Study On Preparation Of Diversified Structures And Structure-activity Relationship Of Covalent Organic Frame

Organic porous materials are promising candidates for applications in sensing,gas adsorption and separation,catalysis,energy storage,and optoelectronic devices owing to their unique pore structures.Organic porous materials mainly comprise covalent organic frameworks（COFs）and metal-organic frameworks（MOFs）,among which COFs are a new class of crystalline porous polymers with periodic backbones and ordered pores.COFs can be classified into two-dimensional（2D）laminar structures and three-dimensional（3D）extended networks based on their covalent connectivity in different dimensions.Due to their low density,high porosity,and designable features,COFs are of great interest,making them ideal candidates for various research fields.This thesis comprises the following main parts:Chapter 1:A brief overview of the development process and current research status of COFs,a detailed description of COFs in terms of their connectivity,dimensionality,and synthesis,and an extensive account of the application of 2D COFs and the effect of crystallinity on COF materials.The chapter aims to facilitate the efficient synthesis of highly crystalline COFs using simple methods and their applications.Chapter 2:Isomerization of COFs is a fascinating and complex phenomenon that requires in-depth study.There is an urgent need for more detailed investigation into the mechanism underlying the formation of isomers with more monomeric structures.We constructed a new[D_2h+C₂]2D COF using a novel D_2hmonomer based on a rotatable biphenyl center.Through experiments,we discovered that this D_2h monomer exhibits high selectivity and prefers to form the backbone structure of monoporous COFs compared to the common D_2h monomer.We also calculated the energies of the two configurations of COFs through simulations,concluding that monoporous COFs are thermodynamically stable structures compared to biporous COFs.Chapter 3:Two 2D covalent organic frameworks（COFs）,namely benzotrithiophene-based COF（BTTh-TZ-COF）and 1,3,5-trithienylbenzene-based COF（TTh B-TZ-COF）,were synthesized with slight differences in their core structures but good planarity andπ-conjugation.Among the two,BTTh-TZ-COF exhibited better photocatalytic activity due to the enhanced charge separation and transfer resulting from better electron delocalization in the trithiophene-based planar core and the improved donor-acceptor interactions between the trithiophene and triazine units.The differences in core structures of the two COFs were identified as the key reason for the significant variation in photocatalytic performance despite having similar crystallinity,porosity,and optical band gap.This study provides a novel approach to preparing efficient organic photocatalysts for solar energy conversion.Chapter 4:Trilateral,tetragonal,and hexagonal monomers were synthesized by varying the number of aldehyde groups and reacting them with ionium salts.This method provides several advantages such as shorter reaction time,milder nucleation conditions,and controllable synthesis conditions as compared to traditional COF synthesis.Furthermore,this approach offers a new perspective for the preparation of large-sized organic framework single crystals.