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A novel fluorescent polymer for Hg2+ recognition was developed based on the phototautomerism mechanism of 7-hydroxycoumarin in aqueous solution. The developed system showed higher sensitivity and specificity towards Hg2+ in the acetonitrile/water mixture over various other metal ions, with a significant fluorescence quenching of the main emission band. It was shown that the presence of Hg2+ affects the chemical equilibrium of the 7-hydroxycoumarin phototautomers through the excited state intramolecular proton transfer (ESIPT) mechanism, which results in ratiometric fluorescence response upon stepwise addition of Hg2+. The occurrence of ESIPT mechanism was explained based on a comparison of the 1H NMR spectra of the starting alkynylated coumarin (4) in a non-polar aprotic solvent (CDCl3) and in a polar aprotic solvent (DMSO-d6). This was further confirmed by 1H NMR of 4 upon stepwise addition of Hg2+ in a polar aprotic solvent (DMSO-d6). From titration experiments, a higher sensitivity with a detection limit at the nanomolar level (50 nM) was observed and the response was fast and reversible. The real applications of the developed system were investigated in real samples and satisfactory results were obtained for both fresh and lake water samples. [ABSTRACT FROM AUTHOR]

A novel fluorescent polymer for Hg2+ recognition was developed based on the phototautomerism mechanism of 7-hydroxycoumarin in aqueous solution. The developed system showed higher sensitivity and specificity towards Hg2+ in the acetonitrile/water mixture over various other metal ions, with a significant fluorescence quenching of the main emission band. It was shown that the presence of Hg2+ affects the chemical equilibrium of the 7-hydroxycoumarin phototautomers through the excited state intramolecular proton transfer (ESIPT) mechanism, which results in ratiometric fluorescence response upon stepwise addition of Hg2+. The occurrence of ESIPT mechanism was explained based on a comparison of the 1H NMR spectra of the starting alkynylated coumarin (4) in a non-polar aprotic solvent (CDCl3) and in a polar aprotic solvent (DMSO-d6). This was further confirmed by 1H NMR of 4 upon stepwise addition of Hg2+ in a polar aprotic solvent (DMSO-d6). From titration experiments, a higher sensitivity with a detection limit at the nanomolar level (50 nM) was observed and the response was fast and reversible. The real applications of the developed system were investigated in real samples and satisfactory results were obtained for both fresh and lake water samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • An azo dye of coumarin connected to phenolic derivative was synthesized via a conventional diazotization reaction in acidic medium. • Investigation of spectroscopic properties of the synthesized dye in different solvents indicated the possibility of azo-hydazone tautomerism to occur which was confirmed by spectroscopic assays such as 1H NMR, absorption and emission assays, and theoretical studies. • Influence of metal ions on the azo-hydrazone chemical equilibrium were studied and found Cu2+ as only metal ions which can affect established chemical equilibrium toward azo form and leads to the change in both visual appearance and spectroscopic properties of the dye. • The limit of detection (0.0779 mg/L) and limit of quantification (0.236 mg/L) for Cu2+ were determined and found to be much lower than the World Health Organization (WHO) guideline limit for Cu2+ levels in drinking water. • The dye showed potential applications as a sensor in colorimetric and spectroscopic detection and quantification of Cu2+ in domestic and environmental water samples, photo-imprinting and as a logic gate. A new tailor-made azo dye of coumarin connected to phenolic derivative is presented herein. Azo-hydrazone tautomerism in aqueous solution of the dye was observed and studied using spectroscopic assays such as 1H NMR, absorption and emission assays, and theoretical studies. Tautomerism was attributed to the presence of a labile phenolic hydrogen in the ortho position to the azo functionality and the hydrazone was found to be the more dominant tautomer. Influence of metal ions on the azo-hydrazone chemical equilibrium and how the accompanying colour and spectroscopic changes can be exploited for various functions, especially the detection and quantification of Cu2+ in aqueous environments was explored. The presence of Cu2+ affects the azo-hydrazone equilibrium resulting in visual appearance and spectroscopic changes and the likely binding sites for Cu2+ were evaluated. Cu2+ pushes the azo-hydrazone equilibrium towards the more conjugated form and the presence of other metal ions does not have any perceivable impact on this mechanism. The dye showed potential applications as a sensor in colorimetric and spectroscopic detection and quantification of Cu2+ in domestic and environmental water samples, photo-imprinting and as a logic gate. The limits of detection (LOD) and quantification (LOQ) for Cu2+ were found to be 0.0779 mg/L and 0.236 mg/L, respectively, much lower than the World Health Organization (WHO) guideline limit for Cu2+ levels in drinking water. [ABSTRACT FROM AUTHOR]