Facial Asymmetry in the Helical Grooves of Chiral Helical Polymers to Create 2D Single-Chain Archimedean Spiral Nanostructures

Abstract

Archimedean spirals are architectural motifs that are found in nature. The facial asymmetry of amphiphilic molecules or macromolecules has been a key parameter in the preparation of these well-organized two-dimensional nanostructures in the laboratory. This facial asymmetry is also present in the helical grooves of chiral helical meta-substituted poly(phenylacetylene)s (PPAs) and poly(diphenylacetylene)s (PDPAs), making them excellent candidates for self-assembly into 2D Archimedean nanospirals or nanotoroids. The facial asymmetry of the helix groove, with different polarities and hydrophobic/hydrophilic behaviors, impacts the self-assembly of meta-PPAs and meta-PDPAs compared to their para-substituted counterparts, which possess facial symmetry in the helix grooves. As a result, while para-substituted PPAs and para-substituted PDPAs self-assemble by drop-casting on highly oriented pyrolytic graphite to form 2D crystals via parallel packing of helical polymer chains, meta-substituted helical polymers undergo intramolecular self-assembly to create a 2D chiral Archimedean spiral nanostructure from a single polymer chain. The structural parameters obtained for the helical polymer in the 2D crystal and 2D chiral Archimedean spiral nanostructures are identical, indicating that the secondary structure of the polymer remains unchanged in both 2D nanomaterials. This finding regarding the self-assembly of the helical polymer into 2D chiral Archimedean spiral nanostructures allows the preparation of chiral nanostructures with potential applications in asymmetric catalysis, molecular recognition, and other cutting-edge applications.