ELECTROCHEMICAL SOLUTION AND SOLID-STATE INVESTIGATIONS ON CONJUGATEDOLIGOMERS AND POLYMERS OF THE ALPHA-THIOPHENE AND THE P-PHENYLENE SERIES

A study of the solution and solid-state electrochemical properties of defined oligomers of the alpha-thiophene and the p-phenylene series wi th chain lengths 2 less than or equal to N less than or equal to 16 is presented. Upon p-doping of the oligomers in the solid state their so lid-state polymerization on the electrode was observed. The investigat ions clearly demonstrate that the important steps of the electropolyme rization of conducting polymers take place exclusively in the solid st ate on the electrode. The degree of polymerization strongly depends on the anodic electrode potential. At low potentials polymers with long, ideally-linked chains are formed, whereas at high potentials strongly cross-linked polymers are generated. A new charge storage mechanism f or conjugated oligomers and polymers is presented taking into account the morphology of the materials. We propose a two-step mechanism to ex plain hysteresis effects observed in voltammograms for charging proces ses on these materials. In the first stage of the charging process we assume that the originally twisted segments become more planar, enabli ng a better delocalization of charges along the chain (intramolecular stabilization). This is the prerequisite for the second step, an inter molecular stabilization through interactions between neighbouring char ged segments, leading to the delocalization of the excess charges over several segments and, therefore, to further stabilization of the syst em. Copyright (C) 1996 Elsevier Science Ltd