Covering the More Visible Region by Electrochemical Copolymerization of Carbazole and Benzothiadiazole Based Donor-Acceptor Type Monomers

An electrochromic copolymer film of 2-(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl)-7-(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-8-yl)-9H-carbazole (M1) and 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (M2) was prepared via electrochemical technique. The copolymerization was performed with one to one monomer feed ratio. Electrochemical and optical properties of the resulting copolymer film (P3) and the homopolymer films of M1 and M2 (P1 and P2) were investigated by using cyclic voltammetry and UV-Vis spectrometry techniques, and the corresponding results were compared. Incorporation of M1 and M2 into copolymer matrix was clearly observed on the resulting cyclic voltammograms and UV-Vis spectra. P3 covered the visible regions coming from both P1 and P2, and exhibited a neutral state darker color than those of homopolymers. P3 film was found to have a multichromic behavior, appearing as brown in its neutral state while changing its color upon oxidation to dark-gray (at about 0.3 V), to blue (at about 0.6 V) and finally to grayish cyan (beyond 0.9 V), with a corresponding optical band gap of 1.65 eV.