Achieving excellent colorimetric properties of low-cost black to transmissive switching electrochromic polymers by incorporating of spacing units into copolymers of 3,4-propylenedioxythiophene and benzothiadiazole

There have been increasing research attention directed towards black to transmissive switching electrochromic polymers, few reports employed simple polymers with a low production cost. Herein, we report the preparation of a series of polymers P2-P6 by incorporating different spacing units (i.e. carbazole, naphthalene, and phenylene) into the well-studied polymer P1, a copolymer of 3,4-propylenedioxythiophene (ProDOT) and benzothiadiazole (BTD). Simple preparation of polymers P2-P6 with spacing units were realized via C-H arylation polymerization between corresponding monomers, which are readily available. By inserting such phenyl-ring containing spacing units into oligoProDOT moieties, conjugation between ProDOT units was disrupted. Thus, polymers P2-P6 based electrochromic devices show a new absorption peak in short wavelength region (400 nm-500 nm) resulting a* and xb* values (<+/- 10), which are closer to a true black hue than that of P1 (-1.2, -15.39) in neutral state. Meanwhile, we demonstrate that the colorimetric properties of P4 (0.32, -6.43) and P6 (-0.06, -4.26) are better performing than most existing black polymers.