Synthesis of Novel D–π–A Dyes for Colorimetric Cyanide Sensing Based on Hemicyanine–Functionalized N-(2-Pyridyl)pyrazoles

Article abstract of DOI:10.1002/ejoc.201901178

Novel integrated N-(2-pyridyl)pyrazole-hemicyanine dyes (PH) were synthesized as promisor chemodosimeters for colorimetric and ratiometric CN^– detection. These dyes, obtained by a three-step sequence starting from acetophenones in up to 69 % overall yield, are donor–π–acceptor (D–π–A) systems consisting of indolium-salts bearing a modular donor aryl group on its pyrazole ring PHa–e. The salts displayed high selectivity and sensitivity for CN^– (LOD of up to 9.9 × 10^–7 m), as determined by interrupting the modular D–π–A system by nucleophilic attack of the cyanide on its iminium group; the mechanism of this process was confirmed by Job′s plot experiment, spectral analysis, cyclic voltammetry studies and TD-DFT calculations. This probe changes its color from deep yellow to colorless and can be used for in-the-field measurements without special equipment, since this change can be easily observed by the naked eye; indeed, yellow test strips were suitably used to detect CN^– in water.