Thermally activated delayed fluorescence materials based on donor-acceptor structures

Thermally activated delayed fluorescence (TADF) materials, capable of efficient reverse intersystem crossing (RISC) from the lowest triplet excited state (T₁) to the lowest singlet excited state (S₁) to use triplet excitons for photoluminescence with theoretically 100% exciton harvesting in emission, have attracted great attention in recent research of organic electronics, especially in the field of organic light emitting diodes (OLEDs). The singlet-triplet energy splitting (ΔE_ST) between S₁ and T₁ should be low, which is a key point to facilitate the RISC process in tuning triplet excitons to singlet excitons for delayed fluorescence emission. With the significant advantages of convenient molecular design, easy preparation, rich optoelectronic properties, and excellent device performance, TADF materials with donor-acceptor (D-A) molecular structures are of central importance in the current development of high-performance TADF molecules. In this article, we review the basic molecular design principles of the D-A type TADF materials and summarize their molecular structure characteristics, optoelectronic properties and device application performance in the latest research progress, according to the varied types of acceptor building blocks. Finally, the existing problems, future opportunities and key challenges of TADF materials with D-A architectures are discussed to give a full view of this kind of new organic optoelectronic materials.