Recent Advances in Concentration Quenching-resistant Multi-resonance Thermally Activated Delayed Fluorescence Emitters.

The research on multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters has garnered increasing attention due to the exceptional photophysical properties of their corresponding organic light-emitting diodes (OLEDs), such as high efficiency and narrow emission features. However, they still face intractable issues like concentration-induced emission quenching, exciton annihilation, and spectral broadening. This review focuses on a sophisticated molecular design strategy named "sterically wrapping of MR fluorophores" to tackle the aforementioned problems. Bulky substituents isolate the MR emission core, thereby significantly reducing intermolecular interactions. Therefore, with these MR-TADF emitters, the OLEDs are capable of maintaining narrow emission bands while achieving high external quantum efficiencies across a wide concentration range from 1 wt% to 20 wt% and even at higher concentrations. This article reviews the latest advancements in MR-TADF emitters with suppressed concentration quenching and spectral broadening, emphasizing their chemical structures, optoelectronic properties, and device performances. Finally, the potential challenges and future perspectives of MR-TADF materials are analyzed to better comprehend the potential of efficient narrowband OLEDs.