Complexation properties of anthracene-bridged bis-crown ethers

Abstract

The complexation properties of new hosts consisting of two crown ethers connected by an anthracene group have been studied using spectrophotometry, fluorescence spectroscopy and cyclic voltammetry. The complexation and recognition properties of these ligands depend significantly on alkyl substituents at the 9- and 10-position of the anthracene group and are also strongly influenced by the solvent. The highest complexation constants with sodium and thallium cations in dimethylformamide were found for ligands with heptyl and ethyl groups. From spectrophotometric titration data it is evident that both crown ether rings participate in formation of complexes with sodium and potassium cations in chloroform–methanol. The determined complexation constants show a negative cooperation effect because K_M2L/K_ML < 0.25. The results of fluorescence experiments with the ligand substituted with two ethyl groups show a decrease in ligand fluorescence upon potassium cation addition, which excludes the formation of sandwich complexes, and suggests that these ligands might be suitable for fluorescence potassium sensors.