High-efficiency narrowband multi-resonance TADF emitters the introduction of bulky adamantane units

The fluorescence quenching of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials has remained a formidable challenge due to the strong π-π packing and intense intermolecular aggregation. To this end, we designed MR-TADF molecules modified with adamantane with large spatial hindrance, named BN-Ad , to mitigate the intermolecular π-π stacking between rigid planar skeletons and prevent aggregation-caused quenching. Photoelectric properties of BN-Ad in solutions and thin films were systematically investigated, and the electroluminescence properties were characterized by fabricating organic light-emitting diodes (OLEDs). The optimized device employing BN-Ad exhibited a maximum external quantum efficiency (EQE max ) of 32.3% peaking at 500 nm with a small full width at half maximum (FWHM) of only 35 nm. When the doping ratio increased to 50 wt%, the EQE max can still be maintained at 11.2% with a slightly red-shifted emission peak at 508 nm and a moderately widened FWHM of 53 nm. New design strategy for MR-TADF emitters by incorporating bulky adamantane unit as steric hindrance into MR skeletons to mitigate intermolecular π-π stacking and green organic light-emitting diodes with high EQE up to 32.3% and low roll-off are achieved.