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The investigations of host/guest structures based on covalent organic frameworks at solution/solid interfaces.

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Cui, Daling (2018). The investigations of host/guest structures based on covalent organic frameworks at solution/solid interfaces. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en sciences de l'énergie et des matériaux, 192 p.

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Résumé

Covalent organic frameworks (COFs) have gained significant attention in many applications due to their porous crystalline structures with high architectural and chemical robustness and customized topologies. A high-quality extended two-dimensional (2D) hexagonal porous COF-1 network can be obtained through cyclocondensation of three 1,4-benzenediboronic acid (BDBA) monomers by using excess water as the chemical-equilibrium-manipulating agent on a highly oriented pyrolytic graphite (HOPG) substrate. The surface-confined COF-1 can be used as template to recognize different guest molecules, allowing formation of a host/guest (H/G) structure. The intrinsic features of H/G structures lead to their wide applications in molecular recognition, catalysis, gas storage, separation and directed crystallization. Driven by the potential applications, the present work in this thesis concentrates on the preparation and properties of H/G structures based on COF-1 templates at the solution/solid interface. Firstly, scanning tunneling microscopy (STM) images show that the surface-supported two-dimensional COF-1 can act as a host architecture for C60 fullerene molecules, predictably trapping the molecules under a range of conditions. C60 adsorbs in the COF-1 template in two different sites, the top-site (T) and the pore-site (P). The fullerenes occupy the COF-1 lattice at the heptanoic acid/HOPG interface, and in dried films of the COF-1/fullerene network that can be synthesized through either drop-deposition of fullerene solution or by a dipstick-type synthesis in which the surface-supported COF-1 is briefly dipped into the fullerene solution. COF-1 can be synthesized from different solvents. When 1,2,4-trichlorobeznene (TCB) is used, STM images reveal the adsorption of TCB in the hexagonal pore of COF-1 template at TCB/HOPG interface. A well-defined loop boundary formed by a chain of pentagonal and heptagonal pores allowed us to investigate the effect of pore shape and size on TCB adsorption, suggesting that both geometrical and size effects are important in binding the TCB. When both C60 and TCB are present at the TCB/HOPG interface, TCB molecules are selectively trapped in the pore-site, whereas fullerenes adsorb on the top-site of COF-1. While the former structure is stabilized by Cl…H hydrogen bonds, the latter is controlled by van der Waals (vdW) interactions. These results suggest that surface-supported 2D porous COFs can selectively bind different molecules at specific sites via different types of interactions and COFs may offer a powerful platform for the recognition and patterning of guest molecules. Moreover, a 2D COF-1 can template solution-processed C60 guest molecules to form several solvent-dependent structural arrangements and morphologies via a 2D to 3D growth process. When TCB is used as solvent, C60 molecules form a template-defined close packed structure. When heptanoic acid is used as solvent, a range of lower density architectures that deviate from the template-defined close packing are observed. This difference is attributed to the co-adsorption of the heptanoic acid solvent molecules, which is only achieved in the presence of the template. This work demonstrates the possibility to precisely control molecular self-assembly to form designed 3-dimensional (3D) structures through the synergistic combination of template and solvent effects.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Rosei, Federico
Mots-clés libres: Molecular self-assembly on 2D surfaces; Covalent Organic Frameworks; COF; development of H/G structures; STM;
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 29 janv. 2019 16:22
Dernière modification: 29 janv. 2019 16:23
URI: http://espace.inrs.ca/id/eprint/7637

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