January 05-2003 -- Combining the properties of polymers and crystals, a team of American and German scientists has created nanocylinders, highly symmetric, structured materials with new electronic properties that could be used to create supramolecular electronic devices.

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Disc-like or ring-shaped organic molecules organize into symmetric cylinders, three nanometers in thickness, and 50-100 nanometers in length, after the attachment of specific functional groups. At the core, these nano-cylinders are composed of conductive molecules or polymers, which are covered with a molecular insulating coating. Such materials are important for optoelectonics and open up new possibilities for supramolecular electronics, according to the Max Planck Institute for Polymer Research.

For some time, researchers have been trying to combine the advantages of polymers and crystals to produce highly ordered but easy-to-handle molecular systems. Crystals have a precise structure and a high electron conductivity but are difficult to handle. Polymers are cheap to produce and easy to handle but have comparatively immobile charge carriers. Liquid crystals have a charge carrier mobility similar to crystals but their preparation and processing is expensive, according to the Max Planck Institute for Polymer Research.

Scientists from the Max Planck Institute and their American collaborators have combined the advantageous properties of classical polymers with those of crystals by synthesizing clusters of fluorine- containing dendritic polymers.

If single electron donor or electron acceptor groups are attached to the end of the dendrons, wedge-shaped building blocks arise, which organize themselves into tiny supramolecular cylinders. Both components, organic materials and polymers, can be used as donor or acceptor groups. Supramolecular liquid crystals can also be formed from different organic materials through self-organization. The donor-acceptor complexes in the center of these molecules display promising optoelectronic properties. Under these conditions, even disordered polymers assemble into well-defined cylinders. The fluorinated periphery of the molecules protects the inner core from external influences such as humidity, according to the Max Planck Institute.

Scientists at the Max Planck Institute probed the stacking of the aromatic ring systems, which determine the optoelectronic properties of the nanocylinders, using solid-state nuclear magnetic resonance (NMR) spectroscopy. The group has developed NMR techniques that resolve the exact arrangement of the nanometer-scale cylindrical structures by measuring the distance between single hydrogen atoms. This information allows scientists to determine the degree to which electron conductivity can be achieved.