Tunable Synthesis of One-Handed Helical Ladder Polymers with a Helical Cavity or Helical Grooves for Advanced Chiral Recognition

Abstract

We report the synthesis of a novel family of one-handed helical ladder polymers incorporating enantiopure 9,9′-spirobifluorene frameworks by an acid-promoted alkyne benzannulation reaction. By varying the para - and meta -substitution patterns of the achiral dialkynylphenylene units of the precursor polymers, we successfully controlled both the helical geometry (helical tube with a helical cavity or helical ribbon with helical grooves) and the helical handedness (right- or left-handed) of the ladder polymers. The resulting polymers exhibited characteristic chiroptical properties due to their unique helical structures and showed complementary enantioseparation capabilities for a series of hydrophobic racemic compounds with point, spiro, axial, planar, and helical chiralities, as well as a chiral metal complex when used as chiral stationary phases for high-performance liquid chromatography. The helical cavity and grooves of the para - and meta -phenylene-embedded helical ladders serve as chiral recognition sites, respectively. These results highlight the potential of spiro-conjugated helical ladder polymers as advanced chiral materials for enantioseparation technologies. In addition, we succeeded in the first direct observation of the periodic helical structure of the meta -phenylene-embedded ladder polymer by high-resolution atomic force microscopy.