Synthesis of nitrile-terminated potential molecular electronic devices

Several potential molecular devices have been synthesized consisting of oligo(phenylene ethynylene) (OPE) backbones containing a terminal nitrile group alligator clip as a means of attachment to a metal surface. The synthesis of four new nitrile-containing OPEs is discussed, including an improved synthesis of an intermediate used in our prior production of OPEs containing acetate-protected thiol alligator clips.     

Synthesis and testing of new end-functionalized oligomers for molecular electronics

Several new classes of oligomers have been synthesized with functionalities designed to aid in the understanding of molecular device behavior, specifically when molecules are interfaced between proximal electronic probes. The compounds synthesized are series of azobenzenes, bipyridines and oligo(phenylene vinylene)s that bear acetyl-protected thiols for ultimate attachment to metallic surfaces. Some initial electrochemical and solid-state test results are also reported.     

Biphenyl- and fluorenyl-based potential molecular electronic devices

New potential molecular electronics devices have been synthesized based on our knowledge of systems that we previously studied. Research has shown that simple molecular systems demonstrate negative differential resistance (NDR) and memory characteristics. The new molecules rely primarily on the redox properties of the compounds to improve upon the solid-state characteristics already observed. Electrochemical tests have been performed in order to evaluate the redox properties with the hope that the electrochemical results can be used as a predictive tool to evaluate the usefulness of those compounds in device configurations.     

Progresses in organic field-effect transistors and molecular electronics

In the past years, organic semiconductors have been extensively investigated as electronic materials for organic field-effect transistors (OFETs). In this review, we briefly summarize the current status of organic field-effect transistors including materials design, device physics, molecular electronics and the applications of carbon nanotubes in molecular electronics. Future prospects and investigations required to improve the OFET performance are also involved. __________ Translated from Huaxue Tongbao (Chemistry), 2006, 69(6) (in Chinese)     

Biomolecular electronics in the twenty-first century

A relentless decrease in the size of silicon-based microelectronics devices is posing problems. The most important among these are limitations imposed by quantum-size effects and instabilities introduced by the effects of thermal fluctuations. These inherent envisaged problems of present-day systems have prompted scientists to look for alternative options. Advancement in the understanding of natural systems such as photosynthetic apparatuses and genetic engineering has enabled attention to be focused on the use of biomolecules. Biomolecules have the advantages of functionality and specificity. The invention of scanning tunneling microscopy and atomic force microscopy has opened up the possibility of addressing and manipulating individual atoms and molecules. Realization of the power of self-assembly principles has opened a novel approach for designing and assembling molecular structures with desired intricate architecture. The utility of molecules such as DNA as a three-dimensional, high-density memory element and its capability for molecular computing have been fully recognized but not yet realized. More time and effort are necessary before devices that can transcend existing ones will become easily available. An overview of the current trends that are envisaged to give rich dividends in the next millen-nium are discussed.     

Biomaterials for molecular electronics development of optical biosensor for retinol

Molecular electronics involves expertise from several branches of science. Various biomaterials and electronics are involved in the fabrication of such devices. While passive biomaterials are involved in anchoring the active biomolecules, the latter are involved in switching and/or signal transduction. In the present investigation we have used a glass-capillary-based approach to design a biosensor for retinol. The sensing element is retinol-binding protein (RBP). The affinity of retinoic-acid-horseradish peroxidase (conjugate) to RBP is tested using a surface plasmon resonance technique. A simple photomultiplier-tube-based system is exploited to monitor the chemiluminescent signal generated upon reaction of hydrogen peroxide and luminol with the conjugate bound to RBP. The photomultiplier tube is directly coupled to a computer for data logging.     

Novel electron-deficient oligo(phenyleneethynylene) derivatives for molecular electronics

This work reports synthesis and characterizations of two new electron-poor “oligo(phenyleneethynylene) (OPE) type” molecular wires for fundamental studies of electron transport in molecular junctions. These OPE derivatives display three aromatic rings functionalized (i) with NO₂ (OPN) or fluorine (OPF) groups on the central aryl core and (ii) with the requisite protected thiolate anchoring groups on the lateral rings at both ends. We show that the moderately effective Sonogashira couplings can give access to such rare electrodeficient molecules but are unfortunately associated with significant side reactions. We detail the choice of adequate reaction conditions to allow the recovery of suitable amounts of compounds bearing several strongly electron-withdrawing substituents on their central ring for further study of the physical properties.     

Molecular and nanoscale materials and devices in electronics

Over the past several years, there have been many significant advances toward the realization of electronic computers integrated on the molecular scale and a much greater understanding of the types of materials that will be useful in molecular devices and their properties. It was demonstrated that individual molecules could serve as incomprehensibly tiny switch and wire one million times smaller than those on conventional silicon microchip. This has resulted very recently in the assembly and demonstration of tiny computer logic circuits built from such molecular scale devices. The purpose of this review is to provide a general introduction to molecular and nanoscale materials and devices in electronics.     

