The electronic structure of the polyynyl complexes [Ru{(CtC) and the oxidized species [Ru{(CtC) n C 6 H 5 }(PH 3 ) 2 Cp] + have been studied using DFT methods. The optimized geometries are in good agreement with the few experimental structures available. The electronic structures are best described in terms of a strong σ-bonding component and a weaker interaction between the filled metal d orbitals and filled polyyne π orbitals. The charge distribution in the molecules and the energies and localization of the frontier orbitals have been examined to help rationalize the reactivity patterns emerging for this important class of compounds.

Nanomechanical shuttles transferring small groups of electrons or even individual electrons from one electrode to another offer a novel approach to the problem of controlled charge transport. Here, we report the fabrication of shuttle-junctions consisting of a 20 nm diameter gold nanoparticle embedded within the gap between two gold electrodes. The nanoparticle is attached to the electrodes through a monolayer of "flexible" organic molecules which play the role of "springs" so that when a sufficient voltage bias is applied, the nanoparticle starts to oscillate transferring electrons from one electrode to the other. Currentvoltage characteristics for the fabricated devices have been measured and compared with the results of our computer simulations.In 1998, a group of theoreticians 1 proposed a novel mechanism of charge transport in nanostructures based on mechanical shuttling of electrons. The basic element (see Fig. 1), which is called a shuttle-junction, consists of a metallic nanoparticle connected by flexible, "elastic" molecules to two nanoelectrodes. For low applied voltages where the nanoparticle is stationary the device is similar to a single-electron transistor (SET). 2 The vibrational process

No abstract

A series of trimethylsilyl-protected monoalkynes (Me3SiC≡C-R) and bis-alkynes (Me3 SiC≡C-R-C≡CSiMe3) incorporating carbazole spacer groups (R = carbazole-2-yl, carbazole-3-yl, carbazole-2,7-diyl, N-(2-ethylhexyl)carbazole-2,7-diyl, carbazole-3,6-diyl, N-(2-ethylhexyl)carbazole-3,6-diyl), together with the corresponding terminal monoalkynes (H-C≡C-R) and bis-alkynes (H-C≡C-R-C≡C-H), have been synthesized and characterized. The CuI-catalyzed dehydrohalogenation reaction between trans-[(Ph)(Et3P)2PtCl], trans-[(Et3P)2PtCl2], and trans-[(P(n)Bu3)2PtCl2] and the terminal alkynes in (i)Pr2NH/CH2Cl2 affords a series of Pt(II) mono- and diynes, while the dehydrohalogenation polycondensation reactions with trans-[(P(n)Bu3)2PtCl2] under similar reaction conditions yields four Pt(II) poly-ynes of the form trans-[(P(n)Bu3)2Pt-C≡C-R-C≡C-]n. The acetylide-functionalized carbazole ligands and the mono-, di-, and polynuclear Pt(II) σ-acetylide complexes have been characterized spectroscopically, with a subset analyzed using single-crystal X-ray diffraction. The Pt(II) mono-, di-, and poly-ynes incorporating the carbazole spacers are soluble in common organic solvents, and solution absorption spectra show a consistent red-shift between the 2- and 2,7- as well as 3- and 3,6-carbazole complexes. Computational modeling is used to explain the observed spectral shifts, which are related to the enhanced electronic delocalization in the latter systems. These results also indicate that the inclusion of carbazole-2,7-diyl units into rigid-rod organometallic polymers should enhance electronic transport along the chains.

We report on the fabrication of nanomechanical devices for shuttling of electrons from one electrode to another. Each device consists of a 20 nm diameter gold nanoparticle embedded within the gap between two gold electrodes. In two different kinds of shuttle-junctions the nanoparticle is attached to the electrodes through either (i) a single layer of 1,8-octanedithiol or (ii) a multilayer of 1-octanethiol molecules. The thiol layers play the role of 'damped springs', such that when a sufficient voltage bias is applied to the junction, the nanoparticle is expected to start oscillating and thereby transferring electrons from one electrode to the other. For both kinds of shuttle-junctions we observed an abrupt increase in the transmitted current above a threshold voltage, which can be attributed to a transition from the stationary to the oscillating regime. The threshold voltage was found to be lower for single-layer shuttle-junctions.