Synthesis and topology control of covalent organic frameworks

• Main Author: Li, Liuxiao
• Other Authors: Zhang Qichun
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/145860
• Institution: Nanyang Technological University

As a class of crystalline porous materials which are built by organic building units, covalent organic frameworks (COFs) are attracting tremendous attention in recent decades. Because of their intrinsic properties of porous, high stability, and low density, this kind of material has drawn great attention in the fields of sensing, catalysis, and gas storage/separation, etc. Topology or crystal structure which is determined by the pore size and shape is one of the most important parameters of COFs. Therefore, this thesis aims to controlled synthesize COFs with novel topologies and explore their application in AIE, drug delivery, and controlled CO releasing. First, a series of 2D COFs with kgd topology, namely HFPB-TAPA, HFPB-TAPB, and HFPB-TABPB are synthesized via solvothermal reaction of HFPB and TAPA, TAPB, TABPB, respectively. The as-prepared 2D COFs constructed from monomers with C6 and C3 symmetry form micropores. As a proof of concept application, HFPB-TABPB with micropores is selected as the drug carrier for drug loading and releasing of ibuprofen (with a size of 6 x 12 Å). Second, by altering substituents of the building block with the same symmetry, two highly crystalline phase-pure 2D COFs, namely TPE-COF-OH and TPE-COF-OMe, with different topologies and porosities were successfully synthesized and characterized. Low-dose HRTEM imaging combined with molecular simulation indicates that the linkage conformations of the COF skeletons governed by intramolecular hydrogen bonding dictate the resulting COF topologies. Additionally, benefit from the abundant existence of (N, O)-bidentate Schiff base moieties in TPE-COF-OH, post-synthetic modifications of TPE-COF-OH to form a boron complexation, namely TPE-COF-BF2, fluorescence “turn on” and “aggregation-induced emission” properties of the obtained TPE-COF-BF2 were also observed. Last, a new porous 3D COF, denoted as TamBpyda was developed via the condensation of (2, 2′-Bipyridine)-5, 5′-dicarboxaldehyde (BPyDA) and tetra (4-anilyl)methane (TAM). The as-prepared TamBpyda was further metalated with Mn(CO)5Br to generate manganese carbonyl complex functionalized Mn-TamBpyda. As a proof-of-concept application, Mn-TamBpyda was applied as the CO releasing materials, which exhibited the ability to deliver and release CO inside the cells upon the light irradiation.