Novel Color-Reinforcing Electrochromic Device Based on Surface-Confined Ruthenium Purple and Solution-Phase Methyl Viologen

Abstract

A novel color-reinforcing electrochromic device (ECD) is described in which the anode and cathode reactions simultaneously exhibit reversible colorless to intense purple changes. Under coloration, the mixed-valence iron(III) hexacy anoruthenate(II) chromophore is formed on oxidation of iron(II) hexacyano ruthenate(II), with simultaneous reduction of the methyl viologen dication to form a mixture of the radical cation monomer/dimer. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry, the color stimulus of such ECDs and the changes that take place on reversibly switching between the colored and colorless states have been calculated from in situ visible spectra recorded under electrochemical control. On ECD color switching, with the excellent color-matching between the two purple states, sharp and reversible changes in the hue and saturation occur, as shown by the minimal hysteresis of the track of the CIE 1931 xy chromaticity coordinates. Extrapolation of the xy track to the color locus gave a complementary wavelength (λ c ) of 565 ((5) nm in close agreement with values obtained for the individual electrochromic materials. The concentration of the solution-phase methyl viologen and its diffusion to the cathode controlled both the proportion of surfaceconfined Ruthenium purple (RP) that is switched to the intense purple form and the overall ECD changes. For the ECDs' "on" states, the CIELAB 1976 color space coordinates were L* = 86, a* = 9, and b* = À15, and L* = 79, a* = 15, and b* = À22, respectively, for 5 and 10 mmol dm À3 methyl viologen solution concentrations. CIELAB 1976 color space coordinates showed that the ECDs were fully transparent and colorless in the "off" states, with L* = 100, a* = 0, and b* = 0. Switching times, as estimated for 95% of the total absorbance change, were 4 and 10 s respectively, for coloration and bleaching for the 5 mmol dm À3 methyl viologen ECD, and 8 and 16 s for the 10 mmol dm À3 methyl viologen ECD.

In situ spectroelectrochemistry and colour measurement of a complementary electrochromic device based on surface-confined Prussian blue and aqueous solution-phase methyl viologen

“…In our recent work [44] with hybrid ECDs based on the surface-confined metal hexacyanometallate, Ruthenium purple (containing the iron(III) hexacyanoruthenate(II) chromophore) and solution-based methyl viologen, the anode and cathode reactions simultaneously exhibited reversible colourless to intense purple changes, the overall ECD coloration being colour reinforcing. By contrast, the IVCT band ( Fig.…”

Electrochromic devices based on surface-confined Prussian blue or Ruthenium purple and aqueous solution-phase di-n-heptyl viologen

“…ECDs in a sandwich configuration were fabricated as described earlier [3,4] Following electrochemical deposition of PB [3] or RP [4] thin films onto one ITO-coated substrate, a Nylon 6 film (0.25 mm thick, from Goodfellows), was applied as a spacer to three sides using epoxy resin. A second ITO-coated substrate was then secured to the first, creating a small volume between the substrates.…”

“…For absorptive/transmissive ECDs, the secondary electrode system is chosen to be a redox reaction where there is imperceptible visible colour change or as an electrochromic material where the change in colour is complementary [3] or reinforcing [4] to that at the primary electrode.…”

“…We have recently described [3,4] the fabrication and colour-switching properties of ECDs, with surface-confined metal hexacyanometallates as the anodically-colouring, and aqueous solution-phase methyl viologen (N,N´-dimethyl-4,4´-bipyridylium) as the cathodically-colouring electrochromic materials. Both Prussian blue (PB, containing the iron(III) hexacyanoferrate(II) chromophore) [3] and Ruthenium purple (RP, containing the iron(III) hexacyanoruthenate(II) chromophore) [4] have been used as the metal hexacyanometallate film in separate ECDs.…”

“…Both Prussian blue (PB, containing the iron(III) hexacyanoferrate(II) chromophore) [3] and Ruthenium purple (RP, containing the iron(III) hexacyanoruthenate(II) chromophore) [4] have been used as the metal hexacyanometallate film in separate ECDs. The initial ('off') state of each ECD is set with the PB (or RP) as the colourless (reduced) form and the methyl viologen as the colourless di-cation.…”