Date of Award
Doctor of Philosophy (PhD)
This dissertation is most interested in how a class of materials known as covalent organic frameworks (COFs) can be designed to capture photon energy to initiate chemical reactions. Different COF designs change how long the energy is held, how it migrates, and how it is dispersed – and these differences can be used to change their performance as artificial photosynthesis platforms. Thus, it is helpful to have an informative discussion about the processes behind natural photosynthesis, that is, nature’s light harvesting strategies and photocatalytic schemes (Section 1.2) and will lead into an introduction of COFs and why they possess unique potential as artificial photosynthesis platforms (Section 1.3). Their beneficial physical qualities are complemented by understanding their electronic structures from theoretically predicted properties with specific focus on topological symmetry (Section 1.4). Synthesizing and characterizing COF systems then becomes an important consideration (Section 1.5) along with how their excited state behaviors are probed and interpreted at reaction timescales by ultrafast spectroscopic techniques (Section 1.6). Finally, a look is taken at how COF structure versatility adds unique potential in catalyst engineering (Section 1.7). The main body of this dissertation will present five main research projects that seek to test theoretical predictions, assess the impact of COF planarity, or fine tune electronic structures. To test theoretical predictions, “Tuning Photoexcited Charge Transfer in Imine-Linked Two-Dimensional Covalent Organic Frameworks," which involves exploring nodal symmetry in topologically similar COFs by varying monomers, is reported. This work has implications on charge separation characteristics of COFs which is important to retain activated catalytic sites for chemical reactions. The second project, “Impact of πConjugation Length on the Excited-State Dynamics of Star-Shaped Carbazole-π-Triazine Organic Chromophores,” doesn’t directly probe COF systems, but looks at the role of dihedral angles on intersystem crossing (ISC) rates in organic chromophores with similar star-shaped motifs like those often found in COFs. Another study on planarity is “Conjugation- and Aggregation-Directed Design of Covalent Organic Frameworks as White-Light-Emitting Diodes” that explores planar and non-planar COFs and the how this affects the deactivation of their photoexcited states. “Wavelength Dependent Excitonic Properties of Imine-Linked Covalent Organic Frameworks,” explores how subtle changes in donor-acceptor arrangements can lead to differences in excited state populations. Finally, the seminal work in this dissertation, “Imine Reversal Mediates Charge Separation and CO2 Photoreduction in Covalent Organic Frameworks,” explores the effect of the imine bond on photophysical and photocatalytic properties.