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

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-pi-acceptor (D-pi-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 x 10(-7) m), as determined by interrupting the modular D-pi-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.