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A new coumarin-based fluorescent chemosensor, 3, incorporating a hydrazone (-NH-N=C-), was designed and synthesized. The chemosensor displayed higher affinity towards Fe3+ in water-acetonitrile solution in the presence of other competing cations in emission and absorption essays. The binding stoichiometry between the chemosensor 3 and Fe3+ was shown to occur in a 1:1 ratio, and the binding modes of the chemosensor towards Fe3+ were identified through the emission response, ¹H NMR, FT-IR and molecular modelling studies. The hydroxyl and amine functionalities on 3 were recognized as possible binding sites. The chemosensor presented a limit of detection, a limit of quantification and the association constant of 0.45 µM, 1.50 µM and 3.01 x 10¹ M-1, respectively. [ABSTRACT FROM AUTHOR]

Two azo dyes, ( E )-3-(benzo[ d ]thiazol-2-yldiazenyl)-4-hydroxy-2 H -chromen-2-one (3CBD) and ( E )-4-hydroxy-3-(quinolin-2-yldiazenyl)-2 H -chromen-2-one (3CQD), were designed and synthesized using facile methods. The structures were validated through FTIR and NMR spectroscopy. The photophysical property analyses were further studied using UV-Vis and fluorescence spectrophotometers. Consequently, the absorption and emission spectra of 3CBD confirmed its selectivity of Hg 2+ and turn-off response to Fe 3+ . On the other hand, the absorption spectra analysis of 3CQD demonstrated selectivity in the presence of Hg 2+ . The colorimetric investigations demonstrated a significant visual response specifically for Hg 2+ , enabling real-time analysis in the corresponding solutions. The presence of other coexisting metal ions does not interfere with the detection of the target metal ion. The fluorescence studies of the two probes revealed that 3CBD was highly fluorescent, which was significantly quenched by Fe 3+ , upon excitation at 340 nm. Utilizing Job plot analyses, it was determined that the complexes 3CBD-Hg 2+ and 3CQD-Hg 2+ exhibit a binding stoichiometry of 1 : 1. The association constants for these complexes were measured to be 7.48 × 10 5 and 9.12 × 10 5 M -1 , respectively, indicating a strong association between both probes and their respective metal ions. Both chemosensors exhibited comparable limits of detection (LOD) and limits of quantification (LOQ) of 0.03 μM and 0.10 μM, respectively. Reversible studies confirmed that only chemosensor 3CQD could serve as a secondary sensor for EDTA. The theoretical studies calculated using Density Functional Theory (DFT) program at B3LYP/6-31G** (Spartan '10 package) level., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)