The Preparation and Study of Novel Ligand Systems

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With the support of the Organic and Macromolecular Chemistry Program, Professor Randolph P. Thummel, of the Department of Chemistry at the University of Houston, investigates the preparation and properties of novel ligand systems. Professor Thummel explores the stereochemical consequences of unsymmetrical substitution within bidentate ligands, focusing on the steric and electronic effects of such substitution in the formation of facial and meridional diastereomers of tris(bipyridyl) complexes of ruthenium(II). Through the synthesis of a series of ligands related to 9-(di-2'-pyridyl)methylenefluorene, designed to undergo rotation about the central pi bond following photoinduced metal-to-ligand charge transfer and thereby present a barrier to internal return to the ground state, Professor Thummel is investigating the generation of long-lived photoexcited states. Related ligands permit assessment of the impact of ligand oxidation state on electronic communication between two bound metal ions, while complexes of pyrene-based ligands offer the possibility to observe room temperature emission. The physical and chemical properties of metal ions may be altered dramatically by capturing them within a molecular structure designed to impact chosen properties. Professor Randolph P. Thummel, of the Department of Chemistry at the University of Houston, is supported by the Organic and Macromolecular Chemistry Program for his investigations of the synthesis and study of molecules designed to affect the chemical processes resulting from the interaction of their metal complexes with light. Such photoprocesses lead to the transfer of an electron from the metal to the supporting molecular structure, and by designing this structure to undergo a significant change in geometry upon such electron transfer, Professor Thummel attempts to stabilize the photoinduced `excited state.` Related studies permit assessment of the effect on the electronic communication between two metal ions of a change in the nature of a molecular grouping which bridges them. These studies address fundamental issues regarding photoinduced electron transfer and are directly related to the harvesting of energy from sunlight.