Recent advances in analytical surface chemistry allow for facile, accurate measurements of single molecule properties. Nuckolls has shown that STM can be used to reliably generate force-conductivity profiles on terminal aliphatic and aromatic diamines¹. The conductance measured in these systems is a function of the STM tip distance from the metal surface and not necessarily conformation of the substrate. We are currently developing systems for which the conductance is a direct function of the molecular conformation. We are investigating a-b-oligothiophenes that predictably yield helical scaffolds in the solid state, as well as substituted [8]annulenes. New synthetic strategies into both classes of molecules will be discussed. Regarding theory, the helical systems are predicted to have a HOMO-LUMO gap that is dependent on the internal dihedral angles of the helices, based on Outer Valence Green's Function (OVGF) calculations. For a helix in its lowest energy conformation, the internal dihedral angles are ca. 45^o, and the HOMO-LUMO energy difference at this conformation is low thus implying a high conductance. As the dihedral angles are increased, tantamount to pulling on the helix via STM, the HOMO-LUMO difference increases until the dihedral angles surpass 90^o, where the energy difference again drops. Conversely, for the [8]annulene systems, a linear response of conductance is predicted for increasing dihedral angles. Theoretical results and synthetic efforts will be discussed.

1. Venkataraman, L.; Klare, J. E.; Tam, I. W.; Nuckolls, C. H., M. S.; Steigerwald, M. L., Nano Lett. 2006, 6, 458 - 462.