Design And Synthesis Of Functionalized Dual-emitting Metal-Organic Frameworks/Complexes For Fluorescence Hydrogen Sulfide Sensing

As a vital signaling molecule,hydrogen sulfide（H₂S）is often used in physiological processes of biological systems with carbon monoxide（CO）and nitric oxide（NO）.Abnormal level of H₂S is also associated with many physical diseases,for example,Alzheimer’s,diabetes,and even cancers.Because of its important physiological role,designing an effective and convenient sensor to monitor H₂S is in demand.The fluorescent probe has many advantages,such as simple operation,high sensitivity,fast response and strong anti-interference ability.Among them,the ratiometric fluorescence sensor overcomes the deficiency that the based on single fluorescence intensity is susceptible to environmental factors,and has the advantages of self-calibration and high sensitivity,becoming a research hotspot.Complexes are a kind of compound formed by a central atom or ion（metal）and a surrounding array of bound molecules or ions（ligand）via various interactions.Metal-organic Frameworks（MOFs）,as a significant branch of complexes,are self-assembled by inorganic metal nodes or clusters and organic ligands through coordination bonds,which have one-dimensional,two-dimensional and three-dimensional organic-inorganic hybrid materials.With the development of MOFs/complexes,the demand for functionalized MOFs/complexes materials is increasing through functional modification of organic ligands or metal sources.Luminescent MOFs/complexes have been widely used in the H₂S small molecule sensing field due to their high designability and excellent luminescent properties.In this paper,based on luminescent MOFs/complexes,the radiometric fluorescence sensor with fast response,high sensitivity and selectivity was designed by functional modification for the target analyte H₂S to be detected.Based on vinyl functionalized terephthalic acid（H₂BCC-CH=CH₂）,a novel three-dimensional metal-organic framework Eu-BDC-CH=CH₂ with fcu-topological structure was constructed by solvothermal method with Eu³⁺.The vinyl groups in the ligands can not only modulate the“antenna effect”of the ligand on Eu³⁺but also serve as the exposed reactive sites to allow for the quantitative detection of H₂S by Eu-BDC-CH=CH₂.The ratiometric fluorescent probe has the advantages of water stability,acid-base stability（p H=2-11）,fast response（<2 min）,high selectivity and sensitivity（LOD=38.4μM）.We also used Eu-BDC-CH=CH₂ to detect and analyze H₂S in tap and lake waters,demonstrating the potential of the probe for biological and environmental applications.In addition,the MOF-based agarose hydrogel film allows for visual detection of H₂S via a smartphone by identifying the RGB values.The vinyl-functionalized MOF can thus be a sensing platform for H₂S.Based on nitro functionalized 2-nitroterephthalic acid（H₂BDC-NO₂）,a nanoscale Zr-MOF Ui O-66-NO₂ with good chemical stability was synthesized by the solvothermal reaction.Because of the electron-wthdrawing of the-NO₂ group,the surface of Ui O-66-NO₂ has a negative electric potential.The cationic dye Rhodamine B（RB）is encapsulated into the pores of the main framework by the charge action,and the host-guest material RB@Ui O-66-NO₂ is obtained.RB@Ui O-66-NO₂ shows dual-emission of ligand and RB,and its fluorescence changes in the presence of H₂S are studied.Steady-state fluorescence titration showed that in the presence of H₂S,ligand luminescence was enhanced as a response signal,while RB luminescence no change as a reference signal.The ratiometric fluorescence specificity detection of H₂S was realized,which provides a good idea for the design of a functional H₂S sensor.A chemical stable metal supramolecular coordination complex Znpda,engineered from the multi-coordination ligand 1,10-phenanthroline-2,9-dicarboxylic acid（pda）is developed and served as the host frameworks to encapsulate the Eu³⁺and Cu²⁺cations,forming the dual-emitting hybrid composite,which can be attributed to the Cu²⁺ion blocking the"antenna effect"of the ligand and Eu³⁺.With the formation of Cu S,the"antenna effect"between the ligand and Eu³⁺recovered,resulting in Eu³⁺fluorescence enhancement in Eu³⁺/Cu²⁺@Znpda.Accordingly,we designed an IMPLICATION logic gate for H₂S recognition by employing the fluorescence intensity ratio between the ligand and Eu³⁺as the output signal.Moreover,the Eu³⁺/Cu²⁺@Znpda exhibits fast response（<1min）and high sensitivity（1.45μM）to H₂S over the interfering species in the HEPES buffer solution,highlighting its potential use for H₂S sensing under environmental and biological conditions.