Photoactive inorganic molecules for the next generation of photoluminescent probes and materials
Ogle, Meredith McDowell
Doctor of Philosophy
Photoluminescent molecules come in many forms from organic molecules to metal complexes to nanomaterials and have a large range of applications as dyes, sensors, catalysts and more. In this thesis three distinct areas will be covered: temperature sensors, nanomaterial antennae, and photooxidation catalysts. Photoluminescent sensors can report on environmental changes at the molecular level. Chapter 1 summarizes the literature on photoluminescent temperature probes and discusses the different reporting techniques and molecular mechanisms. Due to different photophysical properties of the dyes, probes can have temperature dependent changes in emission intensity, a ratio of two emissions, peak emission wavelength, or lifetime of emission. Each of these can be measured by a spectrometer or microscope and some can be seen by eye. The probes with the least number of confounding variables are metal complexes that have variable lifetime with temperature. Therefore, Chapter 2 describes the development of iridium (III) complexes as phosphorescent temperature probes and the challenges of biocompatibility and lifetime determination in living cell using available equipment. Chapter 3 discusses the design of a fluorescent boron-dipyrromethene temperature probe and its implementation as a live cell thermometer. We modified a viscosity probe to solely report on temperature in high viscosity environments like the cell membrane. This probe is non-toxic, membrane permeable and retained by live cells. The fluorescent lifetime is predictively quenched by molecular vibrations as temperature increases and live cell temperature was measured with fluorescent lifetime imaging microscopy. Graphene quantum dots are nanoflakes of graphene isolated from oxidized coal. These nanoparticles are heterogenous by nature of the top down synthesis which leads to broad emission bands and low quantum yields compared to traditional quantum dots. Chapter 4 explores the photophysical properties of these nanoparticles and their use as antennae for lanthanide cations. The energy transfer from graphene quantum dots to lanthanides, and subsequent quantum yield for the emission for the rare earth, was most efficient in the ultraviolet range. This is in contrast with the well know Kasha-Vavilov rule, and shows promise toward development of anti-counterfeit dyes. Metal organic frameworks, a class of mesoporous scaffolds, have been developed as gas storage devices, sensors, and photocatalyst. Chapter 5 describes initial experiments that aims to create a rhenium (I) doped MOF as a photo-oxidation catalyst that is easily recovered from the reaction mixture. A rhenium carbonyl complex, a known singlet oxygen sensitizer, was doped into a highly stable MOF at different concentrations. Photoluminescent characterization determined the optimal concentration to use as a catalyst. Current work focuses on optimizing oxidation reaction conditions and increasing substrate scope.
BODIPY; FLIM; graphene quantum dots; metal organic framework; photocatalyst