Zhang, Kai; Tao, Y; Yang, C; You, Han; Zou, Y; Qin, J; Ma, D
Three new carbazole copolymers, poly(9-(2,5-diarene-[1,3,4]
oxadiazole)-carbazole-alt-9-(2-ethylhexyl)-carbazole-3,6-diyl)s (P1), poly(9-(2,5-diarene-
[1,3,4]oxadiazole)-2, 7-carbazole-alt-9-(2-ethylhexyl)-3, 6-carbazole-diyl)s (P2), and poly(9-
(2,5-diarene-[1,3,4]oxadiazole)-carbazole-alt-9-(2-ethylhexyl)-carbazole-2,7-diyl)s (P3), were
synthesized by the Suzuki coupling reaction. The copolymers were characterized by (1)H NMR, (13)C
NMR, and elements analysis, and their molecular weights were estimated using gel permeation
chromatography. The TGA and DSC results revealed their good thermal stability with high glass-
transition temperatures (T(g)) at 211 degrees C (P1), 194 degrees C (P2), and 208 degrees C (P3),
respectively. The copolymers exhibited blue emission with significantly improved fluorescence
quantum efficiencies compared to their analogous polymers. The triplet energies of PI, P2, and P3
were determined to be 2.52, 2.42, and 2.32 eV, respectively, from their phosphorescent spectra at
77 K. The HOMO/LUMO levels of the carbazole copolymers can be tuned by different coupling
positions and substitution at the 9-position of carbazole. P1 by connecting carbazole units via
their 3 (6) positions shifts the HOMO/LUMO levels to higher energy compared to P2 via 2 (7)
positions, whereas replacing alkyl groups at the 9-position of carbazole with electron-
withdrawing diaryl- 1,3,4-oxadiazole group shifts the HOMO/LUMO levels to lower energy. Finally,
polymer light-emitting diodes employing the P1-3 as host and bis(2,4-diphenylquinolinato-N,C
(2'))iridium(acetylacelonate) (Ir(ppq)(2)(acac)) as guest were constructed and characterized
electrically.