Tunable green electrochromic polymers via direct arylation polymerization

A method to tune the hues of neutral green conjugated electrochromic polymers (NG-ECP) via direct C-H arylation polymerization (DArP) was developed. We used 4,7-dibromo-2,1,3-benzothidiazole and 2,7-dibromofluorene to randomly copolymerize with ProDOT via DArP and successfully obtained a series of green polymers. On varying the ratio of 4,7-dibromo-2,1,3-benzothidiazole and 2,7-dibromofluorene, we can readily adjust the relative intensity of two absorption bands in the visible-light wavelength region, which leads to four green polymers with different hues being obtained. Specifically, increasing the ratio of 4,7-dibromo-2,1,3-benzothidiazole leads to the enhancement of the polymer absorption intensity in the long wavelength (approximate to 550-700 nm) region, while increasing the ratio of 2,7-dibromofluorene will lead to the increase of the polymer absorption intensity in the short wavelength (approximate to 400-500 nm) region. Via the random direct arylation polymerization of multi-component monomers in various ratios, we can precisely control the absorption spectra of neutral green conjugated electrochromic polymers (NG-ECPs) in the visible-light wavelength region. The electrochemical and optical properties, spectroelectrochemical behaviors, and electrochromic performance of these NG-ECPs were characterized and they showed great potential for electrochromic devices such as smart windows and transmissive displays.