Azo dyes based on 8-hydroxyquinoline benzoates: Synthesis and application as colorimetric Hg2+-selective chemosensors

A series of 8-hydroxyquinoline benzoates with diverse azo substituents were synthesized by diazo-reaction of 2-methyl-8-hydroxyquinoline with some arylamines, followed by esterification with benzoyl chloride. All the products allowed selective sensing with Hg2+, which was affirmed by UV–vis absorption spectra. Different spectral changes were observed for these compounds with electron-donating substituent (bathochromic shift) or electron-withdrawing substituent (hypsochromic shift). Particularly, obvious color change was observed for 5-(4-dimethylaminophenylazo)-2-methylquinolin-8-yl benzoate in the presence of Hg2+, which made it possible for distinguishing Hg2+ from other metal ions by naked eye.