Study On Optical Recognition And Sensing Properties Of Metalions By Acylhydrazone Photosensitive Azacrown Ether Chemosensors

In recent years,many methods for detecting metal ions have been studied and developed.Optical chemosensors have stand out in many methods to detect metal ions due to their several outstanding advantages including simplicity,rapidity,versatility,high sensitivity and high selectivity.The crown ether as a supramolecular has been utilized by designers of optical chemosensors,and the acylhydrazone Schiff base compounds with O,N atoms have excellent spectroscopic and pharmacological properties.Therefore,if the benzoazacrown ether ring with special recognition abilities was linked to the photosensitive group by the acylhydrazone chain,it was expected to prepare an optical chemosensor with specific selectivity and excellent photophysical performance.In this paper,three kinds of optical chemosensors based on crown rings-acylhydrazone-photosensitive groups have been synthesized using benzoazacrown ether rings as acceptors and acylhydrazone chains as linkers.In addition,their spectral recognition properties and analysis conditions for several important metal ions have been investigated by UV-vis and fluorescence spectroscopy methods.Moreover,the possible bonding modes and sensing mechanisms of these sensors with the identified ions have been studied by ¹H NMR titration,Infrared spectroscopy?IR?,mass spectrometry?MS?and density functional theory?DFT?calculations methods.The specific research works are as follows.1.In the second chapter,we have designed and synthesized salicylaldehyde-benzoaza-15-crown-5 acetylhydrazone?L1?.And the selective recognition properties of L1 have been tested in the presence of several important metal ions by UV-vis and fluorescence spectroscopy.The results showed that the sensor L1 exhibited unique specific selectivity for Al³⁺through a selective fluorescence enhancement effect in methanol,while other metal ions were not found the significant interference of spectral response for Al³⁺.The binding constant?K_s?of L1-Al³⁺complex was determined to be5.56×10⁹±8.19×10⁷ M^-2,the detection limit reached at 0.24?M,and the linear range was about 0³.95×10^-55 M,and the binding stoichiometries were2:1,which were obtained by the fluorescence titration,Job's plot,and MS spectra.The reversibility experiment demonstrated that the complexation process of L1 to Al³⁺was chemically reversible,which showed the reliability and regenerative capacity of the sensor.The bonding mode and sensing mechanism of L1-Al³⁺complex were investigated by ¹H NMR titration,IR spectra and DFT/B3LYP quantitative theoretical calculation methods.It was speculated that L1 may chelate Al³⁺through interactions with the O atom of the amide carbonyl,the N atom of the imine group and the O atom of phenolic hydroxyl group by the results of the experimental measurements and theoretical calculations.This bonding mode inhibited the C=N isomerization and excited state intramolecular proton transfer?ESIPT?process and produced a strong chelation-enhanced fluorescence?CHEF?effect.The various sensing processes all led to the fluorescence enhancement phenomenon of the sensor L1 with Al³⁺.2.In the third chapter,we have synthesized p-hydroxybenzaldehyde-benzoaza-15-crown-5 acetylhydrazone?L2?.The recognition properties to some important metal ions were investigated by UV-vis and fluorescence spectroscopy.The results indicated that the addition of Cu²⁺reduced the absorption of L2 and resulted in a significant blue shift,and the fluorescence intensity of L2 was strongly enhanced,but other competitive ions had no such similar selective spectral response.According to the linear fitting of UV-vis spectra,the detection limit of L2 for Cu²⁺was 3.0402×10^-6 M,the binding constant?lg K_s?was 2.12×10⁴±2.28×10² M^-1 and the linear range was0⁵5.707?M.According to the linear fitting of fluorescence spectra,the detection limit was 4.8696×10^-6 M,the binding constant?lg K_s?was 1.59×10⁴±3.51×10² M^-1 and the linear range was 16.712?M⁹5.499?M.Moreover,the reversibility experiment by adding Na₂EDTA proved that the sensor L2exhibited chemical reversibility upon binding with Cu²⁺.The results of Job's plot and MS spectroscopy demonstrated the 1:1 binding stoichiometry of L2with Cu²⁺.Furthermore,the bonding mode and sensing mechanism of L2-Cu²⁺complex were determined through ¹H NMR titration,IR spectra and DFT?TD-DFT?/B3LYP quantitative theoretical calculation methods.The results of various experiments showed that the binding sites of L2 with Cu²⁺may be N atom of the imine,N and O atoms of azacrown ether ring.This bonding mode inhibited the intramolecular charge transfer?ICT?process of sensor L2 and produced the effective chelation-enhanced fluorescence?CHEF?effect,which resulted in a significant increase in the fluorescence of L2 with Cu²⁺.3.In the fourth chapter,sensor 6-methyl-4-formaldehyde-coumarin-benzoaza-15-crown-5-acetyl hydrazone?L3?have been developed.The recognition performance of L3 for common important metal ions was studied by UV-Vis and fluorescence spectroscopy.The experimental results showed that L3 exhibitd a specific selective recognition for Cu²⁺in methanol,but other competitive ions didn't cause significant interference on the identification of Cu²⁺.According to the linear fitting of UV-vis spectra,the detection limit of L3 for Cu²⁺was 6.0016×10^-7 M,the binding constant?K_s?was about 2.73×10⁴±6.32×10² M^-1,and the linear range was 0³3.124?M.According to the linear fitting of fluorescence spectra analysis,the detection limit was 5.8474×10^-7 M,the binding constant?K_s?was 2.07×10⁴±4.49×10²M^-1,and the linear range was 6.445?M⁸6.605?M.The sensing process of L3 with Cu²⁺was chemically reversible by reversibility experiments.Moreover,binding stoichiometry of L3-Cu²⁺complex was determined to be1:1 through Job's plot,MS spectra.The binding mode and sensing mechanism of L3-Cu²⁺complex were analyzed by ¹H NMR titration and IR experiments,and the results demonstrated the L3 may chelate Cu²⁺with the N atom of imine,the O atom of coumarin carbonyl and the O and N atoms of azacrown ether ring.The results of various experiments showed that the coordination of L3 with Cu²⁺increased the structural rigidity of the complex,inhibited the photoinduced electron transfer?PET?process,and produced CHEF effect,resulting in an increase in the fluorescence intensity of L3.