Polypyrrole electrochemically induced changes

Jl. Properties of Polypyrrole and Related Polymers and their Electrochemically Induced Changes... 

Chromatic changes caused by electrochemical processes were originally described in the literature in 1876 for the product of the anodic deposition of aniline [271]. However, the electrochromism was defined as an electrochemically induced phenomenon in 1969, when Deb observed its occurrence in films of some transition metal oxides [272]. Electrochromism in polypyrrole was first reported by Diaz et al. in 1981 [273]. Electrochromism is defined as the persistent change of optical properties of a material induced by reversible redox processes. Electronic conducting polymers have been known and studied as electrochromic materials since the initial systematic studies of their electronic properties. 

Employment of a polypyrrole-coated microelectrode brought about the amplification of the electrochemical effect. By the adoption of a high frequency square wave potential application, the susceptibility of the target cell at the interface of the microelectrode to bursting was remarkably enhanced. It should be noted that the polypyrrole film-coated electrode demonstrated interesting functions even under the conditions needed for a bare platinum electrode. This might be interpreted by the electrochemically induced influx of dopant anions onto the polypyrrole film matrix, which seems to result in drastic pH changes in the localized area, i.e., the interface between an electrode and bulk solution. 

Many electrochemically dopant-induced structure-property changes in conducting polymers have been described for use in, for example, electrochromic windows and displays, electrochemically controlled chemical separation and delivery systems, redox capacitors, electromechanical actuators, etc.,32. Some of these are apparently close to commercial application. Polypyrrole capacitors are already in conunercial production,27. 

As a matter of fact, the N-substitution induced in the polymer backbone a much weaker configurational flexibility than the 3-substitution. To circumvent this problem, Moutet et al. have synthesized polypyrroles N-substituted by ferrocene crown ether [270] and aza crown ether-linked bipyridine ruthenium (II) complexes [271]. Poly(19) was found to be Ba + and Ca " "-responsive [270], whereas the ruthenium(II)-based PPy was more sensitive to alkali metal cations [271]. The recognition of the cation binding was based on the changes in the electrochemical response of the metallic center instead of PPy. 

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