Molecular Shapes of Monosubstituted Polyacetylenes in their Liquid Crystalline Phases

In this short review, we discuss the molecular shapes of monosubstituted polyacetylenes (MSPAs) in their liquid crystalline (LC) phases. Their rigid backbone with high stereoregularity can endow MSPAs with significant shape persistency, which largely determines their LC structures. Helical cis-cisoidal and cis-transoidal MSPAs render rod-like shapes and can form columnar LC (Phi) phases. In the smectic LC (Sm) phases of MSPAs with mesogenic side-chains, the main chain, with trans-cisoidal, trans-transoidal or extended cis-transoidal conformation, is in fact largely coplanar with the side-chains, resulting in a sheet-like molecular shape. From a simple geometric point of view, the rod- or sheet-like MSPA molecules serve as the building block of their LC phases.