title: Substituted Septithiophenes with End Groups of Different Size: Packing and Frustration in Bulk and Thin Films.
abstract: We report on three different liquid crystalline compounds with a central septithiophene core and alkylated end groups of strongly increasing bulkiness. In principle, the thiophene cores prefer to pack parallel to optimize their π-π interactions, which becomes sterically impossible for the bulkier end groups. Using X-ray diffraction, we find that the way out of this packing dilemma is toward liquid-crystal phases of higher dimensionality in the order smectic → columnar ↔ bicontinuous cubic. For the smectic phase, packing in a monolayer is no problem; for the other ones packing considerations become more stringent in films due to the boundaries. Surface X-ray techniques and atomic force microscopy indicate an appreciable difference between monolayer and three-layer films, in which the monolayers appear to escape from packing frustration by generating superstructures. We propose a basic structure of columns parallel to the substrate that provides a compromise between preserving some π-π interactions and packing the bulky alkyl groups.
authors.affiliation: DWI-Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, D-52056 Aachen, Germany.
authors.forename: Wim H
authors.initials: WH
authors.lastname: de Jeu
authors.affiliation: DWI-Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, D-52056 Aachen, Germany.
authors.forename: Khosrow
authors.initials: K
authors.lastname: Rahimi
authors.affiliation: Institute of Organic Chemistry III, University of Ulm , Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Ziener
authors.affiliation: Institute of Organic Chemistry III, University of Ulm , Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Vill
authors.affiliation: Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München , James-Franck-Strasse 1, D-85478 Garching, Germany.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Herzig
authors.affiliation: Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München , James-Franck-Strasse 1, D-85478 Garching, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Müller-Buschbaum
authors.affiliation: DWI-Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, D-52056 Aachen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Möller
authors.affiliation: DWI-Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, D-52056 Aachen, Germany.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Mourran