Synthesis And Properties Study Of Fluorescent Chemosensors Based On Coumarin

Fluorescent chemosensor have become an important detection method for identifying cations,anions,and small biological molecules for qualitative and quantitative analysis due to their advantages such as simple operation,high sensitivity,good selectivity,low detection limit,and strong real-time monitoring capabilities.This detection method has a wide range of applications in environmental chemistry,analytical chemistry,biomedicine,and pathology.Among them,coumarin and its derivatives not only have antitumor,antihypertensive,antioxidant and other physiological activities,but also have good optical properties such as high fluorescence quantum yield,large Stokes shift,and strong light stability.It is widely used in the design of new fluorescent chemosensor,and has been widely used in the detection of various ions and molecules.In this thesis,7-diethylaminocoumarin was used as the basic framework,and three types of new-type fluorescent chemosensor were designed and synthesized by inserting different electron-withdrawing groups at the 3-position,and their recognition performance were studied.The details are as follows:We first synthesized the dye 7-diethylamino-3-acyl chloride coumarin,then introduced a strong electron-withdrawing group amide at the 3-position,and finally synthesized a coumarin fluorescent chemical sensor.When Cu²⁺was added,the fluorescence intensity of the sensor was significantly enhanced（21.8 times）,the Stokes shift was 41 nm,and the detection limit was 0.52μM,showing higher selectivity and sensitivity.The results of Job’s plot indicated that sensor CD and Cu²⁺ion coordinated with each other with a binding stoichiometry of 2:1.After speculation,predicting that the recognition mechanism of Cu²⁺by sensor CD belong to photoinduced electron transfer mechanism（PET）.And the pH test results showed that the most suitable pH range for sensor CD was 7⁸.5.Next,we designed and synthesized a fluorescent chemosensor for sequential recognition of Cu²⁺and PPi based on phenanthroline and coumarin.Sensor CP showed obvious“on-off”type fluorescence quenching response to Cu²⁺ion,and the quenching efficiency reached a maximum of 87.33%.and the color of the solution changed significantly,indicating that CP could be used for naked eye detection of Cu²⁺.Additionally,the quenched fluorescence of the CP-Cu²⁺complex was restored upon the addition of PPi.The detection limit of sensor CP was 0.126μM to Cu²⁺and 0.517μM to PPi.The results of Job’s plot indicated that sensor CP showed a 1:1 binding stoichiometry to Cu²⁺and sensor CP-Cu²⁺showed a 2:1 binding stoichiometry to PPi in CH₃OH/HEPES buffer medium（9:1,v/v,pH=7.2）.The stable pH range of sensor CP to Cu²⁺and CP-Cu²⁺to PPi was from 5 to 8.Finally,we synthesized a coumarin derivative dye,7-diethylaminocoumarin-3-carboxaldehyde,and synthesized a fluorescent chemosensor CF by introducing a strong electron-withdrawing group furfuryl at the 3-position.When Fe³⁺was added,the fluorescence intensity of the sensor was significantly enhanced（3.65 times）,the Stokes shift was 98 nm,and the detection limit was as low as 0.82μM,indicating that the sensor has high sensitivity to Fe³⁺.The results of Job’s plot indicated that sensor CF showed a 1:1 binding stoichiometry to Fe³⁺.The stable pH range of sensor CF to Fe³⁺was from 6 to 8.