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Molecular Wires (molecular + wire)

Distribution by Scientific Domains

Chemistry	60%
Polymers and Materials Science	30%

Selected Abstracts

Reversible, Fine Performance Tuning of an Organometallic Molecular Wire by Addition, Ligand Replacement and Removal of Dicobalt Fragments

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2010
Yuya Tanaka
Abstract Communication between the two iron centres in (dithienylethyne)diyl complex 1 can be finely tuned by reversible addition to, ligand replacement at and removal from the C,C moiety in 1 of dicobalt fragments Co2(CO)n(PR3)6,n. Performance analysis reveals that disparate mechanisms are in operation for the two systems. In the case of the dicobalt adducts, indirect communication via the dicobalt steppingstone can be finely tuned by controlling the electronic structure of the dicobalt unit. [source]

Synthesis and Optoelectronic Properties of Nonpolar Polyrotaxane Insulated Molecular Wires with High Solubility in Organic Solvents,

ADVANCED FUNCTIONAL MATERIALS, Issue 21 2008
Michael J. Frampton
Abstract Hydrophilic polyanionic conjugated polyrotaxanes are readily synthesized in water by Suzuki coupling, but their high polarity and ionic nature limit the potential applications of these materials. Here, we demonstrate three methods for transforming these polar polyelectrolytes into nonpolar lipophilic insulated molecular wires. A water-soluble polyfluorene- alt -biphenylene ,-cyclodextrin (CD) polyrotaxane was converted into nonpolar derivatives by methylation of the carboxylic acid groups with diazomethane and conversion of the hydroxyl groups of the CDs to benzyl ethers, trihexylsilyl ethers, benzoyl esters, and butanoate esters to yield polyrotaxanes that are soluble in organic solvents such as chloroform and cyclohexane. Elemental analysis, NMR spectroscopy, and gel permeation chromatography (GPC) data support the proposed structures of the organic-soluble polyrotaxanes. The extents of reaction of the polyrotaxane CD hydroxyl groups were 55% for trihexylsilyl chloride/imidazole; 81% for benzyl chloride/sodium hydride; 72% for benzoyl chloride/pyridine/4-dimethylaminopyridine; and 98% butanoic anhydride/pyridine/4-dimethylaminopyridine. Alkylation, silylation, and esterification increase the bulk of the encapsulating sheath, preventing interstrand aggregation, increasing the photoluminescence efficiency in the solid state and simplifying the time-resolved fluorescence decay. The organic-soluble polyrotaxanes were processed into polymer light-emitting diodes (PLEDs) from solution in nonpolar organic solvents, thereby excluding ionic impurities from the active layer. [source]

Resonant Tunneling Processes along Conjugated Molecular Wires: A Quantum-Chemical Description

ADVANCED FUNCTIONAL MATERIALS, Issue 11-12 2002
Y. Karzazi
Abstract Molecular electronics research is a very active area in the field of nanotechnology. It is now well established that individual or self-assembled molecules can behave as nanoscopic switches in transistor and diode configurations. Molecular wires inserted into nanopores and contacted by two metallic electrodes can also be used as active elements for the fabrication of resonant tunneling diodes (RTDs). The RTD current/voltage (I/V) characteristics can display a negative differential resistance (NDR) behavior (i.e., a negative slope in the I/V curve) for reasons that are not yet fully understood. Here we describe a possible mechanism at the quantum-chemical level that is based on conformational effects and accounts for the experimental observation of strong NDR signatures in substituted phenylene ethynylene oligomers. The occurrence of a peak current in the I/V curves is rationalized by analyzing the evolution of the one-electron structure of the molecular wires upon application of a static electric field aligned along the molecular axis (the field simulates the driving voltage applied between the two electrodes in the RTD devices). The results of our calculations provide a general basis to develop strategies for the design of molecular wires displaying an NDR behavior. [source]

In Situ Stepwise Synthesis of Functional Multijunction Molecular Wires on Gold Electrodes and Gold Nanoparticles,

ANGEWANDTE CHEMIE, Issue 20 2010
Geoffrey
Höchst wirksam: Das Aufreihen von elektronenschiebenden und -ziehenden Komponenten, die durch eine ,-Elektronenbrücke getrennt sind, hat zum höchsten bisher mit einer molekularen Diode erreichten Gleichrichterverhältnis geführt. [source]

