A Processable Green Polymeric Electrochromic

Abstract

We report electrochemical and optical properties of the first electrochemically and chemically prepared green, soluble conducting polymer in its neutral form. Oxidative electrochemical and chemical polymerization of dioctyl-substituted 2,3-di(thien-3-yl)-5,7-di(thien-2-yl)thieno[3,4- b ]pyrazine ( 3b ) results in a soluble polymer ( 4b) with novel optical properties. The neutral polymer 4b absorbs both blue (above 600 nm) and red light (below 500 nm), reflecting a saturated green color. In the oxidized form, these absorptions are depleted, resulting in a transmissive pale brown polymer with very strong absorption in the near-infrared. Electrochemical and spectroelectrochemical semiconductor band gaps of 4b were found to be ca. 1.3 eV. Molecular weight analysis showed that soluble polymers have different conjugation length from oligomers to polymers. Since the monomer 3b has low oxidation potential (0.48 V vs Ag/Ag + ), mild oxidizing agents (i.e., CuCl 2 ) initiate chemical polymerization. The oxidant/monomer ratio should be at least 3:1 to get a desired green polymer. High green color saturation as well as the high solubility in common organic solvents makes this polymer a promising material to bring polymeric electrochromics closer to red, green, and blue (RGB) realization.