We report a theoretical study of a new copolymer based on (Carbazole and Ethylenedioxythiophene)(n) (n = 1-3) in their neutral and oxidized states, by using B3LYP/6-311G(d,p) calculations and thus deduce its optoelectronic properties. We discuss the influence of chain length of these properties. We also discuss the experimental UV-Visible spectrum for (PolyvinylcarbazolePoly(3,4-ethylenedioxythiophene)) (PVK-PEDOT) copolymer powder for comparison. Conformational analysis shows that there are no big changes in the structural parameters of the oligomers in their neutral form. After oxidation the oligomers become more planar and show a quinoidal character. The electronic states of monomers (Cbz-Edot) based Carbazole (Cbz) and Ethylenedioxythiophene (Edot), were elucidated by molecular orbital calculations using B3LYP/6-311G(d,p). The HOMO, LUMO, and gap energies E(g) were also deduced for the stable structure of the neutral, polaronic, and bipolaronic forms. Electronic transition energies and oscillator strengths of copolymers were obtained by the ZINDO, TD-DFT, and CIS methods. Band gaps of the corresponding polymers were obtained by extrapolating oligomer gaps to infinite chain lengths. These results will be compared with the experimental values obtained by optical spectrum. The optoelectronic properties of the (Cbz-Edot) 3 led us to suggest that this oligomer is a good model to reflect those of the parent polymer. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3351-3360, 2011