Chang, S.-Y.S.-Y.ChangLin, G.-T.G.-T.LinCheng, Y.-C.Y.-C.ChengHuang, J.-J.J.-J.HuangChang, C.-L.C.-L.ChangLin, C.-F.C.-F.LinJIUN-HAW LEEChiu, T.-L.T.-L.ChiuMAN-KIT LEUNG2019-08-012019-08-01201819448244https://www.scopus.com/inward/record.uri?eid=2-s2.0-85058362608&doi=10.1021%2facsami.8b15084&partnerID=40&md5=df48a426096d8843503522960b229ff3https://scholars.lib.ntu.edu.tw/handle/123456789/415921Four isomers of carbazol-9-yl-substituted 1,2-diphenylbenzimidazole at 7, 6, 5, and 4 positions, named as 1-CbzBiz, 2-CbzBiz, 3-CbzBiz, and 4-CbzBiz, respectively, have been synthesized. Instead of having an identical molecular weight, the CbzBiz's have their glass transition temperatures (T g ) spanning a large range from 53 to 90 °C. Their T g and melting point (T m ) basically obey the Boyer-Kauzmann rule (T g = g·T m with g ≠0.7) on the absolute temperature scale (in kelvins). However, while 1-CbzBiz and 4-CbzBiz demonstrate a small g value of 0.66, which is significantly smaller than other common organic glass molecules, 3-CbzBiz shows an unexpectedly high g value of 0.73, implying higher intermolecular interactions in the glass. These CbzBiz's are suitable hosts for bis[2-(4,6-difluorophenyl)pyridinato-C 2 ,N](picolinato)iridium(III) (FIrpic) in phosphorescence organic light-emitting diodes (PhOLEDs). The optimized PhOLED of indium tin oxide/4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine]/4Cbz/4-CbzBiz-FIrpic(15%)/diphenylbis(4-(pyridin-3-yl)phenyl)silane/LiF-Al shows a maximum brightness of 18 760 cd/m 2 , a current efficiency of 64.1 cd/A, and the external quantum efficiency of 30.9%. © 2018 American Chemical Society.benzimidazole; bipolar host materials; BoyerâKauzmann rule; carbazole; PhOLEDsjournal article10.1021/acsami.8b15084303600652-s2.0-85058362608