Study On Synthesis Of Bifunctional Fluorescent Probes And Their Recognition Properties Towards Mercury And Fluoride Ions

Coumarin fluorescent compounds have many excellent optical properties and coumarin^-based bifunctional fluorescent probes are widely used in biological, chemical and environmental testing. Detection of mercury and fluoride ions plays an important role in the field of cationic and anionic detection because mercury can cause great harm to human and environment while fluorine is an indispensable trace element in human body and is also associated with various damage to humanity and environment. So we choose the synthesis of the coumarin^-based bifluorescent probe for mercury and fluoride ions as the research subject, which mainly includes the following contents:（1） The reactive^-type coumarin^-derived fluorescent probes for mercury were designed mainly based on the irreversible desulfurization reaction. The probes coupled desulfurization with intramolecular cyclization by introducing thiocarbonyl^-based functionalities to detect mercury. Moreover, the probes contained N and O and therefore might complex with mercury. The recognition sites for fluoride mainly included two categories. One is the Si–O bond, which could be broken by addition of fluoride due to the strong affinity of fluorine to silicon（the very high bond energy of Si–F bond）. The other is active hydrogen（as NH2, NH or OH group）, based on the strong electronegativity of fluorine to bring about deprotonation on the polar groups and thereby change in the fluorescence intensity of the analyte. Bifunctional fluorescent probes for mercury and fluoride based on coumarin has not been reported so far. We designed and synthesized coumarin^-based bifluorescent probes for mercury and fluoride.（2） Twenty^-one coumarin^-based bifunctional fluorescent probes L1^L21 for detection of mercury and fluoride were synthesized. Probe L1 contained thiocarbonyl group and Si^-O bond as the recognition sites. Probe L2 contained NH and O as the recognition sites. Probe compounds L3^L21 were synthesized by introducing thiourea group. The synthetic process involved hydrolysis of coumarin derivatives 1, 2, 3 and the highest yield 80% was obtained when the proportion of HCl in ethanol was 67%. The highest yield of the hydrolysis reaction of coumarin derivative 7 80% was obtained when the proportion of HCl in water was 33%. The structures of the synthesized compounds were characterized by 1H NMR, 13 C NMR, MS and IR spectra.（3） The recognition behavior of probe L1 towards mercury and fluoride was studied. L1 could be used to detect mercury and fluoride in both acetonitrile and aqueous solution with remarkable sensitivity. Measurements on UV^-Vis and fluorescence emission spectra of L1 at different pH showed that L1 acted as fluorescent probe for mercury and fluoride ion at pH 2^-11 and pH 5^-12, respectively. The color of L1 changed from yellow to purple black and deep yellow respectively upon addition of mercury and fluoride ion. In pure aqueous solution, L1 could be used to detect mercury and fluoride ion with high selectivityhe presence of cations Cu²⁺, Li⁺, Zn²⁺, Ni²⁺, Co²⁺, Ce3⁺, Sr²⁺, Na⁺, Mg²⁺, Bi3⁺, Ca²⁺, and Fe²⁺ and anions CH3COO―, Br―, I―, HSO4―, H2PO4―, and Cl― did not interfere the sensing towards mercury and fluoride ion, respectively.