Herein, a series of universal bipolar host materials, 9,9′-([1,2,4]triazolo[1,5-a]pyridine-2,6-diylbis(4,1-phenylene))bis(9H-carbazole) (TP26Cz1), 3-(2-(4-(9H-carbazol-9-yl)phenyl)-[1,2,4]triazolo[1,5-a] pyridine-6-yl)-9-phenyl-9H-carbazole (TP26Cz2), 9,9′-([1,2,4]triazolo[1,5-a]pyridine-2,7-diylbis(4,1-phenylene))bis(9H-carbazole) (TP27Cz1), and 3-(2-(4-(9H-carbazol-9-yl)phenyl)-[1,2,4]triazolo[1,5-a]pyridin-7-yl)-9-phenyl-9H-carbazole (TP27Cz2), using [1,2,4]triazolo[1,5-a]pyridine (TP) as electron-transporting moiety and carbazole as hole-transporting moiety, were designed and synthesized. All four compounds possess remarkable carrier-transporting properties and excellent thermal stability with high glass-transition temperature (T_g) in the range of 136–144 °C. The hole- and electron-transporting abilities could be regulated by adjusting the linkage mode between the carbazole and TP units, and balanced charge-transporting properties were realized in TP26Cz2 and TP27Cz2. The phosphorescent and thermally activated delayed-fluorescence (TADF) organic light-emitting diodes (OLEDs) based on these host materials exhibit superior performance with high efficiency and low roll-off. For example, TP26Cz2-hosted phosphorescent OLED (PhOLED) exhibits the maximum external quantum efficiency (η_ext) of 25.6%, and at the high luminance of 5000 cd m^–2, the η_ext still remained at 25.2%. TP27Cz1-hosted TADF device exhibits the maximum η_ext of 15.5% and only dropped to 15.4% at the luminance of 1000 cd m^–2. Moreover, the influence of linking mode of carbazole unit and TP units in these hosts on their photophysical and carrier-transporting properties as well as the electroluminescence (EL) performance of devices was discussed.

中文翻译：

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[1,2,4]基于三唑并[1,5 - a ]吡啶的基质材料，用于绿色磷光和延迟荧光OLED，具有低效率滚降

在这里，一系列通用双极主体材料，9,9'-（[[1,2,4] triazolo [1,5 - a ]吡啶-2,6-二基双（4,1-亚苯基））bis（9 H -咔唑）（TP26Cz1），3-（2-（4-（9 H-咔唑-9-基）苯基）-[1,2,4]三唑并[1,5 - a ]吡啶-6-基）- 9-苯基-9 H-咔唑（TP26Cz2），9,9'-（[[1,2,4] triazolo [1,5 - a ]吡啶-2,7-二基双（4,1-亚苯基）） 9 H-咔唑）（TP27Cz1）和3-（2-（4-（9 H-咔唑-9-基）苯基）-[1,2,4]三唑[1,5 - a ]吡啶-7- （基）-9-苯基-9 H-咔唑（TP27Cz2），使用[1,2,4]三唑[1,5- a设计并合成了作为电子传输部分的吡啶（TP）和作为空穴传输部分的咔唑。四种化合物均具有出色的载流子传输性能，并且在高玻璃化转变温度（T _g）下具有出色的热稳定性。）的温度范围为136–144°C。可以通过调节咔唑与TP单元之间的键合模式来调节空穴和电子的传输能力，并在TP26Cz2和TP27Cz2中实现了平衡的电荷传输性能。基于这些主体材料的磷光和热激活延迟荧光（TADF）有机发光二极管（OLED）表现出出众的性能，高效率和低滚降。例如，TP26Cz2托管磷光OLED（PHOLED）呈现出最大外部量子效率（η _EXT的25.6％），和在5000烛光米的高亮度^-2，则η _EXT仍保持在25.2％。TP27Cz1托管TADF装置具有的最大η _EXT亮度为15.5％，仅在1000 cd m ^-2的亮度下下降到15.4％。此外，讨论了这些主体中咔唑单元和TP单元的连接方式对其光物理和载流子传输性质以及器件的电致发光（EL）性能的影响。