A Facile Strategy for Enhancing Reverse Intersystem Crossing of Red Thermally Activated Delayed Fluorescence Emitters
A Facile Strategy for Enhancing Reverse Intersystem Crossing of Red Thermally Activated Delayed Fluorescence Emitters
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DOI：
10.1016/j.cej.2021.134423
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发表时间：
2021-12
影响因子：
15.1
通讯作者：
Hui Wang;Lu Zhou;Yizhong Shi;Xiaochun Fan;Jiaxiong Chen;Kai Wang;Jia Yu;Xiaohong Zhang
中科院分区：
文献类型：
--
作者：
Hui Wang;Lu Zhou;Yizhong Shi;Xiaochun Fan;Jiaxiong Chen;Kai Wang;Jia Yu;Xiaohong Zhang
实现高效的反向系间穿越（RISC）工艺制备红色热激活延迟荧光（TADF）发光体仍然是一个艰巨的挑战。在这里，我们证明了电荷转移（CT）的能级逐渐降低，增强吸电子能力的二级受体（A）附件。同时，它们的局部激发三重态（3LEA）水平得到很好的保持，这是由于主框架和附件之间的共轭都是相似的这些A片段。在mDPBPZ-DPXZ体系中，3CT态和3LEA态几乎简并，单重态-三重态能量差（ΔEST）为0.02 eV，RISC速率为1.54 × 106 s-1，光致发光量子产率高达93%。相应的器件实现了21.6%的外量子效率，明显高于其他同行。这项工作表明，CT和3LEA状态之间的能量对齐可以很容易地通过在原始A框架上引入次级A附件来管理，这将1CT和3CT状态转移到较低的能量而不影响3LEA能量。它提供了一个简单的设计策略，以促进RISC过程，这是特别有用的，在设计高效的红色TADF发射器。
Realizing highly efficient reverse intersystem crossing (RISC) process for red thermally activated delayed fluorescence (TADF) emitters remains a formidable challenge. Herein we demonstrate that charge transfer (CT) energy levels are gradually reduced with enhancing electron-withdrawing abilities of the secondary acceptor (A) attachments. Meanwhile, their local excited triplet (3LEA) state levels are well maintained due to the conjugations between the main framework and the attachments are all similar for these A segments. The optimized molecular energy level alignments are obtained in the case of mDPBPZ-DPXZ, in which3CT and the3LEAstates are almost degenerate, and gives rise to a small singlet–triplet energy difference (ΔEST) of 0.02 eV, a fast RISC rate of 1.54 × 106s−1and a high photoluminescence quantum yield of 93%, simultaneously. And the corresponding device achieves an external quantum efficiency of 21.6%, significantly higher than the other counterparts. This work demonstrates that the energy alignment between the CT and3LEAstate can be easily managed by introducing secondary A attachments on original A framework, which shifts the1CT and3CT state to lower energies without affecting the3LEAenergy. It provides a facile design strategy to promote the RISC process, which is particular useful in designing highly efficient red TADF emitters.