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Liquid crystalline physical gels which consist of a chiral racemic nitroxide radical compound (±)-1showing a nematic phase and a diamagnetic, chiral organic gelator (R,R)-2were prepared to investigate the effects of the gelator on the “positive magneto-LC effects” observed in the nematic phase of (±)-1and the molecular alignment of (±)-1in the resulting nematic gels. With the increasing amount of the gelator which decreased the domain size, the molecular reorientation by a magnetic field (0.34 T) was considerably restricted in the nematic gel phase and the intermolecular magnetic interactions (positive magneto-LC effects) increased in the fine and random nematic polydomain structure formed by self-assembled fibers of organic gelator molecules. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]