Tuning the electrical conductance of metalloporphyrin supramolecular wires

In contrast with conventional single-molecule junctions, in which the current flows parallel to the long axis or plane of a molecule, we investigate the transport properties of M(II)-5,15-diphenylporphyrin (M-DPP) single-molecule junctions (M=Co, Ni, Cu, or Zn divalent metal ions), in which the current flows perpendicular to the plane of the porphyrin. Novel STM-based conductance measurements combined with quantum transport calculations demonstrate that current-perpendicular-to-the-plane (CPP) junctions have three-orders-of-magnitude higher electrical conductanc than their current in-plane (CIP) counterparts, ranging from 2.10−2 G0 for Ni-DPP up to 8.10−2 G0 for Zn-DPP. The metal ion in the center of the DPP skeletons is strongly coordinated with the nitrogens of the pyridyl coated electrodes, with a binding energy that is sensitive to the choice of metal ion. We find that the binding energies of Zn-DPP and Co-DPP are significantly higher than those of Ni-DPP and Cu-DPP. Therefore when combined with its higher conductance, we identify Zn-DPP as the favoured candidate for high conductance CPP single-molecule devices

Theory of one-dimension rotational isomerization: A study of the cis-trans isomerization of HS-NS compared to that of HO-NO

A theoretical approach, in which the potential functions representing rotational isomerization processes are expressed in terms of linear combinations of local potentials, is presented. Partitioning the torsional potential allows identification of specific contributions that are at the origin of the shape of potential curves at different regions along the torsional variable. Key properties, such as barrier heights, may then be expressed parametrically in terms of properties associated to the stable conformations. Simple analytical expressions intended to explore, quantitatively and qualitatively, the main characteristics of the transition states connecting stable isomers are formulated. As a first step towards the study of complex systems, we use this procedure to analyse ab initio results concerning the cis-trans isomerization reaction of two simple prototype molecules: HSNS and HONO. We determine the relative stabilities of the different isomers and molecular structures and evaluat

Experimental and theoretical characterization of Ru(II) complexes with polypyridine and phosphine ligands

The synthesis and the experimental and theoretical characterization of ruthenium hydride complexes containing phosphorus and polypyridine ligands [RuH(CO)(N-N)(PPh3)2]+ with N-N = dppz 1, dppz-CH3 2 (2.1 isomer), dppz-Cl 3 (3.1 isomer), ppl 4, and 2,2′-biquinoline 5, (where dppz = dipyrido[3,2-a:2′,3′-c]phenazine), are presented. 1H NMR, 31P NMR, 13C NMR, IR-FT, UV-Vis and elemental analysis are used to characterize the complexes. Optimized molecular geometries in the gas phase at the B3LYP/LACVP(d,p) level showed a distorted octahedral structure for ruthenium, the phosphine ligands are localized in a trans position, while the polypyridine ligand, which in all the cases is planar except in 5, adopt a trans position relative to the carbon monoxide and hydride ligands. The theoretical absorption spectra (one hundred excited states) were calculated for the seven complexes by the time dependent density functional theory (TD-DFT) in the gas phase. They predicted very well the UV-Vis spectr