We have investigated the single molecule conductance of a series of bipyridyl ligands using the scanning tunneling microscopy-based break-junction method. The ligands, which vary in length and conjugation, include pyrazine, 4,4'-bipyridine, bispyridyl methane, bispyridyl ethane, bispyridyl ethene, bispyridyl propane, and bispyridyl propene. Molecular junctions are formed by repeatedly crashing a gold tip into a gold surface and measuring the conductance (inverse of resistance) as a function of tip-surface separation under low bias voltage conditions (25-100 mV). Quantized conductance is observed in steps of G0, the quantum of conductance, both in the absence and presence of analyte molecules (e.g. bypyridine ligands). The molecular conductance is found to vary as a function of the overall length of the ligand, as well as its conjugation. These results will be discussed in light of recent single conductance measurements on similar bipyridyl molecules, the mechanism of charge transfer, and in terms of their use in osmium-based photosensitizer complexes, [Os(bpy)2CO(L)]2+, where L is the one of the series of bipyridyl ligands listed above. Preliminary results on the single molecule conductance and charge transport mechanism for [Os(bpy)2CO(L)]2+ complexes will also be presented.

Single molecule conductance measurements of bipyridyl ligands

244th National Meeting (2012)

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