A fluorescent probe based on pyrazoline with significant Stokes shifts for the detection of Cu²⁺ ions and its applications

A simple pyrazoline derivative BBD has been synthesized for detecting Cu²⁺ in EtOH/HEPES (v/v = 1 : 1, pH = 7). The probe has high selectivity for Cu²⁺ by quenching the fluorescence intensity and was sensitive to pH. When excited at 398 nm, fluorescence is emitted at 520 nm with a Stokes shift of 122 nm, which is larger than that of other reported pyrazoline skeleton probes. The detection limit (LOD) of the probe for Cu²⁺ is 0.862 μM which is lower than the value of the WHO limit (31.5 μM) in water. The 2 : 1 binding mode and probable recognition mechanism of the probe with Cu²⁺ were confirmed by Job's plot, IR, ESI-MS, and TD-DFT analysis. Moreover, the probe has been successfully applied to actual water samples as well as cell and zebrafish imaging.