Organic semiconductors, particularly π-conjugated polymers and small molecules, enable the development of deformable, stretchable and flexible electronics due to a plethora of factors including their tunable redox, optical, electronic and mechanical properties. However, an informed understanding of how multi-scale morphological characteristics of the polymeric and molecular semiconductors influence bulk properties that contribute to electronic and optical performance, especially under operational thermal and mechanical stresses, remains incomplete. 

This lack of understanding poses a challenge to scalability and commercialization of organic electronics. This dissertation develops and deploys computational modeling approaches, particularly atomistic molecular dynamics (MD) simulations, to investigate the multiscale morphological behavior of these synthetic semiconducting materials in the context of thermomechanical stability. Electron-donating π-conjugated polymers and electron-accepting small molecules — systems that are used in combination to develop bulk heterojunction (BHJ) organic semiconductors — are modeled as their neat phases and as blends to elucidate expectations regarding their thermomechanical behavior as they traverse operational thermal and mechanical processes. 

By systematically modeling these organic semiconductors over time and length scales that approach experiments, this dissertation fits into the larger quest for how local (or long-range) molecular morphology, beginning from molecular structural compositions, dictate thermomechanical behavior, thus providing valuable design and processing principles in the bid for electronically efficient, mechanically robust and manufacture-scale organic electronics.

Organic semiconductors, particularly π-conjugated polymers and small molecules, enable the development of deformable, stretchable and flexible electronics due to a plethora of factors including their tunable redox, optical, electronic and mechanical properties. However, an informed understanding of how multi-scale morphological characteristics of the polymeric and molecular semiconductors influence bulk properties that contribute to electronic and optical performance, especially under operational thermal and mechanical stresses, remains incomplete. 

This lack of understanding poses a challenge to scalability and commercialization of organic electronics. This dissertation develops and deploys computational modeling approaches, particularly atomistic molecular dynamics (MD) simulations, to investigate the multiscale morphological behavior of these synthetic semiconducting materials in the context of thermomechanical stability. Electron-donating π-conjugated polymers and electron-accepting small molecules — systems that are used in combination to develop bulk heterojunction (BHJ) organic semiconductors — are modeled as their neat phases and as blends to elucidate expectations regarding their thermomechanical behavior as they traverse operational thermal and mechanical processes. 

By systematically modeling these organic semiconductors over time and length scales that approach experiments, this dissertation fits into the larger quest for how local (or long-range) molecular morphology, beginning from molecular structural compositions, dictate thermomechanical behavior, thus providing valuable design and processing principles in the bid for electronically efficient, mechanically robust and manufacture-scale organic electronics.

Functional materials used for optoelectronic applications are often employed in the solid-state regime. The properties of such solid-state materials are entirely dependent on the inter and intra molecular interactions that the molecules experience. Intermolecular interactions are interactions between two adjacent molecules and can be broken down into two subgroups: repulsive and attractive. Intramolecular interactions are interactions that occur within a molecule and include things like bonding, resonance, and electron distribution. These properties can be tuned through a number of techniques to afford desirable outcomes for various material applications. This dissertation will investigate how the tuning of the inter and intra molecular forces influence a material’s electronic and optical properties.

The dissertation will cover three projects that leverage control over hydrogen bonding, ionic interactions, and electron density to influence the optoelectronic properties of various systems. The first project attempted to increase intermolecular electronic couplings by using hydrogen bonded coproducts between an organic small molecule semiconductor and benzoic acids. Hydrogen bonding is a monodirectional interaction. The second project, in contrast, focuses on ionic interactions, which are multidirectional. These ionic interactions were investigated through the addition of a conjugated organic core to the inorganic anion in an organic inorganic hybrid material (OIHM) to improve material photoluminescence quantum yield (QY) efficiency. Additionally, alkyl substituents and anion size were changed to probe the effect of spacing on QY. In the third project of this dissertation, the focus moves from intermolecular interactions to intramolecular interactions. This project focuses on using electron donating and accepting groups to tune the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of a metal complex to achieve more efficient deep red and near infrared (NIR) emission.

KEYWORDS: Intermolecular Interactions, Intramolecular Interactions, Optoelectronics, Organic Semiconductors, Light Emitting Materials

Functional materials used for optoelectronic applications are often employed in the solid-state regime. The properties of such solid-state materials are entirely dependent on the inter and intra molecular interactions that the molecules experience. Intermolecular interactions are interactions between two adjacent molecules and can be broken down into two subgroups: repulsive and attractive. Intramolecular interactions are interactions that occur within a molecule and include things like bonding, resonance, and electron distribution. These properties can be tuned through a number of techniques to afford desirable outcomes for various material applications. This dissertation will investigate how the tuning of the inter and intra molecular forces influence a material’s electronic and optical properties.

