abstract: Fluorescence spectroscopy is a powerful tool for biophysical studies due to its high sensitivity and broad availability. It is possible to detect fluorescence from single molecules allowing researchers to see the behavior of subpopulations whose presence is obscured by “bulk” collection methods. The fluorescent probes used in these experiments are affected by the solution and macromolecular environments they are in. A misunderstanding of a probe’s photophysics can lead researchers to assign observed behavior to biomolecules, when in fact the probe is responsible. On the other hand, a probe’s photophysical behavior is a signature of the environment surrounding it; it can be exploited to learn about the biomolecule(s) under study. A thorough examination of a probe’s photophysics is critical to data interpretation in both cases and is the focus of this work. This dissertation investigates the photophysical behavior of symmetric and asymmetric cyanines in a variety of solution and biomolecular environments. Using fluorescent techniques—such as time-correlated single photon counting (TCSPC) and fluorescence correlation spectroscopy (FCS)—it was found that cyanines are influenced by the local environment. In the first project, the symmetric cyanines are found to be susceptible to paramagnetic species, such as manganese(II), that enhance the intersystem crossing (ISC) rate increasing triplet blinking and accelerating photobleaching. Another project found the increase in fluorescence of Cy3 in the protein induced fluorescence enhancement (PIFE) technique is due to reduced photoisomerization caused by the proximity of protein to Cy3. The third project focused on asymmetric cyanines; their photophysical behavior has not been previously characterized. Dy630 as a free dye behaves like Cy3; it has a short lifetime and can deactivate via photoisomerization. Preliminary experiments on Dy dyes conjugated to DNA show these dyes do not photoisomerize, and do not show PIFE potential. Further research will explore other conjugation strategies, with the goal of optimizing conditions in which Dy630 can be used as the red-absorbing analogue of Cy3 for PIFE applications. In summary, this dissertation focused on photophysical investigations, the understanding of which forms the backbone of rigorous fluorescent studies and is vital to the development of the fluorescence field. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2017

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Photocatalytic carbon dioxide reduction transforms CO2 to useful chemicals and fuels, reducing CO2 emissions and making fossil fuels more renewable. Due to a lack of earthabundant sensitizers, we want to design new earth-abundant sensitizers to go with the many known carbon dioxide reduction catalysts. Zn(II) dipyrrin complexes strongly absorb visible light, but their excited state properties have not been widely studied. To investigate their photophysical properties, two Zn dipyrrin complexes, with and without heavy atoms, were synthesized and characterized by NMR and mass spectrometry. The photophysical properties of the two complexes were measured in polar and non-polar solvents, particularly fluorescence quantum yield and extinction coefficient. Also, through transient absorption spectroscopy, the triplet state quantum yield of both complexes was measures to determine the effect of solvent polarity and heavy atoms on the triplet state formation.

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This thesis presents theoretical investigations of triplet superfluidity (triplet superconductivity) in quasi-one-dimensional organic conductors and ultra-cold Fermi gases. Triplet superfluidity is different from its s-wave singlet counterpart since the order parameter is a complex vector and the interaction between fermions is in general anisotropic. Because of these distinctions, triplet superfluids have different physical properties in comparison to the s-wave case. The author discusses in this thesis the interplay between triplet superconductivity and spin density waves in quasi-one-dimensional organic conductors, and proposes a coexistence region of the two orders. Within the coexistence region, the interaction between the two order parameters acquires a vector structure, and induces an anomalous magnetic field effect. Furthermore, the author analyzes the matter-wave interference between two p-wave Fermi condensates, and proposes a polarization effect. For a single harmonically trapped p-wave Fermi condensate, the author also shows that the expansion upon release from the trap can be anisotropic, which reflects the anisotropy of the p-wave interaction.

Photon upconversion by sensitized triplet–triplet annihilation (UC-STTA) is a photophysical process that facilitates the conversion of two low-energy photons into a single high-energy photon. A low-energy photon is absorbed by a sensitizer molecule that produces a triplet excited state which is transferred to an emitter molecule. When two emitter triplet states encounter each other, TTA can take place to produce a singlet excited state which decays by emission of a high-energy (upconverted) photon. While traditional single-threshold dye-sensitized solar cells (DSSCs) have a maximum efficiency limit of ca. 30%, it has been predicted theoretically that implementation of UC-STTA in DSSCs could increase that efficiency to more than 40%. A possible way to implement UC-STTA into DSSCs, would be to replace the standard sensi- tized nanostructured TiO2 photoanodes by upconverting ones loaded with emitter molecules. Following TTA, the excited emitter molecule would be quenched by injection of a high-energy electron into the conduction band of the TiO2. To explore the practical aspects of this strategy for a highly efficient DSSC, in this thesis UC-STTA is studied in model systems based on nanostructured ZrO2 films. These ZrO2 films are a good proxy for the TiO2 films used in DSSCs, and allow for relatively easy optimization and study of UC-STTA by allowing measurements of the upconverted photons without the complications of electron injection into the film. Herein it is experimentally proven that UC-STTA is viable on nanostructured metal oxide films under non-coherent irradiation with intensities comparable to sunlight. Two different system architectures are studied, differing in the position of the molecular components involved in the UC-STTA mechanism. Both architectures have the emitter molecules adsorbed onto the ZrO2 surface, but the sensitizers are positioned either in solution around the nanostructure, or co-adsorbed with the emitters onto the ZrO2 surface. A set of challenges in the study and optimization of the UC-STTA process is identified for each type of system. Proposals are also given for how to further improve the understanding and UC-STTA optimization of these systems toward application in DSSCs to overcome the present solar energy conversion efficiency limit.