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SINGLET OXYGEN GENERATION USING NEW FLUORENE-BASED PHOTOSENSITIZERS UNDER ONE- AND TWO-PHOTON EXCITATION
Title
SINGLET OXYGEN GENERATION USING NEW FLUORENE-BASED PHOTOSENSITIZERS UNDER ONE- AND TWO-PHOTON EXCITATION.
Creator
Andrasik, Stephen, Belfield, Kevin, University of Central Florida
Abstract / Description
Molecular oxygen in its lowest electronically excited state plays an important roll in the field of chemistry. This excited state is often referred to as singlet oxygen and can be generated in a photosensitized process under one- or two-photon excitation of a photosensitizer. It is particularly useful in the field of photodynamic cancer therapy (PDT) where singlet oxygen formation can be used to destroy cancerous tumors. The use of two-photon activated photosensitizers possesses great...
Show moreMolecular oxygen in its lowest electronically excited state plays an important roll in the field of chemistry. This excited state is often referred to as singlet oxygen and can be generated in a photosensitized process under one- or two-photon excitation of a photosensitizer. It is particularly useful in the field of photodynamic cancer therapy (PDT) where singlet oxygen formation can be used to destroy cancerous tumors. The use of two-photon activated photosensitizers possesses great potential in the field of PDT since near-IR light is used to activate the sensitizer, resulting in deeper penetration of light into biological tissue, less photo-bleaching of the sensitizer, and greatly improved resolution of excitation. The synthesis and photophysical characterization of new fluorene-based photosensitizers for efficient singlet oxygen production were investigated. The spectral properties for singlet oxygen production were measured at room temperature and 77 K. Two-photon absorption (2PA) cross-sections of the fluorene derivatives were measured by the open aperture Z-scan method. The quantum yields of singlet oxygen generation under one- and two-photon excitation (ΦΔ and 2PAΦΔ, respectively) were determined by the direct measurement of singlet oxygen luminescence at ≈ 1270 nm. The values of ΦΔ were independent of excitation wavelength, ranging from 0.6 - 0.9. The singlet oxygen quantum yields under two-photon excitation were 2PAΦΔ ≈ ½ΦΔ, indicating that the two processes exhibited the same mechanism of singlet oxygen production, independent of the mechanism of photon absorption.
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Date Issued
2007
Identifier
CFE0001860, ucf:47411
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001860
Photochemistry and Applications of Diels-Alder Adducts and Photoacids in Materials Science
Title
Photochemistry and Applications of Diels-Alder Adducts and Photoacids in Materials Science.
Creator
Johns, Valentine, Liao, Yi, Miles, Delbert, Zou, Shengli, Gesquiere, Andre, Su, Ming, University of Central Florida
Abstract / Description
Utilizing light as an energy source for reactions has intrigued many chemists. This has led to the development of the principles of photochemistry. The Photo retro Diels Alder (PrDA) reaction is one such system that has potential for use in materials science as well as in the life sciences. However, there was no guide to predict whether a compound could undergo the PrDA reaction, which limits the widespread use of this reaction. Another system is that of photoacids (molecules that release...
Show moreUtilizing light as an energy source for reactions has intrigued many chemists. This has led to the development of the principles of photochemistry. The Photo retro Diels Alder (PrDA) reaction is one such system that has potential for use in materials science as well as in the life sciences. However, there was no guide to predict whether a compound could undergo the PrDA reaction, which limits the widespread use of this reaction. Another system is that of photoacids (molecules that release protons upon irradiation reversibly). Since most fundamental processes involve proton transfer, these types of photoacids have great potential which is yet to be explored. This thesis describes the design and synthesis of various aromatic DA adducts. These adducts were made to undergo the rDA reaction using UV (Ultra-Violet) light. Experimental results showed that the photoreactivity of these adducts depends on the electron-donating ability of the diene component and the electron-withdrawing ability of the dienophile component. In addition, mechanistic study of this reaction revealed the formation of a charge separated intermediate with a singlet excited state. The potential of the PrDA reaction was also explored in two ways. One was by designing isomeric DA adducts from pentacene and TCNE (tetracyanoethylene) which are capable of switching from one isomer to another via a PrDA process. The other way was the design and synthesis of a polymer with an anthracene diketone moeity which could undergo a PrDA reaction to change from an insulator to a semiconductor. Finally, the syntheses of a number of photoacids which not only become acidic upon irradiation but also respond to visible light reversibly have been explored. A rationale has been developed for the design of photoacids with desired photo-induced response. While electron donating and accepting groups in strategic positions help tune the pH; using different combinations of ethanol and water affect the rate of the forward and the backward processes. A photoacid monomer was also incorporated into three photoacid polymers which respond to visible light reversibly, hence promising widespread applications of these photoacids.
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Date Issued
2012
Identifier
CFE0004556, ucf:49235
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004556