Fine-Tuning the Photophysics of Donor-Acceptor (D-A 3 ) Thermally Activated Delayed Fluorescence Emitters Using Isomerisation
Fine-Tuning the Photophysics of Donor-Acceptor (D-A 3 ) Thermally Activated Delayed Fluorescence Emitters Using Isomerisation
复制标题
使用异构化微调供体-受体 (D-A 3 ) 热激活延迟荧光发射器的光物理学
DOI：
10.1002/cptc.202200248
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发表时间：
2022
期刊：
影响因子：
3.7
通讯作者：
L. Dos Santos P
中科院分区：
文献类型：
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作者：
L. Dos Santos P
这里研究了两种D-A3区域异构体，其包含连接到中心三氮杂环戊二烯核心的三个二苯并噻吩-S，S-二氧化物受体单元。这两种分子都显示出热激活延迟荧光（TADF），然而，TADF机制的效率受到D-A取代位置的强烈影响。与对位取代的发光体（1 a）相比，位取代的发光体（1 B）显示出略高的单重态电荷转移态和较低的三重态，导致单重态-三重态分裂（ΔEST）为0.28 eV，而在1 a中仅为0.01 eV。 正如预期的那样，这种Δ EST差异强烈影响反向系间穿越（rISC）速率，对位异构体1 a表现出更快的延迟荧光发射。计算表明，两种异构体之间的三重态能量差是由于空间位阻的变化沿着在这些分子中的供体-受体旋转轴：作为1双限制较少，其受体单元的旋转导致较低的T1能量，进一步远离高密度的状态（该区域中发现较大的电子振动耦合，有利于rISC）。因此，我们的研究结果表明，如何取代模式有显着的三重态能量和字符的影响，验证了高效TADF材料的关键结构设计。
Here two D–A3regioisomers, comprising three dibenzothiophene‐S,S‐dioxide acceptor units attached to a central triazatruxene core, are studied. Both molecules show thermally activated delayed fluorescence (TADF), however, the efficiency of the TADF mechanism is strongly affected by the D–A substitution position. Themeta‐ substituted emitter (1 b) shows a slightly higher‐lying singlet charge transfer state and a lower‐lying triplet state than that observed in thepara‐ substituted emitter (1 a), resulting in a larger singlet–triplet splitting (ΔEST) of 0.28 eV compared to only 0.01 eV found in1 a. As expected, this ΔESTdifference strongly impacts the reverse intersystem crossing (rISC) rates and thepara‐isomer1 aexhibits a much faster delayed fluorescence emission. Calculations show that the triplet energy difference between the two isomers is due to steric hindrance variances along the donor–acceptor rotation axis in these molecules: as1 bis less restricted, rotation of its acceptor unit leads to a lower T1energy, further away from the region of high density of states (the region where larger vibronic coupling is found, favouring rISC). Therefore, our results show how the substitution pattern has a marked effect on triplet state energies and character, verifying the key structural designs for highly efficient TADF materials.