Chalcone-based fluorescent chemosensors as new tools for detecting Cu²⁺ ions

The design and full characterization of new fluorescent chemosensors for Cu²⁺ is herein presented. The structure of the sensors is based on a chalcone backbone as the chromophoric unit, with di-(2-picolyl)amine (DPA) as a receptor moiety. Two systems, bearing one or two chalcone-DPA units, were synthesized and fully characterized. UV–Vis titrations with several metal ions were performed and both chemosensors exhibited a strong hypsochromic shift in the absorption spectra upon Cu²⁺ addition, indicating a higher selectivity for this metal over other divalent cations. Additionally, fluorescent spectra recorded in the same conditions revealed a stronger quenching effect in the presence of Cu²⁺, even in the presence of other metal cations, with association constants above 10⁶ M⁻¹ and detection limits below the micromolar level for both chemosensors. Paper test-strips with one of the chemosensors were prepared to attest its possible application for detecting copper in aqueous samples.