Organometallic Molecular Wires with Thioacetylene Backbones, trans‐{RS‐(C≡C)n}2Ru(phosphine)4: High Conductance through Non‐Aromatic Bridging Linkers

In this work, the design, synthesis, and single‐molecule conductance of ethynyl‐ and butadiynyl‐ruthenium molecular wires with thioether anchor groups [RS=n‐C6H13S, p‐tert‐Bu−C6H4S), trans‐{RS−(C≡C)n}2Ru(dppe)2 (n=1 (1R), 2 (2R); dppe: 1,2‐bis(diphenylphosphino)ethane) and trans‐(n‐C6H13S−C≡C)2Ru{P(OMe)3}4 3hex] are reported. Scanning tunneling microscope break‐junction study has revealed conductance of the organometallic molecular wires with the thioacetylene backbones higher than that of the related organometallic wires having arylethynylruthenium linkages with the sulfur anchor groups, trans‐{p‐MeS−C6H4‐(C≡C)n}2Ru(phosphine)4 4n (n=1, 2) and trans‐(Th−C≡C)2Ru(phosphine)4 5 (Th=3‐thienyl). It should be noted that the molecular junctions constructed from the butadiynyl wire 2R, trans‐{Au−RS−(C≡C)2}2Ru(dppe)2 (Au: gold metal electrode), show conductance comparable to that of the covalently linked polyynyl wire with the similar molecular length, trans‐{Au−(C≡C)3}2Ru(dppe)2 63. The DFT non‐equilibrium Green's function (NEGF) study supports the highly conducting nature of the thioacetylene molecular wires through HOMO orbitals. The scanning tunneling microscope break‐junction study of thioacetylene ruthenium molecular wires exhibited single‐molecule conductance higher than that of the related organometallic wires indicating the superiority of the acetylene bridging linkers as well as the thioether coordination anchor groups. The DFT non‐equilibrium Green's function study supports the high conductance of the thioacetylene molecular wires, for which HOMOs are the dominant conductance pathways.