Synthesis And Properties Of Coumarin-based Fluorescent Probes

The fluorescent probe has gained widespread interest due to its simplicity of operation,high detection sensitivity,selectivity,bio-imaging effect and real-time on-line detection.Coumarins have attracted the attention of researchers because of their good photostability,good water solubility and many binding sites.In this thesis,three new coumarin-based fluorescent probes,CM1,CM2 and CM3,were designed and synthesized for the specific recognition of anions,cations and neutral small molecules by the modification and introduction of different substituent into the parent ring of coumarin.Their sensing mechanisms were demonstrated by NMR and mass spectrometry analysis.The research of this thesis can be summarized in three parts as follows.1.A"turn on"fluorescent probe CM1 for N₂H₄using coumarin as the fluorophore and 1,4-diketones as the recognition group was synthesize by a simple two-step reaction.Upon adding N₂H₄,the probe CM1 solution changes from yellow to light yellow and turns on blue-green fluorescence.The detection limit for N₂H₄was as low as 3.2×10^-8M,The test strips with probe CM1 can be used for the detection of N₂H₄ in gaseous and real water samples.Furthermore,probe CM1 can image N₂H₄ in living cells.The sensing mechanism of probe CM1 for N₂H₄ was verified by NMR as well as mass spectrometry analysis.The blocked ICT process leads to the switching on of the fluorescence signal.2.The new lysosome-targeting fluorescent probe CM2 with a hydroxyl group at position 7 and an allyl group at position 6 of the parent ring of coumarin has been designed and developed for the ratiometric detection of mercury ion.The sensing mechanism of the Hg²⁺-induced fluorescence response is based on the specifific reactivity of mercury-promoted intramolecular ring-closed reaction.The addition of Hg²⁺to a PBS buffered solution containing 1%DMSO resulted in a rapid response of fluorescence from blue-green to blue-violet in as little as 40 s.After the addition of other analytes,the probe CM2 showed excellent resistance to Hg²⁺.The probe shows low toxicity to cells and can be used for Hg²⁺imaging in cells,where the morpholine ring can target the lysosome,thus enabling the detection of Hg²⁺in cellular lysosomes.The probe CM2 can be used not only as a test strip for the detection of different concentrations of Hg²⁺,but also in different water samples.3.Probe CM3 was prepared by means of 8-hydroxy-2-methylquinoline and coumarin fluorophore for the detection of F^-.After the addition of F^-,the colour of the probe CM3 in acetonitrile and pure water（1:1 v/v）solution changed from yellow to colourless and the fluorescence was quenched at 509 nm,while when other anions and cations were added,the fluorescence remained unchanged,which indicated that the probe CM3 had specific selectivity and good anti-interference ability for F^-.The¹H NMR titration revealed that the mechanism of the reaction was the formation of H-F and dehydrogenation of the two hydroxyl groups in the CM3 probe with F^-,which triggered the UV and fluorescence changes.In addition,we verified that the probe can be used for the detection of F^-in different water samples.