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Pulsed deuterium NMR experiments performed on the isotropic and nematic phases of the banana-shaped liquid-crystalline mesogen 4-chloro-1,3-phenylene bis {4-4'-(11-undecenyloxy) benzoyloxy} benzoate (CIPbis11BB) selectively deuterated on the central ring are analyzed. The outcome of the analysis is taken as indicative of very slow dynamics concerning out-of-plane motions of the molecules.

Two selectively deuterium-labeled isotopomers of the (S)-2-methylbutyl- [4'-(4''-heptyloxyphenyl)-benzoyl-4-oxy-(S)-2-((S)-2'-benzoyl)-propionyl)]-propionate (ZLL7/*), one labeled on the phenyl ring (ZLL7/*-phe-D2) and the other one on the biphenyl fragment (ZLL7/*-biphe-D2), are investigated by using deuterium NMR (DNMR) spectroscopy and other experimental methods. The two self-consistent set of data has helped in associating at the transition from the ferroelectric SmC* to the antiferroelectric Sm[C*.sub.A] phase a change of the molecular conformation.

The first experimental observation of a pecular behavior in the isotropic phase of liquid crystals by means of (super 2)H NMR is reported. The two five-ring banana-shaped mesogens, the 1,3-phenylenebis-{4,4'(11-undecenyloxy)benzoyloxy} benzoate (Pbis 11BB) and its 4-chloro homologue (C1Pbis11BB), selectively deuterium labeled on their central rings, are the main subject of investigation.

A new procedure for the synthesis of the selectively deuterium-labeled chiral liquid crystal 11EB 1 M7 is developed. A study of the structure, orientational ordering, and the dynamic behavior of 11EB 1 M7 is presented.

The difficulty in orientating the [B.sub.2] phase of the banana mesogen 1,3-Phenylene-bis 4-[4-(10-undecenyloxy)-benzoyloxy] benzoate in a relatively high magnetic field is reported based on some observations using both [.sup.13.C] and [.sup.2.H] NMR. The observed [.sup.2.H] NMR spectra could be justified assuming that in the bulk [B.sub.2] phase, there is an isotropic distribution of domains, which do not orient in a particular direction relative to the magnetic field.

A self-consisted dynamic study of the ferroelectric smectic C* (SmC*) phase is presented by means of (super 2) H NMR. The results obtained in both SmA and SmC* phases by NMR have revealed themselves to be useful in calculating dielectric properties and in validating molecular models in both smectic phases.

Liquid crystals that exhibit de Vries smectic A phases are promising materials for new generations of ferroelectric liquid crystal displays and other electro-optical devices. We investigated the molecular dynamic properties of a rod-like de Vries liquid crystal compound, namely the 9HL, a (S)-hexyl lactate derivative, in the whole mesophasic range. This is the first molecular dynamics' investigation on a de Vries phase, and the interest of this system is related to the understanding of the structural and supramolecular organization of de Vries SmA phases, which has been a subject of a broad scientific debate in the last years. Proton NMR spin-lattice relaxation times, T1, were measured in the range 100 MHz to 5 kHz, thus covering a very wide range of motional regimes. 1H NMR dispersion curves and temperature-dependent relaxation rates were analyzed with a global minimum target fitting approach and the main molecular motions, namely reorientational diffusion, translational self-diffusion, layer undulation, and tilting director fluctuations were fully characterized. The molecular dynamics' behavior observed across the SmA-SmC* phase transitions of 9HL was consistent with the proposed cluster diffuse cone model for the de Vries SmA phase. [ABSTRACT FROM AUTHOR]

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Liquid crystals that exhibit de Vries smectic A phases are promising materials for new generations of ferroelectric liquid crystal displays and other electro-optical devices. We investigated the molecular dynamic properties of a rod-like de Vries liquid crystal compound, namely the 9HL, a (S)-hexyl lactate derivative, in the whole mesophasic range. This is the first molecular dynamics' investigation on a de Vries phase, and the interest of this system is related to the understanding of the structural and supramolecular organization of de Vries SmA phases, which has been a subject of a broad scientific debate in the last years. Proton NMR spin-lattice relaxation times, T1, were measured in the range 100 MHz to 5 kHz, thus covering a very wide range of motional regimes. (1)H NMR dispersion curves and temperature-dependent relaxation rates were analyzed with a global minimum target fitting approach and the main molecular motions, namely reorientational diffusion, translational self-diffusion, layer undulation, and tilting director fluctuations were fully characterized. The molecular dynamics' behavior observed across the SmA-SmC* phase transitions of 9HL was consistent with the proposed cluster diffuse cone model for the de Vries SmA phase.

The molecular dynamics of a chiral liquid crystal showing a rich variety of frustrated mesophases has been investigated by means of 1H NMR relaxometry. The interest in this lactate derivative, HZL 7/*, is related to a large range of thermal stabilities of the twist grain boundary (TGB) phases. Dispersions of the 1H spin-lattice relaxation times, T1, in the frequency range from 300 MHz to 5 kHz were measured and consistently analyzed in the isotropic, chiral nematic, TGBA*, and two TGBC* phases. In the isotropic and N* phases, a three-exponential magnetization decay was observed and assigned to three specific molecular groups of the HZL 7/* (molecular core, methyl, and methylene groups). In the TGB phases, all T1 components merge into a single one. The analysis of the T1 dispersion in the TGBA* phase shows that