Conjugated polymer, electrochemical properties

Kobayashi M, Colaneri N, Boy sel M, Wudl F, Heeger A (1985) The electronic and electrochemical properties of poly (isothianaphthene). J Chem Phys 82 5717-5723 Lu W, Fadeev AG, Qi B et al (2002) Use of ionic liquids for -conjugated polymer electrochemical devices. Seienee 297 983-987... 

Electrochemical properties of conjugated polymers. Springer, Berlin Heidelberg New York, p 385... 

Preliminary measurements of electrical conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10 °S/cm which apparently is not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase in conductivity. Ongoing studies of the electrical properties of these conjugated polymers with alternating aromatic/quinonoid units will be reported elsewhere. 

Polythiophenes (including oligothiophenes) are one of the most studied and important classes of linear conjugated polymers [444,445], Versatile synthetic approaches to PTs (chemical [446] and electrochemical [447]), easy functionalization and unique, widely tunable electronic properties have been the source of tremendous interest in this class of polymers. 

J. Rault-Berthelot, Polyfluorenes, a family of versatile conjugated polymers. Anodic synthesis, physicochemical properties, electrochemical behaviour and application fields, Recent Res. Dev. Macromol. Res., 3 425-437, 1998. 

G. Zotti, G. Schiavon, S. Zecchin, J.-F. Morin, and M. Leclerc, Electrochemical, conductive, and magnetic properties of 2,7-carbazole-based conjugated polymers, Macromolecules, 35 2122-2128, 2002. 

The electronic properties of n-conjugated polymers reflect well the basic electron-withdrawing or electron-donating properties of the components of the Ti-conjugated polymer [62]. In view of the electrochemical reduction potential, the thiophene unit and tetrathiafulvalene unit (Nos. 8 and 9 in Table 1) have a similar electronic effect in PAEs. It is reported that poly(arylenevinylene)s are also susceptible to electrochemical reduction [63, 64]. Due to the electron-accepting properties, PAEs are usually inert in electrochemical and chemical (e.g.,by I2 [54]) oxidation. 

The extended 71-systems of conjugated polymer are highly susceptible to chemical or electrochemical oxidation or reduction. These alter the electrical and optical properties of the polymer, and by controlling this oxidation and reduction, it is possible to precisely control these properties. Since these reactions are often reversible, it is possible to systematically control the electrical and optical properties with a great deal of precision. It is even possible to switch from a conducting state to an insulating slate. 

A series of policyclic oxazole derivatives, analogous to compound 124, were synthesised in order to verify their fluorescence properties <07EJO3613>. The oxazole VUV (vacuum ultraviolet) absorption spectrum over the range 5-12 eV was analyzed <07CP154>. New jr-conjugated polymers containing oxazole in the main chain were synthesised and their optical and electrochemical properties analyzed <07P2331>. 

More recently, there has been growing interest in a new type of redox polymer that is a hybrid of materials from PTs and will be referred to as conjugated metallopolymers. The key feature of this class of material is that the metal is coordinated directly to the conjugated backbone of the polymer, or forms a link in the backbone, such that there is an electronic interaction between the electroactive metal centers and the electroactive polymer backbone. This can enhance electron transport in the polymer, enhance its electrocatalytic activity, and lead to novel electronic and electrochemical properties <1999JMC1641>. 

From the late 1970s onwards, efforts to synthesise conjugated polymers rapidly expanded and numerous new materials were prepared. Many of these still proved to be intractable substances that were difficult if not impossible to purify and characterise. The maximum levels of conductivity achieved on doping often fell well short of the metallic range. Such properties meant that the majority of these materials attracted little attention beyond the initial reports, and certainly no commercial interest. An example of the few polymers produced at this time that have been extensively studied subsequently is polythiophene (PTh), Fig. 9.2(h). Although this polymer was also reported in the nineteenth century (Meyer, 1883), the first reliable synthesis appeared in 1980, see McCullough (1998). Another example is polyfluorene, Fig. 9.2(i), which was prepared chemically and electrochemically in 1985, see Rault-Berthelot and Simonet (1986). Much subsequent synthesis has been directed to the inclusion of pendent groups to either enhance solubility,... 

Some conjugated polymers, such as polythiophene and polyaniline were synthesized already in the last century [8a,b], It is not surprising that, for example, polyaniline has played a major role in research directed toward synthetic metals because it possesses a relatively stable conducting state and it can be easily prepared by oxidation of aniline, even in laboratories without pronounced synthetic expertise (see section 2.6). It is often overlooked, however, that a representation of, for example, polypyrrole or polyaniline by the idealized structures 1 and 2 does not adequately describe reality, since various structural defects can occur (chart 1). Further, there is not just one polypyrrole, instead each sample made by electrochemical oxidation must be considered as a unique sample, the character of which depends intimately on the conditions of the experiment, such as the nature of the counterion or the current density applied (see section 2.5). Therefore, one would not at all argue against a practical synthesis, if the emphasis is on the active physical function and the commercial value of a material, even if this synthesis is quick and dirty . Care must be exercised, however, to reliably define the molecular structure before one proceeds to develop structure-property relationships and to define characteristic electronic features, such as effective conjugation length or polaron width. 

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