Electrosynthesis and characterization of viologen cross linked thiophene copolymer

• Electrochemical copolymerization of OOT and HOT-CNP.
• Further reductive coupling of cyanopyridine from HOT-CNP into viologen during cathodic scan.
• Redox response of copolymer along with spectral studies confirms formation of viologen.
• Spectroelectrochemical analysis of copolymer film indicates its future incorporation into practically usable electrochromic devices.

Electrochemical copolymerization of 3-octyloxy-4-methylthiophene (OOT) and 1-[6-[(4-methyl-3-thienyl) oxy] hexyl]-4-cyanopyridinium bromide (HOT-CNP) was carried out using tetrabutylammonium hexafluorophosphate and acetonitrile (TBAPF6/ACN) as electrolyte. The cyanopyridine functionalized HOT-CNP undergoes further electrochemical reductive coupling to viologen. Both polymer (POOT) and copolymer P(OOT-co-HOT-CNP) were characterized by cyclic voltammetry (CV), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and in situ UV–vis spectroscopy. The effect of the monomer concentration ratio and the scan rate on the electrochemical properties of the copolymer was studied by the CV technique. The electrochemical redox response of the copolymer together with FTIR analysis further confirms the formation of viologen. The surface morphology was studied using SEM analysis. The polymer POOT revealed color changes between violet and bright blue, whereas the copolymer showed the most vivid change of color between purple and greenish blue in its fully reduced and oxidized states respectively. The results showed that copolymerization is a valuable approach in order to achieve desired electrochromic and redox properties.

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