| Palladium-catalyzed coupling techniques have been used to prepare a series of 1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-dialkoxybenzenes which can be polymerized chemically or electrochemically. The highly electron rich nature of these materials leads to extremely low oxidation potentials of the monomers and their polymers (E1/2,p = -0.15 to -0.35V vs. Ag/Ag +). Mild oxidation conditions can be used during polymerization and redox switching, resulting in fewer side reactions and more stable polymers; less than 30% loss in electroactivity occurs over 3100 redox cycles.;These polymers are stable over a broad potential range, allowing them to be used as modified electrode materials. For example, ferrocene can be repeatedly oxidized and reduced at the polymer surface. In-situ EPR electrochemistry was used to better understand the polymer redox processes, which are solvent-dependent. Stable polarons are observed in acetonitrile but not in the presence of methylene chloride. In-situ conductivity measurements reveal that these polymers become conductive at much lower potentials than the analogous thiophene polymers. The polymers are electrochromic, reversibly switching from red to blue upon oxidation with electronic bandgaps at ca. 1.9 eV.;A variety of chemical reactions have been used for polymer synthesis. Highest molecular weight (16 repeat units, or 48 rings) and solubility are obtained from oxidative polymerization using ferric perchlorate as the oxidant. Monomers have also been dibrominated to produce materials that can be polymerized using transition metal-mediated coupling reactions. Polymers prepared in this fashion are partially soluble, with molecular weights of the soluble fractions similar to those found in ferric chloride polymerizations (3 to 5 repeat units, or 9 to 15 rings). Heterocoupling polymerizations have been used to incorporate additional EDOT or phenylene rings into the polymer backbone, changing the electron density of the polymers and resulting in significant differences in band gaps (1.7 and 2.4eV, respectively). |
