Synthesis And Properties Of Bipyridinium Functionalized Zr-metal-organic Frameworks

Metal-organic frameworks?MOFs?are a newly porous coordination materials builtof metal-based nodes and organic linkers.Thanks to the combination of crystal init y,porosity,diversity and tailorability in structure and properties,MOFs have been vigorously explored as versatile platforms for materials design relevant to many applications.The extraordinary properties of viologen compounds?1,1?-disubstitued-4,4?-bipyridiniums?have been widely used in many different fields that span from photo-/electro-/bio-chemistry and catalysis which mainly based on its ability to undergo reversible redox chemistry giving rise to differently colore change.In addition,the bipyridylium compounds can form radicals through electron transfer under the external stimulus,or form a charge transfer complex with an electron-rich species through charge transfer interaction.Therefore,incorporating the electron-deficient bipyridini um with the pore structures of MOFs is a nice strategy to design multifunction MOFs.In this work paper,two N-alkylated cationic electron-deficient MOFs?IMOFs?were designed and synthesized,which show good potential applications in ion-/photochromism,fluorescence and the detection of amines.The dissertation includes the following three parts:1.Siynthesis and ion-exchange,ion sensing properties of multifunction IMOFs?1?Two cationic electron-deficient IMOFs,UiO-67-MQ-TfO and UiO-67-DQ-TfO,were synthesized through post-synthetic modification.Zirconium-based MOF UiO-67-bpy was synthesized from ZrCl₄ and 2,2'-bipyridyl-5,5'dicarboxylic acid.It was N-alkylated with methyl trifluoromethanesulphonate and bis?trifluoromethanesulfona te?ethylene glycol,respectively,and the 2,2'-bipyridine units become N,N'-dimethyl and N,N'-ethylidene bipyridylium cation unit?MQ and DQ?,respectively.And the trifluoromethanesulfonate?TfO^-?as a counter ion.IR,NMR,XRD,BET,TGA,etc.were tested on two materials,and the NMR suggested that the ratio of N-alkylatio n were 88%and 65%.?2?Both materials have reversible ion exchange properties and exhibit differe nt colore change and fluorescence response for different anions.UiO-67-DQ-TfO has different degrees of colore change after exchange with Br^-,SCN^-and I^-,and no color change was discerned for the exchange with Cl^-,NO₃^-,SO₄^2-and ClO₄^-.UiO-67-MQ-TfO only undergoes color change when exchange with SCN^-and I^-.The color change accompanied by a new visible region absorption in the ultraviolet-visible spectrum,and there was a Miliken linear relationship between the corresponding band gap and the redox potential.These phenomena suggest that the interactions are more than simple interionic electrostatic forces but include CT from electron-rich anions to electron-deficient DQ²⁺.The difference of DQ²⁺and MQ²⁺is that the approximate coplanar structure in DQ²⁺and hence the electron-accepting LUMO is lowered to the advantage of CT.UiO-67-DQ-X exhibit photochromism properties after ion-exchange.Ultraviole t-visible spectroscopy and electron paramagnetic resonance X-ray diffraction suggested that it is prone to form the DQ^·+radical through photoinduced electron transfer?PET?.For comparison,the UiO-67-MQ-X series show much weaker response to photoirradiation,and it is mainly due to that the twist of MQ leads to a higher LUMO and is disadvantage of PET.In addition,the ionic MOFs also show changes in luminescence in response to ion exchange and photoirradiation.Spectral analysis show that it is due to resonance energy transfer from the luminescent frameworks to the CT complex or free radicals.?3?Based on the above research results,the fluorescence sensing properties andsolvent effects of materials on iodide ions were studied.UiO-67-DQ can be used to prepare test papers and realize the colorimetric discrimination of different anions.Completed chemical simulation from simple logic gates to complex integrated logic circuits.2.Response and sensing performance of electron-deficient IMOFs to alkylaminesAmines are important substances having wide applications,however,it is also acommon pollutant,which is a serious threat to human health and the ecologica l environment.Therefore,the detection of amines has attracted more and more attention.Due to the electron-deficient properties of UiO-67-MQ-TfO and UiO-67-DQ-TfO,they can be applied to the detection of electron-rich alkylamines.?1?UiO-67-MQ-TfO and UiO-67-DQ-TfO show marked and reversible color change immediately in different alkylamines?within 1s?.Both have a weak and slow response to aniline,no response to non-amine volatile organic compounds?VOCs?.This is attributed to the stronger electron-donating ability of alkylamines and is easier to form a stable ground-state CT complexe with the electron-deficient bipyridini um moieties.The host-guest CT interaction not only gives an efficient driving force for recognition and absorption of amine molecules,but also leads to a specific color cahnge.Additionally,the vapochromism is accompanied by a fluorescence quenching of MOFs and the quenching effect can be due to CT complexation,and the energy absorbed by MOFs is transferred to the CT complex.The MOFs can be used as test paper and can detect alkylamine vapors at a low concentration of 5ppm,and it is better than most of the colorimetric sensing materials previously used for alkylamine vapors.?2?The MOFs exhibit color and fluorescence response to amines and can be used as fluorescent probes for quantitative detection.However,due to the solvent effect of water molecules on CT,the detection sensitivity in aqueous solution is not high?0.17mM?.3.Space-confined indicator displacement assay of MOF based on competitive host-guest charge transferWell known,compared to the turn-off,the turn-on mode can have improved signa l-to-noise ratios and anti-interference ability,and has higher sensitivity and selectivit y.In order to improve the detection performance of MOFs for alkylamines in aqueous solution,this paper introduces the concept of indicator displacement analysis?IDA?in supramolecular analytical chemistry.Fluorescence response of UiO-67-DQ to alkylamines from turn-off to turn-on.And greatly improved detection sensitivity of alkylamines in aqueous solution.This is the first application of the IDA concept in MOFs.UiO-67-DQ-PsO was obtained through anion exchange?PsO^-=sodium 1-pyrenesulfonate?,PsO^-in the pore has three duties:counter anion,fluorescent indicator,electron donor interacting with DQ²⁺.The CT interaction between PsO^-and DQ²⁺quenches the emission from the framework and PsO^-.Therefore,UiO-67-DQ-PsO gives an excel ent OFF state.Due to the competition of mine-DQ²⁺CT complexat io n,adding alkylamine can destroy the PsO^--DQ²⁺CT complex,which turns on the fluorescence of PsO^-.Taking the detection of butylamine and dopamine in aqueous solution as an example,The turn-on system based on IDA improved six orders of magnitudes than the turn-off sensing which use the MOF without indicators.Detection is limited to ubnanomolar level and can completely eliminate the interference of aniline.The multiphase IDA system exhibits good recyclability compared to conventio na l homogeneous IDA systems,and since the space confinement effect makes the interaction between the host and the guest stronger,the sensitivity can be greatly improved.