Highly selective colorimetric/fluorometric chemodosimeters for cyanide ions in aqueous solution based on Michael addition to C-atom possessing different polar substituents

Two simple chemosensors, 3-(4-aminophenyl)-2-cyanoacrylic acid (1) and 3-(3-aminophenyl)-2-cyanoacrylic acid (2), exhibited visual colour and fluorescence changes selectively with cyanide ions in aqueous solution. Their anion sensing properties were investigated using UV–vis, fluorescence and 1H & 13C NMR spectral studies and theoretical studies. The mechanism of sensing involves Michael addition of CN− to CC bond. The addition reaction was found to occur relatively easier with p-NH2C6H4 group (Taft’s σ∗ 0.16) substituted CC bond than that with m-NH2C6H4 group (σ∗ 0.58) substituted compound. The detection limits were calculated to be 33 pM and 0.2 nM for the receptors 1 and 2, respectively, which are lower than the maximum permissible concentration of cyanide ion in drinking water (1.9 μM) set by the World Health Organization (WHO).