ABSTRACT
Electrochromism refers to the ability of a material to reversibly change its electromagnetic spectrum when undergoing a redox process. Conjugated electrochromic polymers (ECPs) have been thoroughly explored for this application, as the spectra of their charge neutral form, attributed to the polymer’s π–π* transition, can be synthetically and structurally fine-tuned throughout the visible spectrum and beyond (from ~0.5 to over 4.0 eV or 2.5 microns to 300 nm), in principle affording a material of any color. Electrochemical oxidation/p-type doping or reduction/n-type doping leads to charged states, where light absorption is transitioned to longer wavelengths, often outside of the visible region, with a concurrent loss of absorption from the π–π* transition. When the polymer is converted from a colorless transmissive state to a colored absorptive state upon oxidation (p-type doping), this electrochromism is referred to as anodically coloring. Conversely, when the oxidized form of the polymer is highly transmissive, and the neutral form is absorbing and colored, the material is cathodically coloring. Finally, if the light absorption occurs in the visible in both the charged and neutral state, this gives rise to a multi-colored electrochromic response.
