Dedoped state

Polypyrrole is one of a series of heterocyclic polymers which has attracted much attention due to its characteristic electric and electronic properties. However, there are some problems relating to the physical and material properties associated with its structure. The fundamental structural formulae shown in Fig. 16.5 have been generally proposed for the structures of dedoped and doped polypyrroles, where the aromatic form corresponds to the dedoped state and the quinoid form corresponds to the doped state [9-11]. However, the actual structure appears to be more complicated. At present the exact structure is not known because the polymer is amorphous and insoluble. Consequently, various structures have been proposed for polypyrrole [10]. 

Similarly to the UV-Vis near infrared results, irreversible changes in the conductivity of P3TESH films are observed with temperature (Figure 4.8, A). The conductivity decreases by a factor of 10 (10 to 10 S/cm) from the doped to the dedoped state with temperatures between 20... 

Hienylring substituted aniline monomers like o-toluidine, m-tohiidine (73,14 o-eth>4aniline, o-pheniddine and o-anisidine 15-19) were used to prepare substituted pofyaniline which were soluble in the dedoped state in solvents like dimethylsulfoxide (DMSO), dimethylformamide (DMF), dichloromethane and chloroform. 

After potentiodynamic EDOT electropolymerization is performed from 0.01 M solution in acetonitrile with 0.1 M TBAPF electrolyte, following a procedure published earlier, residual monomer is removed and the polymer film subjected to several cycles, then the investigation is started with the dedoped state. ... 

For a polyanUine film, the light absorption measurements were conducted after the film was exposed to HCl and NH3 vapors, respectively, as shown in Fig. 14 [19]. The difference in the spectra indicated that HCl and NH3 vapors induced a different band structure and conformation of the polymer. Therefore, the optical property of the film changed when the film switched from one state (doped by HCl) to another (dedoped by NH3). The refractive index measurement by ellipsometry showed that the refractive index changed from 2.43 (doped by HCl) to 1.95 (dedoped by NH3). 

NMR spectroscopy will provide a simpler spectral pattern, when compared with NMR spectroscopy, because a given N resonance line may correspond to a given structure. Therefore, the structure of doped and dedoped N-labeled polypyrrole films can be successfully studied by high resolution solid-state NMR [14, 15]. Doped and dedoped samples were prepared by electrochemical polymerization [16] using 20-30% N-labeled pyrrole. To obtain a dedoped sample, the electrodes were inverted after the doping experiment and the same voltage applied. 

A solid-state synthesis has been explored to prepare PANI nanostmctures with many convolutions, which resemble the cerebral cortex of the brain (Figure 2.26), via the oxidative polymerization of solid anilinium citrate with chlorine gas [428]. A reversible doping/ dedoping process (i.e., conducting state/insulating state) for the brain-like nanostructures was realized by using HCl gas/ammonia gas. 

Repetitive square-wave potential techniques switch the potential continuously between the strongly reductive value necessary for the nucleation of the metal particles and a more positive one that is chosen to promote reoxidation of the CP material and thus recuperation of its conducting state, and/or unproved penetration of metal complex anions in the CP layer. Metal complex anions that are used as sources of metal reduction become partially consumed, but also expulsed as doping anions in the course of the reductive dedoping pulse. The size of the electrodeposited metal particles has been found to depend essentially on the frequency of the potential pulses [37,169] (Table 7.3). In fact, the data summarized in Table 7.3 show that by appropriate adjustment of the corresponding parameters, all of the currently exploited electrochemical techniques may result in the deposition of metal NPs in CPs. 

---