Development And Applications Of Fluorescent Probes Based On 2-(2-Hydroxyphenyl) Benzothiazole

Due to its high selectivity,good selectivity and simple operation,fluorescence sensing is widely used in biology and food industry.2-（2-Hydroxyphenyl）benzothiazole（HBT）dyes display an excited state intramolecular proton transfer（ESIPT）process upon excited,which makes them show a large Stokes shift;in addition,HBT fluorescent dyes have good photo-stability,relatively high fluorescent quantum yield and strong solid-state fluorescence.However,classical HBT dyes are subjected to short-wavelength emission,poor water solubility.In this paper,we introduced C=C double bond into HBT dyes at 4-posion to extent their conjugation system in order to lengthen their emission wavelength;moreover,water soluble groups were introduced to increase their water solubility in order to improve their practicapability.As a concenquence,we developed a series of new HBT fluorescent dyes having red emission,large Stokes shift and reasonable solubility.Based on the new HBT fluorescent dyes,several fluorescent probes were developed and applied in real samples.The main studies are as below:（1）Due to the short-wavelength emission and poor water solubility of the classical HBT,a series of new HBT fluorescent dyes were developed by introducing C=C bond to enlarge their conjugation systems at 4-postion and hydrophilic group to improve the water solubility of HBT dyes,which made them suitable for practical applications.The investigated HBT dyes exhibited relatively strong fluorescence signals both in solid state and in solution,large Stokes shifts（>200 nm）and long-wavelength emissions（>600 nm）.The excellent properties of the dyes allow them to be used to construct fluorescent probes for the detection of ions,molecules and biomolecules.（2）The current fluorescent probes for detection of SO₃^2-have the disadvantages of small Stokes shift,dual light source excitation,"off-on"detection,etc.Based on the newly developed HBT dyes,a fluorescent dye,HBTC-S,was served as a ratiometric fluorescent probe for the specific detection of SO₃^2-,which lead to weaken the intramolecular charge transfer（ICT）process.This probe exhibited low detection limit（0.15μM）,fast response（10 min）,large Stokes shift（214 nm）and single light source excitation.Probe HBTC-S was successfully applied to image of SO₃^2-in living cells and detect of SO₃^2-in real food samples.（3）There are few bifunctional fluorescent probes for simultaneously differentiation of H₂O₂ and SO₃^2-.A bifunctional and ratiometric fluorescent probe,HBTC-HS,was designed and synthesized via ESIPT and ICT mechanisms for the detection of H₂O₂ and SO₃^2-through dual-ratiometric manners.This probe emitted green fluorescent signals.Upon the treatment with H₂O₂,probe HBTC-HS displayed red fluorescence singals（ESIPT recovered）.The treatment of probe HBTC-HS with SO₃^2-resulted in the generation of blue fluorescence singals（ICT effect weakened）.This probe displayed excellent selectivity,high sensitivity and large Stokes shift.The simultaneous differentiation of H₂O₂ and SO₃^2-was achieved in solution and real food samples.（4）The fluorescent probes for detection of H₂S and SO₃^2-have the following disadvantages:（a）dual-wavelength excitation,（b）small Stokes shift,（c）“on-off”detection,etc.Based on the combination of ESIPT and ICT mechanisms,a ratiometric fluorescent probe HBTC-SS with a single wavelength emission and large Stokes shift was designed for H₂S and SO₃^2-.The azide moiety can respond to H₂S and the double bond servers as the recognition group for SO₃^2-.Probe HBTC-SS displayed two sets of distinct fluorescent singals in respose to H₂S and SO₃^2-,respectively,(blue for SO₃^2-,blue and green for H₂S).The simultaneous detection of H₂S and SO₃^2-was succesfully demonstrated in solution and food samples.（5）The fluorescent probe for the simultaneous and differentiated detection of F^-and SO₃^2-has not been reported.Two fluorescent probes,HBTC-PM and HBTC-ME,were synthesized using tert-butyldimethylsilane/tert-butyldiphenylsilane as the sensing groups for F^-and the C=C bond for SO₃^2-.The probes responded to F^-and SO₃^2-to give distinct fluorescent signals with good selectivity and high sensitivity.The applictioan of probe HBTC-ME in the detection of F^-and SO₃^2-was successfully demonstrated both in solution,real toothpaste and sugar samples.（6）Current fluorescent probes for the detection of biothiols have the disadvantages of short emission wavelengths and small Stokes shifts.Based on tetrahydroquinoxaline iminocoumarin,a fluorescent probe,THQS,was designed and synthesized for the detection of biothiols using2,4-dinitrobenzenesulfonyl ester as the recognition group.The probe reacted rapidly with biothiols to give off red fluorescence signal with a large Stokes shift（147 nm）.The detection limits of probe THQS for Cys,Hcy and GSH were calculated to be 15 n M,50 n M and 20 n M,respectively.This probe was successfully applied to the imaging of intracellular biothiols in living cells.