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Peripheral Chains (peripheral + chain)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Smectic phases of liquid crystals based on dinuclear palladium(II) complexes with carboxylato bridge

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2010
V. Cîrcu
Abstract In this paper we present the preparation and the investigation of the liquid crystal properties of a series of dinuclear carboxylato bridge Pd(II) complexes bearing six alkoxy peripheral chains in the molecule. Their structures were assigned based on elemental analysis, IR and 1H NMR spectroscopy whereas the thermal behaviour was investigated by polarizing optical microscopy and differential scanning calorimetry. The monotropic smectic A phase displayed by these materials was identified by miscibility studies with a previously reported mesogen. It was found that the transition temperatures and the SmA mesophase stability depend on the alkyl chain length of the carboxylato bridge. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Star Mesogens (Hekates),Tailor-Made Molecules for Programming Supramolecular Functionality

CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009
Matthias Lehmann
Abstract Hekates: Modular synthesis of star-shaped molecules affords mesogens with various functional units and incompatible peripheral chains (see figure). The supramolecular order in the complex, soft, liquid-crystalline, functional materials can be programmed by variation of the elements of diversity at a meso- and nanoscale. This concept article focuses on the simplest branched liquid crystalline (LC) molecules,the three-armed mesogens with arms symmetrically linked to the core. They are basic but fascinating mesogens for the exploration of self-assembling processes into complex, functional, soft materials. Quite a large number of elements of diversity provide the possibility to synthetically program such star-shaped molecules and to control phase formation, if aggregation processes are fully understood. Recently, ABC-cores opened the way to non-symmetric mesogens and, therefore, to the concept of multifunctional materials with defined nanostructures. In the article this outstanding family of mesogens is classified, their peculiar molecular structure and self-assembly are discussed and potential applications are presented, in which this type of mesogen may be beneficial. Dieser Konzeptbeitrag stellt die einfachsten verzweigten flüssigkristallinen Moleküle in den Mittelpunkt,dreiarmige Mesogene mit symmetrisch um einen Kern angeordneten Armen. Diese schlichten, aber faszinierenden Mesogene eignen sich hervorragend für das Studium von Selbstorganisationsprozessen zu komplexen, funktionalen, weichen Materialien. Die große Zahl von Diversitätselementen, der modular aufgebauten Mesogene, ermöglicht das synthetische Programmieren der sternförmigen Moleküle und die Kontrolle der Anordnung in LC Phasen, falls die Aggregationsprozesse völlig verstanden werden. Die kürzlich vorgestellten ABC-Kerne erlauben die Synthese von unsymmetrischen Mesogenen und folglich die Umsetzung des Konzepts der multifunktionalen Materialien mit definierten Nanostrukturen. In diesem Artikel wird diese außergewöhnliche Mesogenfamilie klassifiziert und deren besondere Struktur und Selbstorganisation diskutiert. Schließlich werden mögliche Anwendungen vorgestellt, für die diese Art der Mesogene vorteilhaft sein kann. [source]

Nanoscale Structural and Electronic Properties of Ultrathin Blends of Two Polyaromatic Molecules: A Kelvin Probe Force Microscopy Investigation

CHEMPHYSCHEM, Issue 4 2006
Vincenzo Palermo Dr.
Abstract We describe a Kelvin Probe Force Microscopy (KPFM) study on the morphological and electronic properties of complex mono and bi-molecular ultrathin films self-assembled on mica. These architectures are made up from an electron-donor (D), a synthetic all-benzenoid polycyclic aromatic hydrocarbon, and an electron-acceptor (A), perylene-bis-dicarboximide. The former molecule self-assembles into fibers in single component films, while the latter molecule forms discontinuous layers. Taking advantage of the different solubility and self-organizing properties of the A and D molecules, multicomponent ultrathin films characterized by nanoscale phase segregated fibers of D embedded in a discontinuous layer of A are formed. The direct estimation of the surface potential, and consequently the local workfunction from KPFM images allow a comparison of the local electronic properties of the blend with those of the monocomponent films. A change in the average workfunction values of the A and D nanostructures in the blend occurs which is primarily caused by the intimate contact between the two components and the molecular order within the nanostructure self-assembled at the surface. Additional roles can be ascribed to the molecular packing density, to the presence of defects in the film, to the different conformation of the aliphatic peripheral chains that might cover the conjugated core and to the long-range nature of the electrostatic interactions employed to map the surface by KPFM limiting the spatial and potential resolution. The local workfunction studies of heterojunctions can be of help to tune the electronic properties of active multicomponent films, which is crucial for the fabrication of efficient organic electronic devices as solar cells. [source]

Influence of Molecular Order on the Local Work Function of Nanographene Architectures: A Kelvin-Probe Force Microscopy Study

CHEMPHYSCHEM, Issue 11 2005
Vincenzo Palermo Dr.
Abstract We report a Kelvin-probe force microscopy (KPFM) investigation on the structural and electronic properties of different submicron-scale supramolecular architectures of a synthetic nanographene, including extended layers, percolated networks and broken patterns grown from solutions at surfaces. This study made it possible to determine the local work function (WF) of the different , -conjugated nanostructures adsorbed on mica with a resolution below 10 nm and 0.05 eV. It revealed that the WF strongly depends on the local molecular order at the surface, in particular on the delocalization of electrons in the , -states, on the molecular orientation at surfaces, on the molecular packing density, on the presence of defects in the film and on the different conformations of the aliphatic peripheral chains that might cover the conjugated core. These results were confirmed by comparing the KPFM-estimated local WF of layers supported on mica, where the molecules are preferentially packed edge-on on the substrate, with the ultraviolet photoelectron spectroscopy microscopically measured WF of layers adsorbed on graphite, where the molecules should tend to assemble face-on at the surface. It appears that local WF studies are of paramount importance for understanding the electronic properties of active organic nanostructures, being therefore fundamental for the building of high-performance organic electronic devices, including field-effect transistors, light-emitting diodes and solar cells. [source]