Seiichi Miyajima

A Bent and Asymmetrically Hindered Chiral Alkyl Chain in Smectic-A Phase of an Antiferroelectric Liquid Crystal as Observed by 2H-NMR.

The structure and dynamics of the alkyl chains are investigated by 2 H-NMR for specifically deuterated samples of an antiferroelectric chiral smectic liquid crystal MHPOBC. The 2 H-NMR spectrum for the chiral alkyl chain exhibits very small quadrupolar splittings, and the methylenes close to the chiral center give double splittings ascribable to two different quadrupolar splittings for each methylene unit. The unusual nature of the chiral chain is revealed; the chain is bent from the molecular long axis, and is asymmetrically hindered.

NMR investigation of the oxyethylene unit ordering in some related dialkoxy laterally substituted nematogens

Laterally dialkylated nematogens containing a short terminal polyoxyethylene chain present a wide nematic range starting from room temperature. The ordering of the oxyethylene (OE) unit has been studied by 13C NMR in the liquid crystalline phase. The values of the order parameters were derived from the transient oscillations observed during variable contact-time cross-polarization experiments. Along the oxyethylene chain, the order parameters decrease monotonically. These order parameter values do not present the usual odd-even effect and are noticeably smaller than those found for terminal alkoxy chains. Entering the nematic phase, the 13C thermal evolution of the field-induced chemical shift in the OE unit is far smaller than the one usually observed for terminal alkyl or alkoxy chains, regardless of their non-negligible order parameters. In addition,no linear correlation between the order parameter and the field-induced chemical shift is observed for the carbons in the OE unit. This is an indication th...

Liquid crystals of 4-octyloxy-N-(benzylidene)aniline derivatives bearing trifluoromethyl or trifluoromethoxy end groups

Abstract Seven new derivatives of 4-octyloxy-N-(4-substituted benzylidene) aniline have been synthesized. 4-Trifluoromethyl and 4-trifluoromethoxy derivatives exhibit stable smectic B and A phases, respectively, while both the 4-methyl and 4-methoxy derivatives have monotropic nematic phases. Fundamental liquid crystalline properties such as entropies of the phase transitions, microscopic textures, smectic layer spacings, orientational order parameters, and molecular dipole moments were determined. It has been revealed that moderately polar nature of these mesogens act to stabilizing monolayer smectic states. The smectic A phase of 4-trifluoromethoxy derivative exhibit very high orientational order. None of the disubstituted compounds, 3,5-bis(trifluoromethyl), 3,5-dimethyl, and 3,5-dimethoxy derivatives were mesogenic. The effect of terminal trifluoromethylation on the liquid crystalline properties is discussed.

Freezing of Intramolecular Motion around the Chiral Center of an Antiferroelectric Liquid Crystal as Evidenced by Damped Transient Oscillations in 13C- 1H Cross Polarization

Transient oscillations in 13 C- 1 H cross-polarization dynamics in NMR is studied for an antiferroelectric chiral smectic liquid crystal MHPOBC. Decay time of oscillation, which is determined by proton spin-diffusion, probes intramolecular motions. Different behaviors are found for the chain conformational motions around the chiral center in the paraelectric smectic A(S A ) and the antiferroelectric chiral smectic CA(S CA * ) phases: Intramolecular motion of the chiral chain in the S A phase is frozen in the S CA * phase. This enables a large transverse dipole moment of a molecule to come out.

Fluorine Nuclear Magnetic Relaxation Study of K2SbF5: Anisotropic Reorientation of the Square Pyramidal Ions

Fluorine-19 spin-lattice relaxation time of crystalline K 2 SbF 5 was measured at 10.0 and 26.6 MHz between 77 and 397 K. Angular dependence of T 1 was also examined using a single crystal at 298 K. Magnetic dipolar relaxation due to axial reorientation of the square pyramidal ion SbF 5 2- was observed, its activation energy being 30 kJ mol -1 . A theoretical expression of T 1 due to reorientation of a square pyramidal ion is derived, which is described as a superposition of the two BPP functions with different time constants, τ c and 2π c . Low temperature relaxation behavior was explained in terms of spin diffusion to paramagnetic impurities.

