Design,Synthesis And Property Investigations Of Several Stimuli-Responsive Crystalline Porous Organic Frameworks

In response to the change of natural environment,the life system adjusts its complex structure to adapt to the new environment through its sensor feedback mechanism and driving function.Scientists attempt to develop new materials and applications by referring to nature.However,the main challenge for scientists is to imitate the active microenvironment in nature to create responsive materials with dynamic and adjustable properties.Stimuli-responsive polymers,also known as"smart materials",have received great interests in the scientific community.When subtle changes in external stimuli such as temperature,light,pressure,or electric,the polymer will show structural or segment conformational changes which manifest as detectable macroscopic property changes.This unique stimuli-response property gives stimuli-responsive polymers a variety of applications in the fields of smart devices,pressure sensing,controlled drug release,nanomaterials,and biotechnology.As a subclass of polymer materials with high specific surface area,high porosity,excellent stability and adjustable functionality,Porous Organic Frameworks materials have a wide range of applications such as gas separation and storage,catalysis,energy,and photovoltaics.In recent years,intelligent response as a research direction of porous materials has attracted the attention of scientists.Stimuli-responsive porous organic materials exhibit both the stimulation response of traditional smart polymers and the permanent porosity of porous materials.As a result,they show remarkable advantages in some specific applications(such as controlled adsorption and release of gases).Up to now,only a few examples have achieved the regulation of the structure and functions of Porous Organic Frameworks by stimulating factors such as pressure,light,and temperature.Therefore,how to develop new stimuli-responsive porous organic materials from the structural design is still a huge challenge.Based on the above-mentioned problems,we designed and synthesized a series of stimuli-responsive Porous Organic Frameworks,and explored their stimuli-response mechanism and the effect of such response behavior on the structure and properties of materials.The research content is mainly divided into the following three parts:(1)In the second chapter,we use diamond anvil cell(DAC)to explore the abnormal mechanical response behavior of Porous Organic Salt CPOS-1 under hydrostatic pressure.The test results show that CPOS-1-dried exhibits extremely large Negative Linear Compressibility(NLC)behavior,and the negative compressibility coefficient as high as K_C=-90.7 TPa^-1,which is the strongest NLC performance ever reported in the literature.In addition,we studied the effect of guest molecules on the NLC behavior of CPOS-1 with permanent porosity water@CPOS-1.The Negative Linear Compressibility of water@CPOS-1 is-13.3 TPa^-1 at high pressure.Density Functional Theory(DFT)calculation results show that the colossal NLC behavior in CPOS-1-dried originates from the"supramolecular spring"like framework structure.Finally,there is a unique 1D helix water chain along the c-axis direction based on the water@CPOS-1.By means of high pressure single crystal electrochemical impedance spectroscopy(EIS),we explored the effect of rare NLC behavior along the c-axis direction on the proton conductivity of single crystal.The results show that the proton conductivity along the c-axis 1D helical water chain decreases with increasing pressure.(2)In Chapter 3,three acetylene(-C?C-)bridged 2D Covalent Organic Frameworks TA-COF,TAB-COF and TAT-COF were successfully prepared by the Schiff base reaction of aldehyde monomer containing acetylene(-C?C-)and amino-based monomer with three different linear lengths,respectively.Then,the topochemical cross-linking reaction of acetylene(-C?C-)between layers in 2D COFs was investigated.The formation of polyacetylene structure was confirmed by FTIR and ¹³C solid-state NMR.In this study,for the first time,acetylene(-C?C-)was used as the active site to achieve solid-state crosslinking,and finally Crystalline Porous Polyacetylene Frameworks(PPFs)were formed.In addition,the effects of topochemical crosslinking of acetylene(-C?C-)in 2D-COFs on the crystallinity,stability,pore structure and band gap of the material were investigated by a series of characterization.Finally,the conductivity of the material before and after the solid-state crosslinking reaction was explored by means of iodine doping.The results showed that the conductivity of the PPFs formed after crosslinking was greatly improved,reaching7.38×10^-4 s cm^-1.(3)In Chapter 4,two 3D Covalent Organic Frameworks,3D-TE-COF and 3D-TB-COF,were successfully prepared by the reaction of tetra(4-aminophenyl)methane with aldehyde monomers containing acetylene(-C?C-C?C-)and butylene(-C?C-)via Schiff base reactions.Both 3D-COFs have highly interspersed dia topology structure(3D-TE-COF is 9-fold and 3D-TB-COF is 11-fold),as well as high crystallinity,high specific surface area and good stability.As an active site in classical solid-state polymerization,butylene(-C?C-C?C-)can achieved 1,4-addition reaction under UV light,heating or high pressure.Based on this,we have tentatively explored the topochemical reactivity of 3D-TB-COF which containing butylene(-C?C-C?C-)structure.The test results showed that 3D-TB-COF could not carry out 1,4-addition reaction under UV light,which is mainly attributed to the lack of reactivity in the spatial parameters of the diacetylene(-C?C-C?C-)array in the framework.Fortunately,through high-pressure testing,we found that 3D-TB-COF can form carbon nanotube structure via the Dehydro-Diels-Alder(DDA)solid-state reaction.This study shows that high pressure is an effective tool to overcome the geometric limitations of molecules,thereby driving selective reactions at specific distances.