| The optical chemosensor, having wide applications in biomedicine, environmental detection and chemical analys, was a kind of molecular device which indicated the recognition information toward target molecules by means of outputting the optical signal. The synthesis and property study of optical chemosensors was still of considerable interest in the field of supramolecular chemistry in twenty-first century. Design and synthesis of optical chemosensors with excellent performances was mainly determined by whether we could choose proper connectors, photosensitive groups and acceptors for sensors or not. The azacrown ether group served as an ideal sensor receptor because of its good selectively complexing ability with metal ions; the coumarin fluorophore was a good kind of photosensitive group for the preparation of sensors owing to its larger Stokes shifts, adjustable photophysical and photochemical properties; when a coumarin fluorophore was attached to the crown ether ring by an appropriate linker, it was expected to prepare an optical chemosensor with specific selectivity and excellent sensing property.To help investigate the selective recognition properties and sensing performances which were affected by each part of the group in the structure of crown ether-based sensor molecules, in this paper, two kinds of photosensitive crown ethers and their relevant fragment molecules were designed and synthesized:7-Hydroxy-4-methyl-8-[p-phenylaza-15-crown-5-acryloyl]coumarin(2-L1) and the fragment molecule 7-Hydroxy-4-methyl-8-[p-dimethylaminobenzacryloyl]coumarin(2-L2),6-[p-aza-15-crown-5-benzalaminoylene]coumarin(3-L3) and the fragment molecule 6-[(p-dimethylaminobenzalaminoylene]coumarin(3-L4). They were characterized by melting point determination,1HNMR, elemental analysis and mass spectrometry techniques. We investigated their selective recognition and sensing mechanism with metal ions by UV-vis and fluorescence spectroscopy methods. This paper employed a method of Synthesizing crown ether molecules while synthesizing fragment molecules, and a method of studying the bonding sensing mechanism through spectrometric comparison experiments, which was a try and characteristic of this paper. Specific studies are as follows:1. In the second chapter, spectral behaviors of the crown ether 2-L1 and its fragment molecule 2-L2 in different solvents were tested firstly. Upon this, DMSO-H2O(v/v= 4/1) mixed solvent was chosen to test their spectral behaviors. By UV-Vis and fluorescence spectroscopy methods, we also investigated the spectral response behaviors of compounds 2-L1 and 2-L2 with the change of solution pH in DMSO-H2O (v/v= 4/1) mixed solvent. Herein, the appropriate pH value system was selected. Next the selective recognitions and sensing properties of compounds 2-Ll and 2-L2 in DMSO-H2O (v/v= 4/1) mixed solvent toward 14 kinds of common metal ions were studied. Meanwhile, the differences of selectivities and sensing properties of 2-L2 fragment molecule in absolute ethanol were tested. The result indicated that UV-vis and fluorescence spectra of compound 2-L1 shown a special selectivity for H+; the jump range of pH values given by the spectral changes was 9.18?10.74 for 2-L1, and that was 5.0-8.25 for 2-L2. Under the condition of an acidic environment beyond the jump range of pH values as well as pH values of a higher fluorescence sensitivity, we researched the selectivity for metal ions of these two compounds. The results shown that compound 2-L1 has a specific selectivity to Al3+. In the presence of Al3+,2-Ll displayed a new absorption peak at 526nm and a new fluorescence peak at 610 nm. However,2-Ll could only identify Hg2+ at pH 7.6. With the increase of Hg2+ concentration, a concomitant red shift in the UV-Vis absorption peak of 2-Ll from 409 nm to 485 nm was observed along with an increase in the absorption intensity. Similarly, the fluorescence peaks of 2-Ll generated a red shift from 508 nm to 595 nm gradually upon the gradual addition of Hg2+. The UV-visible and fluorescence spectra of fragment molecule 2-L2 both exhibited a spectral recognition to Mg2+ and Hg2+ at pH 5.0. These two ions both reduced a decrease of absorption peak at 393 nm and the appearance of a new absorption peak at 467nm and 484 nm respectively in UV-Vis spectrum of 2-L2. Mg2+ induced a red shift of the fluorescence peak of 2-L2 from 520 nm to 555 nm, and Hg2+ induced the generation of a new fluorescence peak at 610 nm of 2-L2.The binding stoichiometries of 2-L1 with Al3+ and Hg2+,2-L2 with Mg2+ and Hg2+,which were obtained by the linear fitting of spectroscopic titration datas using Benesi-Hildebrand equation, were 1:1, respectively.2-L2 produced spectral responses to Cu2+, Mg2+ and Al3+ in ethanol, indicating that the change of solvents could cause large changes in selectivity of 2-L2. From the molecular structures and selective differences of 2-L2 and 2-L1, we preliminarily deduced that the variation in peak position and intensity of the absorption spectra and fluorescence spectra were roughly in accord with the ICT and PET sensing process. The results shown that 2-L1 was an excellent optical chemosensor for Al3+ and Hg2+ under different pH values, and 2-L2 could also be used as a fluorescent probe for Mg2+ and Hg2+ under acidic conditions. Otherwise,2-L2 had a significant fluorescence detection signal for Cu2+ Mg2+ and Al3+ at different wavelengths in absolute ethanol, respectively.2. In the third chapter, The selective recognition and sensing properties of 3-L3 and 3-L4 for 14 kinds of common metal ions in THF-methanol(v/v= 9:1) mixed solvent were investigated by spectral methods. The experimental results indicated that the fluorescence intensity of compound 3-L3 located at about 509nm increased dramatically in the presence of Ni2+ and Al3+.The addition of Mg+ efficiently enhanced the fluorescence intensity of compound 3-L3 centered at about 459nm. The characteristic absorption peak displayed a blue shift from 362nm to 334 nm upon addition of Al3+ in UV-Vis spectra of compound 3-L3. The results of the linear fitting by Benesi-Hildebrand equation indicated that the binding stoichiometry of 3-L3 with Ni2+, Al3+or Mg2+ was 1:1,1:2 or 1:2 respetively. In THF-methanol(v/v= 9:1) mixed solvent of compound 3-L4,the fluorescence intensity at 507 nm was enhanced by Ni2+.The peak position and intensity of the absorption spectra as well as the fluorescence intensity changed to some degree upon the addition of Al3+. The results of the linear fitting by Benesi-Hildebrand equation indicated that the binding stoichiometry of 3-L4 with Al3+ or Ni2+was 2:1 or 1:1 respectively. From the molecular structures and selective differences of 3-L3 and 3-L4, we preliminarily deduced that the variations in peak position and intensity of the absorption spectra and fluorescence spectra were basicly in line with the ICT, PET and C=N isomerization sensing process. |
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