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- Title
- SELF-ASSEMBLY AND PHOTOPHYSICS OF SELECTED ORGANIC MATERIALS AND TWO-PHOTON BIOIMAGING WITH PROFLUORESCENT NITROXIDES, POLYELECTROLYTE NANOPARTICLES, AND SQUARAINE PROBES.
- Creator
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Ahn, Hyo-Yang, Belfield, Kevin, University of Central Florida
- Abstract / Description
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Two-photon absorption and upconverted fluorescence has been utilized in a variety of applications in pure science and engineering. Multiphoton-based techniques were used in this research in order to understand photophysical and chemical characteristics of several fluorescent dyes and to demonstrate some of their key applications. Two-photon fluorescence microscopy (2PFM) has become a powerful technique in bio-photonics for non-invasive imaging in the near-infrared (NIR) region (700~1000 nm)...
Show moreTwo-photon absorption and upconverted fluorescence has been utilized in a variety of applications in pure science and engineering. Multiphoton-based techniques were used in this research in order to understand photophysical and chemical characteristics of several fluorescent dyes and to demonstrate some of their key applications. Two-photon fluorescence microscopy (2PFM) has become a powerful technique in bio-photonics for non-invasive imaging in the near-infrared (NIR) region (700~1000 nm) that often results in less photobleaching. In Chapter 1, there is a brief introduction to fluorescence, examples of fluorescence materials, and a discussion of the advantages of two-photon absorption. 2PFM imaging was utilized in Chapters 2 to 4 for various applications. In Chapter 2, a new squaraine dye is introduced and its linear and nonlinear photophysical properties are characterized. This compound has very high two-photon absorption (2PA) cross sections and high photostability both in an organic solvent and when encapsulated in micelles. Based on these properties, this dye was demonstrated as a near-infrared (NIR) probe in in vitro 2PFM imaging with excitation over 800 nm wavelength. In Chapter 3, new profluorescent nitroxides are introduced. Nitroxide radicals are utilized for electron paramagnetic resonance (EPR) spectroscopy and in biological systems as some are known, in some manner, to mimic the behavior of superoxide dismutase (SOD) that detoxifies or mitigates oxidative stress by trapping free radicals. Here, two profluorescent nitroxides investigated for use as a two-photon fluorescent oxidative stress indicator in in vitro two-photon fluorescence microscopy (2PFM) imaging. In Chapter 4, two-photon excited (2PE) fluorescence of a conjugated polyelectrolyte (CPE), PPESO3, was studied in methanol and in water. The results of CPE quenching studies were comparable under both one-photon excitation conditions and two-photon excitation. CPE coated silica nanoparticles were incubated in HeLa cells and 2PFM imaging was demonstrated for this new class of fluorescent probe. Supramolecular structures based on organized assemblies/aggregation of chromophores have attracted widespread interest as molecular devices with potential applications in molecular electronics, artificial light harvesting, and pharmacology. In Chapter 5, J-aggregate formation was investigated for two porphyrin-based dyes, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS, 4) and an amino tris-sulfonate analog (5) in water via UV-vis, fluorescence, and lifetime decay studies. The effect of aggregation on two-photon absorption properties was also investigated. A functionalized norbornene-based homopolymer, synthesized by the ring opening metathesis polymerization technique was used as a J-aggregation enhancement template and had a role of polymer-templating to facilitate porphyrin aggregation and modulate 2PA. In Chapter 6, squaraine dye aggregates templated with single wall carbon nanotubes (SWCNTs) that were atomically clean were studied by using optical absorption spectroscopy, atomic force microscopy (AFM), and photoconductivity measurements. SWCNTs selectively promote the formation of squaraine dye aggregates with a head-to-head stacking arrangement, and these dye aggregates effectively photosensitize SWCNTs, demonstrating that this novel approach can yield highly photosensitized devices.
