Yoav Eichen

DNA-templated assembly and electrode attachment of a conducting silver wire

Recent research in the field of nanometre-scale electronics has focused on two fundamental issues: the operating principles of small-scale devices, and schemes that lead to their realization and eventual integration into useful circuits. Experimental studies on molecular to submicrometre quantum dots and on the electrical transport in carbon nanotubes have confirmed theoretical predictions of an increasing role for charging effects as the device size diminishes. Nevertheless, the construction of nanometre-scale circuits from such devices remains problematic, largely owing to the difficulties of achieving inter-element wiring and electrical interfacing to macroscopic electrodes. The use of molecular recognition processes and the self-assembly of molecules into supramolecular structures, might help overcome these difficulties. In this context, DNA has the appropriate molecular-recognition and mechanical properties, but poor electrical characteristics prevent its direct use in electrical circuits. Here we describe a two-step procedure that may allow the application of DNA to the construction of functional circuits. In our scheme, hybridization of the DNA molecule with surface-bound oligonucleotides is first used to stretch it between two gold electrodes; the DNA molecule is then used as a template for the vectorial growth of a 12 µm long, 100 nm wide conductive silver wire. The experiment confirms that the recognition capabilities of DNA can be exploited for the targeted attachment of functional wires.

Extended Calixpyrroles: meso-Substituted Calix[6]pyrroles

A 1,3,5-alternate conformation of the pyrrole rings is adopted by the calix[6]pyrrole 1 in the crystal (see picture). Compound 1 was synthesized in a two-step process and although it crystallizes in the form of the adduct 1⋅3CH3 COCH3 ⋅H2 O⋅CHCl3 , there are no solvent molecules in the cavity (cross section ca. 60Å2 ) of this macrocycle which possesses alternating dimethyl and diphenyl substitutents at the meso positions.

Self-assembly of nanoelectronic components and circuits using biological templates

Solid State Institute, Technion –Israel Institute of Technology,Haifa 32000, IsraelA multistep self-assembly process is proposed for the preparation of nanometer-scaleelectronics. The process is based onthe assembly of a DNA network that serves, in turn, as a template for the subsequent assembly of functional elements usingdifferent levels of molecular recognition ability. Inter-element connectivity and connection to the “macr oscopic world” isachieved by instilling electrical functionality to the DNA network. The feasibility of this approach was demonstrated by theDNA-templatedself-assembly of a 12 lm long, ca. 1000 A˚wide, conductive silver wire connecting two macroscopic elec-trodes.

Detection and Identification of Alkylating Agents by Using a Bioinspired Chemical Nose

Alkylating agents are simple and reactive molecules that are commonly used in many and diverse fields such as organic synthesis, medicine, and agriculture. Some highly reactive alkylating species are also being used as blister chemical-warfare agents. The detection and identification of alkylating agents is not a trivial issue because of their high reactivity and simple structure. Herein, we report on a new multispot luminescence-based approach to the detection and identification of alkylating agents. In order to demonstrate the potential of the approach, seven pi-conjugated oligomers and polymers bearing nucleophilic pyridine groups, 1-7, were adsorbed onto a solid support and exposed to vapors of alkylators 8-15. The alkylation-induced color-shift patterns of the seven-spot array allow clear discrimination of the different alkylators. The spots are sensitive to minute concentrations of alkylators and, because the detection is based on the formation of new covalent bonds, these spots saturate at about 50 ppb.

Optoelectronic properties of polymer-nanocrystal composites active at near-infrared wavelengths

We report a systematic study of the optoelectronic processes occurring in composites made of near-infrared IR emitting nanocrystals and conjugated polymers. We focus on PbSe and InAs/ZnSe blended with polyphenylenevinylene-type polymers. We find that the process responsible for quenching the visible luminescence of the polymer by the nanocrystal varies depending on the nanocrystal composite. Moreover, the high 66% energy-transfer efficiency from the polymer to the PbSe nanocrystal does result in significant emission at the near IR. Our measurements suggest that the host may be doping the PbSe nanocrystal, thus making the nonradiative Auger process favorable. For InAs we find the energy levels well aligned inside the polymer band gap, making it an efficient charge trap which acts as a luminescence center. Through two-dimensional numerical modeling of the charge transport in such composite films we highlight the importance of morphology nanocrystal distribution control.

The role of template in the synthesis of meso-hexamethyl- meso-hexaphenyl-calix[6]pyrrole: trihalogenated compounds as templates for the assembly of a host with a trigonal cavityElectronic supplementary data (ESI) available: Figs. 1 and 2 showing atom numbering. See http://www.rsc.org/suppdata/cc/b1/b106162n/

Trihalogenated compounds act as effective and selective templates in the template-assisted synthesis of meso-hexaphenyl-calix[6]pyrrole.

p-type doping in organic light emitting diodes based on fluorinated C60

We report on hybrid organic light emitting diodes based on spin coated PVK (poly(vinylcarbazole))/poly-TPD (poly(triphenyldiamine)) formulation electron blocking and conjugated peptide emitter layers while the hole blocking, BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), layer is vacuum sublimed. The device structure is realized through the use of fluorinated C60 as a p-dopant in a cross-linked hole transporting formulation. The lowering of the turn-on voltage is demonstrated using a conjugated peptide as the emitter layer. We suggest that fluorinated C60s could play a major role as tunable dopants in organic electronics.

Site Selective Processes: A Combined Theoretical and Experimental Investigation of Thermally Activated Tautomerization Processes in 2(2,4-Dinitrobenzyl) Pyridine Derivatives

Abstract The thermally activated NH→CH tautomerization process in crystals of 2(2,4-dinitrobenzyl) pyridine derivatives was investigated. The results indicate the absence of any trivial molecular structure–reactivity correlation, in contrast to what is found for similar systems in solutions. The absence of molecular structure–reactivity correlation in the crystalline state is attributed to the participation of neighboring molecules in the proton transfer process. A combined experimental and theoretical approach is presented and applied to the study of the tautomerization reaction in crystalline environments.

Höhere Homologe der Calixpyrrole: meso-substituierte Calix[6]pyrrole

Eine 1,3,5-alternate-Konformation der Pyrrolringe weist das in einer Zweistufensynthese erstmals hergestellte Calix[6]pyrrol 1 im Kristall auf (siehe Bild). Obwohl es in Form des Adduktes 1⋅3 CH3COCH3⋅H2O⋅CHCl3 kristallisierte, befinden sich keine Solvensmolekule im Hohlraum (Querschnittflache ca. 60 A2) dieses an den meso-Positionen abwechselnd dimethyl- und diphenylsubstituierten Makrocyclus.

Illumination-induced metastable polaron-supporting state in poly( p -phenylene vinylene) films

We discovered a new metastable polaron-supporting phase in pristine films of a soluble derivative of poly-p-phenylene vinylene (MEH-PPV) that is induced by UV illumination. In the initial un-illuminated phase A, the films do not show long-lived photogenerated polarons. However, prolonged UV illumination for several hours induces a reversible, me-tastable phase B that shows abundant long-lived photogenerated polarons. Phase B films transform back to the original phase A within 1/2 hour in the dark at room temperature. We propose a reversible mechanism in which UV illumination creates metastable deep defects that substantially increase the photogenerated polaron lifetime.