Multi-color electrochromic copolymer films based on 2,2′-thiophene and 3, 4-ethylenedioxythiophen

In this work, the copolymers were successfully synthesized by electrochemical polymerization of two monomers, bithiophene (BT) and 3,4-ethylenedioxythiophene (EDOT), in a lithium perchlorate/propylene carbonate (LiClO 4 /PC) solution. The as-prepared were characterized with the aid of cyclic voltammetry, colorimetric analysis, Fourier transform infrared spectroscopy, and Ultraviolet-visible spectroscopy. The electrochromic and colorimetric properties of copolymers poly(2,2′-bithiophene-co-3,4-ethylenedioxythiophene) (P(BT-co-EDOT)) and homopolymer poly(2,2′-bithiophene) (PBT) in 0.1 M LiClO 4 /PC solution were investigated, and the coloring process based on the redox reaction of the film was observed. When an anodic potential is applied, the copolymer P(BT-co-EDOT) films show a color change from blue-purple to blue-gray changes, and the homopolymer PBT shows a color change from orange to brown. In addition, spectroelectrochemistry studies indicate that copolymer P(BT-co-EDOT) has a lower optical band gap (1.73–1.87 eV) than homopolymer PBT. The copolymers P(BT-co-EDOT) show a high optical contrast (36.65–42.62%) and coloration efficiency (215.8–296.6 cm 2 C −1 ). The copolymer P(BT1-co-EDOT1) demonstrates excellent redox cycling stability, with 90% of the original optical contrast maintained after 500 cycles, making it an ideal candidate for copolymers.