Issue 44, 2006
From the journal:

Journal of Materials Chemistry

Shape-persistent V-shaped mesogens—formation of nematic phases with biaxial order†

Matthias Lehmann,*a   Shin-Woong Kang,b   Christiane Köhn,a   Sönke Haseloh,c   Ute Kolb,c   Dieter Schollmeyer,d   QingBing Wangb  and  Satyendra Kumare  

* Corresponding authors

a Chemnitz University of Technology, Strasse der Nationen 62, Chemnitz, Germany
E-mail: Matthias.Lehmann@chemie.tu-chemnitz.de
Fax: (+) 49/371 531 1839
Tel: +49 371 531 1205

b Department of Physics, Kent State University, Kent, OH 44242, USA

c Institute of Physical Chemistry, Johannes Gutenberg-University Mainz, Welderweg 11, 55099 Mainz, Germany

d Institute of Organic Chemistry, Johannes Gutenberg-University Mainz, Duesbergweg 10-14, 55099 Mainz, Germany

e National Science Foundation, 4201 Wilson Blvd., Arlington, VA 22230, USA

Abstract

A homologous series of shape-persistent V-shaped molecules has been designed to form the biaxial nematic phase. Phenyleneethynylene moieties are attached to a bent fluorenone unit to create an apex angle of about 90°, which is determined from the single crystal structure. Two mesogens, one symmetric and another unsymmetric, have been synthesized by attaching a cyano group to one or both of the peripheral phenyl units, respectively. These groups introduce local dipoles essential for the formation of the nematic phases. The tendency to form a crystalline phase is reduced by laterally substituted hexyloxy chains which allow the nematic phase to be supercooled to a glassy state. Two of the three fluorenone derivatives exhibit a transition from the uniaxial nematic to the biaxial nematic phase. This transition has an undetectably small transition enthalpy, but the X-ray diffraction, polarizing optical microscopy, and conoscopy reveal the presence of the biaxial order in the low temperature nematic phase.

Graphical abstract: Shape-persistent V-shaped mesogens—formation of nematic phases with biaxial order

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Article information

DOI
https://doi.org/10.1039/B605718G
Article type
Paper
Submitted
21 Apr 2006
Accepted
07 Aug 2006
First published
19 Sep 2006

J. Mater. Chem., 2006,16, 4326-4334

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Shape-persistent V-shaped mesogens—formation of nematic phases with biaxial order

M. Lehmann, S. Kang, C. Köhn, S. Haseloh, U. Kolb, D. Schollmeyer, Q. Wang and S. Kumar, J. Mater. Chem., 2006, 16, 4326 DOI: 10.1039/B605718G

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