Synthese, Characterization And Properties Study Of Microporous Photochromic Metal-Organic Frameworks Based On A Naphthalene Diimide Chromophore

The rational design and synthesis of photochromic MOFs that can respond to external photo-stimuli is an emerging area of current interest,owing to their potential applications in molecular electronics,fluorescent switches,erasable prints,etc.For the synthesis of photochromic MOFs,one promising strategy is to introduce photoactive components?such as diarylethene derivatives,viologen derivatives,naphthalene diimide?NDI?derivatives,and so on?as inherent building-blocks of MOFs.It is conceivable that the introduction of photoactive components into the MOFs may not only incorporate functionality from both inorganic and organic components,but also provide the opportunity to produce novel properties by the synergic interactions between the counterparts.However,because many factors,such as the molecular structure,suitable donors and acceptors,the packing type and orientation between the donor and acceptor moieties,the distance of the pathway for charge transfer,the stability of the charge-separated state,etc,can influence the photochromic properties,the rational design and synthesis of photochromic MOFs with tunable photosensitivity is still a significant and challenging task.NDI derivatives are an attractive class of chemically robust,?-electron-deficient and redox-active molecules,which may undergo a reversible one-electron reduction to form stable radical anions and can thus act as electron acceptors in the photoinduced electron transfer?PET?processes.This makes them excellent candidates for the construction of the photochromic materials.In this thesis,five novel photochromic metal-organic frameworks?MOFs?based on N,N'-bis?5-isophthalic acid?naphthalenediimide?H₄BINDI?were synthesized in the presence of different metal ions,that are,[Zn₂?BINDI??DMA?₂]·2DMA?1?[Cd?H₄BINDI??H₂BINDI?]·4DMF?2?[Ca₂?HBINDI?Cl?DMA?₃]·DMA?3?[Ba₄?BINDI?₂?DMF?₇]·7DMF?4?[Zn₂?BINDI??DMF?₄]·2DMF?5?They have been synthesized and characterized by single-crystal X-ray diffraction,powder X-ray diffraction,elemental analyses,IR spectra and TG analyses,UV-vis and ESR.Compound 1 exhibits a 3D porous framework with lvt topology based on paddle-wheel Zn₂?COO?₄ clusters and BINDI^4-as four-connected nodes.Compound 2features a porous threefold interpenetrating diamondoid framework.Compound 3 shows a microporous 2D double-layer architecture.In the packing arrangement of 3,the adjacent 2D layers are interdigitated with each other to yield a 2D?3D interdigitated framework.Compound 4 displays a porous twofold interpenetrated 3D network.Compound 5 reveals a 2D network based on binuclear units Zn₂?COO?₂,and the adjacent 2D networks are packed parallel in an–ABAB–fashion giving rise to an overall 3D supramolecular framework.Based on the above five MOFs,we discuss their photochromic properties and other excelent performances.That are mainly as follows:?1?Interestingly,these five MOFs exhibit reversible photochromic behaviors concomitant with eye-detectable color change,but different coloration degrees.Upon irradiation,compound 1 exhibited color change from pale brown-yellow to brownish black,compound 2 turned from light-yellow to dark-brown,compound 3 transformed from yellow to black-green,compound 4 changed from yellow to dark green,and compound 5 turned from pale yellow to dark yellow.The irradiated samples of 1-5 can return to the initial color after being held in the dark at room temperature.The time required for reversal to the initial color was found to be 14 days for 1,2 and 5,8h for 3,and 2 days for 4.The comparison of these MOFs indicates that the electron-withdrawing capabilities of metal cations play a significant role in tuning the photosensitive properties of photochromic MOFs,as well as the coordination structures,and this result may provide a feasible route for the design and synthesis of photochromic MOFs with controllable photoinduced electron-transfer properties.?2?Notably,compound 1 also exhibits reversible thermochromic behavior.As we all know,the MOFs materials with both photochromic and thermochromic properties are still rare.?3?Considering the photochromism of compounds 1-5,we tested the photocontrolled luminescence of 1-5.The fluorescence emission intensities of 1-5exhibit gradual decrease with the increase of irradiation time and recover after standing in the dark.?4?It should be noted that 3-5 show solvatochromic behaviors in presence of different solvents.When powder 3-5 were soaked in DMF,DMA,DEF,MeCN and EtOH,the resulting inclusion compounds undergo eye-detectable color change.?5?Additionally,compounds 1-3 are found to be useful as indicators for the qualitative detection of nitrite by naked eye recognition of color change,and we also test the photoluminescence response by adding nitrite into radiated samples of 1-3.The gas adsorption behaviors of 1,2,4 were also studied.