Electrochromic device based on adsorbable viologens

Abstract

An electrochromic device (ECD) can change color absorption when subjected to an appropriate voltage. Such a device includes three components: a working electrode, a counter electrode, and an electrolyte. Viologens (Vio) are commonly used kinds of compounds cathodic electrochromic materials, and triphenylamines (TPA) are anodic electrochromic materials. Here, we designed and synthesized a novel donor-acceptor type electrochromic viologen, 1-(N-phenyl-N-ptolylbenzenamine)-1′-(2-phosphnoethyl)-4, 4′-bipyridinium dichloride (VT), which contained a triphenylamine (TPA) group that tunes the electron cloud structure of viologen, so as to tune the electrochromic color, and a phosphonic acid group that will be anchored onto the surface of TiO2 nano-particles, so as to improve color changing speed. And an electrochromic electrode was prepared by chemisorption using the synthesized VT as the primary electrochromic material, and a Prussian blue electrode was prepared using electrochemical deposition method as the secondary one. IR spectral and X-Ray Photoelectron Spectrometer showed that the VT molecules were well bonded with Titanium dioxide nanoparticles film. And then those electrodes were assembled into one device using PC/LiClO4 as electrolyte. The performances of solid electrochromic device based on adsorbable viologen were also characterized. As expected, the device exhibited vivid changing color, light yellow in the bleached state and indigo blue in the dark state, fast color changing time (less than 1 s) and good stability (up to 10000 cycles), which was contributed by the adsorption structures. By using the CIE 1931 %YLxy colorimetric system (Commission Internationale de I'Eclairage), color coordinates of the ECD were also measured. The good electrochromic performance suggested this device could be widely used to manufacture smart glasses, auto-mobile windows, and anti-dazzle mirrors.