Synthesis and characterization of D-A type conjugated electrochromic polymers with cross-linked structure employing a novel and multifunctionalized molecular as the acceptor unit

In this study, three novel conjugated electrochromic copolymers including PIPE-1, PIPE-2 and PIPE-3 were successfully synthesized via Stille coupling reaction. In the synthetic process, a novel and multifunctionalized electron functional unit 5,8,14,17-tetrabromoquinoxaline [2',3':9,10]phenanthrene[4,5-abc]phenazine (M2) was selected as the acceptor unit, 6,8-dibromo-3,3-bis-decy1-3,4-dihydro-2H-thieno[3,4-11] [1,4]dioxepine (M1, brominated ProDOT-decyl(2)) and bis(trimethylstannane) functionalized indacenodithiophene (M3) as donor units. Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), spectroelectrochemistry, kinetic switching and thermogravimetry (TG) were performed for the three polymers. The three polymers have band gaps at around 2.0 eV, and the absorption peaks and colors of the polymers can be changed to some extent by changing the feed ratios of the monomers. The three polymers exhibited good thermal stability. More importantly, the three polymers exhibited high optical contrast and fast response time both in the visible and nearinfrared regions. The optical contrast of PIPE-1, PIPE-2 and PIPE-3 in the near infrared region were 67.26%, 66.43% and 57.67%, respectively, and the response time of PIPE-2 at 1500 nm was only 0.35 s. PIPE-1 changed from wine red (0 V) to brown (0.90 V) and finally turned blue gray (1.40 V). PIPE-2 changed from rose red color (0 V) to light brown color at 0.90 V, and to light blue color (1.40 V). PIPE-3 changed from magenta (0 V) to light red color at 0.89 V, and to light gray color at 1.02 V, and finally became a blue color (1.40 V), which suggested that the polymer has multi-chromic property.