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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2018)

The sun produces 1020 W m-2 of energy per day; that is, in one hour, the earth receives enough energy to power the earth for an entire year. This energy can be harvested for a range of processes, including water splitting, photocatalysis, and electricity. Photovoltaic technologies, in particular, harness the energy of the sun to produce electrical energy. Organic solar cells, or organic photovoltaics (OPVs), hold advantages over inorganic cells in scalability, range of functionalization, and potential in flexible applications. While the power conversion efficiency (PCE) of this relatively new type of solar cell has made tremendous progress over the last decade, OPVs must continue to improve over 15% PCE in order to become a viable competitor to inorganic cells.

Several factors in the active layer (donor and acceptor layers) of a solar cell can lead to low efficiency, including low carrier mobility, inadequate absorption of the electromagnetic spectrum, and disordered morphology. Therefore, control of morphology in the active layer and tuning of electronic levels of the donors and acceptors in organic photovoltaics are important parameters that need to be controlled for favorable device performance. One approach to improving efficiency is designing molecules that pack closely together to allow for efficient charge transport. These types of systems offer significant possibilities for controlled morphologies, high charge transport, and high efficiencies in solar cells. Towards these types of materials, this work aims to:

1. Understand the effect of torsional behavior in organic materials on the morphology of the active layer to guide the design of materials with low disorder.

2. Determine the effect of crystal packing on charge transport of organic small-molecules and oligomers to lend insight into mechanisms that govern high mobility, and

3. Characterize optical properties of trimeric oligomers to lend insight into potential electronic applications.

Motivated by the potential of new organic photovoltaic materials, this thesis begins with a focus on using computational methods to understand systems of relevance to organic electronics (Chapters 1-7). Early projects aim to use an iterative computational-experimental scheme to understand morphology and charge transport as relevant in organic electronic devices (Chapters 1-3). Molecular properties are calculated and correlated to bulk properties observed experimentally to derive design principles for new molecules that would give rise to interesting packing in solid state. Excited state calculations are used to understand the underlying properties that give rise to optical transitions and to predict new molecules that would absorb strongly in the visible light region (Chapters 4). Mechanistic studies of the degradation pathways of small molecules will also be discussed, and functional handles that would lead to more stable structures are identified (Chapter 5). Calculations are employed to understand the transformation of polydiacetylene polymers to graphene nanoribbons, which lends insight into tuning this reaction for other N-doped materials (Chapter 6). Later in the thesis, the focus diverges to the use of computations to understand the reactivity of a class of ruthenium-based olefin metathesis catalysts towards the design of a stable, E-selective catalyst (Chapter 7-8).

Various methods are employed in the chapters described in this dissertation. Density functional theory is used to characterize ground state geometry, conformational analysis, transition state geometry, molecular orbitals, reorganization energies. Time-dependent density functional theory is used to characterize excited state properties, including bandgap, absorption, emission, excited state geometry, charge transfer properties. ZINDO is used for other excited state properties such as charge transfer, electronic coupling. Molecular dynamics is used for time-scale properties, including electronic disorder, energetic disorder, ordered and disordered morphology. Kinetic Monte Carlo as implemented in the VOTCA program is used for charge transport calculations.

    Cover page: Computational Studies of Organic Electronic Materials
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2015)
    Although pica, the craving and purposive consumption of non-food substances, is common among many populations, especially during pregnancy, the health consequences are not well understood. Further, very little is known about pica among Mexican populations in the United States and Mexico. Therefore, we conducted formative research to understand pica in this understudied population. Our objectives were to identify the frequency and types of pica behaviours, to understand perceived aetiologies and consequences of pica and to ascertain if the behaviour was common enough to warrant a larger study. We held nine focus group discussions (three in the Salinas Valley, California; six in Xoxocotla, Morelos, Mexico) with 76 Mexican-born women who were currently pregnant or had delivered within the past 2 years. Earth, adobe, bean stones and ice were the most commonly reported pica substances. Twenty-eight of the 76 participants (37%) reported ever engaging in pica; 22 participants (29%) reported doing so during pregnancy. The proportion of women reporting pica in the United States and Mexico was 43% and 34%, respectively. Women attributed pica to the overwhelming organoleptic appeal of pica substances (especially smell and texture) and to micronutrient deficiencies. Perceived consequences of unfulfilled pica cravings were birthmarks or fetal loss; fulfilled pica cravings were also thought to be generally harmful to the mother or child, with several women specifying toxic lead, pesticides or 'worms'. In sum, pica among Mexican women is common enough to warrant a larger epidemiologic study of its sociodemographic correlates and physiological consequences.
      Cover page: Pica among Mexican women
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2020)
      The synthesis of graphene nanoribbons (GNRs) that contain site-specifically substituted backbone heteroatoms is one of the essential goals that must be achieved in order to control the electronic properties of these next generation organic materials. We have exploited our recently reported solid-state topochemical polymerization/cyclization-aromatization strategy to convert the simple 1,4-bis(3-pyridyl)butadiynes 3a,b into the fjord-edge nitrogen-doped graphene nanoribbon structures 1a,b (fjord-edge N2[8]GNRs). Structural assignments are confirmed by CP/MAS 13C NMR, Raman, and XPS spectroscopy. The fjord-edge N2[8]GNRs 1a,b are promising precursors for the novel backbone nitrogen-substituted N2[8]AGNRs 2a,b. Geometry and band calculations on N2[8]AGNR 2c indicate that this class of nanoribbons should have unusual bonding topology and metallicity.
        Cover page: Fjord-Edge Graphene Nanoribbons with Site-Specific Nitrogen Substitution
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2017)
        Gene-disruptive mutations contribute to the biology of neurodevelopmental disorders (NDDs), but most of the related pathogenic genes are not known. We sequenced 208 candidate genes from >11,730 cases and >2,867 controls. We identified 91 genes, including 38 new NDD genes, with an excess of de novo mutations or private disruptive mutations in 5.7% of cases. Drosophila functional assays revealed a subset with increased involvement in NDDs. We identified 25 genes showing a bias for autism versus intellectual disability and highlighted a network associated with high-functioning autism (full-scale IQ >100). Clinical follow-up for NAA15, KMT5B, and ASH1L highlighted new syndromic and nonsyndromic forms of disease.
          Cover page: Targeted sequencing identifies 91 neurodevelopmental-disorder risk genes with autism and developmental-disability biases
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