Four novel bipolar host materials, namely 9,9'-(4-(pyridin-2-yl)-1,3-phenylene)bis(9H-carbazole) (2CzPy), 9,9'-(4-(pyridin-2-yl)-1,3-phenylene)bis(3,6-di-tert-butyl-9H-carbazole) (2TCzPy), 5,5'-(4-(pyridin-2-yl)-1,3-phenylene)bis(5H-benzofuro[3,2-c]carbazole) (2BFCzPy) and 9′,9‴-(4-(pyridin-2-yl)-1,3-phenylene)bis(9-phenyl-9H,9′H-3,3′-bicarbazole) (2PBCzPy) were designed and synthesized. Within each host material, one pyridine group serving as electron-transporting unit and two identical electron-donating groups serving as hole-transporting motifs were attached to the central benzene ring. These two donor units are located ortho and para to pyridine group, respectively. The four compounds showed excellent thermal stability with the glass-transition temperature up to 192 °C and decomposed temperature up to 571 °C. These hosts possessed triplet energies over 2.80 eV, indicating that they could be used as suitable hosts for blue phosphorescent organic light-emitting diodes (PHOLEDs). The bis[2-(4,6-difluorophenyl)-pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based PHOLEDs hosted by 2CzPy and 2BFCzPy exhibited high device performance with maximum external quantum efficiencies (EQEs) of 17.8% and 17.4%, respectively. More importantly, 2CzPy exhibited a low efficiency roll-off at a brightness of 1000 cd m⁻² with an external quantum efficiency of 17.1% (3.9% roll-off). The results demonstrate that 2CzPy could be a promising host for blue PHOLEDs.

四种新型双极主体材料，即9,9'-（4-（吡啶-2-基）-1,3-亚苯基）双（9H-咔唑）（2CzPy），9,9'-（4-（吡啶- 2-基）-1,3-亚苯基）双（3,6-二叔丁基-9H-咔唑）（2TCzPy），5,5'-（4-（吡啶-2-基）-1,3 -亚苯基）双（5H-苯并呋喃[3,2- c ]咔唑）（2BFCzPy）和9'，9′-（4-（吡啶-2-基）-1,3-亚苯基）双（9-苯基- 9H，9'H-3,3'-联咔唑）（2PBCzPy）进行了设计和合成。在每种主体材料中，一个作为电子传输单元的吡啶基和两个作为空穴传输基序的相同的供电子基团连接在中心苯环上。这两个供体单元分别位于吡啶基的邻位和对位。四种化合物在高达192°C的玻璃化转变温度和高达571°C的分解温度下均表现出出色的热稳定性。这些主体具有超过2.80 eV的三重态能量，表明它们可以用作蓝色磷光有机发光二极管（PHOLED）的合适主体。由2CzPy和2BFCzPy承载的基于双[2-（4,6-二氟苯基）-吡啶基-C2，N]（吡啶并吡啶）铱（III）（FIrpic）的PHOLED展示出高器件性能，最大外部量子效率（EQE）分别为17.8％和17.4％。更重要的是，2CzPy在1000 cd m ^-2的亮度下显示出低效率的滚降，其外部量子效率为17.1％（滚降3.9％）。结果表明，2CzPy可能是蓝色PHOLED的有希望的宿主。