Cisoid conformation, polyacetylen

Polyacetylene contains conjugated double bonds in a linear structure [51-54], which leads to special electrical conductivity properties. For this reason, polyacetylene and some other related polymers have applications in the optical and electronic industries. Pojyacetylene synthesized at relatively low temperature seems to have a cis-conformation, with two possible cis- forms indicated as c/s-transoid, and frans-cisoid, as shown below ... 

The helical conformation of polyacetylene derivatives bearing chiral side chains was first pointed out by Ciardelli in 197 4 24 and later extended and more clearly demonstrated by Grubbs in 199 1 25 and by Yashima and Okamoto in 1994.26a For poly(phenyl-acetylene) derivatives bearing no chiral side groups, Yashima and Okamoto showed that a helical conformation can be induced by interaction with added chiral small molecules.260 Apart from optical activity, a helical conformation of cis-cisoidal poly(phenyl-acetylene) in the solid state was pointed out by Simionescu and Percec.27... 

A lot of work, mainly synthesis and elementary characterizations, have been performed on substituted polyacetylenes. It is somewhat surprising that almost no companion structural studies are ava able. The lack of structural data does not allow an accurate knowledge of the internal conformation of the polymer. Nevertheless these systems appear very interesting, the existence of a possible cis-cisoid conformatitm may involve a well defined helical structure such that we can speculate a relation between the specific elastic behavior of an helical-spring like stmcture and the optical properties of the conjugated backbone. 

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