Evolution of the physical properties of polyacetylene during the electrochemical intercalation with electron donors

Abstract

A great number of conjugated polymers can be doped up to the metallic state with electron donating or accepting chemical species. Using electrochemical techniques, a reversible and controllable doping can be performed, which can be considered as an actual intercalation process. During such a process all the properties of the system experience marked changes. The main evolution occurs for the structural characteristics of the polymer/dopant system. For instance, in the case of polyacetylene, successive phase transformations are observed during doping with alkali metals, corresponding to various types of ordering.

Transport, optical and magnetic properties are also greatly influenced during the intercalation process. For instance the eight to ten orders of magnitude increase of the electronic conductivity observed during the doping of polyacetylene is in fact due to the transition of the system from the semiconducting to the metallic state. Such a transition can be studied continuously by measuring in-situ the optical or magnetic characteristics. The case of alkali intercalation is particularly interesting as the ion sizes agree reasonably well with the available space in the structure of linear conjugated polymers. In this case, the study of the magnetic properties of doped polyacetylene allow to clarify the role played by the dopant itself in interchain electronic transport.