Three novel pi-conjugated indolo[3,2-b]carbazole derivatives, 2,8-di(thiophen-2-yl)-5,11-dioctyl-indolo [3,2-b] carbazole (TICZ), 2,8-bis(4-ethylthiophen-2-yl)-5,11-dioctyl-indolo[3,2-b]carbazole (ETICZ) and 2,8-bis(2-(3,4-ethylenedioxythiophene))-5,11-dioctyl-indolo[3,2-b]carbazole (EDTICZ), were synthesized and electrochemically polymerized to afford the corresponding polymers. The effects of different substituent groups on thiophen units in terms of optical, electrochemical, and electrochromic properties and the performance of electrochromic devices (ECDs) were investigated in detail. Electrochemical and optical analysis demonstrated that incorporation of strong auxochromic groups resulted in polymer PEDTICZ with low oxidation potentials, red-shifted absorption peaks and corresponding narrow band gap values but is unfavorable for incorporating ethyl groups. Spectroelectrochemical studies indicated an evident variation in the absorption spectra as well as significant color changes for all of the polymer films upon application of an external potential. PTICZ had high optical contrast with visible light (58.6%), fast switching speed (0.92 s), and satisfactory coloration efficiency (167 cm(2) C-1). Of these three systems, the results for PEDTICZ were next best, and those for PETICZ were third. Also, there was a larger contrast (82.7% and 57.8%) in the NIR region (1500 nm) for the PTICZ and PEDTICZ films, respectively. Along with high coloring efficiencies, these results indicate that these systems are favorable for many NIR applications. (C) 2019 Elsevier Ltd. All rights reserved.