Polarons, bipolarons, and solitons in conducting polymers

On the mechanism of conductivity enhancement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film through solvent treatment

Polyaniline: A historical survey

The effect of charge-transfer doping on the geometric and electronic structures of conjugated polymers has been investigated at the ab initio level with explicit consideration of the doping agents. Three systems were chosen for study as prototypical examples of conjugated polymers with nondegenerate ground states: polyparaphenylene, polypyrrole, and polythiophene. As a result of charge transfer with electron-donating dopants, extra charges appear on the polymer chains and induce strong geometry modifications. The lattice evolves from an aromatic structure towards a quinoid-like structure. Charged defects associated with lattice deformations such as spinless bipolarons are formed. The influence on the electronic structure of the polymer chains is such that with respect to the undoped case, new states appear within the gap. For the maximum doping levels experimentally achieved, band-structure calculations demonstrate that the states in the gap overlap to form bipolaron bands, a few tenths of an electron volt wide. The presence of these bipolaron bands is consistent with optical data as well as with magnetic data which suggest that the charge carriers in the highly conducting regime are spinless.

Highly conducting polyparaphenylene, polypyrrole, and polythiophene chains: An ab initio study of the geometry and electronic-structure modifications upon doping

Conducting polymers (CPs) have received much attention in both fundamental and practical studies because they have electrical and electrochemical properties similar to those of both traditional semiconductors and metals. CPs possess excellent characteristics such as mild synthesis and processing conditions, chemical and structural diversity, tunable conductivity, and structural flexibility. Advances in nanotechnology have allowed the fabrication of versatile CP nanomaterials with improved performance for various applications including electronics, optoelectronics, sensors, and energy devices. The aim of this review is to explore the conductivity mechanisms and electrical and electrochemical properties of CPs and to discuss the factors that significantly affect these properties. The size and morphology of the materials are also discussed as key parameters that affect their major properties. Finally, the latest trends in research on electrochemical capacitors and sensors are introduced through an in-depth discussion of the most remarkable studies reported since 2003.

Electrical and Electrochemical Properties of Conducting Polymers.

Oxidized and neutral films of polypyrrole have been prepared electrochemically in the absence of oxygen and water. The neutral films are insulating and can be readily oxidized by chemical oxidizing agents to give films of greater conductivity than can be achieved by electrochemical oxidation. Optical spectroscopy provides evidence for the similarity of the polymeric carbonium ion produced by both types of oxidation. NMR studies are consistent with the α,α’ bonding in these polymers; they also show the expected downfield shifts relative to the neutral polymer on both chemical and electrochemical oxidation. ESR studies of both the electrochemically oxidized and the neutral polymer suggest the presence of highly mobile spins.

Preparation and characterization of neutral and oxidized polypyrrole films

ESR measurements have been performed on samples of neutral polypyrrole, polypyrrole-perchlorate, oxygen-doped polypyrrole, and poly($\ensuremath{\beta}$,${\ensuremath{\beta}}^{\ensuremath{'}}$-dimethylpyrrole perchlorate). A narrow Lorentzian line is observed in oxidized, highly conducting films, but no correlation between conductivity and either linewidth or intensity is found. Electrochemically cycled films, which remain highly conducting, show little or no detectable ESR absorption. It is deduced that the ESR signal seen in the as-prepared material does not arise from the current-carrying species, but rather from accidental neutral $\ensuremath{\pi}$-radical defects. The absence of paramagnetism in the metallic state is discussed within the framework of bipolaron formation.

Electron-spin-resonance studies of pyrrole polymers: Evidence for bipolarons

Conducting films of polypyrrole can be modified by introducing substitutents into the cationic pyrrole polymer or by varying the accompanying anion. The electrochemical route for the preparation of these films is particularly convenient for making these modifications since the variations are made in the selection of the monomer or the electrolyte. This eliminates the need for subsequent chemical treatments of the film. As expected, the electrochemical and conducting properties of the film are changed by these chemical modifications.

M. Krounbi

Papers

Preparation and characterization of neutral and oxidized polypyrrole films

Electron-spin-resonance studies of pyrrole polymers: Evidence for bipolarons

Chemical modification of conducting polypyrrole films

Electrical properties of pyrrole and its copolymers

A chemical route to pyrrole polymer films