Hierarchical amplification of macromolecular helicity in a lyotropic liquid crystalline charged poly(phenylacetylene) by nonracemic dopants in water and its helical structure

摘要

We report a unique hierarchical amplification of chiral information from a nonracemic guest to macromolecular helicity, followed by a mesoscopic, supramolecular cholesteric twist in water. This remarkable chiral amplification involves two-step chirality transfer processes, which enable the detection and sensing of an extremely small imbalance in chiral guest molecules. The macromolecular helicity with an excess single-handed helix was first induced in the positively charged, chromophoric poly( phenylacetylene), the hydrochloride of poly( 4-(N,N-diisopropylaminomethyl) phenylacetylene) (poly-1-HCl) upon complexation with an oppositely charged nonracemic acid as a dopant through electrostatic interaction in dilute water. Subsequently, the macromolecular helicity was further amplified in the polymer backbone as a greater excess of a single-handed helix through self-assembly into a lyotropic cholesteric liquid crystal (LC). Direct evidence for the hierarchical amplification process of the helical sense excess of the polymer during the cholesteric LC formation was demonstrated by direct comparison of the excess of the one helical sense of the polymer in dilute solution with that in the cholesteric LC state. Poly-1-HCl formed a lyotropic nematic LC in water in the absence of chiral acids, indicating its rigid-rod characteristic regardless of the lack of a single-handed helix, as evidenced by the long persistence lengths before (26 nm) and after (28 nm) the one-handed helicity induction in the polymer. X-ray diffraction of the oriented films of the nematic and cholesteric liquid crystalline poly-1-HCls exhibited almost the same diffraction pattern, suggesting that both polymers may have the same helical structure despite the substantial difference in their helical characteristics, dynamically racemic and one-handed helices in dilute solution, respectively. On the basis of the X-ray analyses, the most plausible helical structure of poly-1-HCl is proposed to be a 23 unit/ 10 turn (23/10) helix.