The reduction mechanism of p-cyanophenylviologen in PVA-borax gel polyelectrolyte-based bicolor electrochromic devices

Polyelectrolyte-based electrochromic devices containing p-cyanophenylviologen and PVA-borax gel provide two different well-defined colored states (green and red). In this work, the bicolor electrochromic gel was characterized by in situ electron spin resonance (ESR)/ultraviolet–visible–near infrared (UV–vis–NIR) spectroelectrochemistry to get more information about the electron transfer reactions of the p-cyanophenylviologen dication (p-CV2+) in the PVA-borax gel medium. We have determined the dominant species at each stepwise varying potential and proposed the complete mechanism of the p-CV2+ reduction in polyelectrolyte. The species responsible for the green and red coloration were identified. The switching between bleached and colored states over repeated cycles was performed for the electrochromic devices to evaluate the redox stability of the colored species. In addition, the gel formulations were optimized in terms of optical contrast.