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

Abstract

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.

Chemosensors based on N-heterocyclic dyes: advances in sensing highly toxic ions such as CN− and Hg2+

“…Another pyrazole example based on probe 24 reported by us is the hemicyanine-arylpyrazole hybrid system, where the aryl group electron-donor character was modulated (i.e., Ph, 4-MeOPh, 3,4,5-(MeO) 3 Ph, 4-AcOPh, and 2-AcOPh) to achieve a better design. 58 3-(2-Acetoxyphenyl)pyrazole 25 exhibited the best sensing properties but only as a colorimetric probe given that all the hybrid systems tested showed low uorescence quantum yields in various solvents. This probe works through the nucleophilic attack of CN À on its iminium group (C]N + ), interrupting the D-p-A system.…”

“…Importantly, the steric effect occurring between the acetyl group and the azolic nitrogen (N2) in 25 prevents the p-conjugation from the aryl group towards the acceptor moiety; thus, ICT occurs only from N1, which possibly is the reason for its better performance compared to the other pyrazoles tested. 58 Siva and Beneto reported a similar method using triphenylamine (TPA) derivative 26, having a dicyanovinylidene group as the receptor unit (Fig. 12c).…”

“…Importantly, the steric effect occurring between the acetyl group and the azolic nitrogen (N2) in 25 prevents the π-conjugation from the aryl group towards the acceptor moiety; thus, ICT occurs only from N1, which possibly is the reason for its better performance compared to the other pyrazoles tested. 58 …”

Synthesis and Optimization of Diphenyl Ether‐Based Receptors for the Selective Detection of Cyanide Ions in Neutral Semi‐Aqueous Medium

“…Organic functional groups sense cyanide ions both in the organic and aqueous medium. This includes the use of azine, [28] azo, [29] benzimidazole, [30] benzothiozole, [31,32] BODIFY, [33] coumarin, [34] hemicyanin, [35], imine, [36] indole, [37] malononitrile, [38] napthelene, [39,40] naphthalimides, [41] pyrene [42] and quinolone [43] based functional groups by different mechanisms with a detection range of nano to micro-molar.…”

Synthesis and Antiproliferative Activity of 2,4,6,7-Tetrasubstituted-2H-pyrazolo[4,3-c]pyridines

“…In current medicinal chemistry, the incorporation of a pyrazole nucleus is a common practice to develop new drug-like molecules with anti-cancer, anti-diabetic, anti-viral, anti-inflammatory, anti-bacterial, anti-fungal, antineurodegenerative, anti-tubercular, anthelmintic, antimalarial, and photosensitizing properties [2][3][4][5][6][7][8][9][10], among others, thus giving rise to a great number of approved therapeutics [11]. Besides numerous biological activities, pyrazoles have also been documented to possess dyeing and fluorescence properties [12][13][14][15][16], and some of them can be used as colorimetric or fluorescent probes for sensing small molecules, ions, or pH [17][18][19][20][21][22][23][24][25][26][27][28], which may have applications in in vivo imaging [29][30][31]. Pyrazolopyridines are among the most studied condensed pyrazole systems in organic and pharmaceutical chemistry (Figure 1).…”