Shenzhen Key Laboratory of New Information Display and Storage Materials College of Materials Science and Engineering, Shenzhen University, Shenzhen, 518055, P. R. China.
Chemistry. 2022 Dec 6;28(68):e202202305. doi: 10.1002/chem.202202305. Epub 2022 Oct 10.
The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through-space charge transfer (TSCT) emitters containing benzothiazino[2,3,4-kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π-stacking interactions and calculated spin-orbit coupling (SOC) values are beneficial for TSCT-TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τ ) of 255.0-114.3 μs and lower PLQYs of 45-61 % in comparison with the O-containing congeners (τ =26.9-6.8 μs; PLQYs=74-71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters.
硫属元素的重原子效应的利用为提升纯有机发光材料的热激活延迟荧光（TADF）性能提供了一种途径，因为这类材料可以收集三重态激子。然而，重原子和大原子引起的构象和电子变化也可能对 TADF 性质产生不利影响。在此，我们报道了一类新型的通过空间电荷转移（TSCT）发射体的设计、合成和结构，该类材料包含苯并噻唑并[2,3,4-kl]吩噻嗪（DPTZ）作为给体单元。通过理论模拟、电化学和光谱研究系统地研究了 S 原子对发射性质的影响。尽管π堆积相互作用和计算的自旋轨道耦合（SOC）值有利于 TSCT-TADF 性质，但三重态 TSCT 态被提升到受体部分的局域激发（LE）态之上。因此，与含 O 的同系物相比，新的发射体显示出更长的延迟荧光寿命（τ）为 255.0-114.3 μs 和更低的 PLQY 为 45-61%（τ=26.9-6.8 μs；PLQYs=74-71%）。这项工作强调，在利用重硫属原子设计 TADF 发射器时，充分考虑各种效应是至关重要的。
