Donor-Acceptor Constructs for Optical Oxygen Sensing and Corroles: Photophysics, Electronic Structure, and Photochemistry
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CitationLemon, Christopher Michael. 2016. Donor-Acceptor Constructs for Optical Oxygen Sensing and Corroles: Photophysics, Electronic Structure, and Photochemistry. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractMetabolic tumor profiling illustrates the spatiotemporal distribution of key analytes to assess and quantify tumor growth, metabolism, and response to therapy. Since the tumor microenvironment is characterized by hypoxia, the ability to track and quantify changes in oxygen concentration as a function of disease progression or therapy is crucial to the advancement of targeted therapeutics. The ability to monitor these changes necessitates the development of non-invasive sensors that are small enough to penetrate into tumor tissue and monitor dynamic changes with high resolution in real time.
To address this challenge, this thesis details the design, synthesis, and characterization of optical oxygen sensors that combine a fluorescent semiconductor quantum dot (QD) with a Pd(II) porphyrin or Au(III) corrole as the oxygen-responsive phosphor. In these constructs, the QD donor serves as a photon antenna and transfers the absorbed energy to the appended porphyrin or corrole acceptor by Förster resonance energy transfer (FRET). The triplet state of the phosphor is quenched by molecular oxygen and is responsive over the biologically relevant 0–160 Torr O2 range. These donor–acceptor conjugates are prepared by self-assembly in organic solvents or micelle encapsulation in aqueous media. The Pd(II) porphyrin micelles were then used for in vivo imaging and oxygen sensing in murine models.
In the search for alternative phosphors for optical oxygen sensing, a variety of metallocorrole complexes were prepared. Although these derivatives were not phosphorescent, they have provided insight into the photophysics, electronic structure, and photochemistry of corroles, as described in the second half of this thesis. The photophysical properties of free-base, Au(III), Sb(III), and Sb(V) corroles were interrogated. The role of corrole as a non-innocent ligand was then explored for copper and silver complexes. Analysis of these compounds reveals that copper complexes are Cu(II) corrole radical cations, while the silver analogs are authentic Ag(III) complexes. Finally, the photochemistry of Sb(V) corroles was studied for both C–H activation of organic substrates and halogen evolution as a potential solar fuel. Together, these studies examine fundamental photophysics and electronic structure, as well as provide examples where these complexes may be used to mediate photochemical transformations.
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