The dissertation will cover three projects that leverage control over hydrogen bonding, ionic interactions, and electron density to influence the optoelectronic properties of various systems. The first project attempted to increase intermolecular electronic couplings by using hydrogen bonded coproducts between an organic small molecule semiconductor and benzoic acids. Hydrogen bonding is a monodirectional interaction. The second project, in contrast, focuses on ionic interactions, which are multidirectional. These ionic interactions were investigated through the addition of a conjugated organic core to the inorganic anion in an organic inorganic hybrid material (OIHM) to improve material photoluminescence quantum yield (QY) efficiency. Additionally, alkyl substituents and anion size were changed to probe the effect of spacing on QY. In the third project of this dissertation, the focus moves from intermolecular interactions to intramolecular interactions. This project focuses on using electron donating and accepting groups to tune the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of a metal complex to achieve more efficient deep red and near infrared (NIR) emission.

KEYWORDS: Intermolecular Interactions, Intramolecular Interactions, Optoelectronics, Organic Semiconductors, Light Emitting Materials

Organic semiconductors (OSC) are of interest for a wide range of flexible optoelectronics applications, including transistors, solar cells, and sensors, to name a few. Despite their promise, the design and optimization of OSC pose significant challenges due to the complexity of the structures of the molecular building blocks, varied packing configurations of these building blocks in the solid state, which impacts the optical and electronic response, and sensitivity of the solid-state packing to material processing conditions. Accurately predicting the solid-state properties of OSC traditionally requires high-level quantum mechanical methods. These methods, however, can be computationally demanding, particularly for large molecules or when there is interest in extensive material screenings. Overcoming this computational bottleneck is essential to enabling the efficient design of OSC, which would reduce the experimental trial-and-error approach used in material discovery. Moreso, the holy grail of computational study is to be able to accurately and efficiently predict the molecular packing configurations and associated properties of OSC. This dissertation aims to address some of these challenges by developing computational approaches that leverage machine learning (ML) models to accelerate the study of OSC. ML promises to facilitate faster material screening and optimization by offering an alternative to direct quantum mechanical calculations. Specifically, this dissertation describes the development of ML models for intermolecular interactions, including noncovalent interactions (NCI) and electronic couplings (EC). Conventional quantum mechanical methods used to investigate OSC are introduced, and ML approaches are reviewed. The dissertation then discusses the generation of large, high-quality datasets for NCI from symmetry-adapted perturbation theory (SAPT), and the development of ML models to efficiently predict NCI. An active learning approach for the high-throughput derivation of optimal training sets for NCI predictions is then developed, and the training set is used to train new ML models. Finally, ML models to predict EC from three-dimensional (3D) molecular dimer geometries are implemented for the rapid, on-the-fly prediction of ECs across thermally sampled conformations obtained through molecular dynamics (MD) simulations to enable rapid materials characterization during simulation. Ultimately, this dissertation presents a framework that integrates ML with quantum mechanical insights, offering a scalable solution to accelerate OSC discovery and optimization.

KEYWORDS: Organic Semiconductors (OSC), Density Functional Theory (DFT), Symmetry-Adapted Perturbation Theory (SAPT), Noncovalent Interactions (NCI), Electronic Couplings (EC), Machine Learning (ML).

Organic semiconductors (OSC) are of interest for a wide range of flexible optoelectronics applications, including transistors, solar cells, and sensors, to name a few. Despite their promise, the design and optimization of OSC pose significant challenges due to the complexity of the structures of the molecular building blocks, varied packing configurations of these building blocks in the solid state, which impacts the optical and electronic response, and sensitivity of the solid-state packing to material processing conditions. Accurately predicting the solid-state properties of OSC traditionally requires high-level quantum mechanical methods. These methods, however, can be computationally demanding, particularly for large molecules or when there is interest in extensive material screenings. Overcoming this computational bottleneck is essential to enabling the efficient design of OSC, which would reduce the experimental trial-and-error approach used in material discovery. Moreso, the holy grail of computational study is to be able to accurately and efficiently predict the molecular packing configurations and associated properties of OSC. This dissertation aims to address some of these challenges by developing computational approaches that leverage machine learning (ML) models to accelerate the study of OSC. ML promises to facilitate faster material screening and optimization by offering an alternative to direct quantum mechanical calculations. Specifically, this dissertation describes the development of ML models for intermolecular interactions, including noncovalent interactions (NCI) and electronic couplings (EC). Conventional quantum mechanical methods used to investigate OSC are introduced, and ML approaches are reviewed. The dissertation then discusses the generation of large, high-quality datasets for NCI from symmetry-adapted perturbation theory (SAPT), and the development of ML models to efficiently predict NCI. An active learning approach for the high-throughput derivation of optimal training sets for NCI predictions is then developed, and the training set is used to train new ML models. Finally, ML models to predict EC from three-dimensional (3D) molecular dimer geometries are implemented for the rapid, on-the-fly prediction of ECs across thermally sampled conformations obtained through molecular dynamics (MD) simulations to enable rapid materials characterization during simulation. Ultimately, this dissertation presents a framework that integrates ML with quantum mechanical insights, offering a scalable solution to accelerate OSC discovery and optimization.

