The polycarbazoles have been proved to efficiently suppress the keto defect emission. Three carbazole-based conjugated polymers, poly[9-methyl-3-(4-vinylstyryl)-9H-carbazole] (PBC), poly[9-methyl-3-(2-(5-vinylthiophen-2-yl)vinyl)-9Hcarbazole] (PBT) and poly[9-methyl-3-(2-(5-vinylfuran-2-yl)vinyl)-9H-carbazole] (PBF), were investigated by quantum-chemical techniques, and gain a detailed understanding of the influence of carbazole units and the introduction of electron-donating on the electronic and optical properties. The electronic properties of the neutral molecules, HOMO-LUMO gaps (Delta E), in addition to ionization potential (I-p) and electron affinity (E-a), are studied using B3LYP density functional theory. The lowest excitation energies (E-g) and the absorption wavelength are studied using the time dependent density functional theory (TDDFT). The calculated results show that all three series of polymers have good planarity. And the highest-occupied molecular orbital (HOMO) energies lift about 0.36-0.61 eV and thus the I-p decrease about 0.01-0.19 eV compared to polycarbazole, suggesting the significant improved hole-accepting and transporting abilities. By introducing the electron-donating 1,4-divinyl-phenylene or 2,5-divinylthiophene or 2,5-divinylfuran units in the backbone, and the lowest-unoccupied molecular orbital (LUMO) energies decrease 0.20-0.39 eV. In addition, PBC, PBT and PBF have longer maximal absorption wavelengths than polycarbazole. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 706-714, 2009