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

Abstract

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, H 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.

Dyes based on the 2(1H)‐quinolone skeleton as potential colorimetric and fluorescent sensors for cyanide anions

“…A detailed analysis of their absorption spectra reveals that under the conditions used, in the cases of 1 and 3 , acetate and thiocyanate ions might be the competitors to the cyanide ion, respectively. Our observation is consistent with the data reported in the literature . However, in most cases, the colour change of the dye solutions was observed even with the naked eye and the response was very quick.…”

“…The DLs of 1 ‐ 4 for cyanide anions were 6.7, 11.1, 3.8 and 7.2 μmol/L, respectively. The lowest concentration of cyanide anions that could be detected by tested sensors was 3.8‐6.7 μmol/L, which is comparable with other values reported for compounds in the literature …”

“…Our observation is consistent with the data reported in the literature. 31 However, in most cases, the colour change of the dye solutions was observed even with the naked eye and the response was very quick. The fluorescence spectra of compounds 1-4 in the presence of various anions were also monitored and the spectra of some representative probes 1 and 2 are presented in Figure 3.…”

“…The lowest concentration of cyanide anions that could be detected by tested sensors was 3.8-6.7 μmol/L, which is comparable with other values reported for compounds in the literature. [31][32][33][34]…”

Pyrazolo-fused 4-azafluorenones as key reagents for the synthesis of fluorescent dicyanovinylidene-substituted derivatives

“…Therefore, special reaction conditions were required to yield compounds 7a-d since the traditional methods did not work. 31,32,39 These compounds were synthesized considering the important photophysical properties of pyrazole derivatives 22,[30][31][32]40,41 and the azauorenone moiety. 42 In addition, the dicyanovinylidene is widely used as an acceptor moiety in the design of D-p-A dyes that exhibit intramolecular charge transfer (ICT) photophysical process.…”