Dynamic and Reversible Polymorphism of Self-Assembled Lyotropic Liquid Crystalline Systems Derived from Cyclic Bis(ethynylhelicene) Oligomers.

A self-assembled lyotropic liquid crystal (LLC) system exhibiting dynamic and reversible polymorphism was developed using the synthetic cyclic ethynylhelicene oligomers cyclobis[(M)-D-n] (n = 4 and 6), in which two oligomer moieties are connected by two flexible linkers. The cyclic molecular structure was designed to control aggregation properties ranging from the molecular level to the macroscopic level. The cyclic oligomer changed its structure between random coils and an intramolecular homo-double helix induced by temperature and solvents. In the presence of pseudoenantiomeric acyclic oligomers, cyclobis[(M)-D-4] formed trimolecular complexes with a total molecular weight of over 10 000 Da containing two intermolecular hetero-double helices. The trimolecular complex formation predominated over bimolecular complex formation. The trimolecular complex self-assembled at high concentrations and formed LLCs composed of anisotropically aligned fibers. The result is in contrast to acyclic systems, which form gels composed of randomly oriented fibers. The LLCs changed into turbid gels composed of randomly oriented bundles upon cooling, and the LLCs were regenerated by heating. This is a notable example of a self-assembled LLC system exhibiting dynamic and reversible polymorphism between two ordered structures in a closed system consisting of fully synthetic molecules.