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.