Covalent Assembly and Characterization of Nonsymmetrical Single-Molecule Nodes.

The covalent linking of molecular building blocks on surfaces enables the construction of specific molecular nanostructures of well-defined shape. Molecular nodes linked to various entities play a key role in such networks, but represent a particular challenge because they require a well-defined arrangement of different building blocks. Herein, we describe the construction of a chemically and geometrically well defined covalent architecture made of one central node and three molecular wires arranged in a nonsymmetrical way and thus encoding different conjugation pathways. Very different architectures of either very limited or rather extended size were obtained depending on the building blocks used for the covalent linking process on the Au(111) surface. Electrical measurements were carried out by pulling individual molecular nodes with the tip of a scanning tunneling microscope. The results of this challenging procedure indicate subtle differences if the nodes are contacted at inequivalent termini.