PREPARATION AND CHARACTERIZATION OF TUNGSTEN TRIOXIDE DIBENZYL VIOLOGEN POLYMER BILAYER ELECTROCHROMIC FILMS

A new composite electrochromic material has been prepared by electropo lymerizing -bis[p-(trimethoxysil-yl)benzyl]-4,4'-bipyridinium dichlori de (BPQ2+.2Cl-) on top of a reductively conducting film of tungsten tr ioxide. The resulting bilayer system responds to a potential step from 0.9 to -0.65 V by turning from colourless to blue in two steps: the a bsorbance due to one-electron reduction of each monomer unit in poly(B PQ2+) increases quickly (in <4 s), and is followed by a slower develop ment of the absorbance due to the WO3 reduction (> 1 min). The signifi cance of these bilayer films is discussed with respect to applications to electrochromic devices.