Solution-processable multicolored dithienothiophene-based conjugated polymers for electrochromic applications

The syntheses of conjugated polymers poly(2,6-(dithieno[3,2-b:2′,3′-d]thiophenyl)-alt-2,5-(3,4-dialkoxy)thiophenyl) were achieved by reacting 2,6-dibromodithieno[3,2-b:2′,3′-d]thiophene with respective 2,5-bis(trimethyltin)-3,4-dialkoxythiophene in medium yields via a Stille coupling reaction. The resulting polymers are highly soluble in some common organic solvents. The polymer films are purple at neutral states and gradually become gray upon progressive oxidation by applying an external potential as a result of absorption across the whole visible spectrum. At the fully oxidized state, the polymers become transmissive light blue. In particular, polymer poly(2,6-(dithieno[3,2-b:2′,3′-d]thiophenyl)-alt-2,5-(3,4-didecyloxy)thiophenyl) (P1) film exhibits exceptional high optical contrasts of 46% and 72% in the visible and near-infrared regions, respectively, with good stability over 800 full cycles. An absorptive-transmissive electrochromic device (ECD) of P1 exhibits a contrast ratio of 15% at λmax of 534 nm and 20% at 1321 nm and high coloration efficiency of 449 and 471 cm2/C, respectively. This type of multichromic polymers would thus be promising materials for electrochromic displays and inks.