We synthesized new chiral all-organic liquid crystalline (LC) compounds with nitroxide (NO) and hydroxy (OH) groups, which form intermolecular hydrogen bonds between the NO and OH groups. The LC compounds show hexagonal columnar phases at room temperature, which solidify as LC glasses at low temperature. The experimental magnetic susceptibility of each of the compounds in the LC and isotropic phases is larger than that theoretically estimated on the simple assumption about the amount of the spins, whereas it accords with the theoretical one in the LC glass state. It is called magneto-LC effects. The difference between experimental and theoretical magnetic susceptibilities gradually increases as temperature increases through the LC glass state-to-LC phase transition. It suggests that molecular mobility is one of the origins of the magneto-LC effects.

Metal-free liquid-crystalline (LC) materials consisting of a LC nitroxide radical compound exhibit light-induced reversible switching of the magnetic properties as a new photomagnetic effect. This behavior is based on the abrupt change of magnetic properties at the phase transition directly from a chiral smectic C phase to an isotropic liquid (Iso) phase. The origin of the abrupt change is probably the difference in the inhomogeneity of the intermolecular magnetic interactions between LC and Iso phases. To our knowledge, there are no existing reports on a material showing the reversible and quick phase transitions with the large difference of the inhomogeneity. Here we show a relatively simple way to design a compound to enlarge the difference between LC and Iso phases and to make the response quick and reversible. In addition, the presented analysis method that mines Gaussian components from electron paramagnetic resonance spectra enables us to precisely evaluate magnetic properties in condensed phases.

Abstract:We have prepared novel ferronematics based on a paramagnetic liquid crystalline (LC) material. Our ferronematics can disperse a higher volume fraction of magnetic nanoparticles compared to classical ferronematics because paramagnetic nature of the host LC material prevents the aggregation of magnetic nanoparticles. The interactions between the magnetic nanoparticles and the LC material enhance a magnetic anisotropy of ferronematics and improve the magnetic responsivity.

We have synthesized a racemic and enantiomerically enriched all-organic paramagnetic nitroxide radical (NR) liquid crystalline (LC) compound, which contains a chiral NR unit in the mesogen core and a methyl di(ethylene glycol) chain as one of their terminal units. This new compound showed remarkable substituent effects of di(ethylene glycol) chain on the phase transition behavior and hydrophilic property in contrast to structural analogs of the previous reported NR-LC compounds containing alkoxy chains.