5-(Thiophene-2-yl)oxazole derived "off-on-off" fluorescence chemosensor for sequential recognition of In3+and Cr3+ions

A new fluorescent chemosensor P from 5-(thiophen-2-yl)oxazole-4-carbohydrazide and 4-diethylaminosalicylal-dehyde was designed and synthesized for sequential detection of In3+ and Cr3+ ions. P exhibits strong fluores-cence enhancement at 512 nm upon binding to In3+. The green fluorescence of complex P-In3+ was selectively quenched by Cr3+. The complex stoichiometry of P with In3+ and Cr3+ was identified as 1:2 for both in conjunction with Job's Plot analysis, ESI-MS titration and theoretical calculations. Moreover, P was successfully applied to monitor target ions in actual water samples, and a portable paper sensor for the detection of In3+ was investigated to evaluate the versatility application.