The crucial role of a functional group position in the self-assembly of lyotropic chromonic liquid crystals*

Plank-like lyotropic chromonic liquid crystal (LCLCs) molecules self-assemble face-to-face via non-covalent interactions in water. These aggregates may align to exhibit lyotropic liquid crystalline phases according to the temperature and concentration. Additives such as salt and polymers also affect the aggregate structure and resulting phase behavior. Here, utilizing the representative LCLC, Sunset Yellow FCF (SSY), we report the effects of intrinsic additives, i.e., byproducts of SSY synthesis. First, combining various characterization techniques, including Liquid Chromatography, Mass spectroscopy, and X-ray scattering, we unveil how and why the purification of commercially available SSY affects its aggregate structures and phase behaviors. We further focus on the byproduct impurities that resemble SSY but differ from SSY in the number and location of sulfonate groups. Experimental characterization and quantum chemistry calculation suggest that the sulfonate group near SSY's aromatic core distorts its planar shape, thus disrupt the aggregate formation and the resultant nematic phase.