Credit: © 2007 RSC

The shape and size of self-assembled organic nanoparticles play a large role in their physical properties. However, attempts to control these features by tailoring the structure of the constituent molecules have met with limited success. Rather, previous efforts have focused on adding side chains to the starting molecules to alter the molecule–molecule interactions. Now, Hongbing Fu and co-workers1 at the Chinese Academy of Sciences, in Beijing, China show that the final shape of self-assembled nanostructures can be determined just by tweaking the geometry of the starting molecules.

The team studied molecules that have the same chemical 'core' and two side 'arms' that open up at an angle of 60°, 120° or 180°. Structural studies suggest that this angle governs the interactions that determine how the molecules will stack together to form a nanoparticle. Molecules that open at 60° tend to aggregate in pairs, which are loosely held together to form nanospheres. On the other hand, molecules with larger opening angles tend to stack in a more linear fashion. The interactions between the molecules with a 120° opening angle favour unidirectional growth, leading to wire-like formations, whereas molecules that have a 180° angle ultimately form nanocubes.