Helicate Extension as a Route to Molecular Wires

CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2008
David Schultz
Abstract We describe the preparation of a helicate containing four closely spaced, linearly arrayed copper(I) ions. This product may be prepared either directly by mixing copper(I) with a set of precursor amine and aldehyde subcomponents, or indirectly through the dimerization of a dicopper(I) helicate upon addition of 1,2-phenylenediamine. A notable feature of this helicate is that its length is not limited by the lengths of its precursor subcomponents: each of the two ligands wrapped around the four copper(I) centers contains one diamine, two dialdehyde, and two monoamine residues. This work thus paves the way for the preparation of longer oligo- and polymeric structures. DFT calculations and electrochemical measurements indicate a high degree of electronic delocalization among the metal ions forming the cores of the structures described herein, which may therefore be described as "molecular wires". [source]

Synthesis and fluorescence properties of a porphyrin,fullerene molecular wire,

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2004
Sean A. Vail
Abstract The synthesis and photophysical studies of a butadiyne-linked porphyrin,C60 dyad (ZnP,C60) 6 are described. This is the first porphyrin,[60]fullerene dyad in which the two chromophores are conjugatively linked through a ,molecular wire'. The UV,visible absorption spectrum for dyad 6 is slightly red shifted relative to the porphyrin precursor 5 whose fluorescence is all but quenched by the attached C60. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Synthesis and properties of carbazole-layered polymers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2009
Yasuhiro Morisaki
Abstract New aromatic ring-layered polymers consisting of carbazole as a layered aromatic group and xanthene as a scaffold were designed and synthesized via the Sonogashira,Hagihara coupling reaction. Their optical and electrochemical behaviors were investigated in detail; the results showed that these polymers could be used as hole-transporting materials. Polymers with nitrobenzene moieties at the polymer chain ends quenched the emission from the layered carbazoles to the nitrobenzene termini; thus, the polymers acted as the molecular wire that transferred photoexcited energy and/or electrons to the polymer termini. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4279,4288, 2009 [source]

High-Electron-Density C6H6 Units: Stable Ten-,-Electron Benzene Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2005
Martin Diefenbach Dr.
Abstract The first stable benzene molecule with ten , electrons is predicted. Stability is achieved through barium atoms acting as an electron-donating "matrix" to C6H6 in the inverted sandwich complex [Ba2(C6H6)]. The bis(barium)benzene complex has been computed at the density functional level of theory by using the hybrid functional mPW1PW91. Ab initio calculations were performed by using the coupled-cluster expansion, CCSD(T). Nucleus independent chemical shift (NICS) indices imply distinct aromatic character in the benzene ring of bis(barium)benzene. The D6h -symmetric structure with a 1A1g electronic ground state represents a thermochemically stable, aromatic benzene molecule with four excess , electrons, stabilised by two barium ions. A possible molecular wire, built up from Ba end-capped thorium,benzene "sandwiches", is discussed. [source]

Electron Tunneling through Molecular Media: A Density Functional Study of Au/Dithiol/Au Systems

CHEMPHYSCHEM, Issue 9 2005
Qiang Sun Dr.
Abstract We report a density functional theory study of the electronic properties of n -alkanedithiols (CnS2, with n=4, 8 and 12) sandwiched between two Au(111) infinite slab electrodes. We investigate the influence of the distance between the two electrodes and of the molecular chain length, tilt angle, and coverage on the local density of states (LDOS) at the Fermi energy (Ef). We find that the (small) value of the LDOS at Efnear the center of the molecular wires,a quantity that is related to the tunneling current,is mainly determined by the length n of the alkane chains: it originates from the tails of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) which are broadened by the interaction with the electrodes, and decays exponentially with the length of the molecular wire. This opens a nonresonance tunneling channel for charge transport at small bias voltages. While the length of the hydrocarbon chain appears to be the determining factor, the tilt angle of the molecular wires with respect to the electrode surfaces, and therefore the distance between these, has a small influence on the LDOS at the center of the molecule, while the effect of coverage can be ignored. The picture which emerges from these calculations is totally consistent with a through-bond tunneling mechanism. [source]

Synthesis and fluorescence properties of a porphyrin,fullerene molecular wire,

Carbon-Nanotube Based Electrochemical Biosensors: A Review

ELECTROANALYSIS, Issue 1 2005
Joseph Wang
Abstract This review addresses recent advances in carbon-nanotubes (CNT) based electrochemical biosensors. The unique chemical and physical properties of CNT have paved the way to new and improved sensing devices, in general, and electrochemical biosensors, in particular. CNT-based electrochemical transducers offer substantial improvements in the performance of amperometric enzyme electrodes, immunosensors and nucleic-acid sensing devices. The greatly enhanced electrochemical reactivity of hydrogen peroxide and NADH at CNT-modified electrodes makes these nanomaterials extremely attractive for numerous oxidase- and dehydrogenase-based amperometric biosensors. Aligned CNT "forests" can act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centers of enzymes. Bioaffinity devices utilizing enzyme tags can greatly benefit from the enhanced response of the biocatalytic-reaction product at the CNT transducer and from CNT amplification platforms carrying multiple tags. Common designs of CNT-based biosensors are discussed, along with practical examples of such devices. The successful realization of CNT-based biosensors requires proper control of their chemical and physical properties, as well as their functionalization and surface immobilization. [source]

