Dyes for Visual Distinction between Enantiomers: Crown Ethers as Optical Sensors for Chiral Compounds**

A fascinating idea of modern organic chemistry, the discrimination between enantiomers of an optically active substance by the use of differently colored host–guest complexes, has now been realized by systematically applying what has been learned about supramolecular chemistry. The enantiomers of optically active ammonium salts as guests can be distinguished visually after they are allowed to react with the steroid crown ether host 1 and the host–guest complex is embedded in a cholesteric liquid-crystal matrix.