A novel monomer; 2-(3-nitrophenyl)-4,7-di(thiophen-2-yl)-1H-benzo[d]imidazole) (BIMN) was used for electrochemical copolymerization with 3,4-ethylenedioxythiophene (EDOT). Polymerization was achieved in acetonitrile (ACN)/dichloromethane (DCM) (1:1, 1:3 and 1:5, molar ratios) solution containing sodium perchlorate (NaClO4) and lithium perchlorate (LiClO4) mixture as the supporting electrolyte on an ITO electrode. The chemical structures of monomer and copolymers were characterized by nuclear magnetic resonance (H-1 NMR) and scanning electron microscopy (SEM). The optical and electrochromic properties were investigated by UV-vis spectrophotometer and cyclic voltammetry, respectively. Combination of BIMN and EDOT provides lower oxidation potential, lower bandgap and higher optical contrast. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.