High-contrast electrochromic polymers from alkyl-derivatized poly(3,4-ethylenedioxythiophenes)

The syntheses of two new derivatives of 3,4-ethylenedioxythiophene (EDOT), specifically 5-octyldioxeno[2,3-c]thiophene (EDOT-C-8) (2) and 5-tetradecyldioxeno[2,3-c]thiophene (EDOT-C-14) (3), and their polymers are reported in this paper. Cyclic voltammetry of 2 and 3 in 0.1 M TBAP/CH3CN show irreversible monomer oxidation peaks (E-p,E-m) at 0.89 and 0.93 V, respectively. Multiple scans yield electroactive and conducting polymer films on electrode surfaces. The PEDOT-C-8 and PEDOT-C-14 formed oxidize with relatively low peak potentials at -0.22 and -0.19 V, respectively, indicating the doped form of the polymer to be quite stable. Both PEDOT-C-8 and PEDOT-C-14 show two reduction processes with peaks at -0.18 and -0.16 V (E-c2,E-p) and -0.55 and -0.36 V (E-c1,E-p) respectively. Optoelectrochemical studies reveal an E-g of 1.75 eV for both polymers. The polymers are electrochromic, relatively transmissive and light gray in the oxidized form, while being opaque and deep purple in the reduced form exhibiting high electrochromic contrasts. Long term switching studies carried out in 0.1 M LiClO4/PC with Li/Li+ as a reversible counter electrode shows that PEDOT, PEDOT-C-8, and PEDOT-C-14 retained 65%, 50%, and 62% of their electroactivity after 6000, 9000, and 16 000 double switches, respectively.