Synthesis and Optoelectronic Properties of Nonpolar Polyrotaxane Insulated Molecular Wires with High Solubility in Organic Solvents,

From Molecular Machines to Microscale Motility of Objects: Application as "Smart Materials", Sensors, and Nanodevices

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2007
I. Willner
Abstract Machinelike operations are common functions in biological systems, and substantial recent research efforts are directed to mimic such processes at the molecular or nanoscale dimensions. The present Feature Article presents three complementary approaches to design machinelike operations: by the signal-triggered mechanical shuttling of molecular components; by the signal-triggering of chemical processes on surfaces, resulting in mechanical motion of micro/nanoscale objects; and by the fuel-triggered motility of biomolecule,metal nanowire hybrid systems. The shuttling of molecular components on molecular wires assembled on surfaces in semirotaxane configurations using electrical or optical triggering signals is described. The control of the hydrophilic/hydrophobic surface properties through molecular shuttling or by molecular bending/stretching processes is presented. Stress generated on microelements, such as cantilevers, results in the mechanical deflection of the cantilever. The deposition of a redox-active polyaniline film on a cantilever allows the reversible electrochemically induced deflection and retraction of the cantilever by the electrochemical oxidation or reduction of the polymer film, respectively. A micro-robot consisting of the polypyrrole (PPy) polymer deposited on a multi-addressable configuration of electrodes is described. Au magnetic core/shell nanoparticles are incorporated into a polyaniline film, and the conductivity of the composite polymer is controlled by an external magnet. Finally, the synthesis of a hybrid nanostructure consisting of two actin filaments tethered to the two ends of a Au nanowire is described. The adenosine triphosphate (ATP)-fueled motility of the hybrid nanostructure on a myosin monolayer associated with a solid support is demonstrated. [source]

Length-dependence of electron transfer coupling matrix in polyene wires: Ab initio molecular orbital theory study,

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2009
Govind Mallick
Abstract The electron transfer (ET) properties of ,-electron conjugated quasi-one-dimensional molecular wires, consisting of polyene, [>CC<]n (n = 1,11), including ,-carotene, is investigated using ab initio molecular orbital theory within Koopmans theorem (KT) approach. The ET coupling matrix element, VDA, for 1,3- trans -butadiene molecule calculated with the KT approach shows excellent agreement with the corresponding results obtained with two-state model. The calculated values of VDA for the polyene oligomers exhibit exponential decrease in magnitude with increasing length of the wire. However, the decay curve exhibits three different regimes. The magnitude of the decay constant, ,, decreases with the increase in length of the wire. A highly delocalized ,-electron cloud in the polyene chain appears to facilitate retention of the electronic coupling at large separations between the donor and acceptor centers. Published 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

Correlated, ab initio electron propagators in the study of molecular wires: Application to a single molecular bridge placed between two model leads

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007
Mark R. Sterling
Abstract A correlated, ab initio electron propagator approach is tested for a model system containing 1,4-benzene-dithiolate attached to two gold or two aluminum atoms. Qualitative agreement with available experiment is achieved for the gold dithiolate system. Similar current and conductance curves obtain for both metal leads when the Fermi energy is set to ,1.0 eV. A molecular orbital analysis is given for the gold dithiolate system. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Resonant laser excitation of molecular wires

ISRAEL JOURNAL OF CHEMISTRY, Issue 2-3 2002
Sigmund Kohler
We investigate the influence of external laser excitations on the average current through bridged molecules. For the computation of the current, we use a numerically very efficient formalism that is based on the Floquet solutions of the time-dependent molecule Hamiltonian. It is found that the current as a function of the laser frequency exhibits characteristic peaks originating from resonant excitations of electrons to bridge levels that are unoccupied in the absence of radiation. The electric current through the molecule can exhibit a drastic enhancement by several orders of magnitude. [source]

