Abstract N,N ′-Diphenyl- N,N ′-di( m -tolyl)benzidine (TPD) is a well-known hole-transport material for organic light-emitting diodes (OLEDs). Here, we studied the planarity of triphenylamine moieties of TPD in the amorphous state, by the combined use of solid-state 15 N NMR experiments and density functional theory (DFT) calculations. It was shown that the planarity is of crucial importance for hole-transport performance of TPD, because of the strong effects for the shape of HOMO and for the intermolecular repulsion energy. It was also found that the molecular structure around the nitrogen in its amorphous state is not pyramidal, but is instead planar, which is favorable for hole-transport. Natural bond orbital calculation indicates that the nitrogen atom is sp 2 hybridized. This is unlike most amine compounds, which have pyramidal structures with sp 3 hybridized nitrogens.

中文翻译：

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用于 OLED 的典型空穴传输材料 N,N'-二苯基-N,N'-二（间甲苯基）联苯胺 (TPD) 的三苯胺部分的平面度，处于非晶态

摘要 N,N'-二苯基-N,N'-二（间甲苯基）联苯胺（TPD）是一种众所周知的有机发光二极管（OLED）空穴传输材料。在这里，我们通过结合使用固态 15 N NMR 实验和密度泛函理论 (DFT) 计算，研究了无定形状态下 TPD 的三苯胺部分的平面性。结果表明，由于对 HOMO 形状和分子间排斥能的强烈影响，平面度对 TPD 的空穴传输性能至关重要。还发现非晶态氮周围的分子结构不是金字塔形的，而是平面的，这有利于空穴传输。自然键轨道计算表明氮原子是sp 2 杂化的。这与大多数胺化合物不同，