Home  About us  Contact
 

Switching Devices (switching + device)

Distribution by Scientific Domains
Chemistry66%

Selected Abstracts

Titelbild: The Ouroborand: A Cavitand with a Coordination-Driven Switching Device (Angew. Chem.

ANGEWANDTE CHEMIE, Issue 18 2010
18/2010)
Der Panzergürtelschweif ist ein südafrikanisches Reptil, das als Defensivtaktik seinen Schwanz ins Maul nimmt. Dies erinnert an das antike griechische Symbol des Ouroboros, das eine Schlange zeigt, die ihren eigenen Schwanz verschluckt, und eine berühmte Inspirationsquelle für Kekulés Formulierung der Benzolstruktur vor 150 Jahren war. In ihrer Zuschrift auf S.,3257,ff. berichten F. Durola und J. Rebek, Jr., wie ein Cavitand, der in seinem Hohlraum eine Seitenkette koordiniert und daher "Ouroborand" genannt wird, je nach Zugabe von Zinkionen zwischen dem geschlossenen und dem offenen Zustand schalten kann. (Bild: P.,le F.,N. Mouton) [source]

The Ouroborand: A Cavitand with a Coordination-Driven Switching Device,

ANGEWANDTE CHEMIE, Issue 18 2010
Fabien Durola Dr.
Molekularer Schalter: Ein Ouroborand koordiniert in seiner Kavität eine interne Seitenkette und beißt sich sozusagen selbst in den Schwanz. Die An- oder Abwesenheit von ZnII schaltet den Hohlraum zwischen einem geschlossenen und einem offenen Zustand, in dem externe Gäste aufgenommen werden können (siehe Bild; dunkelblaue Kugel: Zn). [source]

Ion-Triggered Multistate Molecular Switching Device Based on Regioselective Coordination-Controlled Ion Binding

CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2005
Anne Petitjean Dr.
Abstract Molecular devices capable of accessing different controlled conformational states, while optically signaling the occupied state, are attractive tools for nanotechnology since they relate to both areas of molecular mechanical devices and logic gates. We report here a simple molecular system that allows access to four distinct conformational and optical states. It is based on the regioselective complexation of metal ions to a heterocyclic ligand triad, which is dictated by the accessible coordination geometry and electrostatic properties of two distinct binding subunits. Thus, local conformational switching is brought about by tetrahedral coordination (of CuI) or octahedral coordination (of M2+ ions) to bidentate and tridentate binding subunits, respectively. The shape modifications undergone represent an ion-controlled nanomechanical device. They give controlled access to four different states that display different physico-chemical (e.g. optical) properties and provide a basis for logic gate operations. [source]

Dynamic Chemical Devices: Photoinduced Electron Transfer and Its Ion-Triggered Switching in Nanomechanical Butterfly-Type Bis(porphyrin)terpyridines,

CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2006
Myriam Linke-Schaetzel Dr.
Abstract A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (,,,)-diamine substrates to the ZnII,porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the ,3 -terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs. Une série d'architectures moléculaires, présentant une forme de papillon, a été préparée avec de bons rendements en utilisant une méthodologie synthétique comprenant comme étape clé un double couplage de Stille. Ces architectures sont composées d'un squelette terpyridine (terpy), qui compose le torse du papillon, sur lequel deux ailes porphyriniques ont été greffées; la géométrie peut varier entre une conformation étendue en forme de W, et une conformation compacte en forme de U, dû à la complexation du torse terpy par un cation de taille et coordination adéquate. Les ailes porphyriniques se présentent soit comme bases libres ou, peuvent être métallées successivement avec différentes métaux, pouvant ainsi avoir différentes "couleurs". Des études de fluorescence non seulement stationnaire mais aussi résolues dans le temps sur les architectures HZn, ZnAu et Zn2Au, montrent que les propriétés électroniques sont très dépendantes de la géométrie adoptée. Dans la conformation W étendue, nous avons mis en évidence un processus de transfert d'énergie de la porphyrine base libre vers la porphyrine metalée avec du Zn. Dans la conformation U de Zn2Au la luminescence de l'aile donneuse, à cause de l'état excité singulet, est fortement éteinte, non seulement à cause de l'effet d'atome lourd, mais aussi à cause d'un processus de transfert d'électron vers l'état fondamental de l'aile metalée avec de l'or. De plus, par compléxation avec des (,,,)-diamines des atomes de ZnIIdans les tetrapyrroles porphyrinques, la conformation induite du système peut être profondément influencée. Pour le composé Zn2Zn, que nous avons pu obtenir en monocristaux, des expériences de diffraction en utilisant comme source lumineuse un synchrotron, ont fourni des données qui ont permis de résoudre la structure par des méthodes directes et de la raffiner pour montrer la conformation en U attendue. L'atome central de Zn a une coordination de six dont trois provenant du ligand ,3 -terpy, et les autres de deux anions acetates, un monodenté et l'autre semi-chelatizé. La structure est ligotée par des multiples liaisons hydrogène entre des ligands aqueux sur les atomes de Zn externes et les atomes d'oxygène des anions acetates. Le système présenté est un double effecteur qui montre une commutation opto-mechanique dirigée soit par des ions métalliques, soit par d'autres ligands de taille adaptée. En même temps, les processus de transfert d'énergie et d'électrons peuvent être commuté en laissant de la place pour améliorer le rapport "on/off" dans de futures architectures. Abstract in Romanian:O serie de arhitecturi moleculare având o form, de fluture au fost preparate cu randamente bune utilizând o metodologie sintetic, cuprinzând ca etap, cheie un dublu cuplaj Stille. Aceste architecturi sunt compuse dintr-un schelet terpiridinic (terpy) alc,tuind trupul fluturelui, la care au fost implementate dou, aripi porfirinice care sunt capabile sa varieze între o conforma,ie extins, în forma de liter, W ,i o conformai,ie compact, în form, de litera U, datorit, complexarii trupului terpy printr-un cation de talie ,i coordina,ie adecvat,. Aripile porfirinice se prezintã fie ca base libere sau, datorita unei metalari succesive cu diferite metale, pot avea diferite "culori". Studii de fluorescen,a atât sta,ionar, cât ,i rezolvat, în timp, asupra arhitecturilor HZn, ZnAu ,i Zn2Au, arat, c, proprit,,ile electronice sunt foarte dependente de geometria adoptat,. In conforma,ia W extins,, am putut pune în eviden,, un proces de transfer de energie dinspre baza liber, c,tre porfirina metalat, cu Zn. In conforma,ia U a Zn2Au luminescen,a aripei donoare, datorate st,rii singulet excitate, este puternic stins, nu numai datorit, efectului de atom greu, cât ,i a unui proces de transfer de electron c,tre starea fundamental, a aripei metalat, cu aur. Pe deasupra, complexând (,,,)-diamine c,tre atomii de ZnIIîntre tetrapirolii porfirinici, sunt induse profunde influen,e asupra conforma,iei sistemului. Pentru compusul Zn2Zn, care a putut fi crescut monocristalin, experimente de difrac,ie folosind ca surs, luminoas, un sincrotron au condus la un set de date care a permis ca structura sa fie elucidat, prin metode directe ,i rafinat,, ar,tând conforma,ia în U a,teptat,. Atomul central de Zn are o coordina,ie de sase unde pe lang, lignadul ,3 -terpy, atomul de Zn este coordinat de c,tre doi anioni acetat, unul monodentat, iar cel,lalt semi-chelatizant. Structura este br,zdat, de leg,turi de hidrogen care implic, liganzii apo,i situa,i pe centrii de Zn exteriori, ,i atomii de oxigen din ionii acetat. Sistemul prezentat este un dutblu efector, ar,tând comutare opto-mecanic,, datorat, fie lig,rii prin ioni metalici, fie prin al,i liganzi perfect croitori,i. In acel,i timp, atât procese de transfer de energie, cât ,i de electroni, pot fi perfect comutate, l,sând loc pentru imbun,t,,irea raportului "on/off" în arhitecturi viitoare. [source]

