Browsing by Subject "Iridium"

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    Optical properties of Iridium(III) cyclometalates:excited state interaction with small molecules and dynamics of light-harvesting materials.
    (2012-08) Schwartz, Kyle Robert
    The research presented in this thesis concerns the use and understanding of luminescent Ir(III) cyclometalates. Areas of research involve the design, synthesis, and characterization of novel luminescent Ir(III) cyclometalates, including photophysical investigation of their phosphorescent excited states using steady-state and time resolved absorption/luminescence spectroscopies. This broad research description may be further separated into two subareas: study of excited state interaction with small molecules and excited-state dynamics of metal-organic light harvesting dyads. The first chapter of this thesis examines the interaction of Ir(III) cyclometalates with the small molecule carbon dioxide (CO2). It has been the goal of investigators to develop methods for direct optical detection of CO2. This has been difficult as CO2 is considered chemically inert and there are few luminescent probes directly sensitive to CO2. Most optical detection schemes previously developed for CO2 use indirect detection methods, which rely upon measuring changes in pH brought about by hydrolysis of CO2. Research efforts to design a reliable method for the direct optical detection of CO2 were accomplished through development of a system where hydrazine, a simple amino ligand, when coupled into the coordination sphere of an Ir(III) cyclometalate reacts with CO2. The result of this reaction provides a significant shift in the luminescence λmax of the phosphorescent probe, a previously unobserved optical response for the direct detection of CO2. The second chapter investigates phosphorescent excited states and their ability to function as triplet sensitizers for the generation of singlet oxygen (1O2) and luminescent probes for molecular oxygen (O2) concentration. Interaction of phosphorescent excited states with O2 results in energy transfer from the luminescent probe to O2, quenching the phosphorescent excited state. Energy transfer also generates the reactive oxygen species (ROS) 1O2. We have used this duality to develop an analytical methodology to follow the serendipitously discovered photoreactivity of 1O2 with common organic solvent dimethyl sulfoxide (DMSO) using the luminescence profile of Ir(III) and Ru(II) phosphors. Reaction of the triplet sensitized 1O2 with a photooxygenation substrate results in the consumption of O2 from the system and an increase in the observed luminescence intensity. Detailed kinetic investigations of the luminescence recovery and O2 depletion were preformed on air-saturated closed cell systems. Determinations of the quantum efficiencies for the photooxygenation system were performed and differences in choice of triplet sensitizer discussed. Study of 1O2 reactivity with substrates of biological and environmental relevance using this methodology should provide an additional tool to understand better oxidative damage induced by 1O2 within these systems. In chapter three a detailed study involving the design, synthesis, and characterization of the electrochemical and phototophysical properties of Ir(III) cyclometalates with pendant terthiophenes as secondary organic chromophores is presented. The interplay of the excited states between each chromophore represents an interesting photoredox active system for energy-to-light or light-to-energy devices. Greater knowledge of the primary photophysical events within these complexes will provide a better understanding of how energy moves in these hybrid systems after light absorption, leading to increased device efficiency.
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    Synthetic, structural, and spectroscopic study of luminescent transition metal complexes for use in electronic devices and environmental sensors.
    (2008-11) McGee, Kari Ann
    This thesis describes the synthesis, structural, and spectroscopic study of ruthenium and iridium complexes for use in environmental sensors or electronic devices. Chapters 1-2 discuss studies of ruthenium polypyridyl (pp) complexes used for detection of oxygen gas. In Chapter 1 the variation of the counterion and its affect on the packing structure and subsequent detection of oxygen is discussed. The anion tfpb - (tetrakis(bis-3,5-trifluoromethylphenylborate) worked particularly well and provided the inefficient packing structure with desired channels of open space. In Chapter 2 optically pure metal complexes were explored to alter the packing structure. Both means of creating void space enabled oxygen diffusion to give sensitive and reproducible crystalline oxygen sensors. Chapter 3 describes the dual use of a [Ru(pp) 3 ](tfpb) 2 complex for detection of oxygen and the volatile organic, benzene. The crystalline solid undergoes a reversible vapochromic shift of the emission λ max to higher energy in the presence of benzene. Additionally, in the presence of oxygen the solid exhibits linear Stern-Volmer quenching behavior. This crystalline solid was a practical sensor at low concentrations (0.76%) of benzene vapor. In Chapter 4, the synthesis of new compounds of the general form [( p -cym)Ru(pp)Cl]Cl is discussed. This method allowed the study of a series of Ru(II) complexes, with different polypyridyl and β-diketonate ligands. Modification of the substituent group on the β-diketonate ligand has a pronounced effect on the electronic and electrochemical properties of these complexes. The presence of channels in the crystal structures of two of these molecules as well as the low Ru(III)/Ru(II) redox couple led to their examination as chlorine sensors. In Chapter 5, a selective low-temperature synthesis of the highly desired fac and mer tris-cyclometalated Ir(III) complexes used in OLEDs is discussed. The bis-acetonitrile species, [Ir(C^N) 2 (NCCH 3 ) 2 ]PF 6 , and hydroxy-bridged dimers, [Ir(C^N) 2 (OH)] 2 for two cyclometalating ligands (C^N) were synthesized.The fac-Ir(C^N) 3 and mer -Ir(C^N) 3 complexeswere synthesized at 100 ºC in o -dichlorobenzene from the [Ir(C^N)2(NCCH3)2]PF6 or [Ir(CN) 2 (OH)] 2 complexesrespectively. A mechanism is proposed that may account for the selectivity observed in the formation of these fac-Ir(CN) 3 and mer-Ir(CN) 3 isomers.