Studies On The Fluorescent Probes Of Aromatic Aldehyde Schiff Base For The Metal Ions Detection

Due to the development of industry and the changes in farming practices,metal ion pollutants have posed a great threat to human health and environment in today’s society.Therefore,for human health and environmental governance,the need for specific and sensitive detection of metal ions have received considerably attention.In this regard,various technologies and methods have been adopted to detect metal ions,including flame atomic absorption spectrometry,inductively coupled plasma emission spectroscopy,X-ray fluorescence spectroscopy,and inductively coupled plasma mass spectrometry.However,most of them normally require expensive equipments,lengthy time during the sample preparation,and the experienced operators with advanced data analysis skills.Recently,fluorescent chemical sensor has been devolped as a good method to metal ion detection due to its high selectivity,sensitivity,cheap and easy operation.Among many materials,Schiff base is regarded as a class of ideal compound as fluorescent probes for metal ions detection because of its simple synthesis and the lone-pair electrons on the N atom of the imine group.Based on the structural features of aromatic aldehyde Schiff base,three new fluorescent probes for detecting metal ions were designed and synthesized.The main research work and results are as follows:1.Firstly,the structure and response mechanism of fluorescent probes are introduced.Secondly,the research progresses of Schiff base as fluorescent probes in recent years are summarized.Finally,the research background and the significance of this paper are briefly summarized.2.A Schiff base fluorescent probe,namely L1,was synthesized using salicylaldehyde and semicarbazone.L1 is selective for Cu²⁺ion in a 10 m M,p H=7.0,PBS:ethanol 99:1（v/v）system,exhibiting a"turn off"response.It is selective for Mg²⁺ion in acetonitrile solution,exhibiting a"turn on"response.For L1,we also further studied its anti-interference ability to other ions for the selectivity of Cu²⁺and Mg²⁺.According to Job’s plot curve,ESI-MS spectrum,Benesi-Hildebrand curve,etc.,we got that the molar binding ratios of L1 to Cu²⁺and Mg²⁺are both 1:1,the binding constants are 8.58×10⁴M^-1 and 1.35×10⁵ M^-1,respectively.For Cu²⁺and Mg²⁺ions,the detection limit was found to be 40.5 nm and 9.5 nm,respectively.The interaction of L1 with Cu²⁺and Mg²⁺were characterized by UV-visible absorption spectra.The coordination mode between L1and Cu²⁺and Mg²⁺were investigated by ¹H NMR and IR spectra.Finally,L1 was successfully used for the detection of Cu²⁺and Mg²⁺in real water samples.3.A Schiff base fluorescent probe（L2）was prepared through the reaction of naphthol（2-hydroxy-1-naphthaldehyde）and o-phenylenediamine.L2 displays a high selectivity for Al³⁺in acetonitrile solution,and exhibits a"turn on"response.Based on the results of Job’s plot curve,ESI-MS spectrum and the Benesi-Hildebrand curve,we found that the molar binding ratio of L2 to Al³⁺is 1:1,with the binding constant and the detection limit of 1.41×10⁵ M^-1 and 5 n M,respectively.The ion interference test showed that L2 has a strong anti-interference ability for the detection of Al³⁺.Subsequently,the interaction between L2and Al³⁺has been studied by UV-visible absorption spectrum.The coordination mode between L2 and Al³⁺was analyzed by ¹H NMR and IR spectra.Finally,we carry out an applied study to detect the Al³⁺in real water samples.4.A Schiff base dual ion fluorescent probe（L3）for detecting Cu²⁺and Zn²⁺was synthesized from naphthol（2-hydroxy-1-naphthaldehyde）and 2-aminobenzothiazole.L3can be used for high sensitive and selective detection of Cu²⁺and Zn²⁺in different solvent systems,respectively.More concretely,L3 has a specific response to Cu²⁺in H₂O:ethanol（9:1,v/v）solution with a"turn off"mode.However,L3 has a specific response to the detection of Zn²⁺with a"turn on"mode in the ethanol solution.According to Job’s plot curve,Benesi–Hildebrand curve and other studies,it can be calculated that the molar binding ratios of L3 to Cu²⁺and Zn²⁺is 1:1 and 2:1 respectively.Their binding constants are determined to be 1.62×10⁵M^-1 and 1.34×10² M^-1/2,with the detection limits of 85.5n M and 3.33 n M,respectively.Furthermore,the interactions of L3 with Cu²⁺and Zn²⁺were studied by UV-visible absorption spectrum,and the binding modes of L3 with Cu²⁺and Zn²⁺were also predicted.Finally,this probe was used for the detection for Cu²⁺and Zn²⁺in real water samples with the satisfied results.