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 Cr3+ in MeCN with a color change from pink to colorless. They also showed selectivity for Hg2+ 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 Cr3+ in MeCN, and 1.20 ppm and 1.00 ppm for Hg2+ in DMSO, while that obtained from 3σ method are 0.08 ppm and 0.03 ppm for Hg2+ in DMSO. These results demonstrate a potential use of p-nitro azobenzene diaza-18-crown-6 as naked-eye sensors, notably for Cr3+ that brings acute toxic to aquatic life.