One of the ultimate aims of nanotechnology is the development of nanomaterials for dealing with molecular electronics, which require at least one of their dimensions falling in the nanometre scale.¹ Hence, one of the most important steps in the progress of molecular electronics is that of the molecular rectifier systems composed of organic molecules for use in the future electronic circuits.
The work presented, reports on the electrical properties of materials acting as diodes² and wires.^3,4 For this purpose, different types of molecular systems were investigated,
including chevron-shaped molecules, π-conjugated (WIREs) and banana-shaped molecular wires (BWIREs) and molecular wires formed by step-by-step deposition. All of these specified systems were fabricated on a gold-coated substrate using self-assembly.
Self-assembled monolayer (SAM) films were characterised by the quartz crystal microbalance (QCM) technique and scanning tunnelling spectroscopy (STS).
WIRE1, WIRE3 and BWIREs exhibited symmetrical I-V  
characteristics, typical for conventional molecular wires. Contrary, studies of a molecular wire formed from the sequentional synthesis of donor-acceptor-donor (D_w-A-D_s) components demonstrated diode-like behaviour. The bias for rectification was controlled by altering the donor-acceptor sequence. However logically, I-V characteristics observed for the film of the initially formed SAM and the resultant wire were different despite the electron-donating characters of both surface-active moieties. This was due to a stronger character of the terminal donor group.
The unusual phenomenon of assembly via competing S-Au/NO₂-Au interactions was observed for WIRE2. This was ascribed to the very electron deficient difluoronenone core that weakened the conventional S-Au chemisorption.
The single molecule conductivity of the molecular wire systems were determined by the method of Haiss et al.⁵ which relies on the spontaneous bridging of those molecules between a tip and a substrate.