Synthesis and Spectroelectrochemical Characterization of an Electrochromic Phosphole-EDOT Copolymer: poly([1-phenyl-2,5-bis(2-thienyl)thioxophosphole]_0.14 -co- [3,4-ethylendioxythiophene]_0.86)

Summary

We report the synthesis of an electrochromic phosphole-ethylendioxythiophene (EDOT) copolymer, poly(1-phenyl-2,5-bis(2-thienyl) thioxophosphole (1) -co- 3,4-ethylendioxythiophene (2)). This phosphole-EDOT copolymer, (3), with a content of (1) of 14 mol % showed an oxidation potential of 0.6 V, significantly lower than that of poly(1) (1.3 V) but higher than that of poly(2) (0.16 V). The copolymer (3) exhibited an UV/Vis/NIR absorption maximum at 715 nm which is red shifted compared to poly(1) (Δλmax = 200 nm) and blue shifted compared to poly(2) (Δλmax = 135 nm). Copolymer (3) presents a narrower optical band gap than poly (1) as a consequence of association in the copolymer of electron-rich heterocycles (2) with low-lying LUMO repeat units (1) resulting in intramolecular charge transfer and delocalization of the π-system. FTIR and XPS spectroscopic data for the phosphole-EDOT copolymer (3) are consistent with the expected copolymer structure and TGA data showed an increased stability of the material compared to that of neat poly(2). Copolymer (3) displays blue-to-black electrochromic behavior, with a maximum optical contrast of 13 % in the visible region and 15 % in the NIR region. Spectroelectrochemical measurements demonstrate a band at 429 nm (dedoped structure) and the emergence of a new one at 575 nm (doped structure) upon oxidation. Finally, morphological characterization of copolymer (3) by AFM depicts aggregated spherical particles of 100 – 250 nm in size with a RMS roughness of 123 nm, smaller than that observed for poly(2) under the same synthetic conditions.