A simple strategy of steric hindrance engineering is proposed for constructing efficient red thermally activated delayed fluorescence (TADF) emitters and diodes under high doping concentrations. As a concept, a newly TADF emitter, namely 13-(4-(diphenylamino)phenyl)dipyrido[3,2-a:2′,3′-c]phenazin-10-yl)diphenylphosphine oxide (pTPAPO–DPPZ), is designed and synthesized by using triphenylamine (TPA), dipyridophenazine (DPPZ), and diphenylphosphine oxide (DPPO) as the donor, acceptor, and steric groups, respectively. It is demonstrated that the steric hindrance of DPPO enlarges the distances between adjacent molecules, and thus, only weak centroid-to-edge π–π interactions are observed between DPPZ and TPA, which effectively promote the intermolecular charge transfer (CT) to enhance TADF characteristics. Furthermore, locally concentrated intermolecular C–H···O hydrogen bonds between TPA and DPPO of adjacent molecules facilitate the dimer formation, which enhances steric hindrance to alleviate concentration quenching. As a consequence, pTPAPO–DPPZ achieves superior photo- and electroluminescence performances at a high doping concentration of 60%, owing to the optimized intermolecular interactions for the balance of TADF enhancement and quenching suppression.

中文翻译：

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通过氧化膦空间位阻工程实现高掺杂浓度的高效红色 TADF 发射极和二极管


提出了一种简单的空间位阻工程策略，用于在高掺杂浓度下构建高效的红色热激活延迟荧光（TADF）发射器和二极管。作为一个概念，一种新的TADF发射体，即13-(4-(二苯基氨基)苯基)二吡啶并[3,2-a:2′,3′-c]吩嗪-10-基)二苯基氧化膦(pTPAPO-DPPZ)，分别使用三苯胺（TPA）、二吡啶吩嗪（DPPZ）和二苯基氧化膦（DPPO）作为供体、受体和空间基团设计并合成。结果表明，DPPO的空间位阻扩大了相邻分子之间的距离，因此，DPPZ和TPA之间仅观察到弱的质心到边缘的π-π相互作用，这有效地促进了分子间电荷转移（CT）以增强TADF特征。此外，相邻分子的TPA和DPPO之间局部集中的分子间C-H·O氢键有利于二聚体的形成，从而增强了空间位阻，从而减轻了浓度猝灭。因此，由于优化了分子间相互作用以平衡 TADF 增强和猝灭抑制，pTPAPO-DPPZ 在 60% 的高掺杂浓度下实现了优异的光致发光和电致发光性能。