Polyacetylenes conjugation extent

A principle reason for considering the DPP molecules in such detail is that a fairly complete set of oxidation(32) and reduction potentials(26) is available. We are interested in the extent to which such data can be predicted theoretically and in applying theory and oligomer extrapolations to understanding the electrochemical properties of polyacetylene. The latter is especially Important because of the large interest in battery applications of polyacetyleneU and other conjugated polymers.(12)... 

It must be noted that the values reported in the literature vary over broad ranges. Therefore, the values listed here reflect only the general behavior of several classes of compounds. It can be seen in Table 3.5 that trans-polyacetylenes (PAs) and polydiacetylenes (PDAs) exhibit the largest third-order NLO susceptibilities. The x value of cis-PA (not shown) is more than an order of magnitude smaller than that of trans-PA. Derivatives of poly-p-phenylene, poly(phenyl-ene vinylene), and polythiophene also exhibit NLO activity, but to a much lesser extent than PAs and PDAs. As pointed out above, polysilanes also possess quite large x values. This is explained by the cr-conjugation of the silicon chain, which implies a pronounced delocalization of cr-electrons. A very large x value... 

Polyacetylenes are the most typical and basic r-conjugated polymers, and can ideally take four geometrical structures (trans-transoid, trans-cisoid, cis-transoid, cis-cisoid). At present, not only early transition metals, but also many late transition metals are used as catalysts for the polymerization of substituted acetylenes. However, the effective catalysts are restricted to some extent, and Ta, Nd, Mo, and W of transition metal groups 5 and 6, and Fe and Rh of transition metal groups 8 and 9 are mainly used. The polymerization mechanism of Ta, Nd, W, and Mo based catalysts is a metathesis mechanism, and that of Ti, Fe, and Rh based catalysts is an insertion mechanism. Most of the substituted polyacetylenes prepared with W and Mo catalysts provide trans-rich and cis-rich geometries respectively. Polymers formed with Fe and Rh catalysts selectively possess stereoregular cis main chains. 

We now consider various types of charge carriers that can be found in electronically conducting polymers. As previously noted both experimental and theoretical evidence suggest that the precise nature of charge carriers present in conjugated polymer systems depends to a very large extent on the type of polymer. We discuss two representative polymer materials, polyacetylene and polypyrrole, which have been the subject of considerable study. 

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