KEYWORDS: Organic Semiconductors (OSC), Density Functional Theory (DFT), Symmetry-Adapted Perturbation Theory (SAPT), Noncovalent Interactions (NCI), Electronic Couplings (EC), Machine Learning (ML).

Cerebrovasculature refers to the network of blood vessels in the brain, and its coupling with neurons plays a critical role in regulating ion exchange, molecule transport, nutrient and oxygen delivery, and waste removal in the brain. Abnormalities in cerebrovasculature and disruptions of the blood supply are associated with a variety of cerebrovascular and neurodegenerative disorders. Nanocarriers, a nano-sized drug delivery system synthesized from various materials, have been designed to encapsulate therapeutic agents and overcome delivery challenges in crossing the blood-brain barrier (BBB) to achieve targeted and enhanced therapy for these diseases. Unraveling the transport of drugs and nanocarriers in the cerebrovasculature is important for pharmacokinetic and hemodynamic studies but is challenging due to difficulties in detecting these particles within the circulatory system of a live animal. In this dissertation, we developed a technique to achieve real-time in vivo tracking of nanocarriers in the cerebrovasculature using fluorescence correlation spectroscopy (FCS), which has great potential for determining the pharmacokinetics of drugs and nanocarriers, as well as for studying disease-related connections between the cerebrovascular and neurodegenerative diseases.

We utilized novel fluorescent probes composed of DNA-stabilized silver nanocluster (DNA-Ag₁₆NC), that emit in the first near-infrared window (NIR-I) upon two-photon excitation in the second NIR window (NIR-II), encapsulated in liposomes, which were then used to measure cerebral blood flow rates in live mice with high spatiotemporal resolution by two-photon in vivo FCS. Liposome encapsulation concentrated and protected DNA-Ag₁₆NCs from in vivo degradation, enabling the quantification of cerebral blood flow velocity within individual capillaries of a living mouse. We also loaded another DNA-stabilized silver nanocluster (DNA640), which exhibited higher quantum yield and anti-Stokes fluorescence upon upconversion absorption, into cationic mesoporous silica nanoparticles (CMSNs) and successfully coated them with liposomes. The cerebrovasculature was chronically labeled using an adeno-associated viral (AAV) vector encoding Alb-mNG secretion into the bloodstream, combined with FCS under upconversion excitation, enabling real-time observation of the flow velocity and particle number of DNA640-CMSN-liposomes within the capillaries. We applied our proposed techniques to study the cerebrovascular structure and blood flow velocity in Alzheimer's disease mouse models and to explore the effects of disease-related conditions on vasoconstriction and vasodilation.

KEYWORDS: Cerebrovascular, nanocarrier, FCS, NIR fluorescence, DNA-AgNC, in vivo

Zoom link: https://uky.zoom.us/j/5984755867?omn=87194697892

Meeting ID: 598 475 5867.

Cerebrovasculature refers to the network of blood vessels in the brain, and its coupling with neurons plays a critical role in regulating ion exchange, molecule transport, nutrient and oxygen delivery, and waste removal in the brain. Abnormalities in cerebrovasculature and disruptions of the blood supply are associated with a variety of cerebrovascular and neurodegenerative disorders. Nanocarriers, a nano-sized drug delivery system synthesized from various materials, have been designed to encapsulate therapeutic agents and overcome delivery challenges in crossing the blood-brain barrier (BBB) to achieve targeted and enhanced therapy for these diseases. Unraveling the transport of drugs and nanocarriers in the cerebrovasculature is important for pharmacokinetic and hemodynamic studies but is challenging due to difficulties in detecting these particles within the circulatory system of a live animal. In this dissertation, we developed a technique to achieve real-time in vivo tracking of nanocarriers in the cerebrovasculature using fluorescence correlation spectroscopy (FCS), which has great potential for determining the pharmacokinetics of drugs and nanocarriers, as well as for studying disease-related connections between the cerebrovascular and neurodegenerative diseases.

