Controlling the Conjugation Extension inside Acceptors for Enhancing Reverse Intersystem Crossing of Red Thermally Activated Delayed Fluorescence Emitters
Controlling the Conjugation Extension inside Acceptors for Enhancing Reverse Intersystem Crossing of Red Thermally Activated Delayed Fluorescence Emitters
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DOI：
10.1016/j.cej.2022.135775
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发表时间：
2022-03
影响因子：
15.1
通讯作者：
Lu Zhou;Hui Wang;Yizhong Shi;Xiaochun Fan;Jiaxiong Chen;Kai Wang;Jia Yu;Xiaohong Zhang
中科院分区：
文献类型：
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作者：
Lu Zhou;Hui Wang;Yizhong Shi;Xiaochun Fan;Jiaxiong Chen;Kai Wang;Jia Yu;Xiaohong Zhang
提高反向系统间交叉（RISC）率仍然是红色热激活延迟荧光（TADF）发射体的一个挑战，能级排列起着重要的作用。在这项工作中，我们表明，局部激发的三重态能级从受体片段（3LEA）可以很好地调制通过改变受体内部的共轭扩展。我们新设计的化合物pDPAPQ-PXZ和pDPBPZ-PXZ显示出几乎相同的电荷转移（CT）性质，因为相似的供体和受体强度。另一方面，pDPBPZ-PXZ的3LEA态显著低于pDPAPQ-PXZ，这仅仅是因为其更大的π-离域。在pDPBPZ-PXZ的情况下，获得了理想的分子能级排列，具有近简并CT特征的单重态和三重态（1CT，3CT）和3LEA。与pDPAPQ-PXZ相比，pDPBPZ-PXZ的kRISC提高了约10倍，光致发光量子产率也显著提高，达到85.6%。相应的OLED成功地将外量子效率提高了一倍，达到20.3%。这项工作表明，受体的共轭延伸在确定3LEA水平中起着致命的作用，它们可以从控制受体强度中分离出来。这为提高RISC效率和开发高效红色TADF发射器提供了一种有前途的方法。
Increasing the reverse intersystem crossing (RISC) rates remains a challenge for red thermally activated delayed fluorescence (TADF) emitters, and energy level alignments play an important role. In this work, we demonstrate that locally excited triplet energy levels from acceptor segments (3LEA) can be well modulated by changing the conjugation extension inside acceptors. Our newly designed compounds pDPAPQ-PXZ and pDPBPZ-PXZ show nearly identical charge-transfer (CT) properties because of similar donor and acceptor strengths. On the other hand, the3LEAstate of pDPBPZ-PXZ was significantly lower than that of pDPAPQ-PXZ only because of its greater π-delocalization. In the case of pDPBPZ-PXZ, ideal molecular energy level alignments are obtained with near-degenerate CT featuring singlet and triplet states (1CT,3CT) and3LEA. As a result, pDPBPZ-PXZ simultaneously achieves an approximately 10-fold improvedkRISCand a dramatically improved photoluminescence quantum yield of 85.6% compared with pDPAPQ-PXZ. The corresponding OLED successfully doubles the external quantum efficiency to 20.3%. This work demonstrates that the conjugation extensions of acceptors play a fatal role in determining3LEAlevels and that they can be isolated from controlling the acceptor strengths. This provides a promising approach toward enhancing RISC efficiency and developing highly efficient red TADF emitters.