Construction Of Biscoumarin-based Fluorescent Probes And Their Recognition To Transition Metal Ions

Some transition metal ions are essential trace elements in the human body,but the enrichment or deficiency of these transition metal ions may have irreversible adverse consequences on the natural environment and the human body.For example,Cu²⁺is indispensable in various basic physiological processes of living organisms,but excessive intake of Cu²⁺induces various diseases,so rapid and accurate detection of transition metal ions is a priority.Among the detection methods of metal ions,fluorescent molecular probes developed rapidly because of their high sensitivity,unique selection,short response time,simple operation,good reproducibility,small sample size,and uncomplicated equipment.Because coumarin has some excellent properties,such as easy modification,good light stability,large Stokes Shift,high fluorescence quantum yield and low synthesis cost,it can be used as a fluorophore for fluorescent molecular probes.In a fluorescent probe,Schiff base group that is considered to be a"privileged ligand"because Schiff bases and additional electron donor atoms such as N and O are commonly used as ionophores in fluorescent sensors,because they can determinate cations by coordination bond.In summary,this thesis is devoted to the synthesis of fluorescent molecular probes based on coumarin derivatives,which have excellent properties such as high sensitivity,good specificity,good light stability and high quantum yield.The specific research contents and results can be divided into the following three parts:In the first part,fluorescent probes?compounds 1,2?of coumarin-based dihydrazide derivatives were synthesized.The probes showed yellow-green fluorescence under the excitation of ultraviolet light,and the quantum yields reached 20.2%and 60.3%,respectively.The structures of compounds 1 and 2 were determined by means of superconducting nuclear magnetic resonance spectroscopy,mass spectrometry and other characterization methods.The recognition properties of compounds 1 and 2 for transition metal ions were studied by UV absorption,fluorescence emission spectroscopy and nuclear magnetic titration.The Coordination Ratio was determined by Job's plot.The results showed that each probe could forms a 1:2 complex with Cu²⁺,and achieved high specific sensitivity to Cu²⁺,though fluorescence quenching off.At the same time,the detection limits of Cu²⁺for both fluorescent probes reached 10^-9 M,and the binding constant reached 10⁷ M^-1.In the second part,in order to optimize the solubility and detection limit of the probe,the green fluorescein dicoumarin monohydrazide fluorescent probe?compound 3?was successfully synthesized by reducing the carbon chain length and changing the functional group,compound 3 has quantum yield of 13.78%.After confirming the structure of compound 3,the recognition performance of it for transition metal ions was investigated by ultraviolet absorption and fluorescence emission spectroscopy.The coordination ratio was determined by Job's plot and the results show that the probe forms a 1:1 complex with Cu²⁺or Ni²⁺,respectively.The probe can recognize Cu²⁺and Ni²⁺effectively,sensitively and specificly,showing obvious fluorescence quenching.The detection limit of the probe for both metal ions can reach 10^-8 M,and the binding constant can reach 10⁶ M^-1.In the third part,a coumarin dihydrazide fluorescent probe?compound 4?with good solubility and a pale blue fluorescence was synthesized.The unique rigid structure?conjugate system in the molecule makes the quantum yield greatly improved and reaches84.95%.After confirming the structure of compound 4,the recognition performance of it to transition metal ions was studied by UV absorption and fluorescence emission spectroscopy.It was found that the probe exhibited fluorescence quenching for Cu²⁺and could be easily recognized by the naked eye.The probe has a detection limit of 10^-8 M for Cu²⁺and a binding constant of 10⁶ M^-1.The probe forms a 1:2 complex with Cu²⁺determined by Job's plot method.