Low-oxidation-potential conducting polymers: alternating substituted para-phenylene and 3,4-ethylenedioxythiophene repeat units

The effect of alkoxy substituents on the physical and electronic properties of a series of poly{1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-dialkoxybenze}s is reported. Monomers containing methoxy, heptoxy, dodecyloxy and hexadecyloxy substituents were obtained from Negishi couplings in yields ranging from 42 to 83%. The methoxy, heptoxy and dodecyloxy monomers electropolymerized efficiently to form electroactive films, with irreversible monomer oxidation peak potentials ranging from +0.46 to +0.51 V versus Ag/Ag+. The hexadecyloxy-substituted derivative exhibited a higher oxidation potential of +0.66 V and a slower rate of film formation owing to solubility of the oligomer. Cyclic voltammetry of the polymer films revealed reversible redox processes with quite low E-1/2,E-p potentials ranging from -0.28 to -0.35 V. Band gaps of 1.75 eV for the methoxy-substituted polymer and 2.0 eV for the longer-chain-substituted polymers were determined from the onset of the pi to pi* transition observed by optoelectrochemical techniques. Oxidative chemical polymerization of the dodecyloxy and hexadecyloxy monomers with ferric chloride, followed by reduction with ammonium hydroxide, produced slightly soluble polymers. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.