New 7-Hydroxycoumarin-Based Fluorescent Chemosensors for Zn(II) and Cd(II)

Five new 4- or 8-substituted-7-hydroxycoumarin derivatives (1-5) were synthesized as fluorescent sensors for metal ions. Fluorescent changes and selectivity for metal ions were compared based on the introduction of different ligands and/or testing with different substitution positions of 7-hydroxycoumarin in aqueous solution. Especially, probes 2, 3 and 5 displayed large fluorescence enhancements with $Zn^{2+}$ and $Cd^{2+}$ . Probes 2 and 3 showed moderate selectivity for $Zn^{2+}$ over $Cd^{2+}$ . On the other hand, probe 4 showed large fluorescence quenching effects upon the addition of $Ag^+$ and $Hg^{2+}$ .