Synthesis And Properties Of Fluorescence Chemosensors Based On 1,3,4-oxadiazole Derivative

As an important approach to chemical sensing,fluorescence chemosensor has attracted enormous attention due to its advantages such as real-time monitoring with fast response times,intrinsic high selectivity and sensitivity,ease of handling and low-cost.The list of analytes to be detected by fluorescence chemosensor is lengthy and there is much improvement in area of metal ion detection because of the significant character of metal ions to environment and organisms.In this paper,we mainly report two fluorescence chemosensor based on oxadiazole unit.Firstly,2,5-Bis[?2-pyrazolyl?methyl]-1,3,4-oxadiazolewassynthesized successfully and characterized by single crystal X-ray diffraction,nuclear magnetic resonance and mass spectrometry.The symmetrical oxadiazole derivative?sensor 1?containing a 1,3,4-oxadiazole as the fluorophore and two pyrazole moieties as the recptor.It plays a highly sensitive and selective?on-off?fluorescent chemosensor towards Cu²⁺.Fluorescence and UV-vis spectra studies demonstrated that the proposed sensor can detect Cu²⁺directly in acetonitrile solution over a wide range of metal ions.The complex between sensor 1 and Cu²⁺has 1:1 stoichiometry of complex while the binding constant was 4.38×10⁴ M^-1 and the detection limit was 2.14?M.Secondly,2-[5-?2-formylphenyl?-1,3,4-oxadiazol-2-yl]benzyl picolinate?sensor2?was synthesized successfully and characterized by nuclear magnetic resonance and mass spectrometry.Sensor 2 presented high colorimetric sensitivity for Co²⁺with low detection limit?3.92?M?.Sensor 2 also displayed?On-Off?fluorescent sensing for Cu²⁺over a wide range of competitive metal ions and could accurately detect the existence of Cu²⁺in water samples with detection limit of 4.48?M via the fluorescent quenching and color change.The binding constant of sensor 2-Co²⁺complex and sensor 2-2Cu²⁺complex was 5.29×10² M^-1 and 1.33×10¹⁰ M^-2 separately.