An efficient 2,6-di(thiazol-2-yl)pyridine-based chemosensor for dual-response fluorometric and colorimetric detection of Fe2+ and Cu2+

We introduced a straightforward synthetic pathway for two novel, simple chemosensors based on 2,6-di(thiazol-2-yl)pyridine ( dthp ) -core ligands. The first chemosensor, 2,6-di(thiazol-2-yl)isonicotinic acid ( 2 ), is fully water soluble (up to 0.3 g/L (1.04 mmol/L) at ambient temperature). It can be utilized for sensing Fe 2+ ions in an aqueous environment (aqueous phosphate buffer) by monitoring the absorption signal corresponding to the Metal-to-Ligand Charge Transfer (MLCT) band upon formation of the Fe 2+ adduct with the receptor. However, prolonged interaction of the chemosensor ( 2 ) with Fe 2+ ions results in side reactions, such as the autooxidation of Fe 2+ to Fe 3+ by air in phosphate buffer and/or interactions with carboxylic groups, which hamper its application for prolonged measurements or analysis of complex matrices containing metal ions. The methylated analog, methyl 2,6-di(thiazol-2-yl)isonicotinate ( 3 ), is a dual-response chemosensor that enables sensitive and selective detection of Fe 2+ and Cu 2+ ions in organic media. Notably, this receptor can detect and differentiate between Fe 2+ and Cu 2+ metal ions in the presence of 18 different common competing ions. Chemosensor 3 allows for iron and copper speciation; in other words, it can differentiate between Cu 2+ and Cu + as well as Fe 2+ and Fe 3+ , and is capable of quantifying Fe 2+ and Cu 2+ ions at sub-ppm levels. Paper-based solid sensing strips coated with chemosensor 3 were developed for practical, real-time detection of Fe 2+ and Cu 2+ , as well as for their discrimination from competing ions, including Fe 3+ and Cu + . • Easy, straightforward synthetic pathway to new chemosensors based on 2,6-di(thiazol-2-yl)pyridine (dthp)-core ligands. • 2,6-Di(thiazol-2-yl)isonicotinic acid, 2 , is a fully water-soluble sensor for Fe 2+ ions in an aqueous environment. • Methyl 2,6-di(thiazol-2-yl)isonicotinate, 3 , is a fluorometric/ colorimetric chemosensor for Fe 2+ and Cu 2+ ions. • 3 allows the differentiation between Fe 2+ and Cu 2+ metal ions in the presence of 18 different common competing ions. • Sub-ppm level detection and speciation of Fe 2+ and Cu 2+ . • Paper-based test strips with sensor 3 enable rapid, selective “ in-situ ” metal ion detection.