The ability to manipulate single molecules and their electronic properties offers the opportunity to use them as active elements in nanoscale electronics. Moresco et al. demonstrate that a scanning tunneling microscope can be used to induce a conformational change in a single molecule; this alters the electronic properties of the tunnel junction. A derivatized porphyrin molecule is deposited onto a copper surface with its four arms (di-tert-butylphenyl groups) perpendicular to the plane of the porphyrin and the surface. The tip of a scanning tunneling microscope (STM) is brought close to just one of the arms, and a gentle nudge serves to twist the arm into an orientation parallel to the surface. The tunneling current through the arm depends on the extent of the rotation. A 90° rotation induces the maximum change (of over six orders of magnitude) in resistance, which can be reversed by nudging the arm back up to its original position. — ISO
Phys. Rev. Lett.86, 672 (2001).