Electropolymerized pyridine derivatives and linear pyridinium salts for electrochromic applications

Two novel linear pyridine derivatives containing benzothiadiazole (BTZ) (A) and benzoselenadiazole (BSeZ) (B) cores functionalized by triphenylamine (TPA) group, and their corresponding pyridinium salts with hexyl chains 1 and 2, were synthesized and characterized by spectroscopic, electrochemical, and spectroelectrochemical methods. The pyridine derivatives A and B were successfully electropolymerized onto the ITO electrode, obtaining as a result thin polymer films (poly-A and poly-B) with promising optical properties, including multicolor switching, good optical contrast and electrochromic stability. Poly-A and poly-B exhibited three reversible color changes (beige ↔ orange ↔ green-grey) and their electrochromic stability, response times and optical contrasts were defined. In contrast, the pyridinium salts exhibited a higher number of redox processes, showing multielectrochromic properties with up to five distinct and reversible color changes (yellow ↔ purple or slightly pink ↔ colorless ↔ orange ↔ grey), corresponding to occurring suitable redox forms. This study presents the example of pyridinium salts exhibiting multielectrochromism. Both polymeric pyridine derivatives and pyridinium salts indicate promising optical properties for using them as the active materials in electrochromic applications.