A series of polymers comprising alternating phenylene and thienylene repeating units and with electron-donating or -withdrawing groups attached on thienylene units, i.e., poly[1,4-bis(3-X-2,5-thienylene)phenylene-alt-2,5-dioctyl-1,4 (PBTX, X = OMe, H, Cl, Br, CN), has been synthesized and characterized. These polymers are highly fluorescent, among which PBTH shows the highest solution quantum yield, up to 94% relative to quinine sulfate. The absorption and emission peak wavelengths of PBTOMe are bathochromically shifted and band gap (E-g) is lowered by the presence of electron-donating OMe group, in comparison with PBTH. The influence of electron-withdrawing groups, Br, Cl, and CN, on the absorption peak wavelength and E-g, on the other hand, is not so great. Nevertheless, the film of PBTCN shows an emission maximum near to that of PBTOMe due to the strong interchain interactions. The band structures as deduced from electrochemistry give information supporting the optical measurements. The IP of PBTOMe is decreased but EA is increased, resulting in a lower band gap than that of PBTH. The electronic structures of PBTBr and PBTCl change slightly in comparison with PBTH, but both the IP and EA of PBTCN are greatly increased (by 0.5 eV), leading to an unchanged E-g. The changes in electronic structure make PBTOMe a suitable candidate as an active layer in LED device, as it should favor a balanced electron and hole injection, despite its moderate quantum yield. PBTCN can be used as an excellent ETL material in multilayer devices as its EA is even higher than that of CN-PPV. The polymers are dopable by FeCl3 and I-2 except for PBTCN, in agreement with electrochemical results. PBTH shows a good conductivity up to 4 S cm(-1) when doped by FeCl3. The doped samples are examined using XPS and the formation of charge-transfer complex is suggested. The oxidization of both the S and O atoms in FeCl3-doped PBTOMe is also supported by XPS.