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.

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Two multi-resonance (MR) thermally activated delayed fluorescence (TADF) analogous materials, BNCzPXZ and BNCzPTZ, respectively integrating oxygen and sulfur elements were compared to in-depth investigate the influences of introducing elements of...

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.

Thermally activated delayed fluorescence (TADF) materials with aggregationinduced emission (AIE) features can overcome aggregation-caused quenching (ACQ) and emit intensely in aggregate states and thus have attracted enormous attention in the fields of high-efficiency organic light-emitting diodes, bioimaging, photodynamic therapy, photocatalysis, etc. However, their corresponding exact working mechanisms at the microscopic level are still far from clear. Herein, by carefully investigating the physical properties of our newly designed TADF material 6-(10H-spiro[acridine-9,9′-fluoren]-10-yl)nicotinonitrile in various states, we concluded that conformational isomerization plays an important role in realizing high photoluminescence quantum yields in its amorphous neat film state, in which the high-lying quasi-axial conformations with non-TADF features and low-lying quasiequal conformations with TADF characteristics serve as the host matrix and dopant, respectively, thus suppressing ACQ in disordered aggregate states. Our work not only offers a new possible microscopic mechanism by using conformational isomerization for the AIE-TADF phenomenon but also provides a novel method for designing high-efficiency AIE-TADF emitters.