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Crystals 2019, 9(2), 74; https://doi.org/10.3390/cryst9020074

Improved Electronic Transport in Ion Complexes of Crown Ether Based Columnar Liquid Crystals

1
Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
2
Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
*
Authors to whom correspondence should be addressed.
Received: 21 December 2018 / Revised: 28 January 2019 / Accepted: 29 January 2019 / Published: 31 January 2019
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Abstract

The Li+- and K+-complexes of new discotic mesogens, where two n-alkoxy-substituted triphenylene cores are connected by a central crown ether (12-crown-4 and 18-crown-6), provide interesting structural and electronic properties. The inter- and intra-columnar structure was investigated by small and wide angle X-ray scattering. The electronic and ionic transports were studied by temperature dependent photoconductivity and impedance spectroscopy, respectively. Besides a strong increase of the stability and the width of the columnar phases the presence of soft anions (iodide, thiocyanate, tetrafluoroborate) leads to an improved intra-columnar order. The hereby shortened stacking-distance of the triphenylene cores leads to a significant increase of the photoconductivity in the columnar mesophase. Furthermore, the ionic conductivity of the new materials was investigated on macroscopically aligned thin films. The existence of channels for fast cation transport formed by the stacked crown ether moieties in the centre of each column can be excluded. The cations are coordinated strongly and therefore contributing only little to the conductivity. The ionic conductivity is dominated by the anisotropic migration of the non-coordinated anions through the liquid, like side chains favouring the propagation parallel to the columns. Iodide migrates about 20 times faster than thiocyanate and 100 times faster than tetrafluoroborate. View Full-Text
Keywords: liquid crystals; columnar; discotic; crown ether; electron transport; ion transport; ion channels; impedance spectroscopy; photoconductivity; X-ray diffraction; salt effect liquid crystals; columnar; discotic; crown ether; electron transport; ion transport; ion channels; impedance spectroscopy; photoconductivity; X-ray diffraction; salt effect
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Staffeld, P.; Kaller, M.; Ehni, P.; Ebert, M.; Laschat, S.; Giesselmann, F. Improved Electronic Transport in Ion Complexes of Crown Ether Based Columnar Liquid Crystals. Crystals 2019, 9, 74.

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