In this work, we designed and synthesized two bipolar host materials, DBTPC1 and DBTPC2 through different linkage ways between carbazole, pyridine and dibenzothiophene. The photophysical properties and thermal properties of these hosts were systematically investigated. Their rigid molecular structures result in high glass transition temperatures , contributing to excellent thermal stability of molecules. Employing DBTPC1 and DBTPC2 as hosts, red phosphorescent organic light-emitting devices (PHOLEDs) with Ir(piq) 2 acac as an emitter display maximum external quantum efficiencies (EQEs) of 18.8 and 13.2%, respectively. The experimental results reveal that DBTPC1 shows better performance than commercial host 4,4’-bis(carbazol-9-yl)biphenyl (CBP), thus, would be a promising host material for practical application in red PHOLEDs and for the future exploration in multi-color PHOLEDs.
Yi Chen,Jingwei Xie,Zixing Wang,Jin Cao,Hongwei Chen,Jinhai Huang,Jianhua Zhang,Jianhua Su
Two novel indole-based, bipolar, host materials were designed and synthesized by introducing the triazine unit to the 5-position of indole moiety with a meta -linking strategy. The two host materials exhibited excellence bipolar transport abilities and the meta-linking analog presented a high T g value (>120 °C). Furthermore, their electrochemical and photo-physical properties were also fully characterized and all the results exhibited that the meta -linking strategy made a significant effect on the physical properties of the two hosts. Moreover, the PHOLED devices using 9-(4-(5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)- 1H -indol-1-yl) phenyl)- 9H -carbazole and 9-(4-(5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)- 1H -indol-1-yl)phenyl)- 9H -carbazole as hosts were also fabricated to evaluate the practical utilities of host materials. The devices achieved the maximum external quantum efficiencies of 17.53% for para -linking compound and 14.53% for meta -linking analog, respectively. In particular, para -linking compound based device revealed the maximum external quantum efficiency was twice that of the device using 4,4′-bis( N -carbazolyl)-1,10-biphenyl as the host.
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