Preparation and characterization of tungsten trioxide/dibenzyl viologen polymer bilayer electrochromic films

A new composite electrochromic material has been prepared by electropolymerizing N,N′-bis[p-(trimethoxysilyl)benzyl]-4,4′-bipyridinium dichloride (BPQ2+·2Cl–) on top of a reductively conducting film of tungsten trioxide. 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 absorbance due to one-electron reduction of each monomer unit in poly(BPQ2+) increases quickly (in < 4 s), and is followed by a slower development of the absorbance due to the WO3 reduction ( > 1 min). The significance of these bilayer films is discussed with respect to applications to electrochromic devices.