Construction of Hybrid Long- and Short-Range Charge Transfer Excitations for High-Performance Deep-Blue Electroluminescence with CIEy < 0.04 and EQE > 35%

In this work, a design strategy for deep-blue multiresonance thermally activated delayed fluorescence (MR-TADF) molecules was developed by the fusion of the weak O-B-N MR units and the peripheral modification of strong electron-donating diphenylamino group, resulting in hybrid long- and short-range charge transfer excitation characteristics with accelerated delayed fluorescence properties. As a proof-of-concept molecule, DOBN shows a narrowband deep-blue emission peaking at 438 nm and a small full width at half-maximum (fwhm) of 19 nm as well as a high delayed fluorescence efficiency of 51%. Finally, high external quantum efficiencies (EQEs) and small CIEy chromaticity coordinates were realized in both solution-processed (27.7%, 0.03) and vacuum-evaporated (35.4%, 0.04) hyperfluorescence organic light-emitting diodes (OLEDs) employing DOBN as the emitter. These results demonstrate a feasible molecular design strategy for high-performance deep-blue MR-TADF emitters and represent the state-of-the-art performances of deep-blue OLEDs in terms of EQEs and color coordinates.