Retinal hypoxia and inadequate oxygen delivery have been implicated as causal for the development of several eye diseases, including diabetic retinopathy, glaucoma, and retinopathy of prematurity. The imaging of oxygen tension in the retina, generated from a measure of the phosphorescence lifetimes of bolus-injected palladium-porphyrin probes, has been used successfully to study retinal oxygen dynamics in numerous animal models. However, the specific parameters for applying this technique in the mouse have not been thoroughly investigated. The goals of this project were to calibrate a newly-constructed phosphorescence lifetime imaging instrument and data analysis software against known oxygen concentrations, to determine specific parameters for probe excitation and image collection and analysis in the mouse eye, and to assess any damage caused to the eye by the technique using histological analysis. An in vitro system was developed for calibration of the probe and for estimation of power of excitation light and camera settings necessary to produce acceptable oxygen maps. In vivo experiments were then performed, and plots indicating camera settings necessary for producing varying qualities of oxygen maps were constructed. Trypsin digestion of retinal tissue was used in an attempt to assess any damage to experimental subjects, but this histological technique was deemed inadequate for analyzing the capillary structures of the mouse eye. Alternatively, damage was assessed using the instrument itself to calculate changes in oxygen tension during the experimental process. The results of this work will allow the phosphorescence lifetime imaging system to be used in the mouse to study how changes in retinal oxygen tension correlate with the progression of eye diseases where oxygen is implicated, including diabetic retinopathy.

Retinal hypoxia is associated with many retinal diseases, such as diabetic retinopathy. Current retinal research suggests that retinal hypoxia appears prior to the onset of diabetic retinopathy. The preliminary association of retinal hypoxia to the early stages of diabetic retinopathy is stimulating the development of new technologies to measure the oxygen content of retinal tissue. Frequency domain phosphoresence lifetime imaging (PLI) is a promising technology that enables the mapping of the oxygen content across the entire retina in the form of two-dimensional images. The two-dimensional images generated from the PLI process are a spatial mapping of the retinal tissue's oxygen tension. Currently, the phosphorescent based oxygen tension PLI measurements contain contaminating auto-fluorescent signals in addition to the desired phosphorescent signals. These auto-fluorescent signals artificially inflate the oxygen tension readings due to the nature of fluorescent signals in phosphorescent imaging. Additionally, the maps generated through PLI appear to contain oxygen tension information from both the retinal vasculature and the choroidal vasculature. The choroidal vasculature is situated directly behind the retina and can have a different oxygen tension value than the retinal vasculature. This research enhanced the PLI system by mathematically eliminating the contaminating auto-fluorescent signals and investigated the methods aimed at separating the PO2s of the retinal and choroidal vasculature beds. In addition, the application of the enhanced PLI technology to the investigation of retinal oxygen changes in a rat model of type I diabetes yielded results that suggest a hyperoxic to hypoxic trend prior to the onset of diabetic retinopathy.

Luminescent molecules and polymers are active component in light-emitting diodes; however, the aggregation and excimer formation in concentrated solution or in the solid film states had limited their applications. Therefore, this study used poly(methyl methacrylate) (PMMA) as separator to prevent the formations of aggregate and excimer and to enhance quantum efficiency. Basically, two systems are involved: (1) Inorganic phosphorescent irdium complex PMMA was doped with inorganic iridium complex IrQB by using THF as solvent. IrQB/PMMA films prepared from dilute solutions exhibit two emissions centered at 560 and 640 nm, respectively; in contrast, only 640-nm emission was observed for films from concentrated solutions. Experimentally, these two bands showed variations on the emission intensity with increasing temperature. Aggregation of IrQB is suggested to be responsible for the 560-nm emission. Chain conformation of PMMA in the solution state strongly affects the incorporated IrQBs and their emission properties. (2) Polybenzoxazines Polybenzoxazines with the built-in fluorenscent fluorine moiety are linear in nature; however, the inherent hydrogen-bond (H-bond) interactions in polybenzoxazines decrease the inter-chain distance and cause the chain aggregation. With the added PMMAs, new H-bonding from the carbonyl groups in PMMA and the hydroxyl groups in polybenzoxazine enhances the mutual miscibility between these two components and decreases the possibility of aggregate formation in polybenzoxazines. Quantum efficiency is therefore promoted by this approach.

