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Issue 14, 2012
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Observation of positive and negative magneto-LC effects in all-organic nitroxide radical liquid crystals by EPR spectroscopy

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Abstract

The generation of spin glass-like inhomogeneous magnetic interactions (the average spin–spin interaction constant: [J with combining macron] > 0 or [J with combining macron] < 0), which we refer to as positive or negative “magneto-LC effects”, respectively, was observed in the bulk liquid crystalline (LC) phases of chiral all-organic radical compounds 2 with a positive dielectric anisotropy (Δε > 0) under weak magnetic fields. The sign and magnitude of [J with combining macron] depended on the type of LC phase or superstructure; stronger positive interactions ([J with combining macron] > 0) operated in the chiral smectic A (SmA*) phase of (2S,5S)-2b (89% ee) than in the chiral nematic (N*) phase of (2S,5S)-2a (96% ee), whereas weak negative interactions ([J with combining macron] < 0) were observed in the achiral nematic (N) phase of (±)-2a. The origin of the positive magneto-LC effects operating in the SmA* and N* phases was interpreted in terms of the generation of ferromagnetic head-to-tail spin–spin dipole interactions, whereas antiferromagnetic interactions arising from the formation of the RS magnetic dipolar interaction were responsible for the negative magneto-LC effects in the N phase.

Graphical abstract: Observation of positive and negative magneto-LC effects in all-organic nitroxide radical liquid crystals by EPR spectroscopy

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Supplementary files

Article information


Submitted
01 Dec 2011
Accepted
26 Jan 2012
First published
27 Feb 2012

J. Mater. Chem., 2012,22, 6799-6806
Article type
Paper

Observation of positive and negative magneto-LC effects in all-organic nitroxide radical liquid crystals by EPR spectroscopy

K. Suzuki, Y. Uchida, R. Tamura, S. Shimono and J. Yamauchi, J. Mater. Chem., 2012, 22, 6799
DOI: 10.1039/C2JM16278D

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