Electrochromic materials have the property of a change of color as effected either by an electron transfer (redox) process or by a sufficient electrochemical potential. The main classes of electrochromic materials are the metal oxides, conjugated polymers, metal coordination complexes and the viologens. Successful applications of electrochromic materials in devices include anti-glare windows in aircraft and buildings, electrochromic sunglasses, switchable mirrors, camouflage materials, chameleonic fabrics, spacecraft thermal control, an optical iris for a camera lens and light-reflective/transmissive display devices.
In our group, we develop unique viologen/polyviologen based materials, conjugated polymers with viologen functionality and viologen-graphene composites. The viologen is synthesized from cyanopyridinium ion based monomer precursor and reductive electropolymerization method is used to obtain an electroactive thin film directly on the conducting substrate. The as deposited film is thoroughly characterized by different spectral, surface and electrochemical techniques. The films are further subjected to continuous potential charging/discharging cycles to monitor the color/bleach characteristics and long term stability. We show that the viologen based electroactive films possess conducing properties when attached to conjugated polymers like polythiophenes. Moreover, the electrochrome stability is better when a composite is made with graphene, in comparison to pristine viologen/polyviologen system. Such assemblies based on electrochromic viologens would be a valuable alternative to the conventional materials for smart windows.