We utilized novel fluorescent probes composed of DNA-stabilized silver nanocluster (DNA-Ag₁₆NC), that emit in the first near-infrared window (NIR-I) upon two-photon excitation in the second NIR window (NIR-II), encapsulated in liposomes, which were then used to measure cerebral blood flow rates in live mice with high spatiotemporal resolution by two-photon in vivo FCS. Liposome encapsulation concentrated and protected DNA-Ag₁₆NCs from in vivo degradation, enabling the quantification of cerebral blood flow velocity within individual capillaries of a living mouse. We also loaded another DNA-stabilized silver nanocluster (DNA640), which exhibited higher quantum yield and anti-Stokes fluorescence upon upconversion absorption, into cationic mesoporous silica nanoparticles (CMSNs) and successfully coated them with liposomes. The cerebrovasculature was chronically labeled using an adeno-associated viral (AAV) vector encoding Alb-mNG secretion into the bloodstream, combined with FCS under upconversion excitation, enabling real-time observation of the flow velocity and particle number of DNA640-CMSN-liposomes within the capillaries. We applied our proposed techniques to study the cerebrovascular structure and blood flow velocity in Alzheimer's disease mouse models and to explore the effects of disease-related conditions on vasoconstriction and vasodilation.

KEYWORDS: Cerebrovascular, nanocarrier, FCS, NIR fluorescence, DNA-AgNC, in vivo

Zoom link: https://uky.zoom.us/j/5984755867?omn=87194697892

Meeting ID: 598 475 5867.

The health of our communities depends on the effective treatment of both solid and liquid waste to eradicate hazardous pollutants before they can interact with living organisms or contaminate the environment. Daily, society generates solid waste (commonly destined for landfills) and liquid waste, (commonly discharged into wastewater systems) and without proper treatment, these wastes can release hazardous primary secondary pollutants. Industries producing wastewater with high pollutant concentrations, especially those utilizing lignin-based biomass, face complex challenges because each facility may require a tailored treatment approach. In response, this work investigates the use of ozonolysis to transform lignin monomers into smaller, less hazardous components that can be more efficiently managed by public wastewater systems. Furthermore, while conventional wastewater treatment systems are effective for common water quality issues, they can inadvertently allow complex compounds, such pollutants from hospital effluent, to pass through. Under simulated treatment conditions incorporating sunlight and chlorination, a pollutant released from medical facilities is degraded, but this process may also lead to the formation of carcinogenic disinfection by-products (DBPs) that pose direct toxicological risks to nearby communities. The implications extend to solid waste management as well. Chemical phenomena, such as those occurring in poorly understood elevated temperature landfills (ETLFs), can compromise treatment methods and increase community exposure to harmful pollutants. By monitoring hazardous components, such as volatile organic compounds (VOCs), over time, this work aims to elucidate the chemical reactions occurring both during treatment and in the environment thereafter. Ultimately, this research underscores the need for fundamental, innovative approaches to pollution transformation. Bridging the gap between existing practices for solid and liquid waste treatment will be critical to safeguarding environmental and public health.

The health of our communities depends on the effective treatment of both solid and liquid waste to eradicate hazardous pollutants before they can interact with living organisms or contaminate the environment. Daily, society generates solid waste (commonly destined for landfills) and liquid waste, (commonly discharged into wastewater systems) and without proper treatment, these wastes can release hazardous primary secondary pollutants. Industries producing wastewater with high pollutant concentrations, especially those utilizing lignin-based biomass, face complex challenges because each facility may require a tailored treatment approach. In response, this work investigates the use of ozonolysis to transform lignin monomers into smaller, less hazardous components that can be more efficiently managed by public wastewater systems. Furthermore, while conventional wastewater treatment systems are effective for common water quality issues, they can inadvertently allow complex compounds, such pollutants from hospital effluent, to pass through. Under simulated treatment conditions incorporating sunlight and chlorination, a pollutant released from medical facilities is degraded, but this process may also lead to the formation of carcinogenic disinfection by-products (DBPs) that pose direct toxicological risks to nearby communities. The implications extend to solid waste management as well. Chemical phenomena, such as those occurring in poorly understood elevated temperature landfills (ETLFs), can compromise treatment methods and increase community exposure to harmful pollutants. By monitoring hazardous components, such as volatile organic compounds (VOCs), over time, this work aims to elucidate the chemical reactions occurring both during treatment and in the environment thereafter. Ultimately, this research underscores the need for fundamental, innovative approaches to pollution transformation. Bridging the gap between existing practices for solid and liquid waste treatment will be critical to safeguarding environmental and public health.