Imidazoanthraquinone derivatives for the chromofluorogenic sensing of basic anions and trivalent metal cations

Four imidazoanthraquinone derivatives (2a-d) 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 2a-d 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 2a-d together with the appearance of a new red-shifted band. The UV-visible and emission behavior of the four probes in the presence of Cu(2+), Co(2+), Mg(2+), Fe(3+), Ba(2+), Fe(2+), Ni(2+), Ca(2+), Zn(2+), Pb(2+), Cd(2+), Cr(3+), Al(3+), K(+), and Li(+) was also assessed. Only addition of Fe(3+), Cr(3+), and Al(3+) caused a new blue-shifted band in 2a-d 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 2a-d.