Date of Award
Doctor of Philosophy
Jacob W. Petrich
This dissertation explores solvation dynamics, particularly in room temperature ionic liquids. Using the fluorescent probe coumarin 153, a number of alkylimidazolium-based ionic liquids are studied with various time-resolved spectroscopic techniques. Correlation functions, which track the solvation response, are determined from the time resolved emission spectra. In all cases, including the neutral organic starting materials, there is an initial rapid component of the solvation. Using butylimidazole and 1-butyl-3-methylimidazolium hexafluorophosphate, it is explicitly shown that the correlation functions overlap at early times. This indicates that the organic cation dominates the initial solvation of these liquids, in contrast to previous suggestions;In addition to experimental studies, the problem of how to theoretically model the dynamics of room temperature ionic liquids is addressed. Two different systems, an aqueous ionic solution and a room temperature ionic liquid, are examined. Their correlation functions are calculated two different ways: using known dielectric data with and without conductivity effects. For both systems, the curves calculated without conductivity fit the experimental curves within experimental error and fit as well as, if not better than, the curves calculated with conductivity, suggesting that a dielectric continuum model can be sufficient for modeling room temperature ionic liquid dynamics;In the hopes of exploring chiral ionic liquids with chiral fluorescent molecules, the natural product hypericin is separated into its enantiomers. Due to the immediate unavailability of optically pure chiral room temperature ionic liquids, the two hypericin enantiomers are studied in more traditional chiral environments. In all cases, the photophysics of the two enantiomers have no observable differences. This supports the previous conclusion that the extended absorption spectrum of racemic hypericin is not due to ground state heterogeneity;Shifting focus, the prospect of studying solvation dynamics in proteins is addressed. Song (J. Chem. Phys., 116, 9359 (2002).) has developed a method of theoretically modeling proteins using specific polarizability functions for each amino acid residue. To validate and refine this method experimentally, a complex of apomyoglobin and coumarin 153 is made and characterized. The coumarin 153 binds tightly and preferentially in the empty heme pocket, allowing solvation dynamics to be studied inside the protein.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Lindsay Elizabeth Sanders Headley
Headley, Lindsay Elizabeth Sanders, "Ultrafast solvation dynamics in room temperature ionic liquids and protein environments " (2006). Retrospective Theses and Dissertations. 1261.