Helicity Induction of Polymers in Water and Its Memory

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The design and synthesis of helical polymers with controlled helix-sense have aroused considerable interest in recent years because of their unique structures and their possible applications in materials science. Recently, we found that macromolecular helicity with a predominantly one-handed helix could be induced in optically inactive poly(phenylacetylenes) bearing various functional groups upon complexation with chiral amines in DMSO, thus exhibiting an induced circular dichroism (ICD) in the polymer main chain. Moreover, the induced helical structures could be further memorized after replacement of the chiral amines by achiral amines. In this study, we investigated the helicity induction and the memory of helical chirality in water or in organic solvents by means of IR, UV, and CD spectroscopies. We found that the macromolecular helicity of charged poly(phenylacetylene)s induced by small chiral guests in water could be retained by the alternative deposition of achiral polyelectrolyt … More es with opposite charges, resulting in optically active multilayer thin films with a macromolecular helicity memory. This may be a kind of memory of the helicity resulting from helical polymers induced in water.We also demonstrated a novel hierarchical amplification of chirality during the transfer of chiral information from nonracemic guests to the helical systems either at macromolecular and subsequent supramolecular mesoscopic levels. The main chain stiffness with a dynamic helical charged polyacetylene that allows a formation of the liquid crystal (LC) phase is essential for realizing this hierarchical amplification of the chirality system. On the basis of the X-ray analyses, the most plausible helical structure of the LC helical polyacetylene is proposed to be a 23 unit/10 turn (23/10) helix.We further found the dual memory of both the enantiomeric right- and left-handed helical conformations induced in a polyacetylene based on the temperature-and solvent-stimulated helicity inversion of the polymer. The polyacetylene folds into a one-handed helix induced by noncovalent bonding interactions with a single enantiomeric amine. The induced helix underwent a reversible inversion of the helicity by temperature and solvents. The diastereomeric right- and left-handed helices obtained at different temperatures could be further memorized when the optically active amine was replaced by an achiral diamine, generating right- and left-handed helices of the mirror images from each other. Less