| Metal-organic Framework?MOFs?,also known as porous coordination polymer?PCP?,is a new kind of material which is self-assembled under certain conditions by metal ions and Organic ligands.Its outstanding porosity,specific surface area and modificability have made it widely used in hydrogen storage,catalysis,fluorescence sensor,drug delivery,magnetism,gas adsorption and separation.In recent years,although fluorescent sensors based on MOFs have made great progress in the detection of ions,aromatic hydrocarbons,and volatile organic compounds,they still face problems such as poor sensor selectivity,poor sensitivity,and single detection object,which prompted people to build new MOFs material and developed them into a high-performance and multi-detection fluorescence sensor.It is found that the self-assembly site of multiple acid,multiple imidazole ligands and metal salts could not only give full play to the coordination ability of ligands,but also adjust the MOFs structure,so as to effectively improve its recognition performance.In this study,a series of MOFs were prepared based on the self-assembly sites of the mixed ligands of polyimidazole and polycarboxylic acid and metal ions under hydrothermal conditions,and their fluorescence properties were studied.The main contents of the study are as follows:First,three MOFs were synthesized by flexible hydrocarbyl-substituted diimidazole and dicarboxylic acid ligands under hydrothermal conditions,namely{Co2?Bbi?2?A?2·H2O}n?1?,{Co?Bbi??B?2·4H2O)}n?2?and{Cd6?Bbi?1.5?L?6·5H2O}n?3?,{Bbi=1,1?-?1,4-butanediyl?bis?imidazole??H2L=anthracene-9,10-endo-succinic acid,H2A=4,4'-oxybisbenzoic acid,H2B=1,2-diethyl ether-4,4'-dibenzoic acid?.1 constituted a double interspersed cds topology network with Schlafli symbol{65·8};2 formed a larger 3D channel,showed a 4-connected network structure with Schlafli symbol{44·62};the structure of 3 exhibited a rare six-core Cd cluster,and the Schlafli symbol is{42·6}2{43·103}{43·6·82}{43·63}{44·62·62}2{45·62·82·10}{46}4.Fluorescence spectroscopy analysis showed that in acetonitrile solution,1-3 revealed highly selective and cyclic fluorescence quenching response to magnesium nitrate,with detection limit of at least 7.1?M.The recognition mechanism may be due to the partial overlap between the excitation spectra of compound 1-3 and the absorption spectra of magnesium nitrate.Second,used 2,3,5,6-?4-carboxyl-tetraphenyl?pyrazine?H4TCPP?and Tri-?4-imidazyl?phenylamine?Tipa?as ligands,MOF({Co?TCPP?0.5?Tipa?}n?4?was self-assembled with cobalt nitrate under hydrothermal conditions.Crystal structure analysis showed that 4 can be simplified as a new topology of 3-connected nodes,and the Schlafli symbol is{42·6}2{42·84}{43·6·86}2.4 showed excellent fluorescence performance in water,and can be further developed into a dual-function fluorescent sensor with high selectivity and high sensitivity detection capability for ferric ions and picric acid?TNP?,with detection limits up to 0.098?M and 0.326?M.The mechanism study confirmed that the fluorescence quenching of 4 caused by iron ions or picric acid can be attributed to the competition of guest ions or molecules with the subject to absorb excitation energy.Third,through 2,3,5,6-?4-methylene-1-imidazolylphenyl?pyrazine?TIPP?,simple dicarboxylic acids and metal salts are loaded autonomously under hydrothermal conditions,and three MOFs were successfully prepared,{(Mn2?TIPP??C?2·2H2O}n?5?,{Co?TIPP?A}n?6?and{Co?HCOO??TIPP?·H2O}n?7?(H2A=4,4'-Oxybisbenzoic acid,H2C=1,4-naphthalenedicarboxylic acid}.5 can be regarded as a 2-connected 3D framework,and forms a new topology symbol{416·612}{44·62};6 can be simplified into a single-node network structure,and the Schlafli symbol is{32·62·72};7 can be described as a 2-node network structure with a Schlafli symbol of{42·84}.Through fluorescence performance research,it was found that 5-7exhibited excellent fluorescence emission in water,and revealed excellent selective fluorescence response to Cu2+,Cr3+,MnO4-and nitro explosive TNP,and may be developed into a fluorescent sensor with multiple detection functions.5 showed low detection limits for Cu2+,Cr3+,MnO4-and TNP in the aqueous phase,which were0.11,1.16,0.04 and 0.2?M,respectively.The mechanism study showed that the significant fluorescence response of 5 to Cu2+and Cr3+ions may be attributed to the weak force between the exposed N and O in the structure and Cu2+or Cr3+ions.The competition between MnO4-ion or TNP and 5 absorbed the excitation energy,which led to the quenching of fluorescence.In addition,5 could be used as a logic?Logic?gating sensor for the detection of Cu2+/Cr3+. |
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