A series of single-chain monoaza crown ethers was synthesized to study their amphotropic behaviour. Differential scanning calorimetry (DSC) and texture determination show that these compounds exhibit a smectic phase. Surface pressure-area isotherms indicate that all the compounds form stable monolayers at the air-water interface. Transmission electron microscopy (TEM) shows that these crown ethers form vesicles when dispersed in water, DSC of aqueous dispersions yields sharp endothermic peaks which may be attributed to the gel-to-liquid crystalline phase transition. The absorption spectra of aqueous dispersions reflect the formation of J-like aggregates in bilayer assemblies.