Step-by-step growth of epitaxially aligned polythiophene by surface-confined oligomerization

J. A. Lipton-Duffin,1,2 J. A. Miwa,1,2 M. Kondratenko,2,3 F. Cicoira,1,2 B. G. Sumpter,4
V. Meunier,4 D. F. Perepichka,2,3 F. Rosei,1,2

1-INRS-ÉMT, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, QC J3X 1S2 Canada
2-Center for Self-Assembled Chemical Structures
3-Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montréal, QC, H3A 2K6 CANADA
4-Center for Nanophase Materials Sciences, Oak Ridge National Laboratory

Achievement

Using in situ STM imaging combined with first principles density functional theory calculations, we demonstrate the surface-confined growth of ordered arrays of poly(3,4-ethylenedioxythiophene) (PEDOT) chains. This is achieved by using the 110 facet of copper simultaneously as a template and catalyst for polymerization. The method is demonstrated to provide a facile method to assemble aromatic building blocks into ordered structures and is extendable to other halogen-terminated molecules to produce the unique epitaxially aligned conjugated polymers. These types of systems could be of central importance to develop future electronic and optoelectronic devices with high-quality active materials.

Significance

One of the great challenges in surface chemistry is to assemble aromatic building blocks into ordered structures that are mechanically robust and electronically interlinked. In this work, we have demonstrated the formation of epitaxially ordered arrays of the conducting polymer PEDOT. The very high resolution of in situ STM imaging combined with first principles density functional theory calculations allowed the explicit polymerization process to be visually followed, from the formation of a reactive intermediate, to the formation of dimers, trimers, tetramers and longer oligomers, one monomer unit at a time. The strong molecule-surface interactions dictate that all monomer units orient in an upright position with the sulfur atom pointing towards the substrate (see Figure), leading to an unexpected and previously unobserved all-cis conformation of the PEDOT chain. The polymerization process is controlled by the classical Ullmann dissociative coupling mechanism, where the substrate itself acts as a catalyst (scheme 1, below), thus suggesting a general approach for this type of reaction. This demonstrated capability should be particularly useful in the controlled growth of novel 2D conjugated organic structures, which are currently the focus of widespread research in optoelectronics and light harvesting.

Credit

This work was published in PNAS Early Edition (2010) doi: 10.1073/pnas.1000726107. A portion of the research, performed at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences, was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Citation for highlight: J. A. Lipton-Duffin, J. A. Miwa, M. Kondratenko, F. Cicoira, B. G. Sumpter, V. Meunier, D. F. Perepichka, F. Rosei “Step-by-step growth of epitaxially aligned polythiophene by surface-confined oligomerization” Proc. Nat. Acad. Sci. (2010). DOI:10.1073/pnas.1000726107.

Figure. Formation of epitaxially confined cis-PEDOT on a Cu(110) surface depicted in Scheme 1 and a comparison of the calculated trimer geometry with measured structures.