Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Elucidating the impacts of structural heterogeneity on excited state dynamics in solution-processed materials(Montana State University - Bozeman, College of Letters & Science, 2024) Afrin, Sajia; Chairperson, Graduate Committee: Erik Grumstrup; This is a manuscript style paper that includes co-authored chapters.Solution-processed inorganic and organic semiconductors hold enormous promises due to their low manufacturing cost, scalability, and compatibility with flexible substrates. However, solution processing techniques do not require control over crystal growth, which can lead to structural defects within the crystal structure. The defects within solution-processed semiconductors can create significant challenges in optimizing device functionality; therefore, it is crucial to understand the impact of structural defects on photophysical properties. Traditional ensemble measurement techniques can conceal the effects of microscale structural defects on functional properties in the structure-averaged observation of solution-processed materials. The work presented in this dissertation employs time-resolved and spectrally resolved microscopy techniques to investigate the influence of structural heterogeneity on the photophysical properties of microscale solution-processed materials. Measurements collected across multiple discrete and highly crystalline domains of multiple classes of solution-processed materials have helped establish a relationship between the functionality and the local structure of these materials. Initially, the focus was on elucidating anisotropic carrier transport in lead halide perovskites by investigating lattice strain and energetic distribution in microcrystals. Later, the focus shifted towards characterizing and understanding the impact of structural defects on the excited state dynamics in another class of solution-processed material called metal-organic frameworks (MOFs). PCN-222 exhibited rapid exciton transport with time-averaged diffusion coefficients ranging from 0.27 to 1.0 cm2/s and subdiffusive behavior, showing transport slowing on the tens of ps time scale. Subdiffusivity indicated that excited states were rapidly transported through the porphyrin network of PCN-222 before being trapped. Moreover, the first transport measurements and transient absorption microscopic measurements in PCN-222 are reported here. Photoluminescence quenching and heterogeneous relaxation pathways were noted in regions with higher structural heterogeneity. Furthermore, the spectral evolution of porphyrinic PCN-222 MOF was investigated, which revealed excitation-dependent chromophore coupling in the MOF structure. Soret band excitation with enhanced coupling can create more mobile excited states, whereas Q band excitation with reduced coupling will generate fewer mobile excited states. Excitation-dependent chromophore coupling strongly dictates the transport and relaxation properties in MOF microstructures that also illustrate the impact of structural defects on the excited state transport and relaxation dynamics. A significant spectral shift has also been observed in microrods stemming from structural heterogeneity. These findings contribute to a deeper understanding of the impact of structural defects on the photophysical properties of solution-processed materials, facilitating the development of optimized semiconductor devices for various applications. The results reported in this dissertation will not only continue to aid in the characterization of MOFs but will also advance our understanding of excited state dynamics in a variety of solution-processed materials.Item Solute partitioning into model biological membranes studied with time-resolved emission spectroscopy and calorimetry(Montana State University - Bozeman, College of Letters & Science, 2022) Duncan, Katelyn Marie; Chairperson, Graduate Committee: Robert Walker; This is a manuscript style paper that includes co-authored chapters.Bioaccumulation and bioconcentration are terms used to quantify the concentration of the solute in an organism with respect to the source of exposure. Empirical values are commonly used to predict a solutes tendency for bioconcentration. While they are useful zeroth order indicators, empirical values lack the chemical specificity required to fully understand the exact solute-solute and solute-lipid chemical interactions that occur when a solute is introduced to a biological membrane. The work described here uses fluorescence spectroscopy and thermoanalytical techniques to quantify solute partitioning into model biological membranes. The model membranes used in this study are lipid bilayer vesicles that are analyzed as a function of temperature from the rigid gel-phase through the transition temperature and into the fluid liquid-crystalline phase. Studies described in this work seek to create a quantitative, mechanistic description of solute behavior in heterogeneous chemical environments. Each body of work either altered the solute used for partitioning or altered the membrane to add chemical complexity. The first body of work describes a proof-of-concept study analyzing the change in partitioning behavior from small structural changes in the solute. This study found that small changes to the solute affects membrane permeability in a way that is not accounted for in empirical models. The subsequent study sought to understand how the addition of amino acids to the membrane changes partitioning tendencies. Further analysis was done to study the partitioning behavior of amino acid L-Phenylalanine. Studies showed L-Phenylalanine integrates into the membrane and experiences a conformationally restricted environment. Additional studies were done on a pharmaceutical candidate and found membrane permeability does not correlate with drug activity. The drug was predicted to interact with the target-protein directly. Furthermore, analysis on the herbicide Dicamba has shown some indication of membrane interaction; however, more studies are required to fully understand the partitioning behavior.