Molecular Mobility Effect on Magnetic Interactions in All-Organic Paramagnetic Liquid Crystal with Nitroxide Radical as a Hydrogen-Bonding Acceptor

Abstract

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.

Spin Symmetry Breaking: Superparamagnetic and Spin Glass-Like Behavior Observed in Rod-Like Liquid Crystalline Organic Compounds Contacting Nitroxide Radical Spins

“…With this situation in mind, since 2004, we have designed and synthesized a series of chiral and achiral all-organic LC nitroxide radicals such as 1-5 having one or two PROXYL (2,2,5,5-tetrassubstituted-1-pyrrolidinyloxyl) units in the core position and, thereby, with a negative dielectric anisotropy (∆ε < 0) ( Figure 3) [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Their LC phases and magnetic properties have been fully characterized.…”

“…Furthermore, quite recently, by means of molecular dynamic (MD) simulation and density functional theory (DFT) calculations, Uchida et al has revealed that the positive magneto-LC effect can originate from the conservation of the memory of spin-spin interactions between magnetic moments, owing to the ceaseless molecular contacts in the LC and isotropic states. They incorporated the molecular mobility effects [44] into the quantitative Thouless-Anderson-Palmer approach, which was proposed to solve the Edwards-Anderson model for spin-glasses with inhomogeneous magnetic interactions [47].…”

“…These experimental results suggest that the interactions between the electric polarization and the magnetic moment in the magnetic LC phase are likely to Representative PROXYL-based organic radicals synthesized since 2004 and their LC transition temperatures. Rod-like monoradicals trans-1 [28][29][30][31][32][33][34][35][36][37][38][39][40] and biradical (S,S,S,S)-2 [41], discotic diradical meso (R,S)-3, and the non-LC racemic diastereomers (R*,R*)-3 [42], discotic monoradical trans-4 [44], and rod-like hydrogen-bonded monoradical trans-5 [43]. The LC temperatures refer to the heating process, except for monotropic racemice trans-5.…”

Strategy for Stimuli-Induced Spin Control Using a Liquescent Radical Cation

“…Therefore, an urgent topic in the development of future functional radical materials is the creation of molecules with spin properties that can be significantly controlled upon brief and weak external stimuli based on domino-type sequential changes 10 in molecular arrangements. However, such a sophisticated spin control and the necessary rational molecular designs have long remained undiscovered, likely due to difficulties in achieving π-conjugated radicals with sufficient molecular mobility, 11 as they definitively require molecular rigidity in their structures. This dilemma has inspired the development of new methodologies employing molecular fluidity in the radical associates under neat conditions.…”

Magnetically controllable random laser in ferromagnetic nematic liquid crystals

“…In particular, the optical switching owing to the molecular reorientation in a magnetic field [22] has some advantages in remote operability [8]. However, to reorient the nematic director using a weak magnetic field, high magnetic anisotropy ∆ χ of the LC molecule is needed [23,24], which is defined as the subtraction of the molar magnetic susceptibility component ( χ ⊥ ) perpendicular to the molecular long axis from that ( χ ) parallel to the axis [25].…”