http://hdl.handle.net/1721.1/7645 2013-06-19T18:16:35Z http://hdl.handle.net/1721.1/79274 The use of chirped pulse millimeter-wave spectroscopy in chemical dynamics and kinetics Shaver, Rachel Glyn .Chirped-pulse millimeter wave (CPmmW) spectroscopy is a revolutionary technique that has taken advantage of advances in electronics to give high signal to noise broadband rotational spectra in a very short period of time that provides meaningful line intensities. We have implemented this technique in the 58 - 102 GHz range to study the rotational spectra of molecules with two heavy atoms. Photolysis (at 193 nm) and pyrolysis of vinyl cyanide have produced differing HCN and HNC vibrational population distributions. The photolysis experiment does not sample a collisional regime and the resulting spectra show excited states of HCN and HNC, whereas the pyrolysis experiment, which does sample a collisional regime, results in spectra that are devoid of vibrational satellites. This indicates that the intensities of vibrational satellite transitions sample the photolysis reaction only and not post-photolysis collisional effects. Mono-deuterated vinyl cyanide was photolyzed at 193 nm, in which all HCN/HNC are produced via a four-center mechanism and all DCN/DNC are produced via a three-center mechanism. The HCN and HNC products dominate, demonstrating the greater importance of the three-center mechanism. CPmmW spectroscopy is also a valuable tool in studying unimolecular and bimolecular reactions. We have studied the unimolecular decomposition of deuterated methyl nitrite which produces DNO products and bimolecular hydrogen abstraction reaction of NO with acetaldehyde resulting in HNO products. These reactions demonstrate the potential use of nitric oxide radical as a gas-phase catalyst to perform cracking of hydrocarbons and sugars. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 51-53). 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79273 Optical and spin properties of nitrogen vacancy centers in bulk and nanocrystalline diamond Ofori-Okai, Benjamin Kwasi The NV center is becoming a very hot topic in many areas of science, including, Physics, Chemistry, Biology, and Quantum Information. The Degen group has focused on a specific application of the NV center, namely scanning magnetometry. In my time in the group, I focused on building a microscope and studying NV centers in bulk and nanocrystalline diamond. I began by building a confocal microscope which was capable of observing and determine single NV centers. I made measurements on the photon statistics of different defects to determine if they were single emitters or multiple emitters. I also made microwave frequency magnetic measurements to determine the spin properties of single NV centers by measuring their couplings to neighboring paramagnetic nuclei as well as to a spin bath. Through these efforts, I was able to successfully confirm that the microscope was capable of identifying and measuring single NV centers and their properties. Lastly, I worked on the first steps of improving our understanding of NV centers in bulk diamond crystals. The goal of magnetometry involves putting the NV center as close to the diamond surface as possible. I made measurements that were aimed at studying the spin and coherence properties of the NV when it was within 10 nm of the diamond surface. These studies provided insight into the interactions of the NV center with the diamond surface. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.; Cataloged from PDF version of thesis.; Includes bibliographical references. 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79272 The synthesis and characterization of porous, conductive, and ordered materials Narayan, Tarun Chandru Two different classes of polymers were pursued as candidates for materials possessing porosity, conductivity, and crystalline order. Attempts were made with hexaazatrinaphthylene- and dibenzotetrathiafulvalene-based precursors with boronic acids to prepare covalent-organic frameworks (COFs) possessing boroxole linkages. After preparing the precursors, several different reaction conditions were attempted, but the desired COFs proved elusive. The second class of materials was tetrathiafulvalene-based metal-organic frameworks (MOFs). These materials were constructed with tetrathiafulvalene tetrabenzoic acid and zinc, cobalt, and manganese nitrate to give helical structures with approximately cylindrical pores. This structure type has one close S-S contact of 3.8 Å which acts as a potential avenue for charge transfer. Gas sorption measurements suggest that the materials retain porosity upon evacuation. The material possesses high charge mobility as determined by flash photolysis time-resolved microwave conductivity measurements. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2013.; "February 2013." Vita. Cataloged from PDF version of thesis.; Includes bibliographical references (p. 87-92). 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79271 Supramolecular quantum dot-porphyrin assemblies for biological oxygen sensing Lemon, Christopher M. (Christopher Michael) Generating metabolic profiles of tumors provides a spatiotemporal map of the concentration of key species to assess and quantify tumor growth, metabolism, and response to therapy. Because the tumor microenvironment is characterized by hypoxia, the concentration of oxygen is an important indicator of tumor health. Understanding how this parameter changes as a function of disease progression is critical to develop novel targeted therapeutics. New non-invasive sensors must be developed that are small enough to penetrate into the tumor and monitor dynamic changes with high resolution. To this end, this thesis presents new oxygen sensors that are a supramolecular assemblies of a quantum dot (QD) and a palladium(II) porphyrin. High spectral overlap between QD emission and porphyrin absorption results in efficient Förster resonance energy transfer (FRET) for signal transduction in these sensors. Porphyrins with meso pyridyl substituents bind to the surface of the QD to produce self-assembled nanosensors. Since these macrocycles are sensitive in the 0-160 torr range, they are ideal phosphors for in vivo biological oxygen quantification. The QD serves as a two-photon antenna to enable sensing under two-photon excitation. Multiphoton imaging is a powerful technique that is nondestructive to tissue and provides high-resolution images of live tissue at depths of several hundred microns with submicron spatial resolution. Having studied the photohysical properties of these sensors under both one- and two-photon excitation in organic solvents, these sensors were then encapsulated in lipid micelles to quantify oxygen in aqueous media. In these constructs, the quantum dot also serves as an internal intensity standard, furnishing a ratiometric oxygen sensor. Preliminary in vivo multiphoton imaging and oxygen measurements were conducted using mice with chronic dorsal skinfold chambers or cranial windows. Together, the properties of this sensor establish a ratiometric two-photon oxygen sensor for applications in probing biological microenvironments. Thesis (S.M. in Inorganic Chemistry)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.; Vita. Cataloged from PDF version of thesis.; Includes bibliographical references. 2013-01-01T00:00:00Z