Synthesis And Application Of Fluorescent Probes Based On Pyrazole Derivatives

In recent years,organic fluorescent probes have been widely used as visual monitoring tools for target analysis in fields such as food safety and environmental monitoring due to their high selectivity,simple operation,high sensitivity,and low cost.Properly substituted pyrazole derivatives have high fluorescence quantum yields,significant solvent solubility behavior,Gaussian Stokes displacement,nonlinear optical properties,etc.Therefore,we have designed and synthesized fluorescence probes based on 1,3-diphenylpyrazole as the main body,with different substituents at the 4-position of pyrazole,for the detection of Cu²⁺,Fe³⁺and hydrazine.The specific work is as follows:（1）Pyridine derivatives were introduced at the 4-position of pyrazole,and two pyridine-based pyrazole fluorescence probes X₁ and X₂ were developed.The molecular structures of these two compounds were confirmed by ¹H NMR,¹³C NMR,and ESI-MS.Studies have shown that in mixed solutions of THF/H₂O（V/V=9:1）,probes X₁and X₂ exhibit fluorescence quenching and outstanding optical performance for Cu²⁺and Fe³⁺.They have high selectivity,sensitivity,anti-interference ability,and low detection limits.In addition,the fluorescence intensity has a good linear relationship with ion concentration in the range of 10-60μM,and the complex constants of X₂ with Cu²⁺and Fe³⁺are 3.75×10³ M^-1 and 2.52×10³ M^-1,respectively.Job’s plot analysis of fluorescence titration data shows that the chemical stoichiometry of probes X₁/X₂ with Cu²⁺/Fe³⁺is 1:1.The recognition mechanism of the probes was discussed by combining infrared spectroscopy and Gaussian calculation.（2）Chalcone derivatives were introduced at the 4-position of pyrazole,and three fluorescence probes Y_1-3 with different luminescent groups andα,β-unsaturated ketones as recognition sites were synthesized.After interacting with hydrazine,probes Y₁ and Y₂ emitted strong blue and cyan fluorescence,respectively,while the fluorescence color of Y₃ changed from yellow to light blue,achieving colorimetric recognition of hydrazine.The recognition mechanism is that the chalcone part reacts with hydrazine to form dihydro-pyrazole ring closure,which destroys the conjugation of the molecule and reduces the electron interaction ability.Studies have shown that the probes have excellent selectivity for hydrazine and are not affected by other analytes,with detection limits as low as 2.64μM,1.51μM,and 1.98μM,and the optimal recognition time is 60 min.（3）Vinylacrylonitrile was introduced at the 4-position of pyrazole,and two D-π-A-type fluorescence probes Z₁ and Z₂ with acrylonitrile as the recognition group were synthesized.The molecular structures were determined by nuclear magnetic resonance and mass spectrometry,and the recognition mechanism of the probes was studied by testing their optical properties and Gaussian calculation.Due to the strong electron-withdrawing ability of acrylonitrile,the probe has a strong ICT effect.After reacting with hydrazine,acrylonitrile is removed,and the hindered ICT effect leads to strong fluorescence.At the same time,the probe molecule also has an AIE effect.The study found that probes Z₁ and Z₂ have detection limits for hydrazine as low as 0.197μM and 0.185μM,respectively.Through testing on test strips and hydrazine in soil,the probe achieved quantitative analysis of hydrazine in the environment.Cell toxicity and imaging indicate that the probe can be used for monitoring hydrazine in biological systems.