Browsing by Author "Dr. T. Brent Gunnoe, Committee Member"

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    Investigating Structure Property Relationships in Electroactive Molecules via Scanning Tunneling Microscopy
    (2004-11-22) Wassel, Ronald Andrew; Dr. Daniel L. Feldheim, Committee Member; Dr. Edmond F. Bowden, Committee Member; Dr. T. Brent Gunnoe, Committee Member; Dr. Raymond E. Fornes, Committee Member; Dr. Christopher B. Gorman, Committee Chair
    This dissertation will discuss issues related to determining structure property relationships that are relevant to molecular electronics. More specifically, an STM will be used to compare electronic measurements over insulating n-alkanethiolate SAMs and electroactive SAMs composed of ferrocenyl- terminated thiols and viologen terminated thiols, as well as multilayer SAMs created by alternating a metal dication and a thiolate. The surface characterization of these SAMs will be discussed. Current — voltage (I-V) measurements on the SAMs will be discussed as they pertain to the non-linear current voltage behavior of negative differential resistance (NDR). A mechanism for the nature of NDR will be discussed as well as the need to understand how the junctions used to measure I-V curves influence NDR. The attenuation of the apparent tunneling barrier of ferrocenyl-terminated thiolates via non-covalent binding of β-cyclodextrin will be shown. This attenuation will be shown to influence the peak to valley ratio of NDR Stochastic variation in electroactive molecules inserted into an insulating n-alkanethiolate background SAM was observed and is believed to be a general phenomenon. In this dissertation it will also be shown that the electric field generated by the STM tip increases the rate of replacement of electroactive molecules in to the background SAM.
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    Ring-Opening Metathesis Polymerization of Functionalized Cyclobutenes Derivatives
    (2003-12-02) Charvet, Richard Andre; Dr. Stefan Franzen, Committee Member; Dr. T. Brent Gunnoe, Committee Member; Dr. Christopher B. Gorman, Committee Member; Dr. Bruce M. Novak, Committee Chair
    In the last decade, the development of well-defined carbene catalysts has revolutionized the field of ring-opening metathesis polymerization (ROMP). Nevertheless, little attention has been paid to monomer design for ROMP. In this project, a new family of functionalized polycyclic monomers based on the endo-Tricyclo[4.2.2.02,5]deca-3,9-diene structure with a variety of functional groups at the 7,8 positions has been prepared. Polymerization studies were performed with well-defined Schrock's molybdenum catalysts and a variety of Grubbs' ruthenium carbene catalysts. A living polymerization was obtained with Cl₂Ru(=CHPh)(PCy₃)₂ (Ru-III). ¹⁹F NMR analysis indicated that the ortho and meta fluorinated substituents of the N-phenyl succinimide moiety could be regarded as sensitive reporters vis-à-vis the microstructure of the polymer. "Blocky" copolymers from a mixture of cis-cyclooctene and 7,8-N-2,3,4,5,6-pentafluorophenyl succinimide endo-Tricyclo[4.2.2.0[superscript 2,5]]deca-3,9-diene (M-7) could be prepared with Ru-III. The presence of cis-cyclooctene was shown to have an influence on the kinetics of the polymerization and the polymer microstructure. Kinetic studies with Ru-III indicated that faster polymerizations were obtained when the N-succinimide moiety was more electron-rich. The influence of steric hindrance on the polymerization was studied by the functionalization of the monomer structure with bulky polyaryl ether dendrons. A controlled polymerization was obtained with the very active Ru(=CHPh)Cl₂(PCy₃)(1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (Ru-VI). This behavior was explained by the decrease of the propagation rate due to the bulkiness of the dendritic functional groups. Polymers functionalized with a variety of N-succinimide moieties displayed a remarkable thermal stability with decomposition temperatures above 300°C. No Tg was observed below decomposition temperature, indicating the generation of a very rigid polymer backbone. Graft copolymers based on a ROMP polymer skeleton and with poly(methylmethacrylate) branches could be prepared in a one-pot procedure using the single catalyst Ru-III and monomers based on the endo-Tricyclo[4.2.2.0[superscript 2,5]]deca-3,9-diene structure functionalized with a tertiary alkyl bromide, present as an ATRP initiator. Both distinct polymerization processes were shown to occur in tandem and in a controlled fashion.