Chemistry PhD Final Defense – Kristen Johnson

About the event

Title: Axial Ligation of Surface Confined Cobalt Porphyrins: Thermodynamics, Kinetics, and Cooperativity

Abstract: This work presents a detailed investigation of the influence of solid supports on the axial ligand binding properties of cobalt porphyrins. Metal porphyrins and other tetrapyrrole molecules form well-ordered, self-assembled monolayers on solid supports and because of unsaturated character of the metal atom within the macrocycle may form five and six coordinate complexes with axial ligands. Porphyrin chemistry is well understood in the solution environment; however, this knowledge does not always translate to accurate predictions of the behavior of porphyrins confined to a surface. The surface has been reported to influence the porphyrins reactivity, complex stability, and spin character to name a few. Understanding the dynamics of such interactions is imperative to the design and implementation of next generation molecular devices to accomplish diverse tasks such as molecular sensing, electron transport and catalysis. In this work, the axial ligation of cobalt porphyrins will be studied and monitored by scanning tunneling microscopy (STM) with single molecule resolution. I show that imaging can yield qualitative and quantitative information into the dynamics and binding affinity at the single molecule level. In particular, the role of the substrate and intermolecular interactions in influencing the ligand binding affinity, cooperative affects (positive or negative) in the binding affinity of adjacent molecules, and ligand binding kinetics. This presentation will focus on one aspect of the project: the use of STM for stochastic kinetic analysis of on-surface cobalt porphyrin oxygenation. Overall, this work uses experimental evidence and theoretical calculations in order to gain an understanding how a substrate will influence the behavior of surface confined porphyrins.