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-2 H -thieno[3,4- b ][1,4]dioxepin-6-yl)-7-(3,3-dihexyl-3,4-dihydro-2 H -thieno[3,4- b ][1,4]dioxepin-8-yl)-9 H -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.