Elisabeth Kapatsina

Bio: Elisabeth Kapatsina is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Convergent synthesis & Columnar phase. The author has an hindex of 4, co-authored 6 publications receiving 1190 citations.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

Abstract: Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.

Diskotische Flüssigkristalle: Von der maßgeschneiderten Synthese zur Kunststoffelektronik

Abstract: Die meisten Menschen verbinden mit dem Begriff Flussigkristalle sofort die Displays von Laptop-Computern, Mobiltelefonen, Digitalkameras und anderen elektronischen Geraten. Im Unterschied zu ihren stabchenformigen (calamitischen) Verwandten, die erstmals 1907 von Vorlander beschrieben wurden, bieten aber die 1977 von Chandrasekhar entdeckten scheibenformigen (diskotischen) Flussigkristalle andere vielversprechende Verwendungsmoglichkeiten. Ihre einzigartige Anordnung in columnaren Mesophasen macht sie zu idealen Kandidaten fur molekulare Drahte in vielen optischen und elektronischen Geraten, beispielsweise in Photokopierern, Laserdruckern, Solarzellen, organischen Leuchtdioden und Feldeffekttransistoren oder zur holographischen Datenspeicherung. Einer Ubersicht uber die verschiedenen Mesophasentypen und Charakterisierungsmethoden columnarer Flussigkristalle folgen ausgewahlte Beispiele aus den Hauptklassen columnarer Mesogene unter besonderer Berucksichtigung effizienter Syntheseverfahren, mesomorpher Eigenschaften und der fur Anwendungen relevanten physikalischen Eigenschaften der Flussigkristalle. Abschliesend werden Anwendungsbeispiele und Perspektiven fur einen Einsatz in den Materialwissenschaften und der molekularen Elektronik vorgestellt.

Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines

Abstract: Based on 5-(4-hydroxyphenyl)-2-octylpyrimidine 8, 5-phenylpyrimidine derivatives 3–7, 9 with different spacer chain lengths (C2 up to C6) and different terminal polar groups (Br, Cl, N3, OH, CN) were synthesized by etherification and nucleophilic substitution. The mesomorphic behaviour of these compounds was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS and SAXS) and revealed smectic A mesophases for bromides, chlorides and azides 3, 4 and 6. For these compounds a maximum phase width was observed for the C5 spacer regardless of the terminal group, whereas the hydroxy- and cyano-substituted derivatives 5 and 7, respectively, were non mesomorphic and showed only melting transitions.

Convergent Synthesis of 1,1′-BiisoquinolinesTethered to Calamitic Subunits

Abstract: A convergent synthesis of a series of 4,4′-functionalized 1,1′-biisoquinolines via 1-chloro-4-hydroxyisoquinoline and substituted biphenyl- and phenylpyrimidine ethers as building blocks is described. The latter were prepared by Williamson etherification of the respective 4-hydroxybiphenyl and -phenylpyrimidine precursors with dibromoalkanes, allowing variation of the spacer lengths. 1-Chloro-4-hydroxyisoquinoline was obtained from N-phthalimidoglycine ethyl ester through a Gabriel-Colman reaction as a key step. Linkage of the building blocks by etherification in the presence of potassium carbonate gave the isoquinolines, which were submitted to a nickel(II) chloride mediated homocoupling to yield the ligand systems.

Concise Synthesis of [1,1′-Biisoquinoline]-4,4′-diol via a Protecting Group Strategy and Its Application for Potential Liquid-Crystalline Compounds

Abstract: The [1,1′-biisoquinoline]-4,4′-diol (4a), which was obtained as hydrochloride 4a⋅2 HCl in two steps starting from the methoxymethyl (MOM)-protected 1-chloroisoquinoline 8 (Scheme 3), opens access to further O-functionalized biisoquinoline derivatives. Compound 4a⋅2 HCl was esterified with 4-(hexadecyloxy)benzoyl chloride (5b) to give the corresponding diester 3b (Scheme 4), which could not be obtained by Ni-mediated homocoupling of 6b (Scheme 2). The ether derivative 2b was accessible in good yield by reaction of 4a⋅2 HCl with the respective alkyl bromide 9 under the conditions of Williamson etherification (Scheme 4). Slightly modified conditions were applied to the esterification of 4a⋅2 HCl with galloyl chlorides 10a–h as well as etherification of 4a⋅2 HCl with 6-bromohexyl tris(alkyloxy)benzoates 11b,d–h and [(6-bromohexyl)oxy]-substituted pentakis(alkyloxy)triphenylenes 14a–c (Scheme 5). Despite the bulky substituents, the respective target 1,1′-biisoquinolines 12, 13, and 15 were isolated in 14–86% yield (Table).

Aggregation-induced emission

Abstract: Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this critical review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure–property relationships are derived. Through mechanistic decipherment of the photophysical processes, structural design strategies for generating new AIE luminogens are developed. Technological, especially optoelectronic and biological, applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 references).

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

Abstract: In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

Abstract: Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Mechanically induced luminescence changes in molecular assemblies.

Abstract: Altering the shape and properties of a material through external factors such as heat, light, pressure, pH, electric or magnetic fields, or the introduction of a guest molecule, is an attractive prospect. In this Perspective, piezochromic luminescent materials - which change the colour of their luminescence in response to mechanical stimuli - are described. Such piezochromism has been observed for a few molecular materials that contain luminescent cores in liquid-crystalline and crystalline solid states, as well as for polymeric materials doped with dyes. These changes in photoluminescent colour can be activated by various types of mechanical pressure such as shearing, grinding or elongation, which can trigger different mechanisms of producing the colour. Such stimuli-responsive materials have potential for various applications, including sensors, memory and displays.