Multiwalled Carbon Nanotubes Covalently Modified with Fast Black K,

CHEMPHYSCHEM, Issue 4 2005
Henry C. Leventis
Nanoscale electrochemical switching device: A novel material comprising molecules of the azo-dye Fast Black K (2,5-dimethoxy-4-[(4-nitrophenyl)azo]benzenediazonium chloride, FBK) covalently attached to multiwalled carbon nanotubes (MWCNTs) is shown to form the basis of a nanoscale voltammetric switching device (see picture) for use in electronic nanocircuits, or alternatively, in high-density memory storage devices. The FBK-derivatised MWCNTs may also be used as a chemical release reagent. [source]

Seismic control of smart base isolated buildings with new semiactive variable damper

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2007
S. Nagarajaiah
Abstract A new semiactive independently variable damper, SAIVD, is developed and shown to be effective in achieving response reductions in smart base isolated buildings in near fault earthquakes. The semiactive device consists of four linear visco-elastic elements, commonly known as Kelvin,Voigt elements, arranged in a rhombus configuration. The magnitude of force in the semiactive device can be adjusted smoothly in real-time by varying the angle of the visco-elastic elements of the device or the aspect ratio of the rhombus configuration. Such a device is essentially linear, simple to construct, and does not present the difficulties commonly associated with modelling and analysing nonlinear devices (e.g. friction devices). The smooth semiactive force variation eliminates the disadvantages associated with rapid switching devices. Experimental results are presented to verify the proposed analytical model of the device. A H, control algorithm is implemented in order to reduce the response of base isolated buildings with variable damping semiactive control systems in near fault earthquakes. The central idea of the control algorithm is to design a H, controller for the structural system that serves as an aid in the determination of the optimum control force in the semiactive device. The relative performance of the SAIVD device is compared to a variable friction device, recently developed by the authors in a separate study, and several key aspects of performance are discussed regarding the use of the two devices for reducing the responses of smart base isolated buildings in near fault earthquakes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Numerical studies of optical switching and optical bistability phenomena of nano- or meso-size spheres

JOURNAL OF MICROSCOPY, Issue 3 2003
T. Okamoto
Summary We propose the use of numerical calculations of the optical response of nonlinear Kerr-spheres, modifying the Mie theory. As a numerical example, we use a CuCl sphere coated with a Kerr-nonlinear sphere, taking into account the excitation of the Z3 -exciton. The results clearly show that optical bistable and/or optical switching devices can be realized on a nano- and meso-size scale when the real part of the dielectric constant of CuCl is negative. [source]

Random and localized resistive switching observation in Pt/NiO/Pt

PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 6 2007
Jung-Bin Yun
Abstract Resistive memory switching devices based on transition metal oxides are now emerging as a candidate for nonvolatile memories. To visualize nano-sized (10 nm to 30 nm in diameter) conducting filamentary paths in the surface of NiO thin films during repetitive switching, current sensing,atomic force microscopy and ultra-thin (<5 nm) Pt films as top electrodes were used. Some areas (or spots), which were assumed to be the beginning of the conducting filaments, appeared (formation) and disappeared (rupture) in a localized and random fashion during the switching and are thought to contribute to resistive memory switching. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

All-Optical Integrated Logic Operations Based on Chemical Communication between Molecular Switches

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009
Serena Silvi Dr.
Abstract Molecular logic gates process physical or chemical "inputs" to generate "outputs" based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine-type photoacid and a ruthenium polypyridine complex that functions as a pH-controlled three-state luminescent switch. The light-triggered release of protons from the photoacid is used to control the state of the transition-metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical,chemical,optical) signal-transduction mechanism, inputs of violet light modulate a luminescence output in the red/far-red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation. [source]