A donor–acceptor–donor (D–A–D) type monomer (3,6-bis(2-(3,4-ethylenedioxy thiophene))pyridazine, EPE) with pyridazine as an intermediate unit (acceptor) and 3,4-ethylenedioxythiophene (EDOT) as a sealing unit (donor) was prepared. The monomer was then polymerized by adjusting various ratios of FeCl₃/monomer to prepare a donor–acceptor–donor (D–A–D) type conjugated polymer: poly(EPE). The results from a structural analysis indicated that the conjugation length, doping level, thermal stability, crystallinity, as well as the morphologies of the poly(EPE)s can be affected by the oxidant : monomer ratio. The resulting products were characterized by ¹H NMR, FT-IR, UV-vis, TGA, XRD, EDX and SEM. Studies were carried out on the photocatalytic performance of the poly(EPE)s for the photocatalytic degradation of different dyes (methylene blue (MB), methyl violet (MU), methyl orange (MO), rhodamine B (RhB) and phenol) (5 mg L⁻¹) under xenon-lamp irradiation, and the same type of light source and different catalysts (poly(EPE)s and PEDOT) on the degradation efficiency of MU were investigated, which showed that poly(EPE) was an effective photocatalyst, and the presence of Fe ions in the polymer matrix played a significant role in enhancing the photocatalytic activity of poly(EPE). Among the poly(EPE)s, the doped poly(EPE)₂ ([FeCl₃]/[EPE] ratio of 8 : 1) achieved the highest degradation efficiency (95.53%) for MU dye under the simulation of a visible light source for 300 min.