Credit: © 2006 Wiley

Dendrimers are highly branched molecules with structures that are somewhat reminiscent of trees. A number of discrete arms emanate from a central core and each one branches in a regular repeating fashion. The outer ends of these branches can be decorated with molecules of a different type from those that comprise the rest of the structure. These terminal groups often dominate the properties of the ensemble because they sit on the surface.

Rigoberto Advincula and co-workers1 from the University of Houston in the US have shown how the carbazole groups at the ends of the branches of a dendrimer can be linked to one another to form an outer shell with interesting optoelectronic properties. This not only results in a polycarbazole conjugated electronic system (an alternating sequence of single and double carbon–carbon bonds), but also makes the dendrimer much more rigid and slightly more compact. Atomic force microscope images of the dendrimers reflect this change; before crosslinking, they adopt a pancake-like shape, whereas after the reaction, they appear more egg-shaped.

This work highlights how molecular crosslinking can be used to reinforce dendrimers, and demonstrates how conjugated systems can be built simultaneously into these nanostructures.