Tuning Color, Contrast, and Redox Stability in High Gap Cathodically Coloring Electrochromic Polymers

Abstract

The design of high bandgap electrochromic polymers (ECPs) that switch from a high energy absorbing colored state to a near-IR absorbing colorless state requires a challenging balance to be struck between achieving large changes in the absorption profile while maintaining sufficiently low oxidation potentials for use in full-color electrochromic devices. Previous studies on high bandgap ECPs have investigated structure–property relationships in dioxythiophenes copolymerized with various arylenes. Here, we expand this understanding by looking more closely at the effect of the dioxythiophene moiety as well as by varying the substituents on the arylene moiety. Three ECPs have been synthesized to perform this study with repeat units composed of electron-rich dimethoxyphenylene in alternation with dimers of 3,4-dialkoxy- and 3,4-propylenedioxythiophenes, yielding high gap polymers that are vibrant yellow or orange in the charge neutral state. Comparing these newly synthesized polymers to a structurally similar set previously reported, we elucidate the subtle steric and electronic effects that govern bandgap and redox properties in dioxythiophene copolymers.