Interchain trans-polyacetylene

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. 

The crystallinity of m-polyacetylene has been estimated to be 76-84% by x-ray diffraction while trans-polyacetylene is 71-79 %6). Observations on Durham polyacetylene 445) showed that the diffraction peak narrowed, and the interchain -spacing decreased, during isomerization and annealing. The x-ray coherence length, a measure of the crystallite size perpendicular to the chains, increased from 2.6 nm to 7.1 nm, compared with 30 nm for polyethylene. 

There could also be polarons in c/5-poIyacetylene, and these could be mobile. Even without interchain interaction there is a soliton-antisoliton attraction in cis-polyacetylene because of the energy difference between the cw-transoid and the trans-cisoid structure. Figure 1.32 shows polarons and bipolarons in cw-polyacety-lene. In polyaraphenylene the situation is very similar... 

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