Chiral columnar liquid crystals formed by chiral octahedral metallomesogen

The impact of molecular core chirality on helical columnar molecular assemblies has been investigated for enantiopure octahedral metallomesogens with propeller-shaped ΔΔ chirality. Although the inner stacking structures in helical columnar liquid crystals (Helical Col LCs) strongly affect the resultant functional properties such as ferroelectricity, there have been no definitive reported method to determine the inner structure. In this work, we used a combination of grazing-incidence (GI) X-ray diffraction spectroscopy and molecular dynamics (MD) simulations to reveal that the chiral octahedral metallomesogens stack with both the position and C₃ axis rotating along the columnar axis. Therefore, the structure was classified as a hybrid of two proposed major helical stacking types; however, the detailed stacking structure of each type has not been sufficiently understood. Further structural analyses of the simulated structures highlight the interplay of the steric repulsion between the ΔΔ chiral cores, π-stacking, and dipolar interactions in the helical formation. The accommodation of such weak interactions was confirmed for enantiopure samples by vibrational circular dichroism and UV-Vis spectroscopic studies, whereas racemic compounds were found to receive stronger intermolecular interactions to pack tightly.