American Chemical Society, Nano Letters, 10(14), p. 5493-5499, 2014
DOI: 10.1021/nl502466a
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Single molecule break junction experiments and non-equilibrium Green's function calculations using density functional theory (NEGF-DFT) of carbodithioate-and thiol-terminated [5,15-bis(phenylethynyl)-10,20-diarylporphinato]zinc(II) complexes reveal the impact of the electrode-linker coordination mode on charge transport at the single-molecule level. Replacement of thiolate (−S −) by the carbodithioate (−CS 2 −) anchoring motif leads to an order of magnitude increase of single molecule conductance. In contrast to thiolate-terminated structures, metal−molecule−metal junctions that exploit the carbodithioate linker manifest three distinct conductance values. We hypothesize that the magnitudes of these conductances depend upon carbodithoate linker hapticity with measured con-ductances across Au-[5,15-bis(4′-(dithiocarboxylate)phenylethynyl)-10,20-diarylporphinato]zinc(II)-Au junctions the greatest when both anchoring groups attach to the metal surface in a bidentate fashion. We support this hypothesis with NEGF-DFT calculations, which consider the electron transport properties for specific binding geometries. These results provide new insights into the origin of molecule-to-molecule conductance heterogeneity in molecular charge transport measurements and the factors that optimize electrode−molecule−electrode electronic coupling and maximize the conductance for charge transport.