Electrical Conductivity and Some Other Properties of the Partially Oxidized Salt of the Magnus Green Salt with the Formula Pt6(NH3)10Cl10(HSO4)4

The partially oxidized salt of the Magnus green salt with the formula Pt 6 (NH 3 ) 10 Cl 10 (HSO 4 ) 4 was investigated as one-dimensional conductor. Results of the powder X-ray analysis are consistent with a chain structure proposed by Gitzel et al. The electrical conductivity shows a sharp peak between 190 and 200 K with peak value extending over 10 -1 ∼10 -4 \(\varOmega^{-1}\)cm -1 depending on samples. The metal-semiconductor transition thus found is much less gradual than those in KCP and NMP-TCNQ. In one of our samples, another transition from semiconductor to metal on cooling takes place at about 250 K.

Inversion of self-diffusion anisotropy by chemical substitution in smectic A liquid crystals as evidenced by PGSE experiment combined with a quadrupole-coil rotation

A technique of pulsed-field-gradient spin-echo (PGSE) NMR combined with a quadrupole-coil rotation was applied to the study of anisotropic self-diffusion in smectic A liquid crystals. Diffusion anisotropy was found to be inverted by chemical substitution of the terminal groups in homologous compounds: Namely, the diffusion across the layer is faster for the cyano compound, whereas the diffusion within the layer is faster for the trifluoromethoxy compound.

On Thermal Anomalies Due to Phase Transitions in Doubly and Singly Reentrant Liquid Crystals, CBOBP and OBBC

Differential thermal analysis experiments are carried out on two reentrant liquid crystals, CBOBP and OBBC, whose phase sequences are Crystal–S A1 –RN–S Ad –N–I and Crystal–RN–S Ad –N–I, respectively. The reentrant phase transition (RN/S Ad ) is accompanied by a significantly smaller thermal anomaly than the ordinary ones (S A1 /RN and S Ad /N). S A1 /RN had a larger thermal anomaly than S Ad /N. Comparatively strong temperature-dependence of the heat capacity is suggested in RN. All these findings support the picture of competing incommensurate smectic periodicities and the phenomenological optimum density theory.

Modification of electronic structure by charge transfer and molecular motion in titanium disulfide-ethylenediamine intercalation compound

An attempt at modifying the electronic conduction mechanism by guest-host charge transfer and thermally excited molecular motion is reported. Ethylenediamine was intercalated into a semiconducting layered material, titanium disulfide, and a significant increase in charge carriers was evidenced by metallic conductivity, Pauli paramagnetism, and conduction electron spin resonance. Rotational motion of the guest molecule was evidenced by the proton spin-lattice relaxation measurement. However, no anomalous behaviors were found on the electronic properties which are attributable to motion-induced modification of the electronic state.

Proton NMR study of CBOOA, NBOOA, and their chain-deuteriated homologues in smectic Ad and nematic mesophases

Abstract The nature of the smectic Ad to nematic phase transition and the modes of molecular motion were investigated for the homologous mesogens, CBOOA, NBOOA, and their chain-deuteriated compounds. In NBOOA, the SA d[sbnd]N phase transition was found to be first order with a pronounced pretransitional decrease of the orientational order parameter, , both above and below the transition point, while in CBOOA the anomaly in was very small. Despite the different behaviours in terms of the orientational order, the dynamical aspects of molecular motion, probed by the-NMR relaxation, are quite similar. The motional mode characteristic of the N phase is order director fluctuation, but translational self-diffusion becomes the dominant relaxation mechanism in the SA d phase. It is also recognized that the relative importance of these mechanisms changes in a continuous manner as a function of temperature.