Imidazoanthraquinone Derivatives for the Chromofluorogenic Sensing of Basic Anions and Trivalent Metal Cations

Four imidazoanthraquinone derivatives (<b>2a</b>–<b>d</b>) were synthesized and characterized and their coordination behavior against selected anions and cations tested. Acetonitrile solutions of probes showed charge-transfer absorptions in the 407–465 nm range. The four probes emitted in the 533–571 nm interval. The recognition ability of <b>2a</b>–<b>d</b> was evaluated in the presence of F^–, Cl^–, Br^–, I^–, OCN^–, BzO^–, ClO₄^–, AcO^–, HSO₄^–, H₂PO₄^–, and CN^–. Only F^–, AcO^–, and H₂PO₄^– induced a new red-shifted absorption band that was attributed to a deprotonation process involving the amine moiety of the imidazole ring. Moreover, upon increasing quantities of F^–, AcO^–, and H₂PO₄^–, moderate quenching was induced in the emission of <b>2a</b>–<b>d</b> together with the appearance of a new red-shifted band. The UV–visible and emission behavior of the four probes in the presence of Cu²⁺, Co²⁺, Mg²⁺, Fe³⁺, Ba²⁺, Fe²⁺, Ni²⁺, Ca²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Cr³⁺, Al³⁺, K⁺, and Li⁺ was also assessed. Only addition of Fe³⁺, Cr³⁺, and Al³⁺ caused a new blue-shifted band in <b>2a</b>–<b>d</b> that was ascribed to a preferential coordination with the acceptor part of the probes. Moreover, an important quenching of the emission was observed which was ascribed to the interaction between these trivalent cations and <b>2a</b>–<b>d