Decorating Conjugated Polymer Chains with Naturally Occurring Molecules: Synthesis, Solvatochromism, Chain Helicity, and Biological Activity of Sugar-Containing Poly(phenylacetylene)s
journal contributionposted on 17.04.2007 by Kevin K. L. Cheuk, Jacky W. Y. Lam, Bing Shi Li, Yong Xie, Ben Zhong Tang
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Phenylacetylene derivatives containing different sugar moieties and functional bridges (1−5) are synthesized. Their polymerizations are affected by organorhodium complexes, producing corresponding polymers P1−P5 with high molecular weights (Mw up to 1.2 × 106) and stereoregularities (Z content up to 100%) in high yields (up to 99%). The polyene backbones undergo irreversible Z-to-E isomerization at ∼160−230 °C. The solutions of the polymers exhibit solvatochromism: their backbone absorptions change with variations in the surrounding media. The polymers show Cotton effects in the long wavelength region where their polyene backbones absorb, revealing that the chiral sugar pendants have induced the polymer chain to take a helical conformation with an excess in one-handedness. Inserting a flexible methylene spacer between the chiral pendant and the polyene backbone hampers the helicity induction process and lowers the backbone circular dichroism. The acetonide protection groups in most of the polymers can be selectively deprotected by acid-catalyzed hydrolysis, yielding polymers with “free” sugar appendages. The polymers are cytophilic and can stimulate the growth of living cells.