Date of Award

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Committee Chair/Advisor

Prof. Stephen H. Foulger

Committee Member

Prof. Philip Brown

Committee Member

Prof. Olga Kuksenok

Committee Member

Prof. Igor Luzinov

Abstract

Understanding and manipulating quantum light-matter interactions, especially in the context of nanostructured environments, is highly critical for technological progress and inventive solutions in the fields of telecommunications, energy-efficient lighting, and cutting-edge quantum computing technologies. The fundamental interactions of photons with a surrounding environment directly impact the performance and efficiency of devices such as lasers, light-emitting diodes (LEDs), and quantum computing elements, which leverage the unique properties of confined structured environments. Since the late 1980s, the connection between a structured environment and the decay kinetics of an embedded fluorophore has been a highly debated and unresolved topic in the literature. More recently, the relationship between a structured environment and the interactions between multiple embedded fluorophores has ignited further debate in the scientific community. A photonic crystal structure composed of electrostatically-stabilized colloidal nanoparticles known as a crystalline colloidal array (CCA) exhibits a partial photonic bandgap that can be shifted across the full visible spectrum by a change in the interplanar spacing between the nanoparticles. Due to the easily tunable partial photonic bandgap position of a CCA, this structure offers an ideal platform for which the photophysical properties of one or more embedded fluorophore(s) can be explored with and without bandgap coupling. To that end, the nanostructured environment of a CCA was exploited to investigate 1) the connection between a structured environment and the decay kinetics of an embedded emitter and 2) the connection between a structured environment and the interactions between multiple embedded emitters. These phenomena were investigated by three main approaches (1-3). Additionally, the interactions between multiple embedded emitters within the colloidal nanoparticle building blocks of CCA resulted in emission spanning the full visible spectrum upon X-ray excitation and could be extended to the near-infrared (NIR) region using click chemistry. To that end, fully organic nanoparticles exhibiting NIR-emission via four multiple sequential energy transfers for X-ray bioimaging applications were investigated as less toxic alternatives to heavy metal-containing X-ray contrast agents, which are currently a primary research focus in the scientific community. These nanoparticles were investigated using one main approach (4). (1) Nanophotonic manipulation of decay kinetics. The connection between a structured environment and the decay kinetics of an embedded emitter were explored by copolymerizing a naphthalimide derivative within polystyrene-based nanoparticles. The resultant nanoparticles spontaneously self-assembled into a crystalline colloidal array (CCA), resulting in a partial photonic bandgap, or rejection wavelength, in the visible regime. Time-resolved fluorescence of the ordered structure at various rejection wavelength conditions was monitored at high- and low-energy electronic transition frequencies across the emission spectrum of the naphthalimide-copolymerized nanoparticles. Careful attention was given to the reference systems used to quantify photonic effects, the wavelengths at which decay kinetics were monitored, and the quantum yield of the naphthalimide-derived emitter. Increased and decreased fluorescence lifetimes were detected, depending on the position of the rejection wavelength in relation to the emission of the emitter and the monitored wavelength, revealing critical insights in the context of quantum light-matter interactions and opportunities for strategic control over emitter decay pathways. (2) Nanophotonic manipulation of energy transfer in a photoluminescent CCA. Understanding the unresolved connection between a structured environment and the Forster resonance energy transfer between emitters is critical in the realm of quantum light-matter interactions, especially for quantum technology applications. This crucial topic was explored by copolymerizing three emitters capable of energy transfer within two nanoparticle series of polystyrene-based CCAs. Upon excitation by ultraviolet light, sequential energy transfer between the three emitters resulted in emission spanning the visible spectrum. Nanophotonic control over the photoluminescence of each CCA was demonstrated by red-shifting the partial photonic bandgap through the emission spectrum. Nanophotonic manipulation of the energy transfer between two pairs of emitters was observed, revealing insights in the context of quantum light-matter interactions. Specifically, control over the spectral properties, energy transfer efficiency, and decay kinetics was demonstrated by strategic placement of the bandgap. (3) Nanophotonic manipulation of energy transfer in a radioluminescent CCA. The unresolved correlation between a nanostructured environment, like a CCA, and the FRET between multiple embedded emitters is a fundamental aspect of quantum light-matter interactions with implications for various high-priority applications, such as telecommunications, energy-efficient lighting, and quantum computing technologies. This highly debated topic was explored in two series of organic radioluminescent nanoparticles, containing a copolymerized scintillator and two organic fluorophores, that self-assembled into a CCA. The three copolymerized emitters exhibited two sequential transfers of energy upon X-ray radiation, resulting in emission spanning the visible spectrum. Nanophotonic manipulation of the radioluminescence of each CCA and energy transfer between emitters was demonstrated by positioning the partial photonic bandgap of the CCA within the spectral regions attributed to each copolymerized emitter. Enhanced and suppressed energy transfer was exhibited in each nanoparticle series, revealing control over FRET in a radioluminescent system through strategic placement of the bandgap. (4) Fully organic, NIR-emitting nanoparticles for X-ray bioimaging applications. In the efforts to generate a less toxic X-ray bioimaging contrast agent, a fully organic, radioluminescent nanoparticle system that emits in the NIR region when excited with an X-ray source was synthesized using a two-step process. First, red-emitting nanoparticles were fabricated by the emulsion copolymerization of styrene, propargyl acrylate, and anthracene, naphthalimide, and rhodamine B methyl methacrylate derivatives. Subsequently, the nanoparticles were modified with silicon phthalocyanine (SiPc) and indocyanine green (ICG) derivatives via a copper(I)-catalyzed azide/alkyne cycloaddition (CuAAC) click reaction. By coupling an organic scintillator with four FRET pairing dyes, X-ray-induced, multiple, sequential energy transfer was exploited to convert ionizing radiation from an X-ray source into NIR light, which is optimal for biomedical imaging. Proof-of-concept imaging studies show that the X-ray-induced ICG fluorescence from the particulate system can be visualized through porcine tissue. Additionally, toxicity studies in human embryonic kidney (HEK) cells indicate that the particles are non-toxic and applicable in vivo.

Author ORCID Identifier

0000-0002-5258-666X

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