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With the development of science and technology, fluorescent probes are widely used in biological, chemical, pharmaceutical and other areas, and have attracted more and more attention. Coumarin compounds have many advantages including high fluorescence quantum yield, large Stokes shift, excellent light stability, and so on. Therefore, study on coumarin derivatives as fluorescent probes has become one of the hottest research topics.In this dissertation five novel colorimetric and fluorescent pH probes (the compounds 7-11) derived from iminocoumarin and thiophene-carboxaldehyde compounds were designed and synthesized. The structures of the new compounds were characterized by IR,1H NMR,13C NMR, MS and single crystal X-ray diffraction analyses. The compounds 7,8 and 9 were dissolved in ethanol-H2O (1:1, v/v) for measurement of spectral properties. The absorption and fluorescent emission spectra of the solutions were measured and analyzed in acidic and basic conditions, respectively.With the increase in the acidity of the solution, the color of the solutions of the three compounds turns gradually from green to finally yellow in acidic conditions. The color change can be observed by a naked-eye. The relationship between the absorption and fluorescent emission spectra of the solution and pH can be summarized as follows. With the increase of pH value, the intensity of the absorption band at about 450 nm (or 505 nm) gradually increases (or decreases).When pH value increases (or decreases) beyond a threshold value, the intensity of the absorption band remains constant. However, with the increase of the pH value, the intensity of the fluorescence emission at about 510 nm and 540 nm gradually increases. When the pH value increases beyond a threshold value, the intensity of the fluorescence emission remains constant. In addition, the ratio of the fluorescent intensity at about 510 nm and 540 nm is related to the pH value. Therefore, they can be used as ratiometric pH indicators. It can be observed that with the increase in the basicity of the solution, the green color of the solution turns pale gradually to finally very pale green. The relationship between the absorption and fluorescence emission and the pH value is quite clear.Investigation on the influence of common metal ions (Mg2+, Zn2+, Ca2+, Cu2+,Ni2+, Hg2+, Co2+, Fe3+, Al3+, K+) and anions (NO2-, F-, Cl-, HSO3-, HSO4-, CH3COO-, NO3-) has been conducted. The results show that the interference of these ions to the fluorescence intensity is negligible.In conclusion, the target compounds 7,8, and 9 can be used as fluorescent pH probes in the presence of common metal cations and anions without interference.
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