Metal ion chemosensors based on diaza-18-crown-6 coupling with azobenzene dye.

Novel naked-eye cation-selective chemosensors were developed from derivatives of diaza-18-crown-6 bearing one or two azobenzenes functionalized with o-acetic acid or p-nitro groups. The chromogenic acid and nitro derivatives exhibited solvatochromic effects with a majority of quinone-hydrazone tautomer in DMSO. The study of sensing properties of all molecules towards several metal ions showed that the one and two nitro-bearing N1 and N2 derivatives responded selectively to Cr in MeCN with a color change from pink to colorless. They also showed selectivity for Hg in DMSO with a color change from purple to light yellow. The detection limit of N1 and N2 that render visual difference to the naked eye are 0.21 ppm and 0.31 ppm for Cr in MeCN, and 1.20 ppm and 1.00 ppm for Hg in DMSO, while that obtained from 3σ method are 0.08 ppm and 0.03 ppm for Hg in DMSO. These results demonstrate a potential use of p-nitro azobenzene diaza-18-crown-6 as naked-eye sensors, notably for Cr that brings acute toxic to aquatic life.