A series of carbazole/benzimidazole-based molecules, namely, o-CbzBiz, m-CbzBiz, and p-CbzBiz, were readily synthesized in three steps by integrating carbazole with benzimidazole via the ortho-, meta-, and para-positions of phenyl linked to N-phenyl carbazole. These bipolar molecules exhibited a maximum UV absorption band ranging from 310 to 327 nm and a maximum emission band ranging from 380 to 400 nm. Density functional theory calculations showed that the twist angles between the donor and acceptor moieties of these molecules were from 54.9 to 67.1°. Such a twisted structure hampered the π-electron conjugation within the molecule and resulted in high-lying LUMO levels and triplet energies, which make them suitable to be applied as host materials in OLED devices. Our results showed that a maximum external quantum efficiency (EQE) of OLED reached 21.8% when p-CbzBiz was applied as the host of a green phosphorescent emitter, i.e., Ir(ppy)2(acac). In addition, a maximum EQE of OLED reached 16.7% when o-CbzBiz with the host of a green TADF emitter, i.e., 4CzIPN. Moreover, these devices exhibited lower efficiency roll-off than the CBP-hosted device using the same emitters, which demonstrated the bipolar charge carrier property of carbazole/benzimidazole-based molecules.

中文翻译：

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基于咔唑/苯并咪唑的双极分子作为高效 OLED 磷光和热激活延迟荧光发射体的主体。


通过苯基的邻位、间位和对位将咔唑与苯并咪唑整合，分三步轻松合成了一系列咔唑/苯并咪唑基分子，即 o-CbzBiz、m-CbzBiz 和 p-CbzBiz连接至N-苯基咔唑。这些双极分子表现出最大紫外吸收带范围为310至327 nm，最大发射带范围为380至400 nm。密度泛函理论计算表明，这些分子的供体和受体部分之间的扭转角为54.9°至67.1°。这种扭曲的结构阻碍了分子内的π电子共轭，并产生高位的LUMO能级和三线态能量，这使得它们适合用作OLED器件中的主体材料。我们的结果表明，当p-CbzBiz用作绿色磷光发射体Ir(ppy)2(acac)的主体时，OLED的最大外量子效率(EQE)达到21.8%。此外，当o-CbzBiz与绿色TADF发射体（即4CzIPN）为主体时，OLED的最大EQE达到16.7%。此外，这些器件表现出比使用相同发射器的 CBP 托管器件更低的效率滚降，这证明了咔唑/苯并咪唑基分子的双极性电荷载流子特性。