Chemistry Theses and Dissertations

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https://hdl.handle.net/1794/2046

This collection contains some of the theses and dissertations produced by students in the University of Oregon Chemistry Graduate Program. Paper copies of these and other dissertations and theses are available through the UO Libraries.

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Browsing Chemistry Theses and Dissertations by Subject "Absorption spectroscopy"

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    Modeling the Evolving Mixture of H- and J-Aggregates During Organic Film Formation
    (University of Oregon, 2021-04-29) Sosa, Morgan; Wong, Cathy
    Understanding of aggregation in organic semiconducting (OSC) molecules is crucial to ensure desirable interactions in optoelectronics. Weak intermolecular forces driving aggregation can greatly impact the physical and electronic structures, making these materials useful in many applications. Ex situ techniques allow precursor solutions and complete films to be examined but are often unable to give insight into how structural or electronic properties evolve during aggregation. Theoretical models have often been used to explain how physical and spectral characteristics are linked. This dissertation aims to provide a computationally inexpensive method to model the absorption spectra of a mixture of organic molecular aggregates to provide a better understanding of the process of thin film formation and give insight to the evolving physical and electronic properties.This method aims to be fast enough that spectra collected during thin film formation can be analyzed using a typical desktop computer and determine possible aggregate structures. Spectral metrics are used to drastically reduce the computational time required to compare simulated and experimental spectra. This is achieved by discarding simulated spectra that have peak intensity ratios that would not model the experimental spectrum. Spectral metrics also reduces computational time required to compare the experimental and simulated spectra by reducing the total number of energy and intensity comparisons by two orders of magnitude. These two methods reduce the total computational time by over 99% when compared to using a brute force method. The system investigated to demonstrate this technique is a well-studied OSC, pseudoisocyanine (PIC). Although typically thought to be a J-aggregate, we find that the absorption spectrum of PIC cannot be adequately modelled using solely J-aggregates either during molecular aggregation or in the final dry film. Additionally, this dissertation disputes a common assumption that the Huang-Rhys factor of a monomer can be used in simulations of aggregate absorption spectra. The method introduced here could be adopted to simulate the aggregation of other OSCs and can complement other structural characterization and computational techniques to provide feedback for rational design of structural and photophysical properties of OSC materials.