STM and STS Studies of the Structures and Energetics of Axial Ligand Coordination to Metal Porphyrins at the Liquid-Solid Interface

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The Chemical Structure, Dynamics and Mechanisms Program of the Chemistry Division supports Professor Ursula Mazur at the Washington State University for studies of axial ligand coordination to metal porphyrins (MPs) at the liquid-solid interface. Systematic studies will be performed on the reactions of MPs with an axially coordinated ligand and the electronic orbital structures and energies in these systems will be mapped using scanning tunneling microscopy (STM). These studies will measure deviations from planarity of the MP induced by ligand attachment, identify and map both the metal and the ligand orbitals in the MP complexes, compare the observed density of states for the MP systems to model electronic calculations, and measure kinetics in cases where MP ligand association/dissociation occurs on the time scale of minutes. This research will contribute information about the structure and electronic state changes associated with the ligation of planar and non-planar metal porphyrins with varying occupation of the metal 3d orbitals. Investigations of the connection between porphyrin conformational flexibility and the structural/electronic characteristics of an axially ligated complex are generally applicable to distorted metallo-tetrapyrroles and therefore, relevant to a variety of biologically and biomimetically important processes.Metalloporphyrins perform many versatile functions including light harvesting, electron and energy transfer, catalysis, and act as receptors in molecular recognition. Many of these functions depend on some species (called an axial ligand) interacting with the MP. The attachment of an axial ligand to the MP induces changes in the electronic structure of both the porphyrin and the ligand. Identifying the structural and electronic behavior of the MP during ligation/de-ligation processes is crucial for the understanding of the catalytic and recognition functions of MPs. This project will diverse graduate and undergraduate students in surface science, surface microscopy and spectroscopy, and the basic concepts of coordination chemistry. The proposed research will be used as an educational vehicle for an outreach effort to underrepresented Native American and Hispanic high school students. Mentoring relationships with off-campus science and engineering leaders will provide training, mentorship, and facilitate the formation of collaborative research efforts.