Polyconjugated polymers

The rapid development of macromoiecular chemistry has recently brought to light a number of most interesting problems related to the synthesis of polymers with unusual properties. The chemistry of polyconjugated systems undoubtedly occupies a leading place among these problems. 

Various types of the photoconductive polymers are available now. The photoconductivity of such materials may be essentially increased by means of the chemical and spectral sensitization [12-14]. Spectral sensitization is connected with the appearance of the photosensitivity in the new spectral bands and the chemical sensitization with the increase of the proper sensitivity. As a rule both types of sensitisation may take place in the photoconductor at the same turn. The first data about chemical and spectral sensitization in organic photoconductors appeared in [19, 20]. The example of the chemical and spectral sensitization of the photoconductivity by dyes in polymeric copper-phenyl-acetylenide is presented in Fig. 2. Later on it was proposed that not only low molecular weight compounds but polyconjugated polymers could also be used as sensitizers [21] having broad absorption tends and high thermostability compared with dyes. Now it is clear that various types of molecules may be used as a photosensitizers. 

Now the research in the photoconductive properties of the polyconjugated materials is growing fast. Heterocycle or heteroatom-containing polymers are involved in this process due to their excellent mechanical and electric properties. The sensitized photoeffect in polyconjugated materials was first observed in 1964 [19,20] and the high significance of the increase in the photosensitivity of these compounds became apparent... 

Polyacetylene attracts constant attention as an excellent simple model of the polyconjugated polymer on which the main optical and electrical properties can be verified. The possibility of achieving metallic conductivities by doping opens real perspectives of practical application of conducting polymers. The complication is the strong interaction with oxygen. The reproducibility of results strongly depends on the synthesis and measurement conditions. 

Two lower states of the frans-(CH) are energetically degenerated as follows from symmetry conditions. Theory shows that electron excitation invariably includes the lattice distortion leading to polaron or soliton formations. If polarons have analogs in the three dimensional (3D) semiconductors, the solitons are nonlinear excited states inherent only to ID systems. This excitation may travel as a solitary wave without dissipation of the energy. So the 1-D lattice defines the electronic properties of the polyacetylene and polyconjugated polymers. 

Because of its extended polyconjugated framework, polymer (210) exhibits semiconducting properties both by itself and in the presence of additives. Perhaps a more remarkable property, however, is that polymer (210) does not burn when exposed to a flame. Thus, by employing this thermooxidative reaction, woven or knitted poly(acrylonitrile) fibers can be transformed into fire-proof materials. Polymer (210) can be pyrolyzed still further at temperatures generally in excess of 1000 °C to expel all heteroatoms and generate carbonized or graphitized fibers. These fibers find application where an inert, extremely high temperature, e.g. up to 3000 °C, material is required. 

M. Del Zoppo, C. Castiglioni, P. Zuliani and G. Zerbi, Molecular and electronic structure and nonlinear optics of polyconjugated materials from their vibrational spectra, in T. Skotheim (ed.), Handbook of Conducting Polymers, 2nd edn, Marcel Dekker, New York, 1998, and references cited therein. 

Another group of polyconjugated photoconductive polymers reported in the literature are poly(Schiff-bases)33, polycondensates of aromatic diamines and... 

Reucroft et al. 37>38 reported photoconductivity of polymers with polyconjugation in the chain, prepared by polycondensation of 3,3 -diaminobenzidine and 3,3, 4,4 -benzophenone tetracarboxylic acid dianhydride39, pyrrone polymers ... 

In general, the polymers with polyconjugated systems of double and triple bonds are photoeonductive in the UV and at least part of the visible range. In some cases the photoresponse extends to the near infrared range. Although their usefulness in practical applications has been many times suggested, the results have been more or less disappointing. The main problems still remain difficult synthesis, in most cases poorly identified structure, and with few exceptions insolubility and intractability of the polymers. The direct comparison with poly(N-vinyl carbazole) and other photoeonductive polymers is not possible for lack of comparative data. 

Even in the first group of polyconjugated polymers, whenever the type of carriers was identified, it was always a positive type. 

Kozlov, V.V., Karpacheva, G.P., Petrov, V.S., Lazovskaya, E.V. (2001) The feature of forming the system of polyconjugated bonds for polyacryloniyrile by thermal treatment in vacuum, Polymer Science, A 43,15-20. 

The reduction of rhenium salt in a PAN matrix and the formation of the polyconjugated polymer system proceed simultaneously and interdependently during IR-pyrolysis of a film. As result the thin film of carbon with ultra dispersed metal particles is formed on a surface of porous support (Fig. 2). The thickness of defectless Re-containing carbon film was 300 - 500 nm. The size of metallic particles was proved to be from 3 to 10 nm. The average content of rhenium in a metal-carbon composition was about 5 mass %. 

Synthesis of 2-[5-(l//-pyrrol-2-yl)-2-thienyl]-l//-pyrrole 1355, monomer for polyconjugated polymers, is based on the reaction of l,4-di(l//-pyrrol-2-yl)-l,4-butanedione 1354 with Lawesson s reagent (Equation 292) <1997CM2876>. Compound 1356 was prepared by Triton B-catalyzed condensation of 17/-pyrrole-2-carbaldehyde and the appropriate nitrile derivative (Equation 293). 

Owing to the mechanism of the topochemical reaction the polyconjugated polymer chain is of exceptional purity and stereochemical regularity. Polydiacetylene crystals are thus ideally suited to study the inherent optical and electrical properties of polyconjugated chains. These unique features have attracted considerable attention and in recent years the topochemical polymerization of diacetylenes has developed to... 

---