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Structural investigation of resorcinol based symmetrical banana mesogens by XRD, NMR and polarization measurements

Reddy, Kesava M and Varathan, E and Jacintha, B and Lobo, Nitin P and Roy, Arun and Narasimhaswamy, T and Ramanathan, KV (2015) Structural investigation of resorcinol based symmetrical banana mesogens by XRD, NMR and polarization measurements. In: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 17 (7). pp. 5236-5247.

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Official URL: http://dx.doi.org/ 10.1039/c4cp05844e

Abstract

Synthesis and structural characterization of two novel symmetrical banana mesogens built from resorcinol with seven phenyl rings linked by ester and imine with a terminal dodecyl/dodecyloxy chain has been carried out. Density functional theory (DFT) has been employed for obtaining the geometry optimized structures, the dipole moments and C-13 NMR chemical shifts. The HOPM and DSC studies revealed enantiotropic B-2 and B-7 phases for the dodecyl and dodecyloxy homologs respectively. The powder X-ray studies of both the mesogens indicate the presence of layer ordering. The polarization measurements reveal an anti-ferroelectric switching for the B-2 phase of the dodecyl homolog whose structure has been identified as SmCSPA. The B-7 phase of the dodecyloxy homolog was found to be non-switchable. High resolution C-13 NMR study of the dodecyl homolog in its mesophase has been carried out. C-13-H-1 dipolar couplings obtained from the 2-dimensional separated local field spectroscopy experiment were used to obtain the orientational order parameters of the different segments of the mesogen. Very large C-13-H-1 dipolar couplings observed for the carbons of the central phenyl ring (9.7-12.3 kHz) in comparison to the dipolar couplings of those of the side arm phenyl rings (less than 3 kHz) are a direct consequence of the ordering in the banana phase and the shape of the molecule. From the ratio of the local order parameter values, the bent-angle of the mesogen could be determined in a straight forward manner to be 120.5 degrees.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Depositing User: Id for Latest eprints
Date Deposited: 01 Apr 2015 12:11
Last Modified: 01 Apr 2015 12:11
URI: http://eprints.iisc.ac.in/id/eprint/51150

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