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 Vorländer, 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.

Die meisten Menschen verbinden mit dem Begriff Flüssigkristalle sofort die Displays von Laptop‐Computern, Mobiltelefonen, Digitalkameras und anderen elektronischen Geräten. Im Unterschied zu ihren stäbchenförmigen (calamitischen) Verwandten, die erstmals 1907 von Vorländer beschrieben wurden, bieten aber die 1977 von Chandrasekhar entdeckten scheibenförmigen (diskotischen) Flüssigkristalle andere vielversprechende Verwendungsmöglichkeiten. Ihre einzigartige Anordnung in columnaren Mesophasen macht sie zu idealen Kandidaten für molekulare Drähte in vielen optischen und elektronischen Geräten, beispielsweise in Photokopierern, Laserdruckern, Solarzellen, organischen Leuchtdioden und Feldeffekttransistoren oder zur holographischen Datenspeicherung. Einer Übersicht über die verschiedenen Mesophasentypen und Charakterisierungsmethoden columnarer Flüssigkristalle folgen ausgewählte Beispiele aus den Hauptklassen columnarer Mesogene unter besonderer Berücksichtigung effizienter Syntheseverfahren, mesomorpher Eigenschaften und der für Anwendungen relevanten physikalischen Eigenschaften der Flüssigkristalle. Abschließend werden Anwendungsbeispiele und Perspektiven für einen Einsatz in den Materialwissenschaften und der molekularen Elektronik vorgestellt.

Tetrakis(4-acetoxyphenyl and 4-benzoyloxyphenyl)ethenes 1f and 1g were obtained by acylation of tetrakis(4-hydroxyphenyl)ethene 1b. Ullmann etherification of 4,4Ј-dihydroxybenzophenone 2b and subsequent McMurry coupling yielded tetrakis(phenoxyphenyl)ethene 1i. The tetrakis(acetamidophenyl)ethene 1h was prepared in three steps from tetraphenylethene 1c by nitration, Raney-Ni reduction and subsequent acetylation. Alternatively, trifluoroacetamide 1j, 2-methylhexanamide 1k and 2,4-dimethylbenzamide 1l, with less tendency to form 2D hydrogen bonding networks and thus increased solubility as compared to 1h, were prepared by acylation of 4,4Ј-diaminobenzophenone 2a and subse-

Three series of novel chiral tetraphenylethenes have been prepared: citronellyl-derived ethers 1a, b, lactate-derived ethers 2d, g, h, i and lactate-derived esters 3a-c, e-h. Helical twisting powers (HTPs) were determined for those derivatives of 1-3, which were sufficiently miscible with the nematic host 5CB 13 or the discotic nematic host hexayne 14. For binary solutions HTP values of 5.7-10.4 mm À1 for 13/1, 12.8-16.5 mm À1 for 13/2, 8.0-28.7 mm À1 for 13/3 and 2.1-2.9 mm À1 for hexayne 14/3 were determined, indicating a much stronger interaction between the C 4 -symmetrical propeller-shaped tetraphenylethenes 1-3 with the calamitc host 5CB 13 than with the discotic C 6 -symmetrical propeller-shaped host hexayne 14.(2S)-Decyloxypropionic acid (10g) According to the general procedure 0.54 g (83%) of a colourless liquid was obtained. 1 H-NMR (500 MHz, CDCl 3 ): d (ppm) ¼ 0.88 [t, 3 J ¼ 7.0 Hz, 3H, CH 2 CH 2 (CH 2 ) 7 CH 3 ], 1.18-1.38 [m, 16H, CH 2 CH 2 (CH 2 ) 7 CH 3 ], 1.45 (d,

No abstract