title: δ-Methyl Branching in the Side Chain Makes the Difference: Access to Room-Temperature Discotics.
abstract: Although discotic liquid crystals are attractive functional materials, their use in electronic devices is often restricted by high melting and clearing points. Among the promising candidates for applications are [15]crown-5 ether-based liquid crystals with peripheral n-alkoxy side chains, which, however, still have melting points above room temperature. To overcome this problem, a series of o-terphenyl and triphenylene [15]crown-5 ether derivatives was prepared in which δ-methyl-branched alkoxy side chains of varying lengths substitute the peripheral linear alkoxy chains. The mesomorphic properties of the novel crown ethers were studied by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. δ-Methyl branching indeed lowers melting points resulting in room-temperature hexagonal columnar mesophases. The mesophase widths, which ranged from 87 to 30 K for o-terphenyls, significantly increased to 106-147 K for the triphenylenes depending on the chain lengths, revealing the beneficial effect of a flat mesogen, due to improved π-π interactions.
authors: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors: Jochen
authors: J
authors: Kirres
authors: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors: Friederike
authors: F
authors: Knecht
authors: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors: Philipp
authors: P
authors: Seubert
authors: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors: Angelika
authors: A
authors: Baro
authors: Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany. sabine.laschat@oc.uni-stuttgart.de.
authors: Sabine
authors: S
authors: Laschat
keywords: crown compounds; crown ether; discotic; liquid crystals; mesophases