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Asymmetric discotic liquid crystals based on rufigallol

Raja, KS and Ramakrishnan, S and Raghunathan, VA (1997) Asymmetric discotic liquid crystals based on rufigallol. In: Chemistry of Materials, 9 (7). pp. 1630-1637.

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Abstract: Two series of asymmetric hexaethers (asymmetric by virtue of having alkyl chains of unequal lengths) of rufigallol, viz., R442n and R482n (1,5-dialkoxy-2,3,6,7-tetrabutoxy-9,10-anthraquinone and 1,5-dialkoxy-2,3,6,7-tetraoctyloxy-9,10-anthraquinone, respectively) were synthesized. These hexaethers exhibit a typical hexagonal columnar mesophase (D-h) as evidenced from X-ray diffraction and polarized light microscopic studies. Differential scanning calorimetric (DSC) studies suggest that the temperatures of isotropization (TD-i) and the molar isotropization entropy (Delta S-i) fall with increase in asymmetry. The fall in Delta S-i with increase in asymmetry is significantly larger than what may be expected merely from increase in the relative alkyl chain content, suggesting that asymmetry causes a significant decrease in the extent of ordering in the columnar mesophase. However, X-ray diffraction studies suggests that the intercolumnar spacing (D) is not affected by the presence of asymmetry but depends only on the total number of alkyl chain carbon atoms (C-n) present in a molecule. Furthermore, from the linear variation of the disk area, pi D-2/4, versus C-n (which was shown to be system independent), it was possible to calculate the volume occupied by a single alkyl chain methylene (CH2) unit in the columnar mesophase. This value is significantly smaller than that estimated in liquid n-alkanes, suggesting that the alkyl chains are not truely liquidlike in such discotic coulmnar mesophases. A further interesting observation in these systems is that when the alkyl chains are very long, an additional ordering of the side chains suggestive of side-chain crystallization is observed.

Item Type: Journal Article
Publication: Chemistry of Materials
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 06 Mar 2009 12:06
Last Modified: 19 Sep 2010 05:01
URI: http://eprints.iisc.ac.in/id/eprint/18426

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