Construction of Highly Efficient Carbazol-9-yl-Substituted Benzimidazole Bipolar Hosts for Blue Phosphorescent Light-Emitting Diodes: Isomer and Device Performance Relationships
Journal
ACS Applied Materials and Interfaces
Journal Volume
10
Journal Issue
49
Pages
42723 - 42732
Date Issued
2018
Author(s)
Chang, S.-Y.
Lin, G.-T.
Cheng, Y.-C.
Huang, J.-J.
Chang, C.-L.
Lin, C.-F.
Chiu, T.-L.
Abstract
Four 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.
Subjects
benzimidazole; bipolar host materials; BoyerâKauzmann rule; carbazole; PhOLEDs
Type
journal article