Synthesis and Characterization of Alkoxyaniline-Terminated Monomer Monolayers on Gold Surfaces.
Date of Award
Doctor of Philosophy (PhD)
Robin L. McCarley
Monolayers of 2-(6-mercaptohexan-1-oxy)aniline (AnC6SH) and 2-(7-mercaptoheptan-1-oxy)aniline (AnC7SH) on Au were synthesized and investigated by reflection-absorption infrared (RAIR) spectroscopy and electrochemistry. Electrochemical oxidation of AnC6SH/Au and AnC7SH/Au in 1 M H2SO4 to form ox-AnC6SH/Au and ox-AnC7SH/Au resulted in voltammetry indicative of oligomerization and degradation reactions of the aniline functionality. Scanning of the voltammetric potential between 0.0 and +0.9 V and then back to 0.0 V vs. SSCE twice leads to four surface-confined redox waves occurring at +0.25, +0.45, +0.5, and +0.6 V vs. SSCE. The oxidized monolayers were found to exhibit voltammetry similar to that observed for poly(o-phenetidine), which exhibits redox waves for the leucoemeraldine/emeraldine (+0.2 V) and emeraldine/pernigraniline (+0.6 V) transformations and the formation of some quinonemonoimine degradation products (+0.4 V) in the polymer. A redox wave attributed to a quinonediimine dimer (+0.5 V) was also found for the oxidized monolayers. To reduce degradation product formation, AnC6SH/Au and AnC7SH/Au were oxidized in 0.1 M LiClO4/CH3CN to form ox(non-aq)-AnC6SH/Au and ox(non- aq)-AnC7SH/Au. This method of oxidation led to production of only surface-confined, head-to-tail dimers as indicated by comparison of ox(non-aq)-AnC6SH/Au and ox(non-aq)-AnC7SH/Au voltammetry with that of solution-phase model compounds (2-methoxy-N 4-phenyl-1,4-phenylenediamine and 3,3'-dimethoxybenzidine). Reflective-absorption infrared spectroscopy (RAIR) was used to identify the resultant products of aqueous acidic and non-aqueous oxidation of AnC6H/Au and AnC7SH/Au. RAIR spectra for ox-AnC6SH/Au and ox-AnC7SH/Au displayed vibrations indicative of 1,2,4-coupled surface-confined poly(aniline). A small carbonyl band related to a quinonimine hydrolysis product was also noted in the RAIR spectra of both oxidized monolayers. RAIR spectra for ox(non-aq)-AnC6SH/Au and ox( non-aq)AnC7SH/Au indicated surface-confined aniline dimers were formed with no hydrolysis product. The electrochemical and microscopic characteristics of poly(aniline) and poly(o-phenetidine) nucleation/growth on AnC6SH/Au and AnC7SH/Au were investigated using electrochemical and scanning probe methods. Electrochemical polymerization of aniline on AnC6SH/Au and AnC7SH/Au yielded loosely adherent polymer films comprised of poly(aniline) nodules as indicated by scanning tunneling microscopy images. Alternatively, poly(o-phenetidine) films on AnC6SH/Au and AnC7SH/Au formed smooth, featureless films that were strongly adherent to the underlying monolayer.
Schomburg, Keith Cory, "Synthesis and Characterization of Alkoxyaniline-Terminated Monomer Monolayers on Gold Surfaces." (2000). LSU Historical Dissertations and Theses. 7296.