Hapticity-Dependent Charge Transport through Carbodithioate- Terminated (5,15-Bis(phenylethynyl)porphinato)zinc(II) Complexes in Metal−Molecule−Metal Junctions

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 (−CS2 − ) 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.