Thin layers of cobalt and ruthenium polypyridyloligomers with thicknesses between 2 and 8 nm were deposited on gold by electrochemical reduction of diazonium salts. A scanning tunneling microscope was used to create single-molecule junctions (SMJs). The charge transport properties of the Au-[Co(tpy) 2 ] n -Au (n = 1−4) SMJs do not depend markedly on the oligomer length, have an extremely low attenuation factor (β ∼ 0.19 nm −1 ), and do not show a thickness-dependent transition between two mechanisms. Resonant charge transport is proposed as the main transport mechanism. The SMJ conductance decreases by 1 order of magnitude upon changing the metal from Co to Ru. In Au-[Ru(tpy) 2 ] n -Au and Au-[Ru(bpy) 3 ] n -Au SMJs, a charge transport transition from direct tunneling to hopping is evidenced by a break in the length-dependent β-plot. The three different mechanisms observed are a clear molecular signature on transport in SMJs. Most importantly, these results are in good agreement with those obtained on large-area molecular junctions.

Various architectures have been generated and observed by STM at a solid/liquid interface resulting from an in situ chemical reaction between the bipyridine terminal groups of a ditopic ligand and Co(II) ions. Large monodomains of one-dimensional (1D) double wires are formed by Co(II)/ligand coordination, with polymer lengths as long as 150 nm. The polymers are organized as parallel wires 8 nm apart, and the voids between wires are occupied by solvent molecules. Two-dimensional (2D) grids, showing high surface mobility, coexist with the wires. The wires are formed from linear chain motifs where each cobalt center is bonded to two bipyridines. 2D grids are generated from a bifurcation node where one cobalt bonds to three bipyridines. Surface reconstruction of the grids and of the 1D wires was observed under the STM tip. As an exciting result, analysis of these movements strongly indicates surface reactions at the solid/liquid interface.Letter pubs.acs.org/JPCL