Phenylalanine-based ionic liquid crystals with water-induced phase transition behaviors

Abstract

l-Phenylalanine (L-Phe) and d-phenylalanine (D-Phe) were chosen as chiral sources to interact with 1-tetradecyl-3-methylimidazolium hydroxide (C14mimOH). Two ionic liquid crystals (ILCs), [C14mim][L-Phe] and [C14mim][D-Phe], were prepared. Both of the two ILCs exhibit good thermostability and can self-assemble to a smectic A (SmA) mesophase in a pretty wide temperature window (from ~−20 °C to ~105 °C) in the absence of solvents. When water is introduced, the ILCs show rich lyotropic phase behaviors. With the increasing water content, the ILCs transformed from the SmA mesophase to a cubic Ia3d and then to a Im3m mesophase, eventually producing precipitates composed of numerous flat fibers. The rheological properties including mechanical strength and viscosity of the ILCs exhibited temperature- and water content-dependent changes. The ILCs inherited the chirality of the amino acids well. This work proposes a simple one-step self-assembly method to construct natural biomolecule-based chiral materials, providing potential applications in chiral amplification and selectors of chiral extraction or molecule detection.