This thesis is composed to two studies, each of which relies on recent advances in time-dependent density functional theory (TD-DFT) to accurately model fluorescence spectra. The first study focuses on evaluating the fluorescence spectrum of polycyclic aromatic hydrocarbons (PAHs) having a molecular weight of 302. Three isomers are analyzed including dibenzo[a,j]fluoranthene, dibenzo[a,k]fluoranthene and dibenzo[a,l]fluoranthene. These isomers differ in the placement of one of six aromatic rings and in the amount that each molecule deviates from planarity. The TD-DFT methods are used to compute spectra in an environment that simulates solvent (n-hexane). These computed spectra are compared to vibronically resolved experimental data obtained at cryogenic temperatures. Computed spectra for dibenzo[a,j]fluoranthene and dibenzo[a,k]fluoranthene are blue shifted versus experimental data. Conversely, the computed spectra of dibenzo[a,l]fluoranthene is red shifted. This difference is attributed to steric interactions in dibenzo[a,l]fluoranthene that creates a deviation from planarity. The second project describes the characterization of a pH-responsive fluorophore from an endophytic fungus isolated from sand pine. The endogenous fluorescence of the live organism was measured using fluorescence microscopy. Computational interpretation of the spectra was accomplished with the TD-DFT methods and include solvent effects. The combined use of experimental and theoretically predicted spectra revealed the pH dependent equilibria and photo-excited tautomerization of the natural product, 5-methylmellein. This product shows promise both as a stand-alone pH-indicating fluorophore with alkaline pKa, and as "green" feedstock for synthesis of custom fluorophores.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Abd Alelah, Samar, "Fluoresence Spectra Study of Sterically Strained Isomers of C24H14 polycyclic aromatic (PAHs) & Characterization of a Bio-sourced, Fluoresent, Ratiometric pH Indicator with Alkaline pKa" (2020). Electronic Theses and Dissertations, 2020-. 320.