Spectroelectrochemical properties of electrodeposited poly(4,7-dithien-2-yl-2,1,3-benzothiadiazole) (PDTBT) films in 1-butyl-3-methylimidazolium tetrafluoroborate (IL1), hexaflurophosphate (IL2), and bis(trifluromethylsulfonyl)imide (IL3) are reported. The net charges of polymerization, cyclic voltammograms, UV/Vis spectra, and scanning electron micrographs indicated the respective films PDTBT1, PDTB2 and PDTBT3 were nano-textured and the yield increased in the order PDTBT2 < PDTB1 < PDTBT3. The formal potentials of the p-doping and n-doping redox couples, and the band gaps estimated from doping onset-potentials (E-pd(0)'; En(d)(0)'; Eg-ec) were: PDTBT1/IL1 (1.03 V; -1.23 V; 1.67 eV), PDTBT2/IL2 (0.95 V; -1.49 V; 1.49 eV), and PDTBT3/IL3 (1.00 V; -1.38 V; 1.83 eV). The corresponding UV/Vis absorption maxima and the band gaps estimated from absorption onset wavelengths (lambda(max); Eg-opt) were (540 nm; 1.58 eV), (579 nm; 1.42 eV), and (578 nm; 139 eV). Thus, more conjugated PDTBT molecules were formed in the hydrophobic 112 and 3 than in the hydrophilic In In a double potential-pulse (-0.6 V/-1.0 V) redox cycling monitored at 1000 nm, the optical contrast and coloration efficiency (Delta(%T); CER -> Ox) were PDTBT1 (11%; 158 C cm(-2)), PDTBT (17%; 91 C cm(-2)) and PTBT3 (34%; 187 C cm(-2)) with similar color/bleach (1-1.3 s) or reverse (3-4 s) switching times. IL3, the least viscous and most conductive of the three ILs, enabled the most efficient PDTBT electrodeposition and a PDTBT/IL system with superior electrochromic properties. (C) 2015 Elsevier B.V. All rights reserved.