SOLUBLE, CHIRAL POLYACETYLENES - SYNTHESES AND INVESTIGATION OF THEIR SOLUTION CONFORMATION

Soluble and highly conjugated polyacetylene derivatives bearing chiral appendages have been synthesized and characterized. The backbone pi --> pi* transition of these polymers showed substantial circular dichroism (CD). The magnitude of the CD for the polymers is characteristic of a disymmetric chromophore. Thus, the chiral side groups twist the main chain in predominantly one sense rather than just electronically perturbing that chromophore. The ellipticity observed for the polyacetylenes studied here, having an alpha-branched substituent on only one of every eight backbone atoms, is of the order of magnitude observed for previously studied chiral polyacetylenes that had alpha-branched substituents on every other backbone atom. This observation suggests that the chirality imparted to the backbone by the substituent is not greatly influenced by the proximity of neighboring substituents. Decreasing temperature had much more influence on the CD of the cis polymers than on the CD of the trans polymers in their respective pi --> pi* regions. cis-Poly-RCOTs (where RCOT is substituted cyclooctatetraene) are much more conformationally flexible and may be helical, although the CD data do not provide conclusive evidence of this conformation.