Although chemists can create polymers of practically any length and structure, positioning and ordering them on surfaces has been a long-standing challenge. This is a stumbling block, because precise control over properties such as charge mobility and recombination is crucial if polymer chains are to find use in any practical applications in the future.

Now, a team of scientists from Canada and the US have taken a major step towards overcoming this problem, by using a metal surface to synthesize arrays of conjugated polymer chains of PEDOT, a widely used conductive polymer [Lipton-Duffin et al., PNAS (2010), doi: 10.1073/pnas.1000726107].

The trick used by the researchers was to take advantage of the crystalline nature of the metal surface, so that it can act as both a template and the catalyst for the polymerization reaction. Federico Rosei, from the Institut National de Recherche Scientifique at the Université du Québec, explains: “We used a copper surface as a template and as a catalyst to observe the step-by-step formation of PEDOT starting from molecular building blocks of di-iodo-EDOT”.

The researchers monitored the formation of the PEDOT polymer arrays using high resolution Scanning Tunneling Microscopy under ultrahigh vacuum conditions. In combination with theoretical modeling performed using Density Functional Theory, they were able to show that the molecular elements arrange themselves in an upright orientation.

Rosei points out that the surface polymerization approach his team have demonstrated could be extended to many different molecules, so that other wires could be designed using a variety of building blocks. “The objective in this case was to obtain molecular wires. The more general goal is to synthesize two-dimensional conjugated polymers, of which graphene is the only example known so far”, he says.

KW Hipps, Professor of Chemistry at Washington State University in the US, agrees the approach has significant potential: “This is a very nice piece of work that introduces a reaction type that may be of great importance for templated growth of organic conductors and other organic electronic materials. The authors’ approach may have a general role in creating robust and electronically coupled organic surface structures.”
Meanwhile, Rosei and his collaborators plan to focus their efforts on overcoming some of the immediate challenges their work raises. These include inducing the reaction in such a way as to obtain polymers in registry with the substrate, and characterizing the final products of the reaction with conclusive proof of polymerization.