Polythiophene anode

A polythiophene anode in an aqueous electrolytic system, showed irreversible changes at a potential beyond 0.9 V on repeated reduction, suggesting that the breakdown into lower oligomers occurs, as evident from its Raman spectra [268]. However, the loss of electroactivity, electrical conductivity, electrochromic properties, mechanical properties, compact morphology... 

In their voltammetric studies of polythiophene anode in 0.1 M LiC104 in acetonitrile, Harada et al. 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Voltammograms of a polythiophene film showing reasonably reversible electrochemistry of both types are shown in Fig. 2.M The formal potentials (average of the anodic and cathodic peak potentials) for p- and n-doping can provide useful estimates of the energies of the polymer s valence and conduction bands and its band gap35... 

Trace mercury determination by differential pulse (dp) anodic stripping voltammetry on polythiophene-quinoline/glassy carbon modified electrode has been reported [77]. 

A polypyrrole-electrolyte-polypyrrole battery has been described 611) but the n-doped polypyrrole is unstable. This can be avoided by using a polypyrrole-polyanion anode, where the charge and discharge depend upon small cations moving into and out of the electrode612). A polythiophene-polythiophene battery has also been described 135). Polyaniline has been studied as a potential battery cathode, for use with an aqueous electrolyte 613,6I4). 

Anodic oxidation of a-trimethylsilylated thiophene derivatives in nitrobenzene results in desilylation and formation of polythiophenes (equation 4), which have higher conductivity than those prepared from unsilylated thiophenes7-9. The silyl group increases the regioselectivity of carbon-carbon bond formation since the silyl group is an excellent... 

In contrast, anodic oxidation of tetra-2-(/T-methylterthienyl)silane provides polythiophene without desilylation9. The polymer has a 3D electroactive jr-conjugated system (equation 5). 

It has been mentioned already that polypyrrole (25) and polythiophene (26) play an important role as electrical conductors and polymeric anodes in battery cells [2,47,226]. Since the charging and discharging of the conjugated polymer is accompanied by the incorporation and removal of counterions it is clear that the material can also act as a carrier of chemically different anions which influence the physical, chemical and physiological properties of the material [292]. With regard to the full structural elucidation of the polymers it must be added, however, that the electropolymerization process of pyrrole and thiophene does not provide a clean coupling of the heterocycles in the 2,5-positions. Instead, the 3- and 4-position can also be involved giving rise to further fusion processes under formation of complex polycyclic structures [47]. 

Oxide, flouride, and polymeric films, as well as certain others, are used as protective coatings for HTSC materials (for example, see [505]). The electrodeposition of conducting polymers such as polypyrrole [433,491, 493, 506], polythiophene and its derivatives [493, 507], and polyaniline [478] is the most effective process. Anodic electropolymerization in acetonitrile solutions proceeds without any degradation of the HTSC substrate and ensures continuous and uniform coatings. Apparently, this method is promising not only for the fabrication of compositions with special properties based on HTSC [50, 28,295] as mentioned above, but also for the creation of junctions with special characteristics [507]. 

Another example of the anodic oxidation of 7r-systems having a silyl group at the a-position is the electrochemical oxidation of 2,5-bis(trimethylsilyl)thiophene, resulting in the elimination of the trimethylsilyl group to produce polythiophene. Polythiophenes obtained by this method have high conductivity [156]. 

Next, in the 1980s, the organic multilayer structures, which are another key technology of present high-performance OLEDs, appeared. In 1986, Hayashi et al. observed a remarkable reduction of the driving voltage by inserting a polythiophene-electropolymerized thin film between an indium-tin-oxide (ITO) anode and a perylene-deposited film.30 The insertion of the polythiophene thin... 

Studies of the chemical properties of polythiophenes have been limited. As with polypyrroles, a hydrophobic backbone is formed, and the polymer has ion-exchange properties. Modification of chemical properties by incorporation of appropriate counterions is not so readily addressable because polymerization must be carried out from nonaqueous solution and occurs at more anodic potentials compared to pyrrole. 

The semi-conducting properties of conjugated polymers originate from the delocalized n orbitals formed in these carbon-containing compounds such as poly(phenylene vinylene), polythiophene and polyfparaphenylene). Like the OLED s described above, the polymer-OLED consists of a linninescent film, sandwiched between an anode and a cathode. 

Polythiophene (PTh) and its derivatives are unique in that they can be prepared both anodically and cathodically. Anodic preparation of PTh was first mentioned by Diaz et al [21b] during their oxidation experiments of aromatic oligomers and monomers, which was followed by Tourillon and Gamier s work in 1982 [24], The cathodic preparation of PTh is not as straightforward and requires the reduction of an organometallic complex, such as (2-bromo-5-thienyl)-tri-phenylnickel dibromide [25]. 

Polythiophene By a two-step electrochemical process of anodization and electropolymerization 2,3-dichlorophenols 400-800 [590]... 

CPs are able to raise the surface potential and provide anodic protection of the substrate material. Tallman et al. [61] reported that the redox potential of PANI is 0.4 to 1.0 V [vs. standard hydrogen electrode (SHE) at pH 7] and that of polythiophene is 0.8 to 1.2 V. Both values are higher when compared to the corrosion potential of steel and aluminum. This indicates that both PANI and poly thiophene are able to passivate the surface of both steel and aluminum. Anodic protection alone can be fatal if the... 

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