Synthesis Of Novel Schiff Base Chemosensors And Studies On Their Properties For Selective Recognition Metal Ions

The optical chemosensor,having wide application in biomedicine,environmental detection and chemical analysis,is a kind of molecular device which indicate the recognition information toward target molecules by means of outputting the optical singal.The synthesis and property study of optical chemosensors are still the hotpots in the field of supramolecuar chemistry.The optical chemosensor Schiff base chain has good selectivity and novel bonding mechanism,and the difficulty in preparation is relatively small,even if some simple photoactive groups are introduced into the molecule,it is also possible for some specific ions or molecules show excellent sensitivity.In this paper,Schiff base chain such as hydrazone or acylhydrazone is used as the linker.Photoactive groups such as coumarin derivatives,phenolic derivatives and nitrobenzene derivatives are used as the spectral signal system.Part of synthesized compounds select crown ether ring as a capture body.Preparation of coumarin hydrazone derivatives without caputer ring and crown ether-containing hydrazone derivatives with capture ring are total two kinds of seven kinds of photochemical sensor moleculars.Seven kinds of sensor compounds are synthesized and characterized by melting point,¹H-NMR,elemental analysis.The selectivity and sensing mechanism of various metal ions are investigated by UV-Vis and fluorescence spectroscopy.The second chapter of this paper synthesized p-dimethylaminobenzalde-hyde-2-（4′-methylcoumarin-7′-oxy）acetylhydrazone（2-L1）,2,4-dihydroxy benzaldehyde-2-（4′-methylcoumarin-7′-oxy）acetylhydrazone（2-L2）,4-dihydro xybenzaldehyde-2-（4′-methylcoumarin-7′-oxy）acetylhydrazone（2-L3）,4-hydr oxybenzaldehydeα-naphthylamine（2-L4）and 6-methyl-4-formaldehyde coumarin-4-nitrophenylhydrazone（2-L5）,and investigated the spectral fluorescence spectrum methods.The results of UV-Vis spectroscopy showed that 2-L1,2-L2,2-L3,2-L5 have no selectivity to the measured metal ions;2-L4 only behave apparent response to Al³⁺.Fluorescence spectroscopy show that 2-L1 and 2-L2 are selective for Al³⁺and the spectrum of 2-L1 is significantly enhanced at 380nm when added Al³⁺,2-L2 fluorescence spectrum at 415nm fluorescence enhancement of about 15 times,2-L2 has a higher sensitivity compared with 2-L1;2-L3 is selective for Cu²⁺and the fluorescence at 375nm is significantly decreased by the addition of Cu²⁺;2-L4behave obvious recognition and sensing behavior to Al³⁺,Pb²⁺and Tb³⁺,and the fluorescence spectrum at 420nm is significant enhanced by Al³⁺,Pb²⁺and Tb³⁺;2-L5 has no selectivity to the measured metal ions.In order to study the selective performance ofcrown ether to metal ions,thethirdchapterofthispapersynthesizedHydrazone4-（N-aza-15-crown-5）benzaldehyde-4-nitrophenylhydrazone（3-L1）,4-（N-aza-15-crown-5）benzaldehyde-2,4-dinitrophenylhydrazone（3-L2）,investigated the spectral behavious under many kinds of metal ions(K⁺,Ba²⁺,Ca²⁺,Cu²⁺,UV-Vis and fluorescence spectrum methods.The experimental results show that UV-Vis spectrum of compound 3-L1 only behave apparent response to Cu²⁺,and the absorption peak at 433nm after adding Cu²⁺are significant reduce,the binding ratio of crown ether 3-L1 to Cu²⁺is 1:2,and lg K_s is 9.5;3-L2 only behaved response to Cu²⁺and Al³⁺,the binding ratio of crown ether3-L2 to Cu²⁺is 1:2,and lg K_s is 8.6;the binding ratio of crown ether 3-L2 to Al³⁺is 1:1,and lg K_s is 3.1.Cu²⁺can make 3-L1 and 3-L2 ethanol solution change from yellow to colorless,so 3-L1 and 3-L2 can used as Cu²⁺highly efficency selective colorimetric chemical sensors.