Translating molecular concepts to the solid state

Grunenberg, Lars (2023): Translating molecular concepts to the solid state: synthetic modification, dynamics and diffusion in covalent organic frameworks. Dissertation, LMU München: Fakultät für Chemie und Pharmazie

Abstract

Covalent organic frameworks are a novel class of crystalline and porous framework materials composed of light elements linked by covalent bonds between their building units. Their unique combination of properties, including permanent porosity, chemical and structural stability, light absorption, and versatility in structural design and composition, has led to an ever-expanding range of applications, including energy storage and conversion, heterogeneous (photo)catalysis, gas adsorption, and sensing. Even though COFs are solid-state materials, their organic composition promises unparalleled possibilities for modifications in chemical structure with similar versatility and precision as known from small organic molecular compounds. This comparability is inspiring for transferring additional classical molecular concepts to this class of solid-state materials. In this thesis we transfer typical molecular concepts, such as the modification of organic functional groups as part of the chemical structure, stimuli-responsive dynamics and mobility, to covalent organic frameworks – as solid-state materials. We present novel topochemical modification methods for post-synthetic linkage conversion of imine linkages to convert imine COFs into secondary amine-linked and nitrone-linked frameworks. These methods allow for a fine-tuning of materials properties, such as the stabilization of their chemical connectivity, reactivity for further functionalization, and pore channel polarity. To follow the conversion of bonds, properties, and structure, we employ a diverse set of analytical techniques, including FT-IR and solid-state NMR spectroscopy, gas and vapor sorption experiments and X-ray powder diffraction coupled with pair-distribution function analysis. With the aim to study stimuli-responsive dynamics in COFs, we synthesize the first covalent organic framework with light-driven molecular motors embedded as building blocks in its chemical structure. The dynamics of the rotors in the material are probed by in situ spectroscopic techniques including Raman, FT-IR and UV-Vis spectroscopy. Although the presented materials fulfill important characteristics such as permanent porosity and thus, void space for motor rotation, motor isomerization could not be visualized by available analysis techniques, but allowed to gain insights into experimental and design challenges for transferring this property to solid-state materials. These findings allow to extend the design principles for the construction of next-generation dynamic COFs with stimuli-triggered response. Finally, we study mobility by means of self-diffusion of acetonitrile in an imine-linked covalent organic framework by pulsed field gradient NMR experimentation, complemented by computational simulation methods, i.e. molecular dynamics simulations.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 540 Chemie
• Fakultäten: Fakultät für Chemie und Pharmazie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 6. November 2023
• 1. Bericht­erstatter:in: Lotsch, Bettina