Chiral Communication between Enantiomeric Sergeants and Achiral Soldiers in Racemic Triblock Copolymers with Heterochiral Cores for Triggering Multiple Helicity Inversions

Abstract

Amplification of asymmetry in complex supramolecular/polymer system results from the delicate interplay of chiral and achiral structures. Here, a novel approach to the racemic sergeants and soldiers (S&S) effect, using enantiomeric sergeants (Sgt.) and achiral soldiers (Sold.), achieves unique precise control over both intensity and sign of global chirality. Chiroptical assemblies of different dimensions in racemic S&S copolymers can be constructed in-situ via polymerization-induced chiral self-assembly (PICSA). We systemically investigated chiral communication pathways between chiral-chiral, chiral-achiral, and two oppositely configured azobenzene (Azo) segments, which robustly affect the global chiroptical activity of the racemic S&S assemblies. Chain length-, Sgt./Sold. ratios-, and temperature-dependent CD/UV-vis, small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results provided insights into the kinetics for chiroptical inversions. LC phase transitions, the helical preferences of the Sgt. and Sold. units, and the stability of the "chiral core" allow racemic S&S copolymer assemblies to exhibit chiral conflict between heterochiral blocks in an enantioselective fashion.