Lower rim 1,3-di-amide-derivative of calix[4]arene possessing bis-{N-(2,2'-dipyridylamide)} pendants: a dual fluorescence sensor for Zn²⁺ and Ni²⁺

Abstract

Single crystal XRD structure of the lower rim 1,3-di-amide-derivative of calix[4]arene possessing bis-{N-(2,2'-dipyridylamide)} pendants (L) exhibit two distinct binding cores, viz., N₄ and O₆. L was found to be selective for Zn²⁺ by switch-on and for Ni²⁺ by switch-off fluorescence by forming 1:1 complexes. The binding and the composition of the complex formed have been addressed based on steady state and time-resolved fluorescence spectroscopy in addition to the absorption and ESI MS. As L can detect Zn²⁺ and Ni²⁺ to a concentration as low as 142 and 203 ppb, respectively, L can be a very sensitive molecular probe for these ions. The coordination details of the metal ion-bound complexes have been addressed based on ab initio calculations showing that the stabilization energies are commensurate with the coordination formed.