Constructing the Pathway of an Electron Through a Molecule

Motion of charge through molecules is important for everything from the photosynthesis that provides nearly all the energy on earth to electron transfer enzymes that protect the body from bacteria and viruses. But the fundamental structure of such paths – how the electrons actually move through molecules – has never been directly obtained from any experiment. Collaborative work between the MRSEC at Northwestern, NIST in Washington, and the University of Warwick in England has utilized a complex experiment called inelastic electron scattering to construct, directly from experiment, the pathway that an electron takes through a molecule, as it moves from one end to another to produce the charge transfer process that underlies photosynthesis, enzyme action, and other phenomena from rock weathering to suntans. This fundamental insight allows scientists, by knowing the pathways, to change them and therefore to modify the efficiencies and rates of charge transport through molecules.

Inelastic electron tunneling spectrum (IETS) for an extended naphthyl ether molecule, and its interpretation using Green’s function theory and first-principles calculation. The molecule is sketched in the right panel, between gold electrodes, as used in the experiment. The experimental data (black trace) and the model calculation (red trace, offset of clarity) are shown in the upper left. From comparisons of the computed pathways with the experimental data, the path for electron motion through the molecule is deduced (lower left): the pi path segment is in red the sigma in blue. This is the first experimentally-derived pathway for transport in a molecule.