氢键对分子器件电学特性的影响

利用密度泛函理论和弹性散射格林函数方法,研究了被不同官能团取代后的联苯分子的电输运特性.计算结果表明,由于氢键的影响,使得分子的电子结构发生了变化,特别是对电子在分子结内的跃迁几率影响较大,从而直接影响了分子器件的伏安特性.     

Effects of substituents on molecular devices

The current–voltage characteristics of small aliphatic chains of alkanes, alkenes, alkynes, and oligophenylene‐ethylenes, with and without substituents and terminated in sulfur attached nanosized gold electrodes are determined using ab initio procedures for discrete and extended systems in a density functional theory‐Green function's approach where most of the chemistry is considered. It is found that the current–voltage characteristics of small molecules can be tailored by the addition of substituents. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Environmentally benign syntheses of flavanones

Mild and environmentally benign methods for the syntheses of flavanones are described. The reaction of o-hydroxyacetophenones (1) and benzaldehydes (2) in water in the presence of DABCO at room temperature gave 3-hydroxy-1-(2-hydroxylphenyl)-3-arylpropan-1-ones (3a-i) as intermediates. Followed by an intramolecular dehydration of the 3a-i with the modified Mitsunobu’s reaction, the target flavanones (4a-i) were obtained. Moreover, the reaction of 1 and 2 at the same conditions but at reflux gave flavanones in one pot with good yields.     

Synthetic protocols and building blocks for molecular electronics

Simple and readily accessible aryl bromides are useful building blocks for thiol end-capped molecular wires. Thus, 4-bromophenyl tert-butyl sulfide and 1-bromo-4-(methoxymethyl)benzene serve as precursors for a variety of oligo(phenylenevinylene) and oligo(phenyleneethynylene) wires via efficient synthetic transformations as presented in this paper.     

Single-chain and monolayered conjugated polymers for molecular electronics

Exploring the charge transport properties and electronic functions of molecules is of primary interest in the area of molecular electronics. Conjugated polymers (CPs) represent an attractive class of molecular candidates, benefiting from their outstanding optoelectronic properties. However, they have been less studied compared with the small-molecule family, mainly due to the difficulties in incorporating CPs into molecular junctions. In this review, we present a summary on how to fabricate CP-based singlechain and monolayered junctions, then discuss the transport behaviors of CPs in different junction architectures and finally introduce the potential applications of CPs in molecular-scale electronic devices. Although the research on CP-based molecular electronics is still at the initial stage, it is widely accepted that (1) CP chains are able to mediate long-range charge transport if their molecular electronic structures are properly designed, which makes them potential molecular wires, and (2) the intrinsic optoelectronic properties of CPs and the possibility of incorporating desirable functionalities by synthetic strategies imply the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.     

Syntheses of new functionalized azobenzenes for potential molecular electronic devices

New non-symmetrical azobenzene derivatives have been synthesized as potential molecular electronic switching device candidates. The Oxone^® mediated oxidation of anilines provided nitroso-functionalized arenes, which were then condensed with substituted anilines to provide a series of azobenzene derivatives that could be further converted into oligo(phenylene ethynylene)s or diazonium salts. The resulting thiolacetates, thiols, or diazonium salts are capable of forming molecular layers on the surface of gold or silicon, thereby paving the way for molecular electronics testing.     

Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices

The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques.     

In situ measurements of oligoaniline conductance: Linking electrochemistry and molecular electronics

The single-molecule conductance of a dithiolated aniline trimer has been measured under potential control and also under an inert solvent. In each experiment, two sets of currents are found, differing by a factor 4, and these are tentatively assigned to differing connections to the electrodes (e.g., on-top vs. hollow sites). The conductances peak (to 17 ± 1.6 and 5.8 ± 0.85 nS) between the first and second oxidations of the molecule and change smoothly with surface potential. There is no evidence for a coexistence of oxidized and reduced molecules. Measurements made at a fixed surface potential as a function of tip to substrate bias show a peak current at 0.1 V followed by a region of negative differential resistance. This is accounted for semi-quantitatively by modification of the local potential by the applied bias altering the oxidation state of the molecule under the probe. Measurements made in toluene are Ohmic, indicating that the tip does not alter the oxidation state of the molecule in the absence of screening ions. We discuss the role of gap geometry and bonding in these processes.     

Synthesis of biomimetic light-driven molecular switches via a cyclopropyl ring-opening/nitrilium ion ring-closing tandem reaction

A cyclopropyl ring-opening/nitrilium ion ring-closing tandem reaction has been conveniently used in an expeditious synthetic approach to light-driven Z/E molecular switches featuring an imine function conjugated to olefin groups that mimics natural protonated Schiff bases.     

A new strategy for the stereospecific syntheses of C-furanosides

This reaction provided an efficient method to synthesize C-furanoside derivatives in high yields and stereospecificity under mild conditions.The cyclization mechanism regarding benzyl group as a leaving group was discussed and their stereochemistry was deduced by 1H-1H NOESY data.