Consecutive anchoring of symmetric viologens: Electrochromic devices providing colorless to neutral-color switching

In this study, colorless to neutral-grayish color ECDs based on the consecutive anchoring of alkyl-substituted and aryl substituted symmetric viologens (blue and green switching vilogens respectively) are reported. The strong binding affinity towards nanostructured TiO2 layer of both viologens equally provided with phosphonate anchoring group, allows the employment of a single nanostructured layer wherein both viologens were adsorbed (glass/TCO/viologens-modified-TiO2/TCO/glass),while showing very rapid anchoring times (<= 15 min). The effect of the TiO2 layer thickness and grafting conditions on the ECD performance have also been investigated, reaching switching times <= 6 s and good performance up to 2 000 cycles for the optimized ECDs. Additionally, the influence of the electrolyte on the observed coloration has also been explored. The use of water-based gel polyelectrolyte has allowed significant enhancement of the neutral-grayish EC behavior (a* and b*<= vertical bar 10 vertical bar). The beneficial impact of water-based gel polyelectrolyte and potential in color-tailored electrochromics is emphasized.