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

Monomolecular films of amphiphilic derivatives of crown ethers bearing an a zo group in the macrocycle were prepared on surfaces of pure water or aqueo us solutions of alkali metal cations, and studied using the surface pressur e and surface potential measurements. The organization of the azocrown mole cules in monolayers at the air-water interface was found to depend on the g eometry around the N=N- moiety and on the presence of alkali metal cations in the subphase. Transition from E to Z isomer occurred under influence of W-irradiation, while switching back from Z to E isomer was induced by addit ion 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 ty pical 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 iso mer of the azocrown ether to the other under influence of W-irradiation or metal ion addition may be useful for the applications of these ligands as m olecular switches. (C) 1999 Elsevier Science S.A. All rights reserved.