Design,Synthesis And Applications Of Environment-Sensitive Flavonoids-Based ESIPT Fluorescent Probes

Fluorescent probe technology possesses several advantages,including fast response,high sensitivity,high spatio-temporal resolution and non-invasion to samples,ahd thus has been widely used in the fields of analytical chemistry,biological and environmental science.Flavone derivatives are a kind of representative fluorescent probes with the excited-state intramolecular proton transfer(ESIPT)process.These probes normally give two well-separated emissions,corresponding to the excited state in their normal type(N*)and tautomer(T*),respectively.The fluorescence intensity ratio of the two bands of ESIPT-based probes is very sensitive to the microenvironment,such as intermolecular hydrogen bond,polarity,local electric field and so on.Based on these characteristics,in this thesis,eight flavonoid fluorescence probes have been synthesized and applied to the environmental and biological fields by adjusting the molecular structure design.The main research contents of the paper were shown as follows:(1)Flavonoid-based probes 1 and 2 have been designed for calibrating the ethanol content of commercial ethanol gasoline.Probes 1 and 2 have a good linear fit for the common ethanol gasoline E0-E85,and their fluorescence emission peak intensity ratio(I_N/I_T)varies with the change of ethanol content.Compared with the traditional three-dimensional fluorescence spectroscopy method for the calibration of ethanol gasoline,the selectivity and sensitivity of the ratio fluorescence probe provided by this method were significantly enhanced.Moreover,the test result was barely affected by the intrinsic fluorescence of gasoline,leading to a more accurate measurement for ethanol.This method provided a convenient detection method realizing the calibration of ethanol gasoline by naked-eye observation of fluorescent color.(2)The probes 1HHF,2HHF,3HHF and HF have been designed and applied for highly selective recognition of human serum albumin.Interestingly,the fluorescence response of2 HHF to HSA was different from that of the other three compounds.After adding HSA,2HHF gave dual emission peaks,while the other three only gave single emission peak.The results of molecular docking and substitution experiments showed that the binding site of theprobe 2HHF to HSA was located in the IIIA region,which was different from those of other compounds.It could be ascribed to the fact that the carbonyl of the probes form different hydrogen bonds with different amino acid residues in HSA.The strength of the intermolecular hydrogen bonding determined whether the ESIPT effect was inhibited.In addition,HSA provided a hydrophobic environment,which enabled the probe to restore fluorescence similar to that in low-polar organic solvents.This unique binding mechanism was also confirmed by using amide-and guanidine-containing compounds.(3)Based on the research in the previous two chapters,we increased the π-conjugation of the typical flavonoid probe.A novel fluorescent probe Q1 was designed and synthesized by using N-substituted flavonoid as the fluorophore.Furthermore,based on electrospinning technology,the test strips of fiber membranes loaded with fluorescent probe with a large surface area were prepared and their sensing properties were also studied.These test strips could quickly detect the gaseous state of the nerve agent simulant DCP,and the detection limit was less than 10 ppb(parts per billion).These results may provide an important reference for further designing fluorescent probe test strips for detecting neurotoxic agents in solution and gas phase.