Colorimetric Detection of Cu²⁺ and Fluorescent Detection of PO₄^3- and S^2- by a Multifunctional Chemosensor

A simple multifunctional chemosensor 1 was synthesized by a combination of N-aminophthalimide and 8-hydroxyjulolidine-9-carboxaldehyde. The sensor 1 showed a clear color change toward Cu²⁺ from pale to deep yellow and significant fluorescence enhancements toward PO₄^3- and S^2-. The detection limit (0.14 μM) for Cu²⁺ ion was below the World Health Organization (WHO) guideline for drinking water (31.5 μM). The sensor 1 could be used to quantify copper ion in real water samples. In addition, the sensor 1 could detect phosphate and sulfide with the fluorescent enhancements in aqueous solution. The sensing mechanism of Cu²⁺ by 1 was proposed to be an intramolecular charge transfer (ICT) and those of PO₄^3- and S^2- by 1 were proposed to be a deprotonation process, based on the experimental results and theoretical calculations.