The time-resolved electrical conductivity of a short-pulse generated plasma filament in air was studied. Close-coupled metal electrodes were used to discharge the stored energy of a high-voltage capacitor and the resulting microsecond-scale electrical discharge was measured using fast current sensors. Significant differences in the time dependence of the current were seen with the two electrode geometries used. Using sharp-tipped electrodes additional peaks in the time-resolved conductivity were seen, relative to the single peak seen with spherical electrodes. We attribute these additional features to secondary electron collisional ionization brought about by field enhancement at the tips. Additional discrepancies in the currents measured leaving the high-voltage electrode and that returning to ground were also observed. Implications for potential laser-induced discharge applications will be discussed.

Polycyclic aromatic compounds (PACs), which comprise a complex class of condensed multi-ring benzenoid compounds, are important environmental pollutants originating from a wide variety of natural and anthropogenic sources. PACs are generally formed during incomplete combustion of pyrolisis of organic matter containing carbon and hydrogen. Because combustion of organic materials is involved in countless natural processes or human activities, PACs are omnipresent and abundant pollutants in air, soil, and water. Chemical analysis of PACs is of great environmental and toxicological importance. Many of them are highly suspect as etiological agents in human cancer. Because PACs carcinogenic properties strongly depend on molecular structure and differ significantly from isomer to isomer, it is of paramount importance to determine the most toxic isomers even if they are present at much lower concentrations than their less toxic isomers. Gas chromatography (GC), high-resolution GC, and high-performance liquid chromatography (HPLC) are the basis for standard PACs identification and determination. Many cases exist where GC, HPLC, and even HR-GC have not been capable to provide unambiguous isomer identification. The lack of reliable analytical data has lead to serious errors in environmental and toxicological studies. This dissertation deals with the development of novel instrumentation and analytical methods for the analysis of PACs in environmental samples. The developed methodology is based on two well-known high-resolution luminescence techniques, namely Shpol'skii Spectroscopy (SS) and Fluorescence Line Narrowing Spectroscopy (FLNS). Although these two techniques have long been recognized for their capability in providing direct determination of target PACs in complex environmental samples, several reasons have hampered their widespread use for the problem at hand. These include inconvenient sample freezing procedures; questions about signal reproducibility; lengthy spectral acquisition, which might cause severe sample degradation due to prolonged excitation; broadband fluorescence background that degrades quality of spectra, precision of measurements and detection limits; solvent constrains imposed by the need of optically transparent media; and, most importantly, the lack of selectivity and sensitivity for unambiguous determination of closely related PACs metabolites. This dissertation presents significant advances on all fronts. The analytical methodology is then extended to the analysis of fluoroquinolones (FQs) in aqueous samples. FQs are one of the most powerful classes of antibiotics currently used for the treatment of urinary tract infections. Their widespread use in both human and animal medicine has prompted their appearance in aquatic systems. The search for a universal method capable to face this new environmental challenge has been centered on HPLC. Depending on the FQ and its concentration level, successful determination has been accomplished with mass spectrometry, room-temperature fluorescence (RTF) or UV absorption spectrometry. Unfortunately, no single detection mode has shown the ability to detect all FQ at the concentration ratios found in environmental waters. We provide a feasible alternative based on FLNS. On the instrumentation side, we present a single instrument with the capability to collect multidimensional data formats in both the fluorescence and the phosphorescence time domains. We demonstrate the ability to perform luminescence measurements in highly scattering media by comparing the precision of measurements in optically transparent solvents (Shpol'skii solvents) to those obtained in "snow-like" matrixes and solid samples. For decades, conventional low-temperature methodology has been restricted to optically transparent media. This restriction has limited its application to organic solvents that freeze into a glass. In this dissertation, we remove this limitation with the use of cryogenic fiber-optic probes. Our final efforts deal with low-temperature absorption measurements. Recording absorption spectra via transmittance through frozen matrixes is a challenging task. The main reason is the difficulty to overcome the strong scattering light reaching the detector. This is particularly true when thick samples are necessary for recording absorption spectra of weak oscillators. In the case of strongly fluorescent compounds, additional errors in absorbance measurements arise from the emission reaching the detector, which might have comparable intensity to that of the transmitted light. We present a fundamentally different approach to low-temperature absorption measurements as the sought-for-information is the intensity of laser excitation returning from the frozen sample to the intensified-charge coupled device (ICCD). Laser excitation is collected with the aid of a cryogenic fiber optic probe. The feasibility of our approach is demonstrated with single-site and multiple-site Shpol'skii systems. 4.2K absorption spectra show excellent agreement to their literature counterparts recorded via transmittance with closed cycle cryogenators. Fluorescence quantum yields measured at room-temperature compare well to experimental data acquired in our lab via classical methodology. Similar agreement is observed between 77K fluorescence quantum yields and previously reported data acquired with classical methodology. We then extend our approach to generate original data on fluorescence quantum yields at 4.2K.

