Herein, we demonstrate how judicious selection of donor decorating a central multi-resonant thermally activated delayed fluorescence (MR-TADF) core based on quinolino[3,2,1-de]acridine-5,9-dione (DiKTa) can lead to very high-performance organic light-emitting diodes (OLEDs). Decorating the DiKTa core with triphenylamine (TPA) and diphenylamine (DPA) in 3TPA-DiKTa and 3DPA-DiKTa resulted in compounds showing bright, narrowband green/red emission in doped films, respectively. The OLEDs based on these emitters showed excellent performance with record-high maximum external quantum efficiencies (EQEmax) for this family of emitters, with a EQEmax of 30.8% for the device with 3TPA-DiKTa (EL = 551 nm) and 16.7% for the device with 3DPA-DiKTa (EL = 613 nm). The outstanding device performance with 3TPA-DikTa was attributed to preferential horizontal orientation of the transition dipole moment, with anisotropy factor (a) of 0.189. These results demonstrate that the careful selection of the substituents in MR-TADF emitter can tune the color of OLEDs and significantly enhance device performance.
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