Research Progress of Red Thermally Activated Delayed Fluorescent Materials Based on Quinoxaline

Red emitter is one of the three primary materials for display, which is widely used in full-color display, biosensing and photodynamic therapy due to the advantages of small emission energy, strong penetrating ability and low background fluorescence interference. At present, the main bottlenecks for the development of red emitters are as follows. (1) The narrow energy gaps of red emitters often lead to serious non-radiative transition and low quantum efficiency. (2) The largely conjugated structure of red emitters results in strong pi-pi stacking for emission quenching. (3) Molecular design requires greater conjugation, which is difficult in molecular synthesis. Red thermally activated delayed fluorescence (TADF) materials, as a new type of red emitters, can use triplet excitons to release fluorescence through reverse intersystem crossing process, which greatly improves the quantum efficiency. Therefore, red TADF materials have become a hot topic in recent years. Because of the structural advantages, quinoxaline and its derivative are promising building blocks for the construction of red TADF emitters. The research progress of the quinoxaline-based red TADF materials in recent years is summarized, the influence of molecular structure on the properties of materials is discussed, and the prospect is also provided.