Stimuli-response Studies Of MOFs Based On Extend Bipyridinium And Tripyridinium

Stimuli-responsive materials are those that can detect their changes in physical/chemical properties when exposed to an external stimulus,it is a universal phenomenon in nature,especially in biological systems,and is the basis of modern science and technology.Metal-organic frameworks(MOFs)have become a hotspot in the field of materials due to their adjustable pores,structural diversity and stability The diversity come from the design of different organic ligands and second building units.The stimuli-response of MOFs can come from their inorganic/organic components,synergistic effect,or dynamic porous structure.Therefore,MOFs can provide diverse platforms for design of stimuli-responsive materials 4,4'-bipyridinium with redox properties are widely used as functional units for building chromic materials.Because it can generate radicals by electron transfer accompanied by color changes under light or pressure.In recent years,bipyridine units have been incorporated into MOFs,and its chromic properties,as well as its optical,electrical,magnetic,and sensory properties have been studied.However,there are few reports about MOFs based on extended bipyridinium/multipyridinium,and even there is little research on their optical properties.Here,we designed three ligands based on two extended bipyridinium units and tripyridinium units,and synthesized a series of functional MOFs and their stimuli-response have been reportedThe main content of this dissertation include the following two parts1.Synthesis,photochromism and sensing properties of MOFs based on extended bipyridinium-tetracarboxylic ligands(1)Three of MOFs([ML1]·2H2O,M represent 1-Zn,1-Mn,and 1-Co,respectively)were synthesized by utilizing metal ions and extend bipyridinium tetracarboxylic acid ligand([L1]2-,p-phenylenebis(1-[[3,5-dicarboxylatophenyl]methyl]pyrid-4-yl),[H4PhVTC]2-).Single-crystal X-ray diffraction reveals that 1-Zn/-Mn/-Co are isostructural two dimensional(2D)-layer-based MOFs.The 2D coordination network is formed by four-coordinated metal ions and four-linked ligands.Interestingly,Of the three isomorphic MOFs,only 1-Zn exhibits reversible photochromic properties.1-Zn showed reversible photochromic properties under the irradiation of xenon lamps,while the other two cases of MOFs did not show similar properties.ESR and UV-vis spectra show that 1-Zn generates radicals during photochromic processes,that is,MPhV2+accepts one electron to generate MPhV·+.Crystal structure analysis of three MOFs reveal that the distance of interlayer(C-H)pyrdinium…O interaction and ?-?stacking interaction between PhV2+and isophthalate moiety in 1-Zn are shorter than those of 1-Co and 1-Mn.This imply that slight changes in the distance between the electron donor and acceptor can have a great impact effect on photoactivity.In addition,1-Zn shows strong fluorescence owing to interligand charge transfer,and the fluorescence can be reversibly modulated and switched on/off in the photochromic process.Furthermore,1-Zn shows excellent hydrolytic stability and strong fluorescence in water.Investigated the effect of suspension of 1-Zn detection on metal ions.The experimental results show that 1-Zn can be used as a sensitive,selective,and recyclable fluorescence sensor for detecting Fe3+ in aqueous solution and the detection limit is about 0.92 ?M.(2)2-Zn([ZnL2]·4H2O)was synthesized from a flexible thiazolo[5,4-d]thiazole extend bipyridinium tetracarboxylic acid ligand(L2-=2,5-bis(l-(3,5-dicarboxylatobenzyl)pyridin-l-ium-4-yl)thiazolo[5,4-d]thi azole,[TTVTC]2-)and Zn2+.2-Zn and 1-Zn are isostructural 2D layer.The aqueous suspension of 2-Zn exhibits excellent stability and strong cyan fluorescence.Sensing experiments show that 2-Zn can be used as a chemsensor with selectivity,sensitivity and reproducibility to detect Cr(VI)(CrO42-and Cr2O72-)anions in aqueous solution,and its detection limits are 0.31(CrO42-)and 0.41 ?M(Cr2O72-),respectively owing to the excitation spectrum of the aqueous suspension of 2-Zn overlaps well with the absorption bands of CrO42-and Cr2O72-.The quenching effects at different ?ex can be seen from the plots of I0/I versus ?ex.The profiles of the plots are very similar to the absorption spectra of the corresponding Cr(VI)ions.That is,the excitation wavelength at which Cr(VI)(CrO42-or Cr2O72-)shows the strongest quenching of the anion.This provides unambiguous and compelling evidence that the quenching mechanism is predominated by competitive absorption.In addition,Fe3+ only causes relatively apparent quenching effects(38%)but still significantly weaker than those of Cr(?)anions for 2-Zn.The fluorescence of 1-Zn is almost completely quenched by Fe3+ ion,while the quenching effect by Cr(?)