Browsing by Subject "Metal complexes"
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Item Electron transport in single-molecule transistors(2006) Chae, Dong-hun; Yao, Zhen, Ph. D.Electron transport through single molecules is greatly affected by electron-electron interactions, coupling between electron and internal vibrational modes, and the spin degree of freedom. In this thesis, we investigate electron transport in single-molecule transistors incorporating various molecules including trimetal complexes, porphyrins, and expanded porphyrins. A strong coupling of tunneling electron to internal vibrational modes in single-molecule transistors (SMTs) distinguishes the transport characteristics from other single-electron transistors even though SMTs exhibit the single-electron tunneling behaviors due to the Coulomb interaction. In SMTs incorporating trimetal compounds, we have consistently observed low-energy excitations, which are most likely attributed to the internal vibrational modes. Interestingly, we have observed a dramatic change of these low-energy excitations with respect to electron charge state. In porphyrin-SMTs, we have found experimental evidences that higher-order tunneling occur via vibrationally excited states.Item New materials for advanced applications : electrochromism, electrocatalysis, and bioimaging(2017-05-02) Liang, Yawei; Jones, Richard A., 1954-; Que, Emily L; Rose, Michael J; Mullins, Charles Buddie; Campion, AlanElectrochromic materials have the applications in smart-windows, electrochromic mirrors, and electrochromic display devices. Three Fe(II) bis(terpyridine)-based complexes with thiophene (2.2a), bithiophene (2.2b), and 3,4-ethylenedioxythiophene (2.2c) side chains have been synthesized to provide two terminal active sites for electrochemical polymerization. The thin film of poly-2.2b has been electrodeposited on ITO/glass substrate and was characterized using electrochemistry, X-ray photoelectron spectroscopy, UV-vis spectroscopy and atomic force microscopy. The film exhibited great optical contrast with a change of transmittance of 40% upon applying voltage to it, and a coloration efficiency of 3823 cm²C⁻¹ with a switching time of 1 s. It also demonstrated commonplace stability and reversibility, with a 10% loss in peak current intensity after 200 cyclic voltammetry (CV) cycles and almost no loss in change of transmittance after 900 potential switches between 1.1 V and 0.4 V (vs Fc⁺/Fc). Lanthanide complexes have unique photophysical properties that can be utilized in areas such as bioimaging, bio-sensors, fluoroimmunoassays, and organic light emitting diodes. Our group has previously synthesized the complex-Eu(III) tris-(2-thenoyltrifluroacetonate) 2,6-bis(pyrazoly)pyridine [Eu(bppy)(tta)₃], which has a quantum yield of 60% in dichloromethane solution and 90% in solid state. Various functionalities were introduced on the original bppy ligand, such as carboxyl, hydroxyl, and amino groups to provide the active sites for bioconjugation purpose. Four Eu(III)(R-bppy)(tta)₃ complexes (3.2a-3.2d) were synthesized and their photophysical properties were fully characterized. Their quantum yields range from 20.2% to 45.4% and lifetimes range from 383.9-417.2 [mu]s. Efficiently transforming the greenhouse gas CO₂ into liquid fuels or useful synthetic precursors would have a significant impact on balancing the global carbon cycle. A series of mononuclear Re(I) complexes with dipyrido[3,2-a:2’,3’-c]phenazine (dppz) derived ligands (4.2a-4.2d) were synthesized and investigated as homogeneous electrocatalysts for CO₂ reduction. CV studies showed large enhancements of the cathodic currents under CO₂ atmosphere for the Re(I) complexes, indicating the electrocatalytic reduction of CO₂. CO was confirmed as the only gaseous phase product by gas chromatography. Compared to the Lehn catalyst, a benchmark catalyst for reducing CO₂ to CO, the Re(I) dppz complex with a larger degree of conjugation transformed CO₂ into CO at a lower overpotential.Item Novel organometallic precursors for the Chemical Vapor Deposition of metal thin films(2010-08) Rivers, Joseph Henry; Jones, Richard A., 1954-; Cowley, Alan H.; Holliday, Bradley J.; Magnus, Philip D.; Ekerdt, John G.With the growing demand for miniaturization of devices and for new materials with useful properties, the use of Chemical Vapor Deposition (CVD) for the manufacture of thin films is receiving growing attention. The synthesis of potentially volatile metal complexes and investigation of their use as CVD precursors is an important part of this process. The research presented addresses several major areas of this process, (i) the identification and synthesis of ligands which can impart volatility to a metal complex, (ii) the synthesis, characterization, and assessment of volatility of metal complexes containing these ligands, and (iii) the full materials characterization of thin films grown with these complexes. The use of trimethylphosphine, bis(trifluoromethyl)pyrazolate, and bis(trifluoromethyl)pyrrolyl ligands have been successfully used to synthesize volatile new complexes of cobalt, rhodium, and nickel, some of which show promise for use as potential CVD precursors.Item Structural characterization and enhanced detection of flavonoids by electrospray ionization mass spectrometry and molecular modeling(2004-08) Zhang, Junmei, 1970; Brodbelt, Jennifer S.Structural characterization and isomer differentiation of flavonoids was investigated by gas-phase hydrogen/deuterium (H/D) exchange and various metal complexation approaches using electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT-MS). Gas-phase H/D exchange was used to probe the conformations, gas-phase acidities, and sites of deprotonation of isomeric flavonoids. The structural factors that promote or prevent H/D exchange were identified and correlated with collisionally activated dissociation (CAD) patterns and/or molecular modeling data. The use of a transition metal and an auxiliary ligand to form flavonoid/transition metal/auxiliary ligand complexes was proved to be more effective than deprotonation for differentiating isomeric flavonoids using chalcones as an example (a subclass of flavonoids). The relative threshold dissociation energies of such transition metal complexes were measured by energy-variable CAD, and the structural features that influence the threshold energies were identified. The conformations, point charges, and helium (collision gas) accessible surface areas obtained by various computational means were used to rationalize the differences in threshold energies of isomeric flavonoids. Aluminum(III) was used to form strong complexes with flavonoids for more effective isomer differentiation of flavonoids. The CAD patterns of the aluminum complexes were used to differentiate flavonoids, and the structures and conformations of representative flavonoids were also identified by high level computational means. Silver complexation was used to conquer the limitation of the transition metal and aluminum complexation (flavonoids must have a 4-keto group and at least one adjacent hydroxyl group). Silver complexation could not only be used for isomer differentiation of individual flavonoids but could be adapted to characterize flavonoids in mixtures coupled with high performance liquid chromatography (HPLC). HPLC-ESI-MS was used as a sensitive method with high selectivity to detect flavonoids in kale and grapefruit juice and metabolites in urine. The major flavonoids in kale were detected and confirmed as quercetin and kaempferol by CAD and isotopic labeling. The growing conditions were found to significantly affect the flavonoid levels in kale. LC/MS and LC/MS/MS were used to identify the individual metabolites and to gain insight into the overall metabolite profiles in human urine after consumption of grapefruit juice.