Cryogenic Spectroscopy of Anionic Biochromophores


Biochromophores are ubiquitous and have the potential to be modified to suit our needs in many applications involving the absorption or emission of visible light. Many chromophores have already been adapted for this purpose and leading to radical changes in their field, such as the implementation of the chromophore of the Green Fluorescent Protein in bioimaging. Not only are these molecules incredibly useful and versatile, they are also interesting from a more fundamental standpoint. They all involve the excitation of electrons residing in conjugated π systems, and both the excited states and the resulting de-excitation dynamics are influenced by the structure of the chromophore and the functional groups present. A thorough understanding of these properties will aid in their modification. This thesis presents my contribution to the understanding of several biochromophores. The first chapter presents a more in-depth introduction to the field and my place in it. This is followed by a chapter detailing the methodology. The next two chapters focus on two examples of a common functional group in chromophores, the phenolate moiety. This group consists of a deprotonated phenol ring with another functional group branching off the ring, typically in the para- position. In the first of these chapters, the functional group is an NO2 entity, and we explore substitution effects by comparing electronic spectra from the ortho-, meta-, and para- isomers. In the second chapter we look at the chromophore of the Green Fluorescent Protein including experiments on the temperature dependence as well as the effects of microsolvation on the electronic spectra. In iii the last two chapters we look at a second common structural motif, tetrapyrrole. This structure consists of four pyrrole rings linked by methine bridges, with the conjugated system spanning all four rings. The first of these chapters details the properties of protoporphyrin, in which the four pyrrole rings form a conjugated ring. Here we investigate the effect of a strong electric field on the photophysical properties. The final chapter details ongoing experiments on a linear tetrapyrrole known as biliverdin.

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Department of Physics
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University of Colorado Boulder
Boulder, CO
JILA PI Advisors
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