A Highly Twisted Carbazole‐Fused DABNA Derivative as an Orange‐Red TADF Emitter for OLEDs with Nearly 40 % EQE

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) material is currently a research hotspot in organic light‐emitting diodes (OLEDs) due to their high color purity and high exciton utilization. However, there are only a handful of MR‐TADF emitters with emissions beyond the blue‐to‐green region. The very limited emission colors for MR‐TADF emitters are mainly caused by the fact that so far molecular modifications of MR‐TADF do not offer much change in the emission colors. Here, we report a new approach to modifying a prototypical MR core of DABNA by fusing carbazoles to the MR framework. The carbazole‐fused molecule (TCZ‐F‐DABNA) basically maintains the MR‐dominated features of DABNA while red‐shifting the emission. Its OLED achieves an external quantum efficiency of 39.2 % with a peak at 588 nm, which is a record‐high efficiency for OLEDs with peaks beyond 560 nm. This work provides a new approach for significantly tunning emission colors of MR‐TADF emitters. A new approach is reported by fusing carbazoles to a MR framework DABNA to significantly redshift emission while maintaining the MR‐dominated features. The carbazole‐fused molecule TCZ‐F‐DABNA can deliver a high PLQY of 99 %. Its OLEDs reached a record‐high EQE of 39.2 %.