Design,Synthesis And Properties Of Novel Heteropore Covalent Organic Frameworks

Covalent Organic Frameworks are a class of crystalline porous organic polymers.They exhibit low densities,large specific surfaces and high crystallinities.The framework structures and nanochannels of COFs can be precisely arranged at atomic level by changing organic molecular units.These materials have very broad prospects in the fields of gas storage and separation,catalysis,optoelectronics and chemosensing.In this dissertation,we mainly focuse on the design,synthesis and applications of an emerging type of COFs,namely heteropore COFs.The development history and main classification of porous organic polymers are firstly introduced in the dissertation.Then the diversity of COFs materials,and the design,preparation and characterization of topological structures and applications of COFs have been summarized in details.A tetra-aldehyde(BABD)with C2v symmetry was designed and synthesized.Using this molecule as a monomer,two daul-pore COFs,COF-BABD-DB and COF-BABD-BZ with two different kinds of pore structures,have been successfully synthesized.Both the materials have high crystallinity and good thermal stability,and exhibit a rare staggered stacking pattern.The heteropore COFs also exhibit strong fluorescence emission.Based on this characteristic,their applications in the detection and identification of explosive nitroaromatic compounds was investigated,which revealed that they were capable of detecting trinitrophenol(TNP)with high sensitivity and selectivity through the mechanism of fluorescence quenching.The heteropore COFs also showed quick-responding color changes upon the addition of trinitrophenol,which can be used as visual chemical sensors for trinitrophenol detection by naked eyes.Two unique tetra-pore COFs were synthezszied by polycondensation of C2v symmetric BABD with one of two D2h symmetric monomers of different structures,respectively.Unlike the vast majority of COFs reported in literature,the as-synthesized heteropore COFs do not exhibit eclipsed(AA)or staggered(AB)stacking,but adopt a novel inclined stacking manner.Their porous structures were elucidated by powder X-ray diffraction(PXRD)and gas adsorption.This novel strategy for the construction of the tetra-pore COFs will provide a new idea for improving the structural complexity and diversity of heteropore COFs.A triple-pore structure COF-BABD-DB-BZ-1 was firstly prepared by using the heterostructural mixed linker strategy.Taking advantage of the dynamic covalent chemistry(DCC),for the first time,a series of COF-to-COF transformation processes,which include three stages,(1)dual-pore structure COF-BABD-BZ transforming into triple-pore COF-BABD-DB-BZ-1,(2)COF-BABD-DB-BZ-1 transforming into tetra-pore COF-BABD-DB-BZ-2,and(3)the tetra-pore COF transforming into dual-pore COF-BABD-DB,have been realized by heating COF-BABD-BZ with 1,4-diaminobenzene(DB)under solvothermal conditions.This work not only improves the understanding of DCC theory on in-situ COF-to-COF transformation,but also opens a new way to synthesize COFs which are difficult to access by "bottom up" strategy through the post-processing COF-to-COF transformation.It offers a new strategy for the development of COFs materials,especially heteropore COFs with highly complicated structures.Two C3 symmetric ethyl triindole aldehyde(TTDDC-6CHO)monomers were designed according to the multiple-linking-site strategy,for which two aldehyde groups were introduced at each branch of the triindole-based skeleton.Their condensations with a C2 symmetry monomer produced two heteropore COFs.The heteropore COFs constructed by this multiple-linking-site strategy gives dual-pore COFs without other isomers,which achieved precision construction of heteropore COFs.The formation of the imine-bonded COFs backbones was confirmed by PXRD,FT-IR and 13C solid-state NMR.At last,the heteropore COFs designed and prepared in the dissertation work is summarized.The innovations of this dissertation is described and the perspectives of these heteropore COFs is also discussed.