A peripheral modification strategy for high performance multi-resonance TADF emitters to construct sensitized OLEDs

Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show great application potential in high color purity and high-resolution organic light-emitting diodes (OLEDs) display. However, the high-performance narrowband MR-TADF based OLEDs are still scarce. In this work, two new MR-TADF emitters Me-PABCZ and Me-PABDPA with high photoluminescence quantum yields (PLQYs) of 94.6 % and 91.8 % respectively, are designed and synthesized by a one-shot electrophilic C-H borylation reaction. The full-width at half-maximum (FWHM) values of photoluminescence spectra in the high dispersion state of Me-PABCZ and MePABDPA luminogens are 22 nm and 29 nm, respectively. By coating large steric carbazole or diphenylamine units around the multi-resonance core, the intermolecular interactions are suppressed and the aggregationinduced emission quenching effect is inhibited. As a result, the TADF-sensitized TADF (TST) device utilizing Me-PABCZ as sensitizer and Me-PABDPA as emitter achieves a maximum external quantum efficiency (EQE) of 27.9 %. Such a type of light-emitting device exhibits a weak dopant concentration dependence characteristic. The incorporation of molecule conformational engineering and device structural engineering into the MR-TADF technology could usher in a new paradigm of OLEDs.