Self-assembly of supramolecular wires and cross-junctions and efficient electron tunnelling across them

Abstract

The self-assembly of molecules incorporating π-electron rich units into supramolecular wires is shown by scanning tunnelling microscopy (STM) at a graphite–liquid interface. Hydrogen bonds between the side chains of these molecules ensure a face-to-face contact between the functional moieties, which would otherwise lie flat on the surface if the amide groups affording this effect were absent. The organisation in the wires also depends critically on the constitution of the molecule: The cis and trans isomers show ordered and disordered spacing between wires, respectively. The supramolecular wires formed by the cis isomer form crossed architectures, with multilayers of the linear structures being formed. Study of the junction points between the fibres by scanning tunnelling spectroscopy shows that tunnelling electrons are transported efficiently, practically with the same probability as through a single wire. Molecular modelling is used to determine how the π-electron rich units within two crossing wires organise at the crossing. Based on those structural data, the electron tunnelling probability between tip and substrate is then calculated; it shows that electron transmission can indeed take place at the crossing. This result implies that supramolecular fibres can be used as wires in order to build integrated circuits by bottom-up construction from the molecule scale.