Nature Nanotechnol. doi:10.1038/nnano.2009.55 (2009)

Even the strongest molecular bonds break if yanked hard enough. But studying this effect requires a delicate tugging mechanism that can focus force controllably on individual bonds.

Roman Boulatov and his colleagues at the University of Illinois in Urbana-Champaign have found such a device: a rigid U-shaped molecule, stiff stilbene (pictured), the ends of which are attached to the molecule under interrogation. Stilbene twists into a strained shape on exposure to light, pulling on its attached molecule. The force generated can be calculated from quantum mechanical principles, and altered incrementally depending on the length of an adjustable linker.

The researchers confirm a direct relationship between the force their probe exerts on a cyclobutene molecule and the rate at which a central bond falls apart.