ABSTRACT Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) materials provide an attractive platform for narrowband emission. However, achieving simultaneously high efficiency and color purity in green MR‐TADF emitters remains challenging. Herein, a rigid locked donor unit, 13h‐indolo2′,3′:4,5pyrrolo3,2,1‐jkcarbazole (DPCz), is developed by replacing carbazole with a more conjugated indolo3,2‐bindole motif and incorporated into an MR‐TADF emitter, MRIN‐DPCz . Benefiting from synergistic multiple‐resonance effects arising from the DPCz locking unit and the B‐N core, MRIN‐DPCz exhibits enhanced molecular rigidity, suppressed excited‐state relaxation, and narrowband green emission with a peak at 517 nm, a full width at half maximum of 33 nm, and a photoluminescence quantum yield of 93%. Phosphorescent‐sensitized top‐emitting OLEDs based on MRIN‐DPCz deliver high color‑ pure green electroluminescence at 529 nm with an ultranarrow bandwidth of 22 nm, a CIEy value of 0.75 approaching the BT.2020 standard, and a maximum external quantum efficiency of 51.7%. This work highlights locked‐donor engineering as a versatile molecular design strategy for high‐efficiency, color‐pure MR‐TADF emitters.
Chen et al. (Mon,) studied this question.