Design And Synthesis Of Several Small Molecule Fluorescent Probes Based On Imidazole Derivatives

Research in recent years have shown that imidazole derivatives have been widely used in antibacterial drugs,anticonvulsants,analgesics,glucagon receptor antagonists,tuberculosis inhibition etc.,and have attracted more and more attention in the field of chemistry.Meanwhile,reports on the use of imidazole derivatives as novel fluorescent materials and fluorescent probes have emerged.Therefore,four small-molecule fluorescent probes for detecting 2,4,6-trinitrophenol（TNP）,hypochlorous acid（HCl O）and sodium hydrogen sulfite（Na HSO₃）were designed and synthesized.And studied its recognition mechanism and fluorescence properties.The main contents of this paper are as follows:1.Design of the fluorescent probesBased on the prophase work of our group,the FMO energy of TNP was calculated by density functional theory（DFT）,and detailed study the energy and electron cloud density distribution of the HOMO/LUMO orbit of the target compound.Designing of phenanthrene（PTI）and triphenylimidazole（TPI）derivatives with largeπ-πconjugated system using imidazole as the core to detect neutral small molecule 2,4,6-trinitrophenol（TNP）.On this basis,introduced an identification group for the detection of hypochlorous acid HCl O and sodium hydrogen sulfite Na HSO₃.2.The synthesis and fluorescence properties of probes detect for 2,4,6-trinitrophenol（TNP）Using P-bromobenzoic acid and 3-formyl-phenylboronic acid as raw materials,the intermediate 3-formyl-biphenyl-4’-methylformate is obtained by esterification and coupling reaction.Then,respectively,reacting with phenanthrene and benzil via one-pot three componentsstrategytoobtaintwocompounds:3-（1H-phenanthro[9,10-d]-imidazol-2-yl）-biphenyl-4’-methylformate（L1）and3-（1H-4,5-diphenyl-imidazol-2-yl）-biphenyl-4’-methylformate（L2）.The structure of the compound were determined by HRMS and NMR analytical tests.TEM transmission electron microscopy test results showed that the particle size of both compounds were nanoscale.Using two compounds as fluorescent probes,fluorescence spectroscopy studies in V_DMSO:V_H2O=7:3 and V_C2H5OH:V_H2O=7:3 systems showed that the probes L1 and L2 have good recognition of TNP,high selectivity and sensitivity,the detection limits were 0.17 and 0.49μM,respectively.Based on the analysis of UV absorption spectroscopy,NMR titration,Job’s plot research,fluorescence lifetime curve and density functional theory（DFT）,the fluorescence quenching mechanism is inferred to be photoinduced electron transfer（PET）.Tests on different water samples photostability indicated that probes L1 and L2 have practical applications in detecting TNP in water.3.The synthesis and fluorescence properties of probes detect for HCl O or Na HSO₃Based on the above"one-pot reaction",using p-hydroxybenzaldehyde as raw material and reacting with phenanthrene and benzil respectively,two compounds were obtained:2-hydroxy-5-（1H-phenanthro[9,10-d]imidazol-2-yl）benzaldehyde（L3）and2-hydroxy-5-（4,5-diphenyl-1H-imidazol-2-yl）benzaldehyde（L4）.The structure of the compound were determined by analytical test methods HRMS,NMR.Using two compounds as fluorescent probes,fluorescence spectroscopy studies in PBS buffer（1.0 m M,p H=7.4,1%DMF）showed that both probes L3 and L4 show high selectivity and sensitivity,and strong anti-interference ability.Still exhibited good fluorescence performance over a wide p H range,the detection limits were 0.96 and 0.059μM respectively.Both probes L3 and L4 use an aldehyde group as a recognition group,and the recognition mechanism of the probe is confirmed by high-resolution mass spectrometry titration.The test of different water samples and photostability showed that the probe L3 has practical application significance in detecting HCl O in water.Cell imaging showed that probe L4 has good cell membrane permeability and can be used for the detection of exogenous HSO₃^-in biological samples.