Characterization of Chiral Self-Assembly in Sequence-Defined Mesogenic Dimers

Liquid crystals (LCs) are phases of matter that possess properties in between those of liquids and crystalline solids. Due to the intrinsic anisotropy of calamitic LC mesogens, they frequently adopt LC and crystalline structures with useful optical, magnetic, and electronic properties. Recently, the Davidson research group has developed a general approach to using orthogonal protection/deprotection reactions to synthesize discrete and sequence defined liquid crystalline oligomers. This work examines the self-assembly of mesogenic dimers synthesized with two different mesogens: a phenyl benzoate core both with (M) and without (N) a methyl-substituted aromatic ring. The two dimers with alternating sequence (MN and NM) and their mixtures are both examined. Both pure oligomers exhibit chiral superstructures composed of ~100 nm nanocylinders; however, their crystalline morphology and phase behavior are divergent as observed via optical, thermal, and X-ray characterization. We find that blends of the two materials assemble to form banded spherulites. Scanning electron microscopy of the alternating dimers grown in the confined melt or in solvent advances our understanding of their chiral self-assemblies and motivates possible applications in chiroptical materials or catalysis via chemical functionalization of the nanostructures.