Avoiding Energy Loss on TADF Emitters: Controlling the Dual Conformations of D–A Structure Molecules Based on the Pseudoplanar Segments,Advanced Materials

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Avoiding Energy Loss on TADF Emitters: Controlling the Dual Conformations of D–A Structure Molecules Based on the Pseudoplanar Segments
Advanced Materials ( IF 27.4 ) Pub Date : 2017-11-08 , DOI: 10.1002/adma.201701476
Kai Wang _{1,

2,

3} , Cai-Jun Zheng _{2,

3} , Wei Liu _{1,

3} , Ke Liang ₁ , Yi-Zhong Shi ₁ , Si-Lu Tao ₂ , Chun-Sing Lee ₄ , Xue-Mei Ou ₁ , Xiao-Hong Zhang _{1,

3}

Affiliation

The recent introduction of thermally activated delayed fluorescence (TADF) emitters is regarded as an important breakthrough for the development of high efficiency organic light‐emitting devices (OLEDs). The planar D and A groups are generally used to construct TADF emitters for their rigid structure and large steric hindrance. In this work, it is shown that many frequently used nonaromatic (noncontinuous conjugation or without satisfying Hückel's rule) planar segments, such as 9,9‐dimethyl‐9,10‐dihydroacridine, are actually pseudoplanar segments and have two possible conformations–a planar form and a crooked form. Molecules constructed from pseudoplanar segments can thus have two corresponding conformations. Their existence can have significant impact on the performance of many TADF emitters. Two design strategies are presented for addressing the problem by either (1) increasing the rigidity of these groups to suppress its crooked form or (2) increasing the steric hindrance of the linked group to minimize energy of the emitters with the highly twisted form. Following these strategies, two new emitters are synthesized accordingly and successfully applied in OLEDs demonstrating high external quantum efficiencies (20.2% and 18.3%).

中文翻译：

避免TADF发射器上的能量损失：基于伪平面段控制D–A结构分子的双重构象

最近引入的热活化延迟荧光（TADF）发射器被认为是开发高效有机发光器件（OLED）的重要突破。平面D和A组通常用于构造TADF发射器，因为它们具有刚性结构和较大的空间位阻。在这项工作中，表明许多常用的非芳香族（非连续共轭或不满足Hückel规则）平面链段，例如9,9-二甲基-9,10-二氢ac啶，实际上是伪平面链段，具有两个可能的构象-平面形式和歪曲形式。因此，由伪平面片段构成的分子可以具有两个相应的构象。它们的存在会对许多TADF发射器的性能产生重大影响。提出了两种设计策略来解决该问题，方法是：（1）增加这些基团的刚度以抑制其弯曲的形式，或者（2）增加连接基团的空间位阻，以最大程度地减小具有高度扭曲形式的发射体的能量。遵循这些策略，相应地合成了两个新的发射器，并成功地应用于OLED中，这些发射器具有很高的外部量子效率（分别为20.2％和18.3％）。

更新日期：2017-11-08

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