The adsorption and electropolymerization of terthiophene on Au(111) electrode - Probed by in situ STM

In situ scanning tunneling microscopy (STM) was used to examine terthiophene (TT) adsorbed on an ordered Au(111) electrode in 0.1 M H2SO4 and HClO4, as a model system to gain a fundamental understanding of the effects of potential control on the coadsorption of anion and the oxidation of a thiophene - bearing entity. TT was irreversibly adsorbed onto an Au(111) bead crystal from a dosing solution made of ethanol at room temperature. The cyclic voltammogram (CV) recorded with this sample in 0.1 M H2SO4 showed a series of welldefined peaks, resulting from the restructuring of the TT adlayer, coupled with anion coadsorption and the phase transition of the Au(111) electrode. In contrast, the CV obtained in 0.1 M HClO4 was mostly featureless before TT admolecules were irreversibly oxidized at E > 0.7 V (vs Ag/AgCl). TT molecule was adsorbed most horizontally on Au(111) electrode in H2SO4, but displaced by bisulfate anion at positive potential. Anodization of this TT/Au(111) electrode triggered the oxidation and subsequent coupling of TT monomers to yield oligothiophenes, whose internal structures and dimensions were revealed by STM in pH1 and 5 sulfate media. The as - produced oligothiophenes appeared as winding ribbons spanning similar to 200 and similar to 40 angstrom in pH 5 and 1 sulfate media. Their internal structures, particularly the trans and cis conformations of neighboring thiophenes units, were visualized by molecular resolution STM.