Doping electroactive films

The earliest application of the XPS technique to the study of CT interactions in modem electroactive polymers appears to be that of Hsu et al. [144] on the iodine-doped (CH) films. The presence of multiple chemical states for the iodine dopant, such as the and Is species, has been revealed by the combined XPS core-level and Raman scattering studies. The Is species was postulated to have residtcd from the equilibrium process of the type U + Is Is. with the 13ds/2 BEs for the I2 and Ij species lying at about 620.6 and 619 eV respectively. Similar results were... 

Direct registration of DNA hybridization advanced a lot with the use of electroactive films of conductive polymers as electrodes. Conductive polymers, which consist of conjugated backbones that are easily oxidized or reduced (doped) with a concomitant increase or decrease in conductivity, with each polymer having its own redox characteristics. 

Aleshin, A. N., Mironkov, N. B., Suvorov, A. V., Conklin, J. A., Su, T. M., and Kaner, R. B., Electrical properties of ion implanted and chemically doped polyaniline films, in Materials Research Society Symposium Proceedings on Electrical, Optical and Magnetic Properties of Organic Solid State Materials III, Vol. 413, 1996, p. 609. Cameron, D. A., and Reynolds, J, R., Conducting molecular composites of polypyrrole with electroactive polymeric dopant ions, ACS Proc., 37, 684 (1996). 

The one-step immobilization of sulfonated calixarenes as doping anions during the anodic electropolymerization of pyrrole has also been proposed to produce cation-responsive electroactive films [308, 309]. In this way, calix[4]arene-p-tetrasulfonate and calix[6]arene-p-hexasulfonate were irreversibly incorporated into the structure. The recognition abilities of these molecules were retained after the entrapment step, as shown by the redox changes observed in the presence of trimethyl(ferrocenylmet-hyl)ammonium [308] and uranyl [309] as guest cations. 

PPY is a very well known conducting polymer used in numerous works as the electroactive component of an all-solid-state ISE. Most of the papers dealt with a PPY-coated PVC electrode where PPY is doped with different anions, inorganic such as chloride or organic such as dodecyl sulphate. Several techniques were used to characterize these devices. Potentiometric measurements represent a method allowing thermodynamic characterization. AC electrogravimetry was also used to characterize ion and solvent motions at the PVC/electrolyte interface to imderstand how the electroactive film (Prussian blue, conducting polymer, etc.) ensures the mediation between the membrane and the electrode. ... 

Parent (unsubstituted) PF was first synthesized electrochemically by anodic oxidation of fluorene in 1985 [266] and electrochemical polymerization of various 9-substituted fluorenes was studied in detail later [220,267]. Cyclic voltammogram of fluorene ( r1ed= 1.33 V, Eox = 1.75 V vs. Ag/Ag+ in acetonitrile [267]) with repetitive scanning between 0 and 1.35 V showed the growth of electroactive PF film on the electrode with an onset of the p-doping process at 0.5 V (vs. Ag/Ag+). The unsubstituted PF was an insoluble and infusible material and was only studied as a possible material for modification of electrochemical electrodes. For this reason, it is of little interest for electronic or optical applications, limiting the discussion below to the chemically prepared 9-substituted PFs. 

Technically important electrochemical reactions of pyrrole and thiophene involve oxidation in non-nucleophilic solvents when the radical-cation intermediates react with the neutral molecule causing polymer growth [169, 191], Under controlled conditions polymer films can be grown on the anode surface from acetonitrile. Tliese films exhibit redox properties and in the oxidised, or cation doped state, are electrically conducting. They can form the positive pole of a rechargeable battery system. Pyrroles with N-substituents are also polymerizable to form coherent films [192], Films have been constructed to support electroactive transition metal centres adjacent to the electrode surface fomiing a modified electrode,... 

The earliest XPS work on modem electroactive polymers appears to be that of Hsu et al. [63] on the chemical states of the dopant in iodine-doped (CH)X films. In this work, combined XPS and Raman scattering studies revealed the presence of I3 and IJ species. The latter species resulted from the equilibrium process of the type I2 + IJ = I5. Similar findings were also made in at least two separate studies [64, 16]. The presence of polyiodide anion species was also observed... 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 4, number 11). After oxidative dimerization the TMS ether can be mildly hydrolyzed (H and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 4, numbers 9, 12, and 13). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [60]. Dibenzo-crown ethers are converted by anodic oxidation to electroactive polymers. Films of these polytriphenylenes exhibit unusual doping properties 62-64]. 

On the other hand, liquid phase deposition (LPD) has been demonstrated as a flexible wet chemical method for preparing metal oxide nanostructured films on electrode surfaces. By the LPD process, electroactive titanium dioxide (Ti02) films were prepared on graphite, glassy carbon and ITO. The electrochemical properties of such LPD Ti02 films were dependent upon the film thickness controlled by the deposition time. The LPD technique was easily combined with other techniques, e.g., seed-mediated growth, which could provide metal/metal oxide composite nanomaterials. Moreover, hybrid nanostructured films were facilely obtained by doping dyes, surfactants and other... 

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