Yeon-Taik Kim

Organic Monolayers as Nucleation Sites for Epitaxial Growth: II. Synthesis of ω-N-Pyrrolo-Functionalized n-Dialkyl Disulfide

Abstract Pyrrole terminated dialkyl disulfides were synthesized. The molecules self assemble on gold and can be used for the electrochemical epitaxial growth of poly(n-alkyl)pyrrole.

Electrochemical Quartz Crystal Microbalance Studies of Polypyrrole Growth on Self‐Assembled Nucleation Sites

A gold electrode was modified by self-assembly of bis(ω-(N-pyrrolyl)-n-undecyl)disulfide (BPUS), so that the BPUS monolayer serves as nucleation sites for the subsequent growth of polypyrrole. Formation of the BPUS monolayer was monitored by electrochemical quartz crystal microbalance (EQCM). The monolayer coverage of 3.7 x 10 14 molecule/cm 2 was determined by frequency change. The BPUS monolayers were oxidized by cyclic voltammetry, and the charge was determined by integration of the area beneath the oxidative wave of the cyclic voltammogram. Reconciliation of the surface coverage as determined by frequency change and the amount of charge passed led to the n value of 1 for each pyrrole unit of the BPUS monolayer. Two mechanisms were proposed to account for this: (i) the formation of dimers upon electrochemical oxidation of the monolayer and (ii) the formation of ketone-type degradation products because of reaction with oxygen or water. The electrochemical growth of polypyrrole on the BPUS-modified and the bare gold surface was also compared using EQCM. Frequency-charge plots for growth of polypyrrole on the unmodified surface show a nonlinear relationship, indicative of three-dimensional polymer growth. On the other hand, a linear relationship is obtained for the frequency-charge plot on the BPUS-modified surface, characteristic of layer-by-layer growth.

Understanding of molecular assembly with scanning tunneling microscopy at solid/liquid interfaces

Abstract Scanning tunneling microscopy (STM) was used to resolve molecular packing structures of mixed thiophene-N-alkylpyrrole oligomeric molecules at the solid/liquid interfaces. We have systematically synthesized several mixed thiophene-pyrrole oligomers to understand the nature of grains, shapes, and crystalline orientations. The resulting STM images were compared with the structure generated by MM3 molecular modeling simulation. The basal plane of highly oriented pyrolytic graphite (HOPG) surface was used to deposit the molecules.