As the global economy searches for reliable, inexpensive and environmentally friendly renewable energy resources, energy conservation by means of photovoltaics has seen near exponential growth in the last decade. Compared to state-of-the-art inorganic solar cells, organic photovoltaics (OPVs) composed of conjugated polymers are particularly interesting because of their processability, flexibility and the potential for large area devices at a reduced fabrication cost. It has been extensively documented that the interchain and intrachain interactions of conjugated polymers complicate the fundamental understanding of the optical and electronic properties in the solid-state (i.e. thin film active layer). These interactions are highly dependent on the nanoscale morphology of the solid-state material, leading to a heterogeneous morphology where individual conjugated polymer molecules obtain a variety of different optoelectronic properties. Therefore, it is of the utmost importance to fundamentally study conjugated polymer systems at the single molecule or nanoparticle level instead of the complex macroscopic bulk level. This dissertation research aims to develop simplified nanoparticle models that are representation of the nanodomains found in the solid-state material, while fundamentally addressing light harvesting, energy transfer and interfacial charge transfer mechanisms and their relationship to the electronic structure, material composition and morphology of the nanoparticle system. In preceding work, monofunctional doped nanoparticles (polymer-polymer) were fabricated with enhanced light harvesting and Fӧrster energy transfer properties by blending Poly[(o-phenylenevinylene)-alt-(2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene)] (BPPV) and Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) at various MEHPPV doping ratios. While single particle spectroscopy (SPS) reveals a broad distribution of v optoelectronic and photophysical properties, time-correlated single photon counting (TC-SPC) spectroscopy displays multiple fluorescence lifetime components for each nanoparticle composition, resulting from changing polymer chain morphologies and polymer-polymer aggregation. In addition, difunctional doped nanoparticles were fabricated by doping the monofunctional doped nanoparticles with PC60BM ([6,6]-phenyl-C61-butyric acid methyl ester) to investigate competition between intermolecular energy transfer and interfacial charge transfer. Specifically, the difunctional SPS data illustrated enhanced and reduced energy transfer mechanisms that are dependent on the material composition of MEH-PPV and PC60BM. These data are indicative of changes in inter- and intrachain interactions of BPPV and MEH-PPV and their respective nanoscale morphologies. Together, these fundamental studies provide a thorough understanding of monofunctional and difunctional doped nanoparticle photophysics, necessary for understanding the morphological, optoelectronic and photophysical processes that can limit the efficiency of OPVs and provide insight for strategies aimed at improving device efficiencies.

Heterobimetallic catalysts offer large potential for efficient and selective catalysis of a wide range of reactions. Better understanding of these catalytic mechanisms could yield further improvement in their catalytic abilities. Cp(CO)2Fe-Cu(IPr) (IPr = N,N-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) is a catalyst that has been reported to catalyze arene borylation. The catalytic mechanism of this catalyst that had been previously proposed had the initial step being a metal-metal cleavage. However, computational modeling suggested an alternate mechanism that could be more energetically favorable. Rather than a metal-metal cleavage as the initial step, we proposed a photoactivated carbonyl dissociation. To support this proposition, we performed time resolved Fourier transform infrared spectroscopy experiments that found evidence supporting our proposed mechanism. Based on these experimental results, we have proposed a new catalytic cycle. The determination of collisional cross section is a powerful tool in analytical chemistry for distinguishing isomers. Techniques such as ion mobility spectrometry can be used to find the collisional cross section of ions but require specialized equipment. Fourier transform ion cyclotron resonance (FTICR) mass spectrometry is a widely used technique for determining ion mass. A technique known as CRoss sectional Area from Fourier Transform Ion cyclotron resonance (CRAFTI) uses a standard FTICR instrument to measure the collisional cross section of ions. This is done by performing a Fourier transform on the data and measuring the Lorenztian width of the peak at the resonant frequency and relating that to the exponential decay of the signal in the time domain. We developed a new data analysis technique that is able to extract just the signal at the resonant frequency in the time domain and directly fit the exponential decay. This new data analysis technique opens new possibilities for expanding the capabilities of CRAFTI measurements, including simultaneous measurement of isomers and a new experimental technique that could measure ions above the mass limit of traditional CRAFTI measurements.

Time-resolved terahertz (THz) spectroscopy is an emerging optical characterization technique with the potential of becoming standard practice in fundamental research and in industry. These systems have the ability to be extremely broadband and can retrieve the phase and amplitude information of a THz pulse transmitted through a material, allowing the complex dielectric function of the material to be extracted. Although these systems are already extremely impactful, they nonetheless have their shortcomings. Namely, the data acquisition time required for a single measurement hinders their practicality in an industrial setting or retrieving interesting dynamics within a sample that are occurring on faster timescales. Moreover, broadband THz systems carry a significant financial burden as they rely on ultrafast near-infrared (NIR) sources delivering sub-100 fs pulses, limiting their accessibility. In this work, we address these issues plaguing time-resolved THz systems with the implementation of optical fibers. We begin by describing the physical processes governing ultrashort pulse propagation in fiber and the generation and detection of THz pulses via nonlinear effects in semiconductor crystals. We then design and demonstrate a THz detection scheme able to resolve each of the generated THz pulses at a repetition rate of 50 kHz. This includes using fiber to generate a chirped NIR supercontinuum, imprinting THz waveforms onto the NIR spectrum and thereby enabling single-shot THz detection; and using fiber to achieve photonic time-stretch, a technique allowing us to detect each of the THz-encoded NIR pulses with high-speed electronics at a rate determined by the repetition rate of the laser. The resulting system is then used to track carrier dynamics in a semiconductor as they are dynamically accumulating and recombining. We then combine nonlinear propagation in optical fiber with a time-resolved THz system allowing us to achieve broadband THz generation and detection. We describe two systems relying on this general scheme: The first system relies on a compact and cost-effective laser source and a standard fiber to generate and detect a THz spectrum extending up to 6 THz, alleviating the financial strain imposed by systems relying on sophisticated laser sources without sacrificing performance. The other system relies on an amplified laser source and gas-filled hollow-core photonic crystal fiber (PCF) to generate a tunable spectrum up to 20 THz. Finally, we investigate the generation of a supercontinuum spanning more than two octaves inside a highly nonlinear solid-core PCF. For the first time, we explore both the spectral intensity and polarization structure of such a broad optical spectrum approaching the mid-infrared region.

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