The dream of molecular electronics is to wire up circuits using individual molecules as the basic components. A basic problem is how you connect your (typically semiconducting) molecules to the metallic connectors; the leading candidate at the moment is to use molecules with a terminal thiol (-S-H) group. Thiols stick very effectively to the surface of gold; this thiol-gold chemistry has quietly become one of the most widely used tools of today’s nanotechnologists, and has been referred to as a molecular alligator clip. But it’s not without its drawbacks; rather than bonding to a single metal ion the thiol group complexes with a group of neighbouring gold atoms, and the electrical properties of the bond through the single linking sulphur atom aren’t ideal. Two papers in this week’s Science magazine suggest an alternative.
The two papers – by Siaj and McBreen (Université Laval, Québec) and Nuckolls and coworkers (Columbia University) (subscription required for access to the full articles) both describe ways of getting a molecule linked to a metal surface by a double bond (i.e. M=C- where M is a metal atom and C is the terminal carbon of an organic molecule). The surface bonded organic molecule can then be used to initiate polymerisation by a method known as ring opening metathesis polymerisation (ROMP). This is vey interesting because ROMP provides a way of growing organic semiconducting molecules with great precision. In short, we have here a better alligator clip for wiring up molecular electronics.