Using Solid-State Nuclear Magnetic Resonance to Relate Chemical Structure With the Function of Materials
Solid-state Nuclear Magnetic Resonance (ssNMR) combined with x-ray diffraction and first-principles computational chemistry, in a method called NMR-assisted crystallography, is used to determine the chemical structure of a variety of materials. 9-ter-butyl-anthracene ester (9TBAE) in molecular crystal nanorods can undergo a photodimerization that causes expansions of up to 15%. The expansion is a result of the formation of a metastable crystalline intermediate, the solid-state reacted dimer (SSRD). A molecular level understanding of 9TBAE using NMR-assisted crystallography is required to fully explain this expansion. ssNMR experiments on aligned nanorods and powder samples of 9TBAE allows for the observation that the nanorod expansion is a result of a rotation of the unit cells from monomer to SSRD. Additionally, the magnitude of expansion or contraction during the reaction can be predicted if the initial orientation of the unit cell with respect to the nanorod axis is known. These results are confirmed by diffraction and computational methods. ssNMR is used to reveal the structure of a few different materials in this work. Silica surface sites, where a lack of sensitivity in NMR makes observation of non-covalent bonding difficult, are observed using Dynamic Nuclear Polarization – Surface Enhanced NMR Spectroscopy (DNP-SENS). Thermally sensitive monomers can also be characterized and the negative thermal expansion they undergo can be described on a molecular level. Finally, a statistical method is described that can be used to discriminate between UV-Vis data of 1:1 and 1:2 host-guest complexes. Statistical methods are also used to compare different non-uniform sampling (NUS) methods in NMR.