Electronic Theses and Dissertations

Identifier

685

Date

2012

Date of Award

7-25-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Concentration

Organic Chemistry

Committee Chair

Tomoko Fujiwara

Committee Member

Theodore Burkey

Committee Member

Gary Emmert

Committee Member

Charles Webster

Abstract

A major goal in material science is being able to influence macro-scale behavior by controlling the interactions occurring at the molecular level. For example, a surface functionalized with photochromic molecules can reversibly change its polarity, conductivity, or absorption properties. These unique characteristics can be achieved by changing the molecular state from passive to active using external stimuli. The specific goal of this research is to create a family of biphotochromic systems that display unique functionalities in various media for potential use in biomedical applications. For example, these photochromic systems can be applicable for different purposes, such as drug delivery or extraction of impurities from solution. Biphotochromes displaying reversible photo responses and binding abilities make these applications possible. In this study, two spirooxazine monomers (i.e. types of photochromes) are used because of their photostability, matrix compatibility, distinctive photo-isomers, and absorption spectra upon irradiation. These monomers are connected via rigid bonds so that the structure produced has a fixed angle between the two photochromes, thus creating a dimer with an ionic cavity for interactions with guest molecules upon photo irradiation. The dimer is synthesized using Sonogashira coupling to connect the two spirooxazine monomers to a phenyl ring spacer in moderate yields. A series of dimers are created using this type of design. Their photochromic properties are studied under continuous UV irradiation in solvents of different polarity that indicate positive solvatochromism. Kinetic studies of each dimer reveal that substituents and solvent polarity affect the response to external stimuli as well as the stability of the photo-induced isomer under UV irradiation. The thermal closing rate at 25oC varied depending on the dimer and solvent. By analyzing the thermal closing rates and absorbance spectra of the photo-induced isomer, the binding capabilities of the dimer are examined. In the presence of organic/inorganic guest compounds, the dimers demonstrate a selective binding affinity. Particularly, the dimers exhibit interactions toward a palladium catalyst, a common agent in cross coupling reactions. Coupling dimers onto varying polymeric substrates generates environmentally, independent, reversible isomerization and binding ability within the self-assembled structure or on a solid surface. The results of this study show the photo-switchable systems have potential use as stimuli responsive material for selective recognition. Particular interest has been placed on the performance of these systems as catalytic controllers for carbon-carbon bond forming chemistry.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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