Cyanide and fluoride colorimetric sensing by novel imidazo-anthraquinones functionalised with indole and carbazole

Novel imidazo-anthraquinones functionalised with indole and carbazole have been synthesised and characterised and their evaluation as colorimetric chemosensors was carried out in acetonitrile as well as in acetonitrile/H2O (97:3) in the presence of several anions such as F-, Cl-, Br-, I-, CN-, NO3-, ClO4-, AcO-, BzO(-), NO3-, ClO4-, HSO4-, and H2PO4-. In addition, their behaviour in the presence of H+ and OH- was also studied. Upon addition of CN- and F- to acetonitrile solutions of compounds 1-3, a marked colour change from yellow to orange was observed and the fluorescence emission of 1 and 2 was switched on'. The recognition in organic aqueous solution leads to the selective and sensitive naked-eye detection (mM) of CN- for all receptors, with an easily detectable colour change from yellow to orange. The binding stoichiometry between the receptors and the anions was found to be 2:1. The binding process was also followed by H-1 NMR titrations showing that two different binding modes occurred in the presence of fluoride or cyanide anions, which is in agreement with the spectrophotometric titrations.