Supramolecular control of spin-crossover phenomena in lipophilic Fe(II)-1,2,4-triazole complexes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006
Keita Kuroiwa
Abstract The spin-crossover properties of lipophilic, supramolecular Fe(II) complexes bridged by 4-(3-dodecyloxy)propyl-1,2,4-triazole [Fe(II)(1)3Cl2] were investigated in chloroform and cast films. A purple low-spin (LS) complex in a powdery form was transformed into pale yellow high-spin (HS) polymers by dissolution in chloroform. The formation of lipophilic molecular wires in chloroform was observed with transmission electron microscopy. The casting of chloroform solutions onto solid supports produced purple, transparent films (LS state). The cast films exhibited sluggish spin-crossover (LS , HS) behavior without thermal hysteresis. On the other hand, the cocasting of equimolar dodecanol or tetradecanol with Fe(II)(1)3Cl2 produced composite films in which alcohol molecules were bound to the complex by ionic hydrogen bonding (ROH···Cl,) and van der Waals interactions. At room temperature, the cast films exhibited regular lamellar structures before and after alcohol doping; this was confirmed by wide-angle X-ray diffraction measurements. Interestingly, the Fe(II)(1)3Cl2/CnOH (n = 12 or 14) ternary films showed a reversible abrupt spin crossover accompanied by thermal hysteresis. The observed bistability was related to dynamic structural transformations between lamellar and hexagonal structures. This study provides a novel supramolecular approach to designing spin-crossover polymer films with controlled thermal bistability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5192,5202, 2006 [source]

Electropolymerizable Terthiophene S,S -Dioxide-Fullerene Diels-Alder Adduct for Donor/Acceptor Double-Cable Polymers

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2007
Yolanda Vida
Abstract The preparation of a novel fullerene-thiophene derivative by Diels-Alder addition of terthiophene S,S -dioxide was demonstrated. Extrusion of SO2 from the adduct is an effective process that yields a stable cyclohexadiene-1,4-bisthiophene,C60 adduct in good isolable yield. The product has been accurately characterized and opens the way to synthesize new C60 derivatives "via" Diels-Alder methodology without the possibility of cycloreversion. Electrochemical and spectroscopic properties of this macromolecule were studied and supported by theoretical calculations to interpret its electronic structure. The first approach to the electropolymerization of this macromonomer produces donor-acceptor molecular wires providing a new and versatile way to fullerene-based double cable polymers. [source]

Atomic study of molecular wires composed of thiophene oligomers

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007
P. Bai
Abstract In this paper, we study the electron conductance of thiophene oligomers based molecular wires through atomic structures using the first principles method based on density functional theory and nonequilibrium Green's function. The molecular wires are built by sandwiching various thiophene oligomers between two metal electrodes via terminal groups at atomic levels. The effects of alkyl substituents on the thiophene oligomers are modelled by varying inter-ring angles of the oligomers. Thiophene dimers, tetramers and hexamers are used to studied thiophene size effects. The projected orbitals, energy gaps, transmission functions and current,voltage characteristics of the molecular wires are calculated and analyzed. Results show that the molecular wires with the planar structures of thiophene oligomers have larger electron transmission functions, hence better electronic conductance than those with twist structures. The conductance of molecular wires decreases when the chain length of the thiophene oligomer increases. The results can provide guidance for design of thiophene molecular electronic wires and other devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Electronic and Magnetic Properties of Bimetallic Ytterbocene Complexes: The Impact of Bridging Ligand Geometry

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2008
Christin
Abstract Bimetallic ytterbocene complexes with bridging N-heterocylic ligands have been studied extensively in recent years due to their potential applications ranging from molecular wires to single-molecule magnets. Herein, we review our recent results for a series of ytterbocene polypyridyl bimetallic complexes to highlight the versatility and tunability of these systems based on simple changes in bridging ligand geometry. Our work has involved structural, electrochemical, optical, and magnetic measurements with the goal of better understanding the electronic and magnetic communication between the two ytterbium metal centers in this new class of bimetallics. [source]

Electron Tunneling through Molecular Media: A Density Functional Study of Au/Dithiol/Au Systems

Wiring Enzymes in Nanostructures Built with Electrostatically Self-Assembled Thin Films

CHEMPHYSCHEM, Issue 1 2005
Ernesto J. Calvo Prof.
Abstract The construction of electrostatically self-assembled intelligent nanostructures on electrodes with redox enzyme layers and redox polymer molecular wires defined in space allowed the analysis of redox charge transport from the redox enzyme to the electrode along nanometric distances. Recent results on the electrical connection of enzymes to electrodes and perspectives of generating electrical signals from molecular recognition in integrated enzyme electrodes are discussed. [source]