Show less - Date Issued
- 2011
- Identifier
- CFE0003978, ucf:48665
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003978
- Title
- THE STUDY OF THREE DIFFERENT LAYERED STRUCTURES AS MODEL SYSTEMS FOR HYDROGEN STORAGE MATERIALS.
- Creator
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Oztek, Muzaffer, Hampton, Michael, University of Central Florida
- Abstract / Description
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The strength and success of the hydrogen economy relies heavily on the storage of hydrogen. Storage systems in which hydrogen is sequestered in a solid material have been shown to be advantageous over storage of hydrogen as a liquid or compressed gas. Many different types of materials have been investigated, yet the desired capacity and uptake/release characteristics required for implementation have not been reached. In this work, porphyrin aggregates were investigated as a new type of...
Show moreThe strength and success of the hydrogen economy relies heavily on the storage of hydrogen. Storage systems in which hydrogen is sequestered in a solid material have been shown to be advantageous over storage of hydrogen as a liquid or compressed gas. Many different types of materials have been investigated, yet the desired capacity and uptake/release characteristics required for implementation have not been reached. In this work, porphyrin aggregates were investigated as a new type of material for hydrogen storage. The building blocks of the aggregates are porphyrin molecules that are planar and can assume a face to face arrangement that is also known as H-aggregation. The H-aggregates were formed in solution, upon mixing of aqueous solutions of two different porphyrins, one carrying positively charged and the other one carrying negatively charged functional groups. The cationic porphyrin used was meso-tetra(4-N,N,N-trimethylanilinium) porphine (TAP) and it was combined with four different anionic porphyrins, meso-tetra(4-sulfonatophenyl)porphine (TPPS), meso-tetra(4-carboxyphenyl) porphine (TCPP), Cu(II) meso-tetra(4-carboxyphenyl) porphine, and Fe(III) meso-tetra(4-carboxyphenyl) porphine. The force of attraction that held two oppositely charged porphyrin molecules together was electrostatic attraction between the peripheral groups. Solid state aggregates were successfully isolated either by solvent evaporation or by centrifuging and freeze drying. TCPP-TAP and Cu(II)TCPP-TAP aggregates were shown to interact with hydrogen starting from 150 °C up to 250 °C. The uptake capacity was about 1 weight %. Although this value is very low, this is the first observation of porphyrin aggregates absorbing hydrogen. This opened the way for further research to improve hydrogen absorption properties of these materials, as well as other materials based on this model. Two other materials that are also based on planar building blocks were selected to serve as a comparison to the porphyrin aggregates. The first of those materials was metal intercalated graphite compounds. In such compounds, a metal atom is placed between the layers of graphene that make up the graphite. Lithium, calcium and lanthanum were selected in this study. Theoretical hydrogen capacity was calculated for each material based on the hydriding of the metal atoms only. The fraction of that theoretical hydrogen capacity actually displayed by each material increased from La to Ca to Li containing graphite. The weight % hydrogen observed for these materials varied between 0.60 and 2.0 %. The other material tested for comparison was KxMnO2, a layered structure of MnO2 that contained the K atoms in between oxygen layers. The hydrogen capacity of the KxMnO2 samples was similar to the other materials tested in the study, slightly above 1 weight %. This work has shown that porphyrin aggregates, carbon based and manganese dioxide based materials are excellent model materials for hydrogen storage. All three materials absorb hydrogen. Porphyrin aggregates have the potential to exhibit adjustable hydrogen uptake and release temperatures owing to their structure that could interact with an external electric or magnetic field. In the layered materials, it is possible to alter interlayer spacing and the particular intercalates to potentially produce a material with an exceptionally large hydrogen capacity. As a result, these materials can have significant impact on the use of hydrogen as an energy carrier.
Show less - Date Issued
- 2011
- Identifier
- CFE0003752, ucf:48769
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003752
- Title
- Quantum Chemical Studies for the Engineering of Metal Organic Materials.
