Date of Thesis

Spring 2021

Description

There is a need to design novel next-generation materials for water filtration and desalination in order to meet growing global demand for clean, potable water. Three-dimensional Covalent Organic Frameworks (3D COFs) are porous, crystalline polymers with designable structures self-assembled from rigid organic monomers, and this structural approach has been identified as a promising class of materials capable of effective water purification. This application requires introducing usable chemical functionalization into the framework scaffold. Despite the purported interchangeability of 3D COF monomers, recent attempts to synthesize functionalized versions of the model system imine-linked COF-300 have been unsuccessful. This failure is due to a lack of understanding of the nucleation processes that occurs at the earliest stage of 3D COF crystallization. We hypothesize that a thorough understanding of model small molecule crystallizations will provide a better insight into functionalized 3D COF nucleation. To achieve this, we synthesized a library of eight small molecules structurally analogous to the linking bridge of COF-300 to evaluate the impact of side-chain functionalizations. We gathered solubility data across a range of concentrations and temperatures with the aim of imine linkage formation and growing single crystals all within the same experiment, to best model 3D COF growth. We evaluated crystal structural data and the packing behavior of the small molecule systems, which showed a wide range of solubilities and packing structures. All functionalized systems demonstrated lower solubility than the unfunctionalized COF linker, suggesting that functionalized COF synthesis will require identifying and employing conditions that are optimized for each linker. Computational DFT modeling suggests interaction with the water fraction of the solvent is the major driving force in solubility. The structural data revealed that a dimethoxy functionalized linker packed in a potentially COF compatible manner, while a tetrafluoro functionalized linker does not demonstrate COF compatible geometry. In the future, we look to continue to grow the crystal library as well as employ what was learned through small molecule analysis to develop novel synthetic strategies for functionalized COF growth.

Keywords

Covalent Organic Frameworks, COFs, Crystallization, Nucleation, DFT, COF-300

Access Type

Honors Thesis (Bucknell Access Only)

Degree Type

Bachelor of Science

Major

Chemistry

First Advisor

Brian J. Smith

Available for download on Friday, May 20, 2022

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