Single-molecule conductance of three sulphur-functionalized organometallic wires with two ruthenium(II) centres spaced by 1,3-butadiyne was firstly investigated using an electrochemically assisted-mechanically controllable break junction (EC-MCBJ) approach. It is demonstrated that single-molecular conductance of these diruthenium(II) incorporated systems is significantly higher than oligo(phenylene-ethynylene) (OPE) having comparable lengths and exhibits weaker length dependence. The conductance improvement in these diruthenium(II) molecules is ascribable to the better energy match of the Fermi level of gold electrodes with the HOMO that is mainly resident on the Ru-C^C-C^C-Ru backbone.Furthermore, modulation of molecular conductance is achieved by changing the length and pconjugated system of the chelating 2,2 0 :6 0 ,2 00 -terpyridyl ligand.

A series of ruthenium acetylide complexes [Ru(BPI)(PPh3)2(CCR)] (BPI = 1,3-bis(2-pyridylimino)isoindolate; R = −C6H5 (2), −Cp2Fe (3a), −C6H4C6H4CCCp2Fe (3b)) and bis(acetylide)-linked binuclear ruthenium complexes [{Ru(BPI)(PPh3)2}2(CCRCC)] (R = none (4), 1,4-benzenediyl (5), 1,4-naphthalenediyl (6), 9,10-anthracenediyl (7)) were synthesized and characterized by ESI-MS spectrometry, IR, 1H and 31P NMR, and UV–vis–near-IR spectroscopy, and cyclic and differential pulse voltammetry. Oxidation of 3–7 with 1 equiv of ferrocenium perchlorate afforded the corresponding one-electron-oxidized complexes 3 +–7 +. In contrast to the case for 3a + , where spin density is localized at the Fe center due to moderate electronic communication between RuII and FeIII centers along the Ru–CC–Cp2Fe backbone, the spin density is primarily populated on Ru for 3b + without an appreciable electronic interaction between RuIII and FeII across the quite long bridging system RuCCC6H4C6H4CCCp2Fe. For bis(acetylide)-linked binuclear ruthenium complexes 4–7, electrochemical, UV–vis–near-IR spectral and TD-DFT computational studies reveal that electronic delocalization along the bridging RuCCRCCRu backbone is highly dependent on the R spacer. It is demonstrated that with the gradual increase of a π-conjugated system in aromatic R spacer, the electronic delocalization shows progressive enhancement along the Ru–CCRCC–Ru backbone due to an increasing participation of the bridging ligand. 4 + displays highly electronically delocalized behavior, whereas 5 +–7 + are on the borderline of electronic delocalization.

Heteronuclear complexes FeCp2 -DTE-C≡C-Ru(dppe)2 Cl (1 o; dppe=1,2-bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp2-DTE-C≡C-Ru(dppe)2-C≡C-DTE-FeCp2 (2 oo), with redox-active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe⋅⋅⋅Ru electronic communication. Upon UV-light irradiation of 2 oo, the Fe⋅⋅⋅Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo→2 co→2 cc; this is ascribed to the gradual increase in π-conjugated systems. The near-infrared absorptions in mixed-valence species [2 oo](+) /[2 co](+) /[2 cc](+) are gradually intensified following the conversion of [2 oo](+) →[2 co](+) →[2 cc](+) , which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes.