Nuclear Magnetic Resonance Studies of Molecular Structure and Dynamics

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The research proposal describes a program to investigate the detailed structure and dynamics of materials that are of fundamental interest to the scientific community. A wide range of materials will be investigated including hybrid perovskites that are building blocks of solar cells, natural products and pharmaceuticals that are important in medicine, and transition metal complexes, some of which catalyze chemical reactions and have important industrial applications. Our principal experimental tool for investigating the structure and dynamics of materials is nuclear magnetic resonance spectroscopy, a general tool upon which MRI, magnetic resonance imaging, is based. Many of the natural products that we examine, e.g., curcumin, have strong hydrogen bonds that play a fundamental role in determining their molecular structure and hence their molecular properties. In these molecules with intramolecular hydrogen bonds we have very recently observed deuterium isotope effects on NMR chemical shifts in the solid state that we believe have the potential to provide detailed information about the positions of hydrogen atoms, information difficult to obtain by X-ray diffraction. We are working with theoreticians to compute accurate potentials and zero-point energies for systems with unsymmetrical double-well potential surfaces. It is interesting to point out that the US FDA has approved the first deuterium-labeled drug, tetrabenazine-d6, for human use. We have extensive experience working with methylammonium lead iodide, a compound that belongs to a class of compounds known as organic-inorganic hybrid perovskites. Although we started working with this material in 1985, not long after it was first prepared by Weber, it was not until 2009 that it was realized that this material could be used to convert solar energy into electrical energy. In 2009, the efficiency of converting solar energy to electrical energy was approximately 3.8 %, but now, by careful control of the preparation procedures, efficiencies in excess of 22% have been achieved. Today, we join many research groups scrutinizing related organic-inorganic perovskite materials as possible candidates for solar energy applications. From the recent literature, it seems clear that the cation and halide ion dynamics significantly influences the performance of these materials. We plan to use mechanochemical synthetic methods to prepare several lead mixed-halide perovskites and characterize both the cation and anion dynamics using solid-state NMR.