Selective fluoride chemosensors based on coumarin semicarbazones

Twelve (five new) colorimetric anion sensors based on coumarin semicarbazone were studied for selective sensing of fluoride anion. The distinct colour change (by 44-125 nm) under ambient light observed in the Vis region makes the present sensors suitable for naked eye detection of fluoride anion, with detection limit (LOD) 6.6-8.6 ppm for the most sensitive ones. Whereas significant colorimetric changes are observed in the presence of fluoride anion in Me2SO, the commonly competing AcO-, Cl-, Br-, HSO4-, NO2- or NO3- ions induce none or relatively negligible changes. Depmtonation of the semicarbazone NH group is responsible for the sensing event, albeit the mechanism depends on electron density distribution in the coumarin moiety. Quantum chemical calculations suggest several possible geometries for the semicarbazones; the geometry with a hydrogen bond between the hydrazone nitrogen and the NH hydrogen of all of the aniline, cyclohexylamine and aminopyridine fragments, however, results in the most stable structures.

Automated summary

The research focused on twelve colorimetric anion sensors based on coumarin semicarbazone for selective sensing of fluoride anion, with detection limits ranging from 6.6-8.6 ppm. The sensors demonstrated distinct color changes in the visible light region, making them suitable for naked eye detection of fluoride anion.