Multifunctional chemosensor properties of fluorescein-coumarin hydrazones

Previously unknown fluorescein-coumarin hydrazones have been synthesized. These are multifunctional chromogenic and/or fluorogenic capable of naked eye detecting Zn2+, Cu2+ (in acetonitrile) and Al3+ (in ethanol). The longest wave-length absorption maxima of the synthesized compounds are observed in the range of 364-396 nm, which in combination with the absence of emission properties, corresponds to their existence in the spirolactam form. Fluorescein containing 6,7-dihydroxy-4-methylcoumarin substituent in the spirocyclic bridge possesses optimal sensor properties. In acetonitrile in the presence of the Zn2+ ion, a change in the color of its solution from pale yellow to bright yellow is observed, while other cations do not have a significant effect on the absorption pattern. The addition of Cu2+ (in acetonitrile) or Al3+ (in ethanol) cations leads to a contrasting naked-eye effect with the coloring of the solutions in a characteristic pink color due to the formation of long wave-length absorption maxima in the region of 440-470 nm. Emission in the range of 471-506 nm is also observed, indicating the transformation of the spirolactam form of the fluoresceincoumarin hydrazone to the open form. The resulting compounds can be used for the selective determination of several analytes using a single sensor molecule.