A new “ON-OFF” fluorescent and colorimetric chemosensor based on 1,3,4-oxadiazole derivative for the detection of Cu2+ ions

Abstract A symmetrical oxadiazole derivative (OXD) containing two pyrazole moieties was synthesized successfully and characterized by single crystal X-ray diffraction, nuclear magnetic resonance and mass spectrometry. The synthesized compound displayed “On-Off” fluorescent sensing towards Cu 2+ with high selectivity and sensitivity. Fluorescence and UV–vis absorbance spectra studies demonstrated that the proposed sensor can detect Cu 2+ directly in acetonitrile solution over a wide range of metal ions including Ag + , Na + , K + , Hg 2+ , Mg 2+ , Cd 2+ , Co 2+ , Ni 2+ , Zn 2+ , Fe 2+ , Pb 2+ , Ca 2+ , Mn 2+ , Ba 2+ , Fe 3+ , Al 3+ , and Cr 3+ . Moreover, the synthesized sensor exhibits an instantaneous naked-eye color change from colorless to yellow with the presence of Cu 2+ ion. The fluorescence intensity of the sensor has shown a linear response to Cu 2+ in the concentration range of 0–15 μM with a detection limit of 2.14 μM. Fluorescence titration, 1 H NMR spectrum, ESI–MS, and DFT calculation confirmed that fluorescence quenching is caused by the complex formation between the sensor and Cu 2+ with 1:1 stoichiometry.