Reversible Shrinkage of Self-Assembled Two-Component Organogels by Lithium Salts: Synthesis of Gelation Property and Lithium Salt Response Using Bidomain Helicene Oligomer

A bidomain oligomer containing a (P)-amido-helicene tetramer domain and a (P)-ethynylhelicene tetramer domain formed self-assembled organogels in the presence of an (M)-ethynylhelicene pentamer. Strong Cotton effects were observed for gels in pyridine, piperidine, cyclohexanone, and I,2-dimethoxybenzene (Type A solvents), and weak Cotton effects in anisole, ethyl benzoate, and toluene gels (Type B solvents). The amido domain was in the random-coil state in the gels of the Type A solvents, and in the helix-dimer state in the gels of the type B solvents. The pyridine gels shrank upon the addition of lithium perchlorate to 25% of their original volume, and the volume recovered when the supematant was removed, the solvent was added, and the mixture was briefly heated and cooled. The shrinkage process could be reproducibly repeated five times. In contrast, the gels of anisole and toluene did not shrink in the presence of lithium perchlorate. The gelation property and lithium salt response were induced using the bidomain oligomer to achieve the reversible shrinkage property of self-assembly organogels.