The Design, Synthesis And Properties Of Novel Ratiometric Coumarin-based Fluorescent Probe

Coumarin derivatives, whose parent structure is benzopyrone, are classified as the lactones according to functional groups. The compounds are ubiquitous in stem and leaf tissue of plants, with important biological and optical properties. The biological properties mainly refer to excellent anti-bacterial, anti-virus, anti-aging, anti-cancer, et al. And optical properties primarily refer to potential fluorescence characteristics. Their fluorescence properties can be controlled well by changing substituents on the mother nucleus. In addition, coumarin derivatives have high fluorescence quantum yields, large Stokes shift and excellent photostability. Thus, they are widely designed as the fluorophore of fluorescent probe, and the excellent fluorescence properties of which have been confirmed by many studies.The present thesis reviews the related literatures in recent years. Based on that, we have synthesized a series of novel coumarin-based fluorescent probes. Then their properties were studied and discussed. The main research contents are as follows:First, coumarin compounds 2 and 3 with different substituents on the 3-position have been synthesized by 2,4-dihydroxybenzaldehyde and the corresponding active a-H compounds. Compound 5 was obtained by formylation and subsequent cyclization of compound 3. Then, three novel aqueous F- fluorescent probes CS1, CS2 and CS3 were obtained by silicification of the probe precursor 2,3 and 5 with TBDMSC1 under anhydrous conditions, whose structures were identified by 1H NMR,13C NMR, HRMS and IR spectra. In addition, the crystal structure of probe CS3 was obtained. This kind of probes, with coumarin derivatives as fluorophore and silicon-oxygen bond as recognition sites, can recognized F- selectively and sensitively. The experimental results showed that the fluorescence intensity of the above probes was weak and the wavelength was short. When they reacted with F-, the fluorescence intensity of the system was enhanced and maximal emission wavelength shows bathochromic effect and thus ratiometric detection to F- was achieved. Meanwhile, the present thesis also studied the relationship between the substituents and the fluorescence characteristics of probe. Experimental results showed that the emitted fluorescence intensity was increased with the enhancement of electron-deficiency ability of substituents on 3-position and fluorescence emission wavelength of probe red-shift as the conjugated area of substituents on 3-position enlarged.Four novel fluorescent probes CHI, CH2, CH3 and CH4a, which can selectively recognize Ag+, were synthesized by condensation reaction of 7-hydroxy-3-formyl coumarin,7-hydroxy-3-acetyl coumarin,7-(diethylamine)-3-formyl coumarin or 7-(diethylamine)-3-acetyl coumarin with 2-hydrazino benzothiazole respectively. The four probes were confirmed by 1H NMR,13C NMR, HRMS and IR spectra, and the crystal structure of probe CH4a was obtained via the solvent evaporation. We found that the structure of the probe CH4a was different from probe CHI, CH2 and CH3. By the influence of the substituents, probe CH4a carried out a further aminolysis reaction, resulting that the lactones structure turned into a five-membered heterocycles containing two nitrogen atoms. Fluorescence spectroscopy experiments showed that the probe itself has strong yellow fluorescence, which the maximum emission wavelength was between 520 nm and 540 nm, and the fluorescence could be quenched by Ag+. Setting a short period of time, the probe CHI, CH2 and CH3 emitted new blue fluorescence between 440 nm and 480 nm, however, probe CH4a changed a little even a long time later, which also verified the CH4a special structure. Thus, probe CHI, CH2 and CH3 gone through a further hydrolysis reaction after complexation with Ag+. While, probe CH4a just stayed in the stage of complexation. In addition, we also did the back titration experiment:dropping Na2S solution into probe system whose fluorescence has been quenched by Ag+, only probe CH4a got the complete recovery of fluorescent intensity, and the intensity has good linear relationship with concentration of Na2S. Back titration experiment reconfirmed that the reaction between probe CHI, CH2 or CH3 and Ag+ was complexation and then hydrolysis, namely the three fluorescent probes are reaction type. While probe CH4a only carried out complexation with Ag+, namely complex type fluorescent probe.