Dynamic pendulum strategy enables both anti-quenching and fast spin flipping for efficient blue multiple-resonance thermally activated delayed fluorescence emitters

Abstract

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters have attracted considerable interest due to their superiority in high-resolution organic light-emitting diodes (OLEDs), but suffer from severe aggregation-caused quenching and slow reverse intersystem crossing. Herein, a dynamic pendulum strategy is proposed, in which electron donors are tethered to the classic boron–nitrogen MR core (BCzBN) by employing an oxygen atom as a flexible anchoring point. Benefitting from the distinctive oxygen linkage and dynamic swinging behavior, the resultant MR-TADF emitters can access multiple isomeric conformations, thereby simultaneously achieving blue-shifted emission, preserved narrow full width at half maximum, enhanced quenching resistance, and faster spin flipping compared with BCzBN. As a consequence, the corresponding OLEDs achieve bright blue narrowband electroluminescence in an extremely wide doping window of 1–30 wt%, revealing a record-high external quantum efficiency of 30.4% even at 20 wt%. The results clearly highlight the great potential of the dynamic pendulum strategy for efficient blue MR-TADF emitters.