Article (Scientific journals)
On the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants
Enz, Eva; Findeisen-Tandel, Sonja; Dabrowski, Roman et al.
2009In Journal of Materials Chemistry, 19 (19), p. 2950-2957
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Keywords :
FERROELECTRIC LIQUID-CRYSTALS; SPONTANEOUS POLARIZATION; SHAPED   COMPOUNDS; FIELD; MESOPHASES; MOLECULES
Abstract :
[en] A series of achiral hockey-stick-shaped mesogens forming tilted smectic liquid crystal phases of synclinic SmC- as well as anticlinic SmCa-type was prepared and characterized. While all homologues exhibit both phases, the balance shifts from anticlinic to synclinic order upon elongation of the terminal chain at the meta-position, defining the hockey-stick shape. The elongation also leads to an increased kinetic hindrance of the transition between syn- and anticlinic phases and a decreased transition enthalpy. These observations indicate that a well-defined kink (short meta-substituted chain) promotes the anticlinic structure while a higher flexibility between kinked and rod-shape (long meta-substituted chain) promotes synclinic order. An intermediate chain-length homologue was selected as host material for doping with syn- and anticlinic rod-shaped chiral dopants, respectively, at varying concentrations. Opposite of what might be expected the balance between syn- and anticlinic order was not simply dictated by the choice of dopant. Instead, both types of tilting order prevailed with roughly the same strength as in the achiral host regardless of which chiral material was added, up to concentrations well beyond normal doping conditions. Thus, at least with hockey-stick-shaped achiral hosts, syn- as well as anticlinic chiral compounds can be used effectively as chiral dopants without necessarily having an important impact on the clinicity of the resulting mixture. The hockey-stick design concept should be useful in producing achiral anticlinic-forming mesogens for low-polarization, long-pitch antiferroelectric liquid crystal mixtures. Finally, we point out that a mixture study like the one carried out here yields a conclusive means of establishing the clinicity of achiral tilted smectics, an endeavour that can sometimes be far from trivial.
Disciplines :
Chemistry
Author, co-author :
Enz, Eva
Findeisen-Tandel, Sonja
Dabrowski, Roman
Giesselmann, Frank
Weissflog, Wolfgang
Baumeister, Ute
Lagerwall, Jan  ;  Martin-Luther-Universität Halle-Wittenberg
External co-authors :
yes
Language :
English
Title :
On the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants
Publication date :
2009
Journal title :
Journal of Materials Chemistry
ISSN :
1364-5501
Publisher :
Royal Society of Chemistry, Cambridge, United Kingdom
Volume :
19
Issue :
19
Pages :
2950-2957
Peer reviewed :
Peer Reviewed verified by ORBi
Commentary :
[Enz, Eva; Findeisen-Tandel, Sonja; Weissflog, Wolfgang; Baumeister, Ute; Lagerwall, Jan] Univ Halle Wittenberg, Inst Chem Phys Chem, D-06108 Halle, Germany.   [Enz, Eva; Giesselmann, Frank; Lagerwall, Jan] Univ Stuttgart, Inst Phys Chem, D-70569 Stuttgart, Germany.   [Dabrowski, Roman] Mil Univ Technol, PL-00908 Warsaw, Poland.   [Findeisen-Tandel, Sonja] Univ Cambridge, Dept Engn, Ctr Mol Mat Photon Elect, Cambridge CB2 1TN, England. Lagerwall, J, Univ Halle Wittenberg, Inst Chem Phys Chem, Muehlpforte   1, D-06108 Halle, Germany.
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