热激发延迟荧光分子的受体基团研究进展

Research Progress on Acceptor Groups of Thermally Activated Delayed Fluorescent Molecules

近年来,热激发延迟荧光材料(Thermally activated delayed fluorescence,TADF)及其电致发光器件取得了快速发展。TADF材料应具有小的单线态-三线态能级差,从而使其三线态激子可以通过反向系间窜越过程到达单线态,进而辐射发光。因此,与传统的荧光及磷光材料相比,TADF材料除了理论上可以实现100%的内量子效率(Internal quantum efficiency,IQE)和电生激子利用率外,它还具有更高的发光效率,且大部分TADF分子为纯有机给-受体体系,分子结构简单,基团选择范围广。通过增强TADF受体单元的吸电子能力,可以有效促进前线轨道的分离,从而降低单重态-三重态能级差,提高反向系间窜越速率。同时,调节受体的分子构型还可以抑制分子间的相互作用,改善载流子注入传输。然而,相对于给体单元,受体单元类型多样且功能差异较大,这对选择合适的受体基团以实现有效的光电性质调控造成了一定影响。近年来,人们构建热激发延迟荧光材料更侧重于受体基团的选择,且取得了显著成果。常见的受体基团有膦氧、氰基、三嗪和羰基等。深入研究受体基团对调控分子内电子效应和分子间相互作用至关重要。本文对近年来报道的TADF体系中主要的受体基团进行了梳理,对其结构和光电性质之间的关系进行了总结,以期为高效TADF分子的设计开发提供借鉴。

In recent years,thermally activated delayed fluorescence( TADF) materials and their electroluminescent devices are developed rapidly. TADF molecules should have small singlet-triplet energy gaps,therefore can facilitate the triplet exciton upconverted to singlet exciton via reverse intersystem crossing( RISC) for radiation. Compared to traditional fluorescence and phosphorescence emitters,besides 100% theoretical internal quantum efficiency and electrogenerated exciton utilization ratio,TADF materials have higher luminescent efficiencies based on pure organic donor-acceptor systems with the features of simple structures and large group library,which attract the extensive attentions. In TADF molecules,acceptors with strong electron-withdrawing ability can effectively facilitate the frontier molecular orbital separation,reduce singlet-triplet energy gaps,improve RISC rate,and simultaneously suppress intermolecular interactions and modify carrier injection and transportation through adjusting molecular configurations.However,in contrast to donor units,the acceptor groups are diverse and completely different regarding to functions,which influences the rational acceptor selection for optoelectronicoptimization. In recent years,the construction of thermally activated delayed fluorescent materials has focused more on the choice of acceptor groups and has achieved remarkable results. Common acceptor groups are phosphine oxide,cyano,triazine,carbonyl,and so on. Intensive research on acceptors groups is critical for regulating intramolecular electronic effects and intermolecular interactions.This review paper summarizes the main acceptor groups used in recently reported TADF molecules and discusses the relationships between acceptor structure and optoelectronic performance,which would be helpful for the subsequent researches on efficient TADF molecular development.