溶剂化对有机给、受体分子热激活延迟荧光的影响及调控

Effect of Solvation on Thermally Activated Delayed Fluorescence Within Electron Donor/Acceptor Chromophores

具有热激活延迟荧光(Thermally activated delayed fluorescence,TADF)特性的有机给、受体(Donor-acceptor,D-A)分子体系通过反向系间窜越捕获三重态激子,可以将内量子效率的理论上限提高到100%,因而受到极大关注。通常,具有分子内电荷转移特性的D-A体系可以通过构建扭曲的分子构象来减小单、三重态之间的能差ΔES-T,以确保反向系间窜越快速发生。当分子被激发后,若激发态构象中D-A的二面角更接近90°时,ΔES-T会更小,延迟荧光也会增强。然而,快速的溶剂化过程常常会影响激发态构象、分子内电荷转移过程、延迟荧光发射,这使得研究TADF分子发光过程更富有挑战。本文综述了本课题组近期在溶剂化对D-A体系延迟荧光的影响及调控方面所取得的初步进展。结果显示,强极性溶剂会导致非辐射弛豫增加,不利于TADF发射;改变溶剂粘度会影响激发态构象弛豫,从而可以实现对TADF的增强或减弱的调控。这些结果有助于理解溶剂化效应与构象弛豫、TADF之间的关系,为TADF分子的设计与合成提供指导。

Thermally activated delayed fluorescence(TADF)materials with distinct electron donor and acceptor(DA)segments can achieve theoretically 100%internal quantum efficiencies via the reverse intersystem crossing(RISC)process,thus receiving tremendous attention in lighting,display,and biomedical fields.Generally,D-A systems with intramolecular charge transfer(ICT)characteristics minimize singlet-triplet energy gap(ΔES-T)by having molecular con⁃formations twisted,so that the RISC process takes place rapidly.Once the dihedral angle of D-A segments in the excit⁃ed molecular conformation is further twisted,approaching 90°,ΔES-T will be smaller and the TADF characteristics will be also enhanced.However,conformational changes of excited states,ICT process and TADF emission are often influ⁃enced by solvent effect,which poses a challenge for understanding luminescence mechanism of TADF molecules.This review mainly summarizes the recent progresses in the influence of solvation on the delayed fluorescence made by our groups.As a result,it is shown that strongly polar solvents lead to an increase in non-radiative relaxation that is averse to TADF,as well as alteration of solvent viscosities affects the excited state conformational relaxation,resulting in the enhancement or weakening of TADF.These results are valuable for understanding the role of solvation in conformation⁃al relaxation and TADF emission,and provide guidance for the design and synthesis of TADF molecules.