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 nonequilibrium 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 conductances 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.