This dissertation focuses on the phosphorescence of organic chromophores using perfluoro-ortho-phenylene mercury (1) and bis(pentafluorophenyl)mercury (2) as external heavy atom effect inducers. To ascertain the suitability of these luminescent adducts for OLED applications, several research objectives have been investigated. To further shorten the triplet lifetimes of adducts involving 1, a strategy was developed which combines both internal and external heavy atom effects. Specifically, complexes involving 1 and N-methylcarbazole, N-methylindole and the 1- halonaphthalenes were investigated. The existence and stability of the complexes could be confirmed in solution by fluorescence spectroscopy. In the solid state, these adducts form supramolecular binary stacks where the molecules of 1 alternate with the aromatic substrate. As a result of the mercury external heavy atom effect, all of these adducts display intense room temperature phosphorescence of the free arene. With the Nheterocycles, the triplet lifetimes were drastically reduced to below 100 mu-s. To appreciate the origin of the unusual heavy atom effects observed in arene adducts with 1, 2 was studied as a monofunctional analog to 1. By utilizing fluorescence spectroscopy, naphthalene, biphenyl, and fluorene complexes of 1 and 2 have been detected in solution. The solid state structure of the adducts with 2 reveal supramolecular binary stacks. Comparison of the photophysical results supports the occurrence of cooperative effects between the Lewis acidic mercury centers of 1, which make it a more efficient external heavy-atom effect inducer. Polymeric materials which are amenable to deposition in thin layers were investigated as substrates for 1 and 2. Both poly(vinyl-2-naphthalene) and poly(vinylcarbazole) interact with 1 and 2 in solution as evidenced by fluorescence spectroscopy. With the solid blend 1•PVK, a small doping percentage of 1 results in white emission, while larger percentages of 1 yield bright orange emission. This dissertation presents the first structurally characterized ternary complex with 1, carbazole, and coordinating solvents THF and triethylamine. IR spectroscopy and short N···O and N···N distances in the solid state indicates that the acidic N-H moiety of carbazole interacts with the solvent by hydrogen bonding. In the extended structure, molecules of 1 and the hydrogen bonded complex alternate to form supramolecules.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: imaging; phosphorescence; eye; retina. Includes bibliographical references (p. 50-55).

Thesis (Ph. D.)--University of North Texas, Dec., 2009. / Title from title page display. Includes bibliographical references.

Two major topics that involve synthetic strategies to enhance the phosphorescence of organic and inorganic luminophores have been investigated. The first topic involves, the photophysical and photochemical properties of the gold (I) complexes LAuIX (L = CO, RNC where R = alkyl or aryl group; X = halide or pseudohalide), which have been investigated and found to exhibit Au-centered phosphorescence and tunable photochemical reactivity. The investigations have shown a clear relationship between the luminescence energies and association modes. We have also demonstrated for the first time that aurophilic bonding and the ligand p-acceptance can sensitize the photoreactivity of Au(I) complexes. The second topic involves conventional organic fluorophores (arenes), which are made to exhibit room-temperature phosphorescence that originates from spin-orbit coupling owing to either an external or internal heavy atom effect in systematically designed systems that contain d10 metals. Facial complexation of polycyclic arenes to tris[{m-(3,4,5,6-tetrafluorophenylene)}mercury(II)], C18F12Hg3 (1) results in crystalline adducts that exhibit bright RGB (red-green-blue) phosphorescence bands at room temperature. This arene-centered phosphorescence is always accompanied by a reduction of the triplet excited state lifetime due to its sensitization by accelerating the radiative instead of the non-radiative decay. The results of both topics are significant for rational design of efficient metal and arene-centered phosphors for molecular light emitting diodes in addition to the fundamental novelties in inorganic chemistry and molecular spectroscopy.

