We report the electrical conductance at the single molecule level of the oligoyne molecular wires Py-(C[triple bond]C)(n)-Py (n = 1, 2 and 4; Py = 4-pyridyl) using STM-molecular break junction techniques in Au|molecule|Au configurations. The conductance histograms reveal multiple series of peaks attributed to differing contact geometries between the pyridyl head groups and the gold electrodes. Both experimental and theoretical evidence point to the higher conduction groups being related to adsorption of the pyridyl group at more highly coordinated sites such as step edges or alongside gold adatoms. All three conduction groups in the oligoyne series show a remarkably low beta value of (0.06 +/- 0.03) A(-1), that is, the conductance is almost independent of molecular length. 4,4'-Bipyridyl studied under the same conditions does not follow this exponential decay series. Theoretical calculations using a combination of density functional theory and nonequilibrium Green's function formalism support the experimental results. We conclude that oligoynes and polyynes are a very promising class of molecular wires for integration into electronic circuitry.

In this paper, we focus on the synthesis and structure of the new bis(1,3,4-oxadiazole) system 2,5-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]pyridine (PDPyDP). We have fabricated light-emitting diodes (LEDs) using poly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH-PPV) as the emissive material, with and without a thermally evaporated electron-injection/hole-blocking layer of either PDPyDP or its vinylene analogue (E)-1,2-bis-[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]ethene (PDVDP) or its phenylene analogue 1,4-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]benzene (PDPDP). PDPDP is the para isomer of OXD-7, which is a widely used molecular electron-transporting material. Electroluminescence spectra indicate that light is emitted only from the MEH-PPV layer. Using aluminum as the cathode, the bilayer LED with PDPyDP is considerably more efficient than the corresponding single-layer device or devices with PDVDP or PDPDP as the electroninjection layer.

Articles you may be interested inStudy on structures and properties of ammonia clusters ( NH 3 ) n ( n = 1 -5 ) and liquid ammonia in terms of ab initio method and atom-bond electronegativity equalization method ammonia-8 P fluctuating charge potential model Beyond electronegativity and local hardness: Higher-order equalization criteria for determination of a groundstate electron density A study of N -methylacetamide in water clusters: Based on atom-bond electronegativity equalization method fused into molecular mechanics J. Chem. Phys. 125, 064311 (2006); 10.1063/1.2210940 Molecular-dynamics simulations of alkaline-earth metal cations in water by atom-bond electronegativity equalization method fused into molecular mechanics

We describe the synthesis of 2,5-diaryl-1,3,4-oxadiazole-fluorene hybrid molecules, e.g. 2,7-bis[2-(4-tert-butylphenyl-1,3,4-oxadiazol-5-yl]-9,9-dihexylfluorene 6, 2,7-bis{4-[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]phenyl}-9,9-dihexylfluorene 10, 2,7-bis{4-[2-(4-dodecyloxyphenyl)-1,3,4-oxadiazol-5-yl]phenyl}-9,9-dihexylfluorene 11, 2,7-bis{4-[2-(4-dodecyloxyphenyl)-1,3,4-oxadiazol-5-yl]phenyl}-spirobifluorene 13 and analogue 16, comprising the 9,9-dihexylfluorene or spirobifluorene core units to which are attached aryl-or diaryl-oxadiazole units to provide linearly extended p-conjugated systems. The X-ray crystal structure is reported for compound 11. We have fabricated single-layer organic light-emitting diodes (OLEDs) using blends of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as the emissive material with the electron transport (ET) compounds 6, 10, 11, 13 and 16 added to enhance electron injection. For all the devices studied electroluminescence originates exclusively from the MEH-PPV material. The external quantum efficiencies of the devices increased with increasing concentration of the ET compound up to 95% by weight, and are greatly enhanced (.two orders of magnitude) compared to pure MEH-PPV reference devices. Further improvements have been achieved by adding a layer of PEDOT : PSS and efficiencies reach ca. 0.4% at 30 mA cm 22 for devices in the configuration ITO/PEDOT : PSS/MEH-PPV-13 (5 : 95% by weight)/Al.{ Electronic supplementary information (ESI) available: B3LYP/6-31G(d) optimised geometries (figures and tables of coordinates) and orbital energy levels diagrams for compounds 6a, 11a, 13a and 16a and OXD-7. See

An analytic potential energy function is proposed and applied to evaluate the amide-amide and amide-water hydrogen-bonding interaction energies in peptides. The parameters in the analytic function are derived from fitting to the potential energy curves of 10 hydrogen-bonded training dimers. The analytic potential energy function is then employed to calculate the N-H...O=C, C-H...O=C, N-H...OH2, and C=O...HOH hydrogen-bonding interaction energies in amide-amide and amide-water dimers containing N-methylacetamide, acetamide, glycine dipeptide, alanine dipeptide, N-methylformamide, N-methylpropanamide, N-ethylacetamide and/or water molecules. The potential energy curves of these systems are therefore obtained, including the equilibrium hydrogen bond distances R(O...H) and the hydrogen-bonding energies. The function is also applied to calculate the binding energies in models of beta-sheets. The calculation results show that the potential energy curves obtained from the analytic function are in good agreement with those obtained from MP2/6-31+G** calculations by including the BSSE correction, which demonstrate that the analytic function proposed in this work can be used to predict the hydrogen-bonding interaction energies in peptides quickly and accurately.