Single-molecule conductance in a series of extended viologen molecules was measured at room temperature using a gold-molecule-gold scanning tunneling microscopy break junction arrangement. Conductance values for individual molecules change from 4.8 ± 1.2 nS for the shortest compound to 2.9 ± 1.0 nS for the compound with six repeating units and length of 11 nm. The latter value is almost 3 orders of magnitude higher than that reported for all-carbon-based aromatic molecular wires of comparable length. On the basis of the length of the molecules, an attenuation factor of only 0.06 ± 0.004 nm(-1) (0.006 ± 0.0004 Å(-1)) was obtained. To the best of our knowledge, this is the smallest value reported for the conductance attenuation in a series of molecular wires.

§Institute of Materials and Environmental Chemistry Research Centre for Natural Sciences Hungarian Academy of Sciences Pusztaszeri strasse 59 67 H 1025 Budapest Hungary

†J Heyrovský Institute of Physical Chemistry of ASCR v v i Dolejškova 3 18223 Prague Czech Republic

‡Institute of Organic Chemistry and Biochemistry of ASCR v v i Flemingovo n 2 16610 Prague Czech Republic

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Environmental Control of Single-Molecule Junction Evolution and Conductance: A Case Study of Expanded Pyridinium Wiring