Construction Of Olefin-based Metal-organic Frameworks And Application In Photoresponsive Behavior

Flexible solid materials that demonstrate molecular level or macroscopic shape mechanical response in the presence of external stimuli,such as light,heat,magnetic/electric field and humidity,have a rich potential in smart devices,memory storage,and drug delivery.The solid-state[2+2]photodimerization reactions in olefin-based metal-organic frameworks(MOFs)that lead to an anisotropic or isotropic swelling of the unit cell open the path towards a new photo-driven approach for the design and synthesis of supra-sensitive photo-mechanical actuators,as well as negative or zero expansion materials.This dissertation focuses on the demonstration of the crystal lattice,plane and macroscopic morphology changes of olefinic MOF crystals upon photo-induced[2+2]cycloaddition reactions,by combining single crystal X-ray diffraction and atomic force microscopy(AFM).Furthermore,the photo-controlled swelling,optical drivers,fluorescence sensing and photoactuators have been inviestigated in photoresponsive olefinic MOF materials.The main research contents of this dissertation are briefly describedin the following sections.Chapter 1.Construction of a two-dimensional flexible MOF[Zn2(bdc)2(3-CH3-spy)2]·H2O(1,H2bdc=1,4-benzenedicaboxylic acid;3-CH3-spy＝3-methylstyrylpyridine).Upon irradiation with 365-420 nm light,MOF 1 transforms into a family of isomeric,3D MOFs[Zn2(bdc)2(rctt-tcdp)](2x,x=a-d)With photo-controlled anisotropic contraction in a single-crystal to single-crystal(SCSC)manner,triggered by photo-induced[2+2]cycloadditions.The photo-induced nonlinear contraction behavior of this material is presented at both the molecular and macroscopic levels,with physical changes in the bulk crystal of the material being observed.The AFM shows that the nanoscopic grooves are formed through the photo-induced SCSC transformation,showing the macroscopic effect led by this structural change.Chapter 2.Based on the results of Chapter 2,in this chapter,we have developed a coordination-driven self-assembly strategy for the fabrication of hierarchical photoactuator system by incorporating photoreactive olefin derivatives into a fluorinated MOF[Zn(bdc)(3-F-spy)](3,3-F-spy＝4-(3-fluorostyryl)pyridine).Three types of photomechanical deformation(including bending,twisting and splitting)of single crystal 3 are observed under UV light irradiation.These distinctive deformation patterns are caused by the asymmetric geometrical variation from photo-induced[2+2]cycloaddition reactions.The detailed results imply that the photomechanical deformation is a consequence of a delicate balance of factors including crystal dimensions,tensile stress,and the exposure time to the incident light source.Additionally,we have successfully fabricated a hierarchical photoactuation system of the composite membrane 3-PVA from MOF 3 and PVA,through hydrogen-bonding that amplifies the mechanical stress to achieve macroscopic actuation behavior under UV light irradiation,and demonstrated the kinetics of the photomechanical deformation.To the best of our knowledge,these findings demonstrate for the first time the photoactuation of photo-responsive MOFs.We anticipate that these results shall shed light on the photoactuation mechanisms of materials,and open up new avenues toward photoactuator devices to achieve the desired photochemical responsive movement,and will ultimately lead to potential applications in optomechanical microdevices and smart microrobotics.Chapter 3.This chapter reports a protonated mononuclear complex[Zn(Hbpvp)Cl3](4,bpvp=3,5-bis-(2-(pyridin-4-yl)vinyl)pyridine)assembled from solvothermal reaction in strong acid solution.Hydrogen-bonded zigzag chains of complex 4 crystallizes over time to form a large-size hollow hexagonal tubular crystal.We employed scanning electron microscopy and powder X-ray diffraction to monitor the morphological evolution of the crystals of 4 during crystallization and observed that the crystal morphology updated continuously from irregular seeds to stable crystal morphology.In addition,crystals of 4 is capable of undergoing a stereoselective[2+2]photocycloaddition.It also selectively absorbs Methyl Blue from a mixture of dyes with the retention of its crystallinityChapter 4.This chapter reports the construction of a 3D flexible pillared-layered MOF[Zn2(tdc)2(pvq)]·1.5DMF(MOF-5as,H2tdc＝2,5-thiophenedicarboxylic acid,pvq=5-(2-(pyridin-4-yl)vinyl)quinoline)with stimuli-responsive switchable breathing behavior.The N2 adsorption isotherm of desolvated MOF-5des reveals an abnormal negative gas adsorption phenomenon at low relative pressures.The flexible MOF-5des shuttles back to the original collapsed phase even after fourth adsorption-desorption cycles.This adsorption phenomenon could not be observed in the CO2 adsorption isotherm.The noticeable differences in the adsorption properties of MOF-5des are likely attributed to the electron affinity and geometrical features of guest molecules toward the polar micropore walls decorated with thiophene groups,as well as the self-correction of the flexible structure.The results provide a deep fundamental understanding of the nature of stimulus-responsive flexible MOF.Chapter 5.This chapter demonstrates that with the introduction of V-shaped tridentate ligand,we are able to construct a fluorescent MOF,[Zn4(Hbpvp)2(BTC)3(HCOO)(H2O)2]·4H2O(6,H3BTC=1,3,5-benzenetricarboxylic acid,bpvp=3,5-bis-(2-(pyridin-4-yl)vinyl)pyridine).The rigid and partially protonated Hbpvp+ligand plays a critical role in the strong fluorescent emission of MOF 6.Specifically,MOF 6 can fluorescent probe for the dual detection of nitroaromatics(ie.2,4-DNP)and ketones(ie.p-BQ)in water.