Synthesis and studies of selective chemosensors for anions and cations by azo-containing salicylaldimine-based receptors

Three new chromogenic receptors containing electron-withdrawing groups appended to the azophenol moiety were synthesized, characterized, and their chromogenic behavior toward various anions and cations investigated. These chemosensors show visual changes towards biologically relevant anions like F and OH, and also towards various cations such as Cu2+, Co2+, Ni2+, Mn2+, and Zn2+. Yet, other anions such as Cl, Br, and NO3 could not cause any color change. The sensing action was further confirmed by UVVis titration. 1H-NMR experiments were carried out to explore the nature of interaction between receptors with F and OH. The binding constants (K a) of the hostguest complexes formed were determined.