Integrated pyrazolo[1,5-a]pyrimidine–hemicyanine system as a colorimetric and fluorometric chemosensor for cyanide recognition in water

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

“…It should be noted that hydrazones 5a–e were obtained through microwave (MW) irradiation with higher yields, shorter reaction times and easier purification processes that in our previous work . Furthermore, in the case of compounds PHd–e , acetylation of the OH group in their respective precursors also occurred, while the Knoevenagel reaction did not occur under conditions similar to those used in our other previous work (MW in acetic acid) (Scheme and Scheme ).…”

“…The PpHe probe showed a lower LOD value that DP , probably because the structure of PpHe contains higher π‐conjugation (Scheme a–b). Therefore, we expect that the new synthesized PHa–e probes have a shorter response time in CN – sensing with than does PpHe , as well as lower LODs than DP , since PHa–e combine the best structural properties found in our previous works , …”

“…There are diverse systems for CN – detection, based on the displacement of metals in complexes, aldehydes activated by hydrogen bonds and nucleophilic addition reactions, but some have drawbacks such as low selectivity and hydrophilicity and high detection limits (LOD) . Thus, research on methods for CN – sensing based on small molecules is highly desirable; in fact, our lab recently reported two new probes, pyrazole derivatives bearing conjugated dicyanovinylidene DP or an indolium salt (hemicyanine moiety) PpHe (Scheme ). These donor–π–acceptor (D–π–A) type dyes usually suffer from an intramolecular charge transfer (ICT) process with a ratiometric response that allows two points to follow‐up and thus provides an integrated correlation for environmental interference …”

“…Considering the aforementioned aspects together with our interest in developing efficient methods to prepare ion chemosensors,, , we proposed the synthesis of novel hemicyanine‐functionalized N ‐(2‐pyridyl)pyrazoles PHa–e with a modular‐donor aryl group at its pyrazole ring (Scheme c). In our previous works, formylpyrazole 1b was used to obtain a DP probe that acts quickly since the 2‐pyridyl group of the pyrazole ring favors its reactivity,, while the 3‐formylpyrazolo[1,5‐ a ]pyrimidine Pp reacted with indolium salt 2 to obtain PpHe , which acts more slowly . The PpHe probe showed a lower LOD value that DP , probably because the structure of PpHe contains higher π‐conjugation (Scheme a–b).…”

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.…”