Potential and Anion Effects on the Adsorption of 3',4'-Bis(hexylthio)-2,2':5',2''-Terthiophene on Au(111) Electrode Characterized by in Situ Stm

The adsorption of organic molecules on gold electrodes serves as a model to understand the organic/inorganic electrified interface, which is relevant to the study of molecular electronics and organic thin film semiconduc-tors. Our previous study on terthiophene (TT) adsorption on an Au(1 1 1) electrode shows that immersing Au (111) crystals in a TT ethanol dosing solution installs an ordered TT adlayer on the sample. The current study addresses the adsorption of 3',4'-bis(hexylthio)-2,2':5',2''-terthiophene (DTDST), a molecule with a TT back-bone attached with two thiolhexyl chains, on an ordered Au(1 1 1) electrode. High-quality STM images were obtained to reveal the internal and 2D spatial structures of DTDST admolecules. The potential greatly influ-enced the organization of DTDST on the ordered Au(1 1 1) electrode. Although the pristine DTDST adlayer was disordered, it transformed into ordered Au(1 1 1) -(3 & RADIC;3 x 9) and (5 & RADIC;3 x 26) structures after applying a potential more negative than 0 V (vs. Ag/AgCl) in 0.1 M H2SO4 and HClO4, respectively. Shifting the poten-tial more positive than 0.25 V resulted in coadsorption of bisulfate anions and restructuring of the DTDST adlayer. High-quality molecular resolution STM images were collected to reveal the azimuthal orientation of the DTDST admolecule on the Au(1 1 1) electrode. The thiolhexyl chains of DTDST admolecules could arrange in such a way that allowed intermolecular van der Waals interactions. Oxidation of adsorbed DTDST molecules to yield oligomers was also revealed by in situ STM.