| Abstract
| - A series of novel phenylacetylenes bearing optically active cyclodextrin (CyD) residues such asα-, β-, and γ-CyD and permethylated β-CyD residues as the pendant groups was synthesized andpolymerized with a rhodium catalyst to give highly cis−transoidal poly(phenylacetylene)s, poly-1α, poly-2β, poly-3γ, and poly-2β-Me, respectively. The polymers exhibited an induced circular dichroism (CD) inthe UV−visible region of the polymer backbones, resulting from the prevailing one-handed helicalconformations. The Cotton effect signs were inverted in response to external chiral and achiral stimuli,such as temperature, solvent, and interactions with chiral or achiral guest molecules. The inversion of theCotton effect signs was accompanied by a color change due to a conformational change, such as inversionof the helicity of the polymer backbones with a different twist angle of the conjugated double bonds, thatwas readily visible with the naked eye and could be quantified by absorption and CD spectroscopies. Thedynamic helical conformations of poly-2β showing opposite Cotton effect signs in different solvents couldbe further fixed by intramolecular cross-linking between the hydroxy groups of the neighboring β-CyD unitsin each solvent. The cross-link between the pendant CyD units suppressed the inversion of the helicity;therefore, the cross-linked poly-2βs showed no Cotton effect inversion, although the polymer backboneswere still flexible enough to alter their helical pitch with the same handedness, resulting in a color changedepending on the degree of intramolecular cross-linking.
|
