Synthesis And Properties Of Fluorescent Probes Based On Imidazole Derivatives

In recent years,the content of metal ions in rivers and farmlands has been increasing,finally,they may accumulate into the human body with the food chain and cause various diseases.Therefore,in terms of ecological environment and food safety,researchers have taken the detection of metal ion content as one of the focuses of research.Fluorescent probe analysis has attracted great interest from researchers due to its good selectivity,low detection limit,short reaction time and easy operation,and has been widely used in the detection of metal ions in food safety,bio-medicine and ecology.In this thesis,three fluorescent probes of imidazole derivatives L1～L3 with high selectivity and sensitivity were designed and synthesized by alehy-ammoni a condensation betwwen 7-diethylamino coumarin aldehyde or o-vanillin and benzoylpyridine or 2-formylpyridine.First,the structures of the designed probes were characterized by ¹H NMR,¹³C NMR and ESI-MS.Then,the optical properties of L1～L3 and the coordination ability to Ag⁺,Cu²⁺and Fe³⁺ions were investigated by UV-Vis absorption spectroscopy and fluorescence emission spectroscopy.Finally,the recognition mechanism of the above three probes was explored using ¹H NMR titration.The specific work is as follows.（1）Firstly,the role of metal ions in production and life and the impact of high concentrations of metal ions on the ecological environment and people’s own health are introduced.Secondly,the recent development of fluorescent probes,response mechanisms and applications in real water samples and live cell imaging are summarized,and the recent progress of fluorescent probes for the detection of Ag⁺,Cu²⁺and Fe³⁺ions is described.Finally,the research content of this thesis is presented in the context of probes that have been developed so far.（2）A fluorescent quenching type probe 7-（diethylamino）-4-（4,5-diphenyl-1H-imidazol-2-yl）chromen-2-one（L1）was synthesized from 7-diethylamino-4-methylcoumarin,benzil and ammonium acetate.In DMF:H₂O=1:1（v:v）solution,the coordination of L1 with Ag⁺caused a sharp decrease in fluorescence intensity at 538when excited at 379 nm nm,the fluorescence of solution showed a color change from bright yellow to no fluorescence under UV lamp（365 nm）irradiation.The change of fluorescence indicated that L1 could selectively recognize Ag⁺,and the presence of other metal ions did not affect the selectivity of L1 to Ag⁺.The detection limit was calculated to be 4.6×10^-8 mol/L,the binding constant was 2.9×10⁴ L/mol,and the coordination ratio betweenprobe L1 and Ag⁺is 1:1.It was speculated by ¹H NMR titration that Ag⁺might bind to the N of-C=N-group and O of carbonyl group in probe L1 to form stable complexes.Finally,the test strip experiment proved the usefulness of probe L1 in Ag⁺detection.（3）A fluorescent quenching type probe 7-（diethylamino）-3-（4,5-diphenyl-1H-imidazol-2-yl）chromen-2-one（L2）was synthesized from 7-diethylamino-3-methylcoumarin,benzil,and ammonium acetate.In acetonitrile solution,the fluorescence emission intensity of L2 at 508 nm was greatly reduced after Cu²⁺was added when excited at 448nm,the fluorescence of solution showed a color changed from bright green to no fluorescence under UV lamp（365 nm）irradiation,indicating that L2could coordinate with Cu²⁺.The detection limit was calculated to be 8.2×10^-8 mol/L,and the binding constant was 1.7×10⁴L/mol.The coordination ratio between probe L2and Cu²⁺is 2:1.It was speculated by ¹H NMR titration that Cu²⁺might form stable complex by binding to the N of-NH-group and O of carbonyl group in L2.Finally,the test strip experiment demonstrated utility of the probe L2 in selectively Cu²⁺.（4）A fluorescent"on-off-on"tyoe probe 2-methoxy-6-（1-phenylimidazo[1,5-a]pyridin-3-yl）phenol（L3）was synthesized from 2-benzoylpyridine,o-vanillin and ammonium acetate.The fluorescence intensity of L3 at 472 nm decreased greatly after the addition of Fe³⁺in DMSO:H₂O=1:1（v:v）solution when exciated at 294 nm,and the fluorescence of solution recovered after F^-was added,which indicated that F^-can seize Fe³⁺from probe L3 according to the UV-vis absorption spectra.Therefore,probe L3 an selectively recognize not only Fe³⁺but also F^-,the detection limits of L3to Fe³⁺and F^-were calculated to be 6.9×10^-8 mol/L and 3.0×10^-7mol/L,respectively.The coordination ratio between L3 and Fe³⁺is 2:1 and the binding constant was 1.3×10⁴ L/mol.It was speculated that Fe³⁺may form stable complex by combining with the N of-C=N-group and O of hydroxyl atom in L3 according to the ¹H NMR titration.Finally,the test strip experiment proved the practical value of probe L3 in selective identification of Fe³⁺and F^-.