UC Riverside

ABSTRACT OF THE DISSERTATION

Theory and Applications of NMR to Problems in Material Science and Analytical Chemistry

by

Arun Agarwal

Doctor of Philosophy, Graduate Program in Chemistry

University of California, Riverside, August, 2010

Dr. Leonard J Mueller, Chairperson

Recent developments in NMR spectroscopy have seen an increase in its application for the study of structure and dynamics in the field of material science. NMR can be used as a complementary technique to X-ray diffraction and other structure probing techniques such as AFM and STM in the study of complex systems. Due to its non-invasive nature, measurements can be made on samples without altering their structural or functional properties.

In this thesis three different application of solid-state NMR will be highlighted. First, the butyl-substituted spiro-biphenalenyl radical will be studied. This molecule is a member of a new class of organic conductors which posses the highest conductivity of any neutral organic molecular solid via a magnetic phase transition. ¹³C chemical shift measurements allow us to track the transition between the diamagnetic and paramagnetic states, which we find builds in as a gradual increase in the spin-density at the aromatic sites and a decrease in the electron spin-spin coupling between adjacent radicals. Our model suggests that the electron is not delocalized over the entire molecule, but is in fast exchange between the phenalenyl rings.

Next, the photophysics of photomechanically responsive molecular crystal nanostructures based on anthracene esters is studied using solid-state NMR. A detailed study of these materials provides significant insight into the molecular-level dynamics that give rise to the micron-scale response of the nanorods. This work provides insight into how solid-state photochemistry within nanostructured molecular crystals can give rise to novel photomechanical behavior on micron lengthscales.

Finally, the last chapter discusses several examples of analytical applications of NMR. A combined approach of using solid as well as solution state NMR spectroscopy to study the stereo-chemical and functional properties of industrially useful compounds has been presented. The approach taken has the potential to be used for a wide variety of industrial applications.