Spectroelectrochemical study of alkyl-aryl asymmetric viologens in poly(vinyl alcohol) (PVA) – borax electrolyte

Viologens are widely established as organic electrochromic compounds. The electrochromic properties of the viologen systems can be modulated by varying the molecular structure of the viologens (substituents at the nitrogen atoms) and by changing their environment (electrolytic media). Polyelectrolyte-based electrochromic devices containing viologens provide well-defined colored states. In this work, recently reported alkyl-aryl asymmetric viologens in polyvinyl alcohol (PVA) – borax gel electrolyte were studied by spectroelectrochemistry and compared with their corresponding dialkyl and diaryl symmetric viologens. The simultaneous use of cyclic voltammetry, ESR and UV–vis–NIR spectroscopy enables unequivocal correlation between an observed coloration and the specific redox species involved. It has been found that the dimer structures significantly contribute to the color observation under specified conditions. The influence of the molecular structure and the electrolytic media on the electrochemical, magnetic and optical properties of the viologen was studied.