Synthesis Of Benzoxazoles And Squaraine Dyes And Their Application In The Detection Of Ions And Bioactive Molecules

Fluorescent probes are gaining more and more attention because of their high selectivity,sensitivity,fast response,simple operation and low detection limit.Benzoazoles are an important class of molecules with high fluorescence quantum yield and thermal stability,and they have broad application prospects in natural products,biomedicine and other fields.Squaraine?SQ?dyes possessing strong absorption and fluorescence emission in the near infrared?NIR?region have been widely used as fluorophores in design of NIR fluorescent sensors.In this thesis,three fluorescent probes were designed and synthesized using benzoxazoles and squaraine dyes as parent fluorophores and they were respectively used for the detection of free radicals?ClO^-and ONOO^-?,ions(CN^-and Cu²⁺)and adenosine triphosphate?ATP?.We synthesized a small molecule 2-?2,3-dihydroxyphenyl?benzothiazole?2?.Based on the reaction of the o-diphenol structure of compound 2 and 2-formaldehyde phenylboronic acid,we constructed a detection system.Upon addition of radicals ClO^-and ONOO^-,the fluorescence intensity of the detection system was significantly enhanced.In aqueous solutions,the reation product of compound 2 and 2-aldehyde phenylboronic acid could quantitatively detect ClO^-and ONOO^-with a wide linear detection range,and the detection limit for ClO^-and ONOO^-were calculated to be 5.91 and 3.64 nM,respectively.In addition,the detection system was successfully used for intracellular ClO^-and ONOO^-detection and imaging of cellular endoplasmic reticulum.Based on the advantages of benzoxazole derivatives,we designed and synthesized a series of compounds S1-S10 containing two Schiff base structures and studied their oxidation-cyclization reactions.The Schiff base compounds modified by different substituent groups showed different fluorescence responses to CN^-and Cu²⁺,and they could be converted into ring-closing products by CN^-and Cu²⁺with different conversion efficiency.Compound S1 with electron donor group exhibited excellent property and could rapidly respond to CN^-and Cu²⁺with 400 folds fluorescence enhancement.In the presence of cyanide ions,the fluorescence intensity of compound S1 showed a good linear relationship with Cu²⁺concentration ranged from 1-6?M,and the detection limit was 1.53 nM.Besides,compound S1 had good tissue membrane permeability,which successfully applied to the detection of CN^-and Cu²⁺in the intracellular and plant Arabidopsis root tissues.Based on the near-infrared fluorescence emission of SQ,we synthesized a novel dye molecule SQ-3N by linking two molecules of SQ.SQ-3N has low background fluorescence intensity in aqueous solution through?-?and hydrophobic interactions.In the presence of ATP,SQ-3N can combine with ATP through electrostatic and?-?interactions,and realize high signal to noise ratio and high selectivity detection of ATP.The fluorescence intensity of SQ-3N showed a good linear relationship with ATP concentration ranged from 0-2.4 mM,and the detection limit was calculated to be 1.18?M.SQ-3N had excellent cell membrane permeability and low cytotoxicity,and it could be used for intracellular ATP detection and imaging of cellular mitochondria.