Chemistry Chemistry Seminar - Student Thesis Talks; Eric Conklin, Samantha Nyovanie, and Niyi Odewade.

Eric Conklin. Seminar Title: "Supramolecular Assembly of Donor-Acceptor Energy Transfer System."
Abstract: A supramolecular complex in a collection of two or more molecules held together by noncovalent forces. Supramolecular assembly of model systems enables researchers to control an interaction of interest in order to shed light on an unfamiliar pathway or process. For example, supramolecular chemists are gaining new insight on Alzheimer’s disease by imposing small chemical modifications to synthetic model systems of fibrillar structures that inhibit or limit the molecular aggregation. In our study of supramolecular assembly, a hydrogen-bonded (--[H]--) model system for energy transfer was created using a porphyrinoid derivative, phlorin, and a carboxylate-appended BODIPY moiety. The phlorin is hydrogen bonded to the BODIPY-carboxylate through the axial position, thus changing the electronic structure of the phlorin moiety as evidenced by changes in the UV-visible absorption spectrum. Using transient absorption and time-resolved photoluminescence techniques, the lifetime of the excited-state for both BODIPY-carboxylate, the energy transfer donor, and the BODIPY-carboxylate--[H]--phlorin complex, the energy transfer donor and acceptor, were measured. Binding of the phlorin to the BODIPY-carboxylate, shortened the excited state lifetime of the BODIPY-carboxylate moiety. The lifetimes were used to yield a quenching rate of 1.52*10-10 s-1. The use of supramolecular assembly to control energy transfer will pave the way to creating model systems that undergo electron transfer through the axial position of the phlorin, and the donor-acceptor interactions can be opened up to studies of proton-coupled electron transfer.

Samantha Nyovanie. Seminar Title: Synthesis of Organosiloxanes and Organoclays for Polymer-Clay Nanocomposites (PCNs)"
Abstract: Polymer–clay nanocomposites (PCNs) have been a growing field of interest and research since the discovery that the presence of clay (at less than 5 wt%) can improve the mechanical, barrier, flame retardant, electrical, and biodegradable properties of the polymer. The synthesis of these nanocomposites is challenging due to the potential incompatibility of the inorganic clay and organic polymer components, due to their different chemical compositions and properties. The Burkett lab has devised a synthetic technique that enables the polymer chains to be end-tethered onto the surfaces of the clay layers, creating a polymer brush structure. This technique involves functionalizing an existing clay with a polymerization reaction initiator, such as a hydroxymethyl group, and inducing polymerization from those sites, creating polymer brush PCNs. This thesis develops a different approach for preparing initiator-functionalized clays: first functionalizing a commercial organosiloxane, 3 aminopropyltriethoxysilane, with an initiator-containing group, 5 (hydroxymethyl)salicylaldehyde, and then using this new organosiloxane for the synthesis of the clay. This method provides good control of the composition of the clay, and it facilitates the synthesis of clays with mixtures of functional groups, such as 5 (hydroxymethyl)salicylideneimine (HMS) and salicylideneimine (Sal). This research will investigate the possibility of tailoring the distribution of polymerization initiator sites: 100% HMS, 50% HMS/50% Sal, and 25% HMS/50% Sal. This strategy will create polymer brush PCNs with different polymer chain densities

Niyi Odewade. Seminar Title: "Ruthenium-Based Donor Compounds as Building Blocks in Proton Coupled Electron Transfer Model Systems."
Abstract: The rapid growth in world population will not only double global energy needs by 2050 but will also increase CO2 emission by another 50%. Consequently, there is a growing demand for carbon-neutral energy that can adequately and safely satisfy the needs of the planet. Herein lies the imperative to study proton-coupled electron transfer (PCET). PCET theory articulates a concerted transfer of protons and electrons via an overlap of donor and acceptor wave functions, which drastically decreases the activation barrier of energy-related molecules. Significantly, this process underpins the molecular chemistry of renewable energy, specifically chemical reactions that drive the capture, conversion, and storage of energy. In our work, we examine several newly synthesized ruthenium-based donor molecules - Ru(II)Cp*benzoate (Ru-Benz), Ru(II)Cp*carbamidinate (Ru-CarbAm) and Ru(II)Cp*methylcarbamidinate (Ru-MeCarbAm) and their PCET reaction with a well-studied ruthenium-based photo-oxidant, ruthenium trisbipyridine (Ru(bpy)3). Through the use of UV-visible absorption and fluorescence spectroscopy and electrochemistry, we have been able to discern early correlations between thermodynamic and kinetic properties. With further characterization, we aim to provide experimental results that can be used to further develop the PCET theory.