QUANTUM INTERFERENCE BASED SINGLE-MOLECULE INSULATORS & HELICAL CURRENTS IN CUMULENES

When a small voltage bias is applied to a single-molecule junction, an electric current runs through the molecule via a coherent tunneling process. This charge-transport process depends on the molecule and in particular its electronic structure. In this project, we have explored two particular charge-transport phenomena which are inherently related to the quantum mechanical nature of molecules and their electronic structure. In the first part, we identified the first class of saturated molecules that exhibit destructive quantum interference in their electronic transmission. In these bicyclo[2.2.2]octasilanes, the singlemolecule conductance is almost completely suppressed which makes them extremely efficient single-molecule insulators. In the second part, we have explored the possibility of helical electron-transport in linear molecules. We find that in chiral odd-carbon cumulenes the frontier -orbitals have a helical nature. This orbital helicity makes the current move in a circular fashion around the wire. It is the helicity of the orbitals that controls whether the current runs clockwise or counterclockwise around these perfectly linear organic molecules. Both of these findings are remarkable examples of how molecules can provide novel electronic functionality and, more generally, how the properties hiding inside the vastness of chemical space never cease to amaze.