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

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 Fe²⁺ 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 Fe²⁺ adduct with the receptor. However, prolonged interaction of the chemosensor (2) with Fe²⁺ ions results in side reactions, such as the autooxidation of Fe²⁺ to Fe³⁺ 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 Fe²⁺ and Cu²⁺ ions in organic media. Notably, this receptor can detect and differentiate between Fe²⁺ and Cu²⁺ 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 Cu²⁺ and Cu⁺ as well as Fe²⁺ and Fe³⁺, and is capable of quantifying Fe²⁺ and Cu²⁺ ions at sub-ppm levels. Paper-based solid sensing strips coated with chemosensor 3 were developed for practical, real-time detection of Fe²⁺ and Cu²⁺, as well as for their discrimination from competing ions, including Fe³⁺ and Cu⁺.