Properties of Z and E isomers of azocrown ethers in monolayer assemblies at the air–water interface

Abstract

Monomolecular films of amphiphilic derivatives of crown ethers bearing an azo group in the macrocycle were prepared on surfaces of pure water or aqueous solutions of alkali metal cations, and studied using the surface pressure and surface potential measurements. The organization of the azocrown molecules in monolayers at the air–water interface was found to depend on the geometry around the –NN– moiety and on the presence of alkali metal cations in the subphase. Transition from E to Z isomer occurred under influence of UV-irradiation, while switching back from Z to E isomer was induced by addition of appropriate alkali metal cation forming a complex with the azocrown ligand. The Z and E isomers can be recognized by the different values of typical monolayer parameters: compressibility modulus and the mean molecular area in the monolayer. fChanges in the monolayer parameters allow to follow isomerization processes in the monolayer. The ability to transform one isomer of the azocrown ether to the other under influence of UV-irradiation or metal ion addition may be useful for the applications of these ligands as molecular switches.