Intramolecular charge transfer assisted multi-resonance thermally activated delayed fluorescence emitters for high-performance solution-processed narrowband OLEDs

-substitution as a pendant on an organoboron multi-resonance core. The newly designed MR-TADF emitters not only maintain short range charge transfer characteristics in emissive states without sacrificing color purity but the accelerated spin flips facilitated by the ICT process at a high-lying state are also confirmed by ultrafast spectroscopy and theoretical calculation, achieving over a 10-fold increase in the reverse intersystem crossing rate compared with unsubstituted counterpart emitters. In sensitizer-free solution-processed OLEDs, a cutting-edge external quantum efficiency of 27.8% can be achieved together with reduced efficiency roll-offs and an attractive full width at half maximum of 29 nm, representing a breakthrough in efficiency for solution-processed MR-TADF based narrowband OLEDs.