Enhanced Orientation of Liquid Crystals Inside Micropores of Metal-Organic Frameworks Having Thermoresponsivity

With the aim of controlling the orientation of liquid crystals (LCs) toward realizing external stimuli-responsive materials with tunable functionalities, we synthesized a composite of LCs and metal-organic frameworks (MOFs) by filling LCs into the pores of MOFs (LC@MOFs) for the first time. The included LCs interact with the MOFs through coordination bonds between the cyano groups of the LCs and the metal ions of the MOFs, enabling the orientation of the LC molecules inside the pores of the MOFs and the realization of birefringence of LC@MOFs. The three-dimensional nanometer interstice frameworks maintained the LC orientation even at temperatures much higher than the isotropic phase transition temperature of bulk LCs. Furthermore, the orientational state changed upon heating or cooling, inducing temperature-dependent birefringence. This study provides a new approach to the development of stimuli-responsive optical materials and stimuli-responsive MOFs. The composite material LC@MOF was synthesized by incorporating liquid crystals (LCs) into the pores of metal-organic frameworks (MOFs). The LCs were aligned within the pores of the MOFs, even when heated beyond their isotropic phase transition temperature. As the temperature changed, the LCs underwent a change in orientation, resulting in a thermoresponsive birefringence. The LC@MOF is a novel type useful stimuli-responsive material with potential applications in various fields.image