Synthesis And Characterization Of The Symmetric And Unsymmetric Molecule And Polymer Viologen And Research Of Their Electrochromic Properties

Electrochromism can be defined as the phenomenon of the electrochromic material to undergo color reversible change upon oxidation or reduction, which was ensued from changing the potential applied. Electrochromic material is a kind of newly-functional material which can change people's life style and the way of utilizing energy sources. It can be widely applied to large-area display devices, smart windows and electronic paper. Owing to its plentiful colors, better optical performance, fast color change, low cost, good cycling reversibility, organic electrochromic material has become a dominant direction in the electrochromic research in recent years. Viologen is an outstanding class among them.In this paper, we synthesized thirteen target viologen compounds, including four symmetric viologen compounds(1-4), six unsymmetric viologen compounds(1b-6b), three side chain viologen polymers(1c-3c), which were prepared by 4,4'-bipyridine reacted with benzyl chloride, 1-bromo-n-octane, p-chloromethylstyrene, ethyl chloroacetate respectively. These compounds were characterized with FT-IR,¹H NMR and were proved to be consistent with the design.We studied the optical and electric properties of the thirteen viologen compounds by ultraviolet-visible spectrophotometry and cyclic voltammetry. The ultraviolet-visible absorption spectra shows that these viologen compounds have absorption from 191 to 198nm and from 256 to 263nm in near ultraviolet area. The cyclic voltammograms shows that these viologen compounds have two pairs of redox peaks. There is a one-electron redox course between -0.3V and -0.6V(V²⁺ (?) V^·+), and there is another one-electron redox course between -0.6V and -0.9V(V^·+(?)V⁰).We prepared the viologen electrochromic films on conductive ITO glass and solved the problem of the equalization of the films by improving conditions. We prepared the transparent solid electrochromic devices based on the viologen compounds on conductive ITO glass and tested the performance of the devices. The result shows that the best charged voltage range is from 2.5V to 3.0V. The devices can change color between violet and colorless circularly. The color time is about 3 s and the fade time is less than 1s. Their electrochromic performance are excellent and they may be used to produce electronic paper.