Redox reaction of conducting polymers

The stoichiometry of the redox reactions of conducting polymers (n and m in reactions 1 and 2) is quite variable. Under the most widely used conditions, polypyrroles and polythiophenes can be reversibly oxidized to a level of one hole per ca. 3 monomer units (i.e., a degree of oxidation, n, of ca. 0.3).7 However, this limit is dictated by the stability of the oxidized film under the conditions employed (Section V). With particularly dry and unreactive solvents, degrees of oxidation of 0.5 can be reversibly attained,37 and for poly-(4,4 -dimethoxybithiophene), a value of n = 1 has been reported.38 Although much fewer data are available for n-doping, it appears to involve similar stoichiometries [i.e., m in Eq. (2) is typically ca. 0.3].34,39"41 Polyanilines can in principle be reversibly p-doped to one... 

III. THE REDOX REACTION OF CONDUCTING POLYMERS A. Preliminary Considerations... 

Co 7Co02) and metal ion/metal systems (Ag7Ag) can be used [4]. In the former system, metal ions are oxidized to colored metal oxides by holes generated in the valence band of the photo-irradiated semiconductor and bleached by electrochemical reduction of the oxide. In the latter, metal ions are reduced to colored metal particles by photoexcited electrons in the conduction band. A system with Prussian white/ Prussian blue is also used. Prussian white on Ti02 is oxidized to Prussian blue by UV irradiation [5]. Redox reactions of conducting polymers such as... 

A consequence of the unique redox reaction in conducting polymers is that ion transport through the polymer considerably influences the kinetics of the charge transfer, unlike the situation in solution electrochemistry. This is due to the concomitant nature of the two processes. The injection or extraction of charge that occurs via the back contact requires charge transport from the solution side, and these two aspects have to be considered together. 

In the previous section it was shown that detailed information about electrochemical processes and the kinetics of follow-up chemical reaction steps can be investigated by UV/Vis/NIR spectroelectrochemical experiments in transmission mode in the diffusion layer at optically transparent or microstructured non-transparent electrodes. Many metal electrodes show a high reflectivity and therefore optical spectra may also be recorded under in situ conditions in reflection mode [70, 71]. This approach is essential for the study of adsorbed species, the formation of solid layers at the electrode surface, reactions of solids [72-74], and the redox behaviour of conducting polymer layers [75-77]. Furthermore, in reflection mode, the angle of incidence may be modified and polarised light maybe used in ellipsometry studies [78]. 

The Menschutkin reaction has been used to prepare poly(viologens) (115) directly (Scheme 31). These polymers were found to be quite useful as polyelectrolyte redox-polymers and for the preparation of conductive polymers when complexed with the 7,7, 8,8 -tetracyanoquinodimethane (TCNQ) radical anion (71MI11100). 

We describe here that the redox oligomer wires fabricated with the stepwise coordination method show characteristic electron transport behavior distinct from conventional redox polymers. Redox polymers are representative electron-conducting substances in which redox species are connected to form a polymer wire.21-25 The electron transport was treated according to the concept of redox conduction, based on the dilfusional motion of collective electron transfer pathways, composed of electron hopping terms and/or physical diffusion.17,18,26-30 In the characterization of redox conduction, the Cottrell equation can be applied to the initial current—time curve after the potential step in potential step chronoamperometry (PSCA), which causes the redox reaction of the redox polymer film ... 

One successful strategy to improve ET rates between enzyme and electrode is the modification of conducting polymers with redox mediators in order to obtain reagentless biosensors [11, 270, 271, 292-299]. The drawback of electropolymerization of conducting polymers is that the reaction is sensitive to oxygen, which complicates fabrication at the industrial scale. 

The ion transport during the redox reactions of PPy has been attracting interest for two major reasons as an effort to explain charge transfer reactions and to apply the ion exchange properties to chemical analysis. More studies on this subject have been conducted on PPy compared to other 71-conjugated polymers thanks to its easy preparation in non-aqueous and aqueous media electrochemically or chemically, its reasonable stability in air, and simple methods of modification of the monomer, leading to a chemically functionalized polymer. On the other hand, the ion exchange properties of PTh have not been studied as extensively as for PPy since its electrochemistry in aqueous solutions is rather limited. We thus summarize recent advances in this area only on PPy. 

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