Molecular topology of three ring nematogens from C-13-H-1 dipolar couplings

Lobo, Nitin P and Das, Bibhuti B and Narasimhaswamy, T and Ramanathan, KV (2014) Molecular topology of three ring nematogens from C-13-H-1 dipolar couplings. In: RSC ADVANCES, 4 (63). pp. 33383-33390.

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Abstract

Molecules in their liquid crystalline phase undergo rotational motion about the long axis of the molecule and the shape adopted by the rotating molecule plays an important role in influencing the mesophase morphology. In this context, obtaining the topology and the relative orientation of the different sub-units are important steps. For studying the liquid crystalline phase, C-13 NMR spectroscopy is a convenient method and for certain specifically designed nematogens, 2-dimensional separated local field (2D-SLF) NMR spectroscopy provides a particularly simple and straightforward means of arriving at the molecular topology. We demonstrate this approach on two three ring based nematogens designed with a phenyl or a thiophene ring at one of the termini. From the C-13-H-1 dipolar couplings of the terminal carbon obtained using the 2D-SLF NMR technique, the order parameter of the local symmetry axis of the terminal phenyl ring as well as of the long molecular axis could be easily estimated. For the thiophene nematogen, the lack of symmetry of the thiophene moiety necessitates some additional computational steps. The results indicate that the thiophene unit has its local ordering axis oriented away from the long molecular axis by a small angle, consistent with a bent structure expected in view of the thiophene geometry. The experiment also demonstrates the ability of 2D-SLF NMR to provide high resolution spectra by separation of several overlapped resonances in terms of their C-13-H-1 dipolar couplings. The results are consistent with a rod-like topology of the core of the investigated mesogens. The investigation demonstrates the potential of 2D-SLF NMR C-13 spectroscopy for obtaining atomistic level information and its utility for topological studies of different mesogens.

Item Type:	Journal Article
Publication:	RSC ADVANCES
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 Chemical Sciences > NMR Research Centre (Formerly Sophisticated Instruments Facility) Division of Physical & Mathematical Sciences > Physics
Date Deposited:	18 Oct 2014 07:00
Last Modified:	18 Oct 2014 07:00
URI:	http://eprints.iisc.ac.in/id/eprint/50048

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