Introducing Dihedral Angle Torsion in a Flexible Dicarboxylic Acid: Evolution from a Sequential Symmetry Condensing Liquid Crystalline Gel to a Step-Halting Heat-Set Gel

Through systematic molecular engineering, versatile properties can be incrementally introduced into supramolecular materials. Nonetheless, even a minor internal modification in the molecular backbone can outperform the conventional molecular engineering approach to fine-tune its corresponding supramolecular properties. A dicarboxylate salt, categorically primary ammonium dicarboxylate (PAD) salt derived from a flexible dicarboxylic acid such as adipic acid, imparts conformational flexibility to the salt in gelling solvents. This results in the exhibition of sequential symmetry condensing the liquid crystal gel against rising temperatures. Gentle heating can unzip van der Waals interactions, showcasing a gradual 2D to 0D phase-changing ability and generating liquid crystalline properties. Such gradual symmetry reduction quantifies the entropy enhancement during heating. On the other hand, the manipulation of dihedral angle torsion within a dicarboxylic acid backbone offers a means to tailor solubility. By increasing the dihedral angle torsion, the molecule loses alignment against the solvent's polarity or temperature, resulting in insolubility and conformational rigidity. Conversely, manipulating dihedral angle torsion within a dicarboxylic acid backbone provides a means to tailor solubility. Increasing dihedral angle torsion causes the molecule to lose alignment against the solvent's polarity or temperature, resulting in insolubility and conformational rigidity. Incorporating higher dihedral angle torsion energy, such as introducing an azo or ferrocene backbone into a dicarboxylic acid, renders the resulting molecule resistant to solubilization, even at high temperatures, resulting in a heat-set gel. This transformation turns sequential symmetry-condensing liquid crystal gelator molecules into two-step halting polymorphic state-based heat-set gelator molecules. This review demonstrates that a conventional functional group is not always mandatory for introducing supramolecular properties. Instead, a physical parameter, such as dihedral angle torsion, can be generated to finely tune the thermostatic properties in developing supramolecular heat-set or liquid crystal gels.