Abstract. The conductance of molecular junctions formed of N,N'-bis(n-thioalkyl)-4,4'-bipyridinium bromides or alkanedithiols between a gold (Au) scanning tunnelling microscope tip and a Au(111)-(1 × 1) electrode has been studied at electrified solid/liquid interfaces. A statistical analysis based on large sets of individual current–distance traces was applied to obtain the electrical conductance of single junctions. The one-electron reduction of the viologen moiety from the dication V²⁺ to the radical cation state gives rise to a 50% increase of the junction conductance. Increasing the length of the alkyl spacer units leads to a tunnelling decay constant β_CH2 = 5.9–6.1 nm⁻¹. This value is significantly lower than β_CH2 = 8.2 nm⁻¹ estimated for molecular junctions of alkanedithiols. The difference is attributed to conformational changes within the two junctions. The contact conductance was estimated to 10 µS.

Print publication: Issue 4 (31 January 2007)
Received 19 August 2006, in final form 27 October 2006
Published 12 December 2006