(CrO42-and Cr2O72-)ions is less than 30%.Density functional theory(DFT)calculations indicate that the difference in excitation wavelength is due to the conjugating core group of extended bipyridinium.Therefore,the excitation energy can be modulated by varying the core motif of the extended viologen to gain a better match between the sensor and the analyte.(3)A novel MOF,formulated as[Cd2(L2)Cl2(H2O)3]·2H2O(2-Cd)was synthesized from the ligand(L2-=[TTVTC]2-).Single-crystal X-ray diffraction analysis demonstrates that the six-coordinated Cd(?)ions are bridged by the isophthalate fragments to form a helical chain,either left-or right-handed.Each helical chain is connected to four others with opposite handedness through TTV2+moieties leading to a 3D structure.2-Cd exhibits reversible photochromic properties and it is the first photochromic MOF based on thiazolothi azole extended viologen.electron-spin-resonance(ESR)spectroscopy and UV-vis confirmed the generation of radicals in the process of photochromism.That is,TTV2+accepts an electron to generate TTV·+.According to the structural data,there are suitable electron transfer pathways in 2-Cd.It is the mutual interpenetration of the frameworks that enables the occurrence of elector transfer(carboxylate O and pyridinium N).XPS also confirmed electron transfer between carboxyl oxygen and pyridine nitrogen.Reversible photochromism and fluorescence quenching are in agree with the first-order kinetic process.The fluorescent quenching rate is in good agreement with the rate constant of the photochromic reaction estimated from optical absorbance,which means that photoquenching is synchronous with the photochromic reaction.So the fluorescence of 2-Cd can be modulable or switchable through photoirradiation.2.Synthesis and functionality of MOFs based on tris(pyridinium)-hexacarboxylate ligand(1)A MOF formulated as[Cd2Cl(L3)(H2O)]·11H2O(3-Cd)was constructed from a tris(pyridinium)-based hexacarboxylate zwitterionic ligand(L3-=2,4,6-tris(l-(3,5-dicarboxylatobenzyl)pyridinium-4-yl)pyridine).Each[L3]3-ligand is connected to six seven-coordinated Cd2+ions to form a 2D coordination network 3-Cd shows a novel fashion of 2-fold 2D?2D parallel entanglement and naked-eye detectable photochromic behaviors.ESR confirmed the formation of radicals and XPS showed that carboxyl oxygen serves as electron donor and pyridine nitrogen acts as electron acceptor in the process of photochromism.Single crystal structure analysis reveals that the short distance between carboxyl oxygen and pyridine nitrogen for electron transfer,as suggested by XPS.Besides,the photochromic behavior is accompanied by fluorescent quenching of 3-Cd.3-Cd shows excellently chemical stabilities can be used as a regenerable luminescent sensor for the detection of nitrofuran antibiotics in water,with low detection limits and high selectivity among other classes of antibiotics(2)A novel MOF formulated as[Zn3(L3)2]·18H2O(3-Zn)with the[L3]3-ligand was constructed.Single-crystal X-ray diffraction analysis of 3-Zn reveals 2-fold interpenetrated 3D frameworks with small irregular open voids.Each ligand binds six four-coordinated Zn(?)ions with its six carboxylate groups.The Zn(?)ions are connected with isophthalic moieties from different ligands to form a 44 layer.The 2D layers are interlinked by the tris(pyridinium)moieties to give a 3D structure.3-Zn shows distinct responsive behavior specific to amines and alcohols among a large range of volatile organic compounds.The MOF responds to some amines with a direct color change and to some alcohols with a UV photoassisted color change(that is,the alcohols makes the MOF photochromic).The chemophotochromism is essentially unexplored.ESR confirmed the formation of radicals during the process chemochromism(amine)and alcohol-specific chemophotochromism.The chemophotochromic reaction reveal a first-order kinetics.The different responses of 3-Zn to amines and alcohols can be related to their different electron donor abilities It is established that an aliphatic amine has stronger donor ability than an alcohol With various spectral techniques and DFT calculations revealed that the chemo-/chemophotochromic behaviors of 3-Zn are associated with radical formation through spontaneous/photoinduced guest-to-host electron transfer in a unique confined microenvironment with accessible electron-accepting pyridinium sites.Due to the small and irregular open voids of 3-Zn,it shows obvious size and shape selectivity for analytes during the chemo-/chemophotochromic process.The material has important implications for applications,Especially the dual-stimuli chemophotochromism can prevent false signalling,improve anti-interference.