Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes.

The preparation and properties of novel ruthenium carbon-rich complexes [(Ph-C≡C-)2-nRu(dppe)2(-C≡C-bipyM(hfac)2)n] (n = 1, 2; M = CuII, MnII; bipy = 2,2'-bipyridin-5-yl) characterized by single-crystal X-ray diffraction and designed for molecular magnetism are reported. With the help of EPR spectroscopy, we show that the neutral ruthenium system sets up a magnetic coupling between two remote paramagnetic CuII units. More specifically, these copper compounds are unique examples of bimetallic and linear heterotrimetallic compounds for which a complete rationalization of the magnetic interactions could be made for exceptionally long distances between the spin carriers (8.3 Å between adjacent Cu and Ru centers, 16.6 Å between external Cu centers) and compared at two different redox states. Surprisingly, oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to weaker magnetic interactions. In contrast, in the simpler parent complexes bearing only one paramagnetic metal unit [Ph-C≡C-Ru(dppe)2-C≡C-bipyCu(hfac)2], one-electron oxidation of the ruthenium bis(acetylide) unit generates an interaction between the Cu and Ru spin carriers of magnitude comparable to that observed between the two far apart Cu ions in the above corresponding neutral trimetallic system. Evaluation and rationalization of this coupling with theoretical tools are in rational agreement with experiments for such complex systems.

Fast Electron Transfer Exchange at Self-Assembled Monolayers of Organometallic Ruthenium(II) σ-Arylacetylide Complexes.

A new series of ruthenium organometallic carbon-rich complexes, exhibiting fast electron transfer kinetics combined to a low oxidation potential, was synthesized for self-assembled monolayer (SAM) formation on gold surfaces. The molecules consist of highly conjugated ruthenium(II) mono(σ-arylacetylide) or bis(σ-arylacetylide) complexes functionalized with different bridge units with specific (protected) anchoring groups that possess high affinity for gold, such as thiol, carbodithioate, and isocyanide. Single component and mixed SAMs were prepared and fully characterized by wettability studies, infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), and electrochemical analyses. By applying the Laviron's formalism, fast electron transfer kinetics (≈10(4) s(-1)) were found at the derived self-assemblies while no significant effect could have been evidenced with variation of the bridging unit and of the anchoring moiety. Interestingly, a hexyl aliphatic spacer in the bridging unit with a thiol group and dilution with suitable nonelectroactive thiols lead to better SAM organization and packing, in comparison with undiluted complexes with shorter spacers. Such features make these compounds suitable alternatives to the widely used ferrocene center as redox-active building blocks for reversible charge storage devices.

Ruthenium Carbon-Rich Complexes as Redox Switchable Metal Coupling Units.

With the help of EPR spectroscopy, we show that the diamagnetic [Ru(dppe)2(-C≡C-R)2] system sets up a magnetic coupling between two organic radicals R, i.e., two nitronyl nitroxide or two verdazyl units, which is stronger than that of related platinum organometallic systems. Surprisingly, further oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to the switching off of this interaction. On the contrary, in simpler complexes bearing only one of the organic radical ligands [C6H5-C≡C-Ru(dppe)2-C≡C-R], one-electron oxidation of the transition metal unit generates an interaction between the two spin carriers of comparable magnitude to that observed in the above corresponding neutral systems.

d-f heterobimetallic association between ytterbium and ruthenium carbon-rich complexes: redox commutation of near-IR luminescence.

We describe how the association between an ytterbium ion and a ruthenium carbon-rich complex enables the first switching of the near-IR Yb(III) luminescence by taking advantage of the redox commutation of the carbon-rich antenna.

A "cyanine-cyanine" salt exhibiting photovoltaic properties.

Association between cationic and anionic heptamethine dyes led to the formation of a new organic salt (3) displaying exceptional light-harvesting properties in the NIR spectral range and having amphoteric redox character. Preliminary results of molecular bulk heterojunction solar cells based on the title compound 3 and [60]PCBM as the only active layer reveal this new dye as a promising light-harvesting material for photovoltaics.

Stable near-infrared anionic polymethine dyes: structure, photophysical, and redox properties.

The concept of cyanine has been successfully extended to an anionic heptamethine dye featuring tricyanofuran (TCF) moieties in terms of structure, reactivity, and photophysical properties. Importantly, absorption and emission are red-shifted compared to its classical cationic analog without any cost in terms of thermal stability. In addition to its "cyanine" behavior, this molecule exhibits further redox properties: oxidation and reduction led to the reversible formation of radical species whose absorption is in marked contrast with that of cyanines.