Synthesis And Property Research Of Fluorescent Probes Based On Coumarin

Recent years, coumairn and its derivative have been found to be widely used in the fields of biology, medicine, perfumes, cosmetics and dyes etc. Due to its unique optical properties such as high fluorescence quantum yield 、 large stokes shifts 、excellent light stabilities and less toxicity, coumairns have received considerable attention in construction of fluorescence chemosensors. In this study, we successfully established a series of chemosensor modules based on coumarins. This class of compounds were served as significant fluorescent sensors in the highly selective recognition of Pd²⁺ or Hg²⁺ among the other metallic cations investigated in aqueous solutions.Through the improved Knoevenagel reaction, the 2,4-dihydroxybenzaldehyde,ethyl cyanoacetate was respectively reactioned with o-phenylenediamine,o-aminophenol, o-aminothiophenol, to get a kind of rigid N-heterocyclic coumarin derivatives. The structures of the new compounds were characterized by NMR and IR spectra. We studied the fluorescent properties of this class of compounds and found that they could serve as candidates for fluorescent Pd²⁺ sensing in aqueous solutions.Moreover, we explored the assembly of the structurally simple and conformationally rigid N-heterocyclic coumarin derivatives with Pd²⁺ to creat a new type of metal-organic gel.The coumarin-based fluorescent chemosensor for Hg²⁺ has been designed and synthesized via Hg²⁺-induced desulfurization reaction. In HEPES buffer, the probe exhibited specific recognition for Hg²⁺ among the other metal ions such as Ni²⁺,Zn²⁺,Cu²⁺,Cd²⁺,Mn²⁺,Pd²⁺. The results demonstrated that upon the addition of Hg²⁺, the fluorescence intensity decreased and an obvious fluorescence change from bluish to almost colorless were observed. The Hg²⁺-promoted desulfurization led to a distortion of the amine moiety with a decrease in ICT character, which resulted in the fluorescence quenching.In addition, we successfully prepared a novel amino-coumarin derivative from2,4-digydroxybenzaldehyde, in which there are an electron-donating substituent（-OCH₃） in position 7 and an electron with-drawing group（-Br） in position 3. The structure was characterized by NMR and IR spectra respectively. We investigated the UV spectra and fluorescent spectra of the new compound in different organic solvents and the compound indicated highly solvent-dependent emission bands.