Satoshi Shimono

Anisotropic and Inhomogeneous Magnetic Interactions Observed in All-Organic Nitroxide Radical Liquid Crystals

An anisotropic and inhomogeneous magnetic interaction (the average spin-spin interaction constant (-)J > 0) was observed in the various liquid crystalline (LC) phases of racemic and nonracemic all-organic radical LC compounds 1a and 1b. We discussed how the LC superstructures induced the magnetic interaction to operate in the LC phases in terms of spin-spin dipole and exchange interactions by means of VT-EPR spectroscopy. The magnitude of the magnetic interaction depended on the type of LC phase, or the superstructure. Furthermore, these radical LC droplets floating on water were commonly attracted to a permanent magnet and moved freely under the influence of this magnet, whereas the crystallized particles of the same compounds never responded to the magnet. The response of the LC droplets to the magnet also varied depending on the type of LC phase, that is, the extent of the magnetic interaction.

Paramagnetic FLCs Containing an Organic Radical Component

We have prepared new all-organic ferroelectric liquid crystalline materials containing a polar and dichiral cyclic-nitroxide unit within the rigid core. These compounds show distinct ferroelectricity in SmC* phases. The spontaneous polarization (Ps) has been measured by the triangular wave method and the tilt angle has been determined by polarizing microscopy. The relationship between the Ps and the molecular structure has been investigated by the MO calculations. The tilt angles, which are estimated from the layer distances of the SmC* phases determined by X-ray diffraction data and the molecular lengths calculated by the MO calculations, are consistent with those by polarizing microscopy.

Unusual intermolecular magnetic interaction observed in an all-organic radical liquid crystal

Here we show the first observation of an unusual intermolecular magnetic interaction in the liquid-crystalline (LC) state of an all-organic radical compound at 73 °C on water; the magnetic interaction actually allows the LC droplet on water to be attracted by a weak permanent magnet, whereas the crystalline phase did not respond to the magnet.

Magnetic-field-induced molecular alignment in an achiral liquid crystal spin-labeled by a nitroxyl group in the mesogen core

Here we show magnetic-field-induced molecular alignment in the achiral nematic and smectic C phases of an all-organic radical compound (1) by variable-temperature electron paramagnetic resonance (EPR) spectroscopy at a magnetic field of 0.33 T and by polarized optical microscopy (POM) observation under variable magnetic fields (0–5.0 T).

Synthesis and Characterization of Novel All-Organic Liquid Crystalline Radicals

We have synthesized a new series of all-organic liquid crystalline (LC) radical compounds (2), which are the structural isomers of the previously reported series (1) containing a chiral nitroxide unit in the mesogen core. Only difference between the two isomers is the orientation in the ester functionality (‒OCO‒ vs ‒COO‒). The new LC compounds 2 with C4 to C8 alkoxy terminal chains showed the distinct odd-even effects of alkoxy terminal chains with respect to the thermal stability of nematic phases, while such effects were not observed for the isomers 1.

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

The generation of spin glass-like inhomogeneous magnetic interactions (the average spin–spin interaction constant: > 0 or 0) under weak magnetic fields. The sign and magnitude of depended on the type of LC phase or superstructure; stronger positive interactions ( > 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 ( < 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.

Influence of applied electric fields on the positive magneto-LC effects observed in the ferroelectric liquid crystalline phase of a chiral nitroxide radical compound

By measuring the electric field dependence of EPR spectra of the ferroelectric liquid crystalline (FLC) phase of (2S,5S)-1 confined in a surface-stabilized liquid-crystal cell, two magnetic bistable states were observed. These states occur because of the anisotropy in spin–spin dipole interactions responsible for positive ‘magneto-LC effects’, which refer to the generation of a sort of spin glass-like ferromagnetic interactions (average spin–spin exchange interaction constant > 0) induced by weak magnetic fields in the various liquid crystalline (LC) phases of nitroxide radical compound 1.

Characterization of the Crystalline Nature of the Racemates of Novel Chiral Five-Membered Cyclic Nitroxides

ABSTRACT Racemic samples of chiral five-membered cyclic nitroxides, 2,2,5,5-tetrasubstituted pyrrolidine-1-oxyls bearing one or two 4-hydroxyphenyl groups on the stereogenic centers [C(2) or C(2) & C(5)] adjacent to the NO radical moiety, exist as a racemic conglomerate in the crystalline state, whereas those having one or two 3-hydroxyphenyl groups at the same positions belong to a racemic compound. The key intermolecular interactions in controlling whether these racemates crystallize in a homochiral way or a heterochiral manner have been investigated by X-ray crystallographic analysis and magnetic susceptibility measurements.

Use of Cyclotriphosphazene as a Molecular Scaffold for Building Chiral Multispin Systems

ABSTRACT Chiral mononitroxide-, dinitroxide-, tetranitroxide- and hexanitroxide- cyclotriphosphazene hybrid compounds, along with a chiral 2,2′-bridged trinitroxide-bis(cyclotriphosphazene) hybrid compound, have been prepared to examine the potential use of the cyclotriphosphazene framework as a molecular scaffold for elaborating chiral multispin systems. EPR spectroscopic studies in solution and in frozen solvent matrixes indicate that strong intramolecular through-space electron-exchange interactions are observed for the tetranitroxide and hexanitroxide hybrid compounds, while magnetic susceptibility measurements show that weak antiferromagnetic interactions are uniformly recognized in the solid states for all of them. The X-ray crystallographic analysis of the dinitroxide hybrid compound ascribes the latter antiferromagnetic behavior to an intermolecular origin.

Electric Field Dependence of Molecular Orientation and Anisotropic Magnetic Interactions in the Ferroelectric Liquid Crystalline Phase of an Organic Radical Compound by EPR Spectroscopy

To confirm whether chiral organic radical compound 1, which showed the generation of a sort of spin glass-like inhomogeneous ferromagnetic interactions (the average spin-spin interaction constant J > 0) in the bulk liquid crystalline state under weak magnetic fields, has a spin easy axis or exhibits anisotropic magnetic interactions in the SmC* or SmC phase, we have measured the temperature dependence of g-value and relative paramagnetic susceptibility (χrel) for the ferroelectric SmC* phase of (2S,5S)-1 confined in a thin sandwich cell by EPR spectroscopy.