A colorimetric and fluorometric investigation of Cu(ii) ion in aqueous medium with a fluorescein-based chemosensor

Abstract

As a selective colorimetric and fluorometric chemosensor, a novel fluorescein-based Schiff base (FNSB), 1,4-bis(1-fluorescein)-2,3-diaza-1,3-butadiene (L, 3) exhibits efficient binding for Cu²⁺ ion in water and allows naked-eye detection as a result of the formation of a 1 : 1 copper–ligand complex. The complexations of Cu²⁺ ion due to molecular interaction with 3 resulted in a rapid change in color from colorless to deep yellow with a characteristic change in the UV-vis absorption to a longer wavelength by 130 nm in acetonitrile and significant quenching of the fluorescence intensity (∼2.5 fold for Cu²⁺ ion) with maxima at 519 nm in 1% DMSO–Tris buffer solution at physiological pH (7.4). The detection limit of Cu²⁺ ion in acetonitrile is found to be 20 μM by UV spectroscopy, whereas in aqueous solution, the limit is reduced to 1.25 μM by fluorescence spectroscopy.