Research On The Synthesis And Sensing Properties Of Three Kinds Of Schiff-base Based Metal Ion Fluorescence Probes

A large number of organic molecule-based fluorescence sensors have been reported in the past decades.The mechanisms of fluorescence sensing have also been explored in depth.Fluorescence probes based on Schiff-base structure are widely used in the field of detecting cationic,anionic,organic,organometallic compounds and cell imaging due to their facial synthesis and low cost.However,there are still some room for improvement in water solubility,selectivity and limit of detection.In view of the above shortcomings,three kinds of fluorescent probes for Al³⁺and Zn²⁺based on the Schiff-base structure were designed and synthesized,and their detection performance for metal ions have been studied.Firstly,a facile water-soluble fluorescence sensor 2-??2-hydroxybenzylidene?amino?-2-?hydroxymethyl?propane-1,3-diol?ST?was synthesized via one-step reaction,and the sensing performance for Al³⁺was evaluated in aqueous solution as well as on paper substrate.Upon addition of Al³⁺,the fluorescence emission at 459 nm increased sharply,exhibiting a specific fluorescence OFF-ON response to Al³⁺without the interference from other cations.Besides,the performance of ST was tested in tap water and it also could be made into test paper.The limit of detection was found to be 3.2×10^-7 M,which revealed that ST had a high potential for the rapid,quantitative and qualitative detection of Al³⁺.Secondly,a dual functional water-soluble fluorescence sensor 2-???2-??2-hydroxyethyl?amino?ethyl?imino?methyl?phenol?SA?was easily obtained via a one-step condensation reaction between commercially available 2-?2-aminoethylamino?ethanol and salicylaldehyde with high yield.SA could be utilized in detecting Zn²⁺and Al³⁺in aqueous.The addition of Zn²⁺and Al³⁺to SA all showed sharp enhancements of the fluorescence emission intensities?458 nm and 376 nm,respectively?,while exhibiting negligible disturbance against typical competitive ions such as Fe³⁺,Cr³⁺,Hg²⁺and Cd²⁺.However,the detection process for Zn²⁺was interfered by Al³⁺.We achieved the detection of Zn²⁺and Al³⁺without bothering by screening different buffer solution and masking agent.This phenomenon indicates that SA may be helpful for swift and effective detection for Zn²⁺and Al³⁺in aqueous solution.The limit of detection for Zn²⁺and Al³⁺were6.4×10^-7 M and 6.1×10^-7 M,respectively.Moreover,the performance of SA was tested in tap water.Finally,a bipyridine derivant-based fluorescence probe N'⁴,N'''^4'-bis?2-hydroxybenzylidene?-[1,1'-biphenyl]-4,4'-dicarbohydrazide?LBD?was designed and synthesized via a facile one-pot reaction,and LBD exhibited a specific detection performance toward Al³⁺,which can be seen both in UV-Vis and fluorescence spectra.A significant turn-on fluorescence response of LBD at 500 nm and an apparent fluorescence emission variation from non-fluorescent to strong bright cyan were observed by naked eye due to the inhibited C=N isomerization and photo-induced electron transfer?PET?in LBD after the addition of Al³⁺.Bipyridine is a kind of excellent ligand,which can be combined with a variety of metal ions.The detection of trace amounts of metal ions can be achieved by the strategic introduction of bipyridyl groups in fluorescent probes.The detection limit of LBD was found to be 9.0×10^-9 M.The performance of LBD was also tested in tap water.