Electrochemical synthesis, characterization, and electrochromic properties of poly(3-chlorothiophene) and its copolymer with 3-methylthiophene in a room temperature ionic liquid

Electrochemical homopolymerization of 3-chlorothiophene (ClT) and copolymerization with 3-methylthiophene (MeT) were carried out via potentiodynamic and galvanostat methods by using ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM]PF6) as the growth medium and the supporting electrolyte. Both homopolymer(PClT) and copolymer P(ClT-co-MeT) were characterized via cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR), spectroelectrochemical analysis and kinetic study. Homopolymer revealed color changes between deep red and deep blue, whereas copolymer showed the most vivid change of color between bright red and greenish blue in fully reduced and oxidized states. Via kinetic studies, switching time and the maximum optical contrast % ΔT were found to be 2.4 s and 17% for PClT, 0.9 s and 26% for P(ClT-co-MeT). Compared with PClT (580 times), the copolymer exhibited a long-term switching stability up to 2300 double switches. Results implied that copolymerization is a valuable approach to achieve the desired electrochromic properties.