Polyacetylene charge transport

The charge transport in a conjugated chain and the interchain hopping is explained in terms of conjugation defects (radical or ionic sites), called solitons and polarons. Several possible conjugation defects are demonstrated in Fig. 5.33 on the example of trans-polyacetylene. 

When the 7r-systerns of two or more double bonds overlap, as in conjugated dienes and polyenes, the 7r-clccIrons will be delocalized. This has chemical consequences, which implies that the range of possible chemical reactions is vastly extended over that of the alkenes. Examples are various pericyclic reactions or charge transport in doped polyacetylenes. A detailed understanding of the electronic structure of polyenes is therefore of utmost importance for development within this field. We will first discuss the structure of dienes and polyenes based on theoretical studies. Thereafter the results from experimental studies are presented and discussed. 

Stretched polyacetylene with very low sp3 defect concentration has much higher conductivity and anisotropy than other materials. This point emphasizes the importance of oriented, low-defect systems if charge transport is principally along the conjugated chains. This discussion illustrates that no complete, consistent theory of transport in PA has yet been developed. 

Finally, theoretically insight into the mechanisms of charge transport should continue to improve. This will happen in concert with the development of better experimental probes of the solid state. Better understanding of the structural origins of the exceptional properties of N-polyacetylene is needed, and such work may point the way toward the syntheses of new families of materials. 

Epstein, A.J. 1986. AC conductivity of polyacetylene distinguishing mechanisms of charge transport. In Handbook of conducting polymers, ed. T.A. Skotheim. New York Marcel Dekker, p. 1041. 

Kaiser, A.B., S.A. Rogers, and Y.W. ParL 2004. Charge transport in conducting polymers Polyacetylene nanofibers. Mol Cryst Liq Ctyst 415 269. 

For the ECPs with degenerated ground state, solitons are responsible for the charge transport. Such a polymeric system is polyacetylene. The major problem on the preparation of polyacetylene/Cgjj nanocomposite is the insolubility of polyacetylene. This has led to the discovery of soluble polyacetylene derivatives such as poly(o-trimethylsilylphenylacetylene) (PTMSiPA) [28]. Small amoimts of doping in PTMSiPA is found to enhance the photoconductivity of pristine PTMSiPA [29]. 

In a polyacetylenes chain, strongly oxidized, these solitons are responsible by the electric charges transport along the chain and between the pol5nneric chains at macroscopic scale, se also (Further Readings on Moletronics, 1956-1997). 

If there are mobile charged solitons in polyacetylene (Figure 1.14), it may be expected that they are responsible for the electrical conductivity. If there were samples with very long perfect chains of trans-polyacetylene, then it would be probable that this solitonic charge transport would be observed. If,... 

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