Synthesis of Dicyanovinyl-Substituted 1‑(2-Pyridyl)pyrazoles: Design of a Fluorescent Chemosensor for Selective Recognition of Cyanide

A fluorescence “turn-off” probe has been designed and successfully applied to detect cyanide (CN–) based on a Michael-type nucleophilic addition reaction and intramolecular charge transfer (ICT) mechanism. For this research, a family of 3-aryl-4-(2,2-dicyanovinyl)-1-(2-pyridinyl)­pyrazoles as donor-π-acceptor (D-π-A) systems have been synthesized in 58–66% overall yield, by a three-step synthesis sequence starting from p-substituted acetophenones. The substituted p-methoxyphenyl showed good fluorescence emission and large Stokes shifts in different solvents due to its greater ICT. Likewise, this probe evidenced high selectivity and sensitivity and fast recognition for CN– with a detection limit of 6.8 μM. HRMS analysis, 1H NMR titration experiments, and TD-DFT calculations were performed to confirm the mechanism of detection and fluorescence properties of the chemodosimeter of CN–. Additionally, fluorescent test paper was conveniently used to detect cyanide in aqueous solution.