Dans cette thèse, des vitrocéramiques et composites à matrice verres ont été élaborés avec pour objectif principal d’étudier les interactions entre la fissure et les différentes inclusions. Dans un premier temps, la nucléation et la cristallisation volumique de sphérulites dans un verre du système BaO-Al2O3-SiO2 ont été étudiées. Puis, l’influence de la cristallisation sur l’élasticité, la dureté et la ténacité a été mesurée. Il est apparu une augmentation de ces propriétés suite à la cristallisation. Après dopage avec des oxydes de terres rares, le verre a été fonctionnalisé par l’apparition de cristaux phosphorescents à la surface du matériau. Dans un second temps, l’influence d’un différentiel de coefficient de Poisson (entre la matrice et les inclusions) sur la propagation d’une fissure a été étudiée. Pour cela des composites à particules et matrices vitreuses ont été élaborés par Spark Plasma Sintering (SPS) et étudiés par Double Cleavage Drilled Compression (DCDC). Il a été mis en lumière une déviation de la fissure quand cette dernière arrive à proximité des inclusions vitreuses dans le cas où le coefficient de Poisson de l’inclusion est inférieur à celui de la matrice. Une déviation de moindre importance a été observée dans le cas inverse. Enfin, des nanocomposites fonctionnalisés par des particules de magnétite (Fe3O4) et d’or ont été obtenus suite à un frittage SPS. Les propriétés apportées par ces particules ont permis le chauffage du matériau, respectivement, par induction et par irradiation laser. Dans le deuxième cas, après un traitement laser de 10 min, une cicatrisation partielle de fissures d’indentation a pu être observée. / In this thesis, glass-ceramics and glass matrix composites have been developed in order to study the interactions between the crack and the various inclusions. Firstly, the nucleation and volume crystallization of spherulites in a glass of the BaO-Al2O3-SiO2 system were studied. Then, the influence of crystallization on elasticity, hardness and toughness was measured. An increase of these properties due to crystallization was observed. After doping with rare earths oxides, the glass was functionalized by surface crystallization of phosphorescent crystals. Secondly, the influence of a Poisson’s ratio differential (between the matrix and inclusions) on the crack propagation was studied. For this purpose, glassy particulate glass matrix composites have been elaborated by Spark Plasma Sintering (SPS) and studied by Double Cleavage Drilled Compression (DCDC). A deviation of the crack in the vicinity of the glass inclusions has been identified in the case where the Poisson’s ratio of the inclusion is lower than the one of the matrix. In the opposite case, less important deviations were noticed. Finally, nanocomposites functionalized with magnetite (Fe3O4) and gold particles were obtained after a SPS treatment. The properties provided by these particles allowed the material to be heated, respectively, by induction and by laser irradiation. In the second case, after a 10 min laser treatment, a partial healing of indentation cracks could be observed.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Diabetes; imaging; phosphorescence; retina. Includes bibliographical references (p. 69-70).

The major topics discussed are all relevant to the bright phosphorescent emissions of coinage metal complexes (Cu(I), Ag(I) and Au(I)) with an explanation of the theoretical background, computational results and ongoing work on the application in materials and optoelectronic devices. Density functional computations have been performed on the majority of the discussed complexes and determined that the most significant distortion that occurs in Au(I)-phosphine complexes is a near and beyond a T-shape within the P-Au-P angle when the complexes are photoexcited to the lowest phosphorescent excited state. The large distortion is experimentally qualified with the large Stokes' shift that occurs between the excitation and emission spectra and can be as large as 18 000 cm-1 for the neutral Au(I) complexes. The excited state distortion has been thoroughly investigated and it is determined that not only is it pertinent to the efficient luminescence but also for the tunability in the emission. The factors that affect tunability have been determined to be electronics, sterics, rigidity of solution and temperature. The luminescent shifts determined from varying these parameters have been described systematically and have revealed emission colors that span the entire visible spectrum. These astounding features that have been discovered within studies of coinage metal phosphorescent complexes are an asset to applications ranging from materials development to electronics.