Oxidative and reductive doping

The end result is the same with both oxidative and reductive doping, however, because it is not the sodium or iodide ion formed that is mobile, but the deformation of the polymer chain itself that results in a flow of current through the molecule. 

The electrochemical behavior of poly(RCOT)s has also been examined [40]. As expected from the electrochemical properties of unsubstituted polyacetylene, films of poly(RCOT)s coated on an electrode and immersed in an acetonitrile electrolyte solution (in which the polymers are not soluble) are found to undergo reversible oxidative and reductive doping. Unlike unsubstituted polyacetylene, these films may be prepared readily by casting from solution, or, in the case of poly(scc-butylCOT), by electrodecomposition from a THF solution. In contrast to the voltammetry of polymer films, cyclic voltammograms of methylene chloride... 

The conducting and physical properties can be modified by the use of 3- and/or 4-substitutents, or A -substituents in the case of pyrrole. The counterions can be incorporated into a side-chain (self-doping) as in the polymer of 3-(thien-3-yl)propanesulfonic acid. Variation in the size of side-chains allows control of solubility. Mixed polymers with, for example, thiophenes and pyridines, are capable of both oxidative and reductive doping. 

Walter, M. and Hakkinen, H. (2006) A hollow tetrahedral cage of hexadecagold dianion provides a robust backbone for a tuneable sub-nanometer oxidation and reduction agent via endohedral doping. Physical Chemistry Chemical Physics, 8, 5407-5411. 

These processes can be made to occur in a number of ways, for example with gas phase reagents such as AsF5 and I2, solution species such as FeCl3 or using electrochemical oxidation and reduction, but regardless of the method used the basic process is the same. If the material is to maintain overall electrical neutrality during and after doping, a counter ion is required, i.e., for p-doped materials,... 

The electrochemical behavior of poly(ferrocenylsilanes) has been studied at three levels—in solution by cyclic voltammetry, as films deposited on electrodes, and in the solid state via iodine doping. Solution cyclic voltammetric oxidation and reduction has shown that the polymer, where R/R is Me/Me, reversibly oxidizes in methylene chloride in two stages, apparently with the first oxidation being on alternating iron atoms along the chain.29 Films cast on electrodes behave in a similar way and also show an electrochromic response to oxidation and reduction.30... 

Electrochemical data have been used to predict ionization energies and stability relative to doping in air for semiconducting polymers. Bredas et al. [43] derived an empirical correlation for determination of ionization energies from electrochemical oxidation and reduction potentials (Eq. 5) in which the onset of oxidation is referred to the standard calomel electrode, S.C.E.)... 

Fig. 18.8. Doping and undoping of a poly(pyrrole) film during oxidation and reduction cycles. When a poly(pyrrole) coated electrode is cycled between the reduction and oxidation potentials, the current observed at the oxidation potential is related to the ability of anions to enter the polymer film and dope the polypyrrole.

Oxidation and Reduction Potentials (versus SCE) and Maximum Doping Levels for Selected Conducting Polymers... 

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