs can achieve maximum external quantum efficiency (EQEmax) of exceeding 30%. Especially, the alleviated exciton quenching effects can be firmly demonstrated by marginally decreased EQEmax values, attaining 29.2% in 10 wt%-based OLEDs and 27.3% even in heavily doped devices (20 wt%), which is at a record high for MR-TADF with blue emission at such high doping concentration.