Credit: © 2006 ACS

It is essential to control the arrangement of molecules in organic conductors in order to provide a path for the flow of electrons. However, this is a challenging task as there are many ways in which molecules can assemble. Now, Klaus Müllen and co-workers1 at the Max-Planck-Institut für Polymerforschung in Mainz, Germany have found a new way to make highly ordered structures from disk-shaped molecules comprising a graphene-like core surrounded with hydrocarbon side chains.

The molecules, which may have potential as organic semiconductors, were placed in a 2-mm-diameter capillary tube and heated to 60 °C. At this temperature they formed a disordered liquid. When cooled to room temperature, the molecules aggregated to form ordered structures. This ‘liquid crystal’ behaviour began on the sides of the capillary tube from where the crystallization spread. X-ray scattering studies revealed that the ordered structure existed for several centimetres along the tube.

To make the material on a nanoscale, the process was repeated using an alumina template with 100–200-nm-wide tubular pores. After removal of the template, scanning electron microscope images showed bundles of regularly sized nanorods. Such a material could be used in photovoltaic cells because of its charge-carrying capacity and ordered structure.