Single Crystal Growth,structures Analysis And Crystallization Mechanism Of Covalent Organic Frameworks

Covalent organic frameworks(COFs)represents a new class of crystalline porous organic polymers,the structures of which are diversely constructed via the covalent bonding of pre-designed organic monomers.Most research in this fascinating area has been focusing on applications such as gas sorption,catalysis,photoelectricity,energy storage,sensor,drug delivery etc,then it can be served as “organic zeolites” in organic material.However,as a solid crystalline material,single crystals of COFs haven't been obtained since the first report from 2005.In difference from hydrogen or coordination bonding,strong covalent-bonding and porosity are the significant obstacle in growing single crystals.Therefore,structure solution and reality of further application were hindered.Powder X-ray diffraction and advanced electron diffraction analyses were usually used to determine the COF structures based on reticular chemistry and topology analysis,but many of their structures are still ambiguous.In this contribution,we developed a modulator method to obtain large single-crystal COFs,and the singlecrystal X-ray diffraction structures of COFs are reported here first time.In this process,a new topology of lon-b-c3 was explored,and the interpenetration isomerism in COFs was also observed.Furthermore,host-guest chemistry in COFs was confirmed.On this basis,the crystallization mechanism can be studied.We hope our work can contribute to the field of crystal engineering,porous material,covalent self-assembly,supramolecular chemistry,host-guest chemistry,and so on.In this thesis,we reviewed research background such as structure determination and crystallinity improvement for COFs in chapter 1;in chapter 2 we reported the growth of large single-crystal COFs and their characterization;chapter 3 is about singlecrystal X-ray diffraction structure determination;chapter 4 is observation of interpenetration isomerism,which can occur as a vivid example of diversity and is one of supramolecular isomerism.This work provides a novel example to the category of interpenetration isomerism.In order to know interpenetrated dia-structure better,we further deduced a general formula to calculate the interpenetration degree of dia-based COF structures in chapter 5.The interpenetrated isomers possess their different structure flexibilities with them,and we also observed host-guest effect between water and COF framework by single-crystal X-ray diffraction,all of these were talked in chapter 6.Furthermore,by generalizing the synthetic method,controllable synthesis of different-sized COF crystals was shown in chapter 7;and exploring of crystallization mechanism in chapter 8 resulted in a conclusion that,imine exchange reaction in the combinatorial library we built is benefit to nucleation and growth of single-crystal COFs.In chapter 9,we studied the reduction and oxidation of imine bonds in COFs to access more stable COFs,and realize a single-crystal-to-single-crystal process in COFs.We believe our work not only breaks traditional thinking for making a covalent crystals,but also sheds new lights to the further development of COFs.These works will have profound impact on structural investigation,structure-performance relationship,and the universal acknowledge for future application of COFs.