- Creator
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Rivera Jacquez, Hector, Masunov, Artem, Balaeff, Alexander, Harper, James, Heider, Emily, Zou, Shengli, Kaden, William, University of Central Florida
- Abstract / Description
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Metal Organic Materials (MOM) are composed of transition metal ions as connectors and organic ligands as linkers. MOMs have been found to have high porosity, catalytic, and optical properties. Here we study the gas adsorption, color change, and non-linear optical properties of MOMs. These properties can be predicted using theoretical methods, and the results may provide experimentalists with guidance for rational design and engineering of novel MOMs. The theory levels used include semi...
Show moreMetal Organic Materials (MOM) are composed of transition metal ions as connectors and organic ligands as linkers. MOMs have been found to have high porosity, catalytic, and optical properties. Here we study the gas adsorption, color change, and non-linear optical properties of MOMs. These properties can be predicted using theoretical methods, and the results may provide experimentalists with guidance for rational design and engineering of novel MOMs. The theory levels used include semi-empirical quantum mechanical calculations with the PM7 Hamiltonian and, Density Functional Theory (DFT) to predict the geometry and electronic structure of the ground state, and Time Dependent DFT (TD-DFT) to predict the excited states and the optical properties.The molecular absorption capacity of aldoxime coordinated Zn(II) based MOMs (previously measured experimentally) is predicted by using PM7 Theory level. The 3D structures were optimized with and without host molecules inside the pores. The absorption capacity of these crystals was predicted to be 8H2 or 3N2 per unit cell. When going beyond this limit, the structural integrity of the bulk material becomes fractured and microcrystals are observed both experimentally and theoretically.The linear absorption properties of Co(II) based complexes are known to change color when the coordination number is altered. In order to understand the mechanism of this color change TD-DFT methods are employed. The chromic behavior of the Co(II) based complexes studied was confirmed to be due to a chain in coordination number that resulted in lower metal to ligand distances. These distances destabilize the occupied metal d orbitals, and as a consequence of this, the metal to ligand transition energy is lowered enough to allow the crystals to absorb light at longer wavelengths.Covalent organic frameworks (COFs) present an extension of MOM principles to the main group elements. The synthesis of ordered COFs is possible by using predesigned structures andcarefully selecting the building blocks and their conditions for assembly. The crystals formed by these systems often possess non-linear optical (NLO) properties. Second Harmonic Generation (SHG) is one of the most used optical processes. Currently, there is a great demand for materials with NLO optical properties to be used for optoelectronic, imaging, sensing, among other applications. DFT calculations can predict the second order hyperpolarizability ?2 and tensor components necessary to estimate NLO. These calculations for the ?2 were done with the use of the Berry's finite field approach. An efficient material with high ?2 was designed and the resulting material was predicted to be nearly fivefold higher than the urea standard.Two-photon absorption (2PA) is another NLO effect. Unlike SHG, it is not limited to acentric material and can be used development of in vivo bio-imaging agents for the brain. Pt(II) complexes with porphyrin derivatives are theoretically studied for that purpose. The mechanism of 2PA enhancement was identified. For the most efficient porphyrin, the large 2PA cross-section was found to be caused by a HOMO-LUMO+2 transition. This transition is strongly coupled to 1PA allowed Q-band HOMO-LUMO states by large transition dipoles. Alkyl carboxyl substituents delocalize the LUMO+2 orbital due to their strong ?-acceptor effect, enhancing transition dipoles and lowering the 2PA transition to the desirable wavelengths range.The mechanism 2PA cross-section enhancement of aminoxime and aldoxime ligands upon metal addition of is studied with TD-DFT methods. This mechanism of enhancement is found to be caused by the polarization of the ligand orbitals by the metal cation. After polarization an increase in ligand to ligand transition dipole moment. This enhancement of dipole moment is related to the increase in 2PA cross-sections.
Show less - Date Issued
- 2015
- Identifier
- CFE0005990, ucf:50777
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005990
