LSU Historical Dissertations and Theses

1997

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Robin L. McCarley

Abstract

Exploration into the nature of ultrathin, surface-confined films capable of electronic conduction has been the primary purpose of this dissertation. Specifically, the confinement of pyrrole monomer to Au surfaces through organosulfur linkages has been investigated. The synthesis of these new $\omega$-(N-pyrrolyl)alkanethiols is described herein. Cyclic voltammetry was utilized in this work to polymerize the monolayers and characterize the resulting films. Voltammetric analysis yielded currents in the correct potential region for poly(N-alkylpyrrole) charging/discharging. Other electrochemical studies revealed the ability of strong nucleophiles and electroinactive diluents to quench surface-confined polymer formation though they did not affect oxidation of the monomer. Exchange experiments performed with an electroactive thiol in solution indicated a much higher degree of monolayer stability to desorption after electrochemical polymerization of the monolayer. Infrared reflection-absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structural changes in the monolayer upon electrochemical polymerization. Infrared analysis yielded the loss of all pyrrole ring absorbance bands upon polymerization due to changes in the absorption cross-section of the resulting pyrrole units. Additional infrared studies on surface-confined oligomers indicated that some band intensity could be seen for the shorter chains. In agreement with literature reports on bulk species, the infrared intensities of oxidized (conducting) oligomers was higher than undoped oligomers of similar length. IRRAS analysis of the methylene stretching region for the alkane chains showed no change in band intensity indicating no loss of material from the surface. This was confirmed by integrating nitrogen and sulfur abundances on pristine and electrochemically oxidized surfaces using XPS. Microscopic investigations were carried out using various scanning probe microscopy (SPM) techniques but were hampered by the sensitivity of these monolayers to oxygen and airborne contaminants. These monolayers were also studied using physical and scanning electron microscopy (SEM) techniques. Pyrrole-terminated SAMs on Au electrodes were found to significantly increase the adhesion of thick poly(pyrrole) films to the electrode surface.

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