Liquid crystalline crown ethers.

In this chapter, a comprehensive review over the entire reserarch on liquid crystalline crown ethers since their discovery will be given. Monomeric and polymeric molecules containing crown ethers as well as aza crown ethers, thia crown ethers and crown ethers with several different heteroatoms will be presented. Liquid crystallinity is, in most cases, caused by the substituents attached to the crown ethers. The respective macrocycle can be surrounded by multiple substituents or attachment can take place terminally or laterally. Within the substituents, a variety of geometries, such as rods, discs or tapers have been reported, resulting in different types of mesophases. The effects of complexation will be discussed in detail as complexation has a varying influence on the properties, ranging from the induction or stabilization of a mesophase to the destabilization or even the complete loss of the mesophase, depending on the crown, the salt or the counterion of the salt. For selected examples, the synthesis of the materials will be discussed. Possible applications in sensor or membrane technology as well as in chromatography will be shown.