New electrochromic materials

A number of inorganic and organic materials exhibit redox states (reduced and/or oxidised forms) with distinct UV-Visible (electronic) absorption bands. When electrochemical switching of these redox states gives rise to different colours (i.e. new or different visible region bands), the material is described as being electrochromic. By virtue of their numerous applications, both of academic and commercial interest, electrochromic materials are currently attracting a great deal of interest. This review provides an introduction to the major classes of electrochromic materials, namely transition metal oxides, Prussian blue systems, viologens, conducting polymers, transition metal and lanthanide coordination complexes and metallopolymers, and metal phthalocyanines. Examples of some new materials and of prototype and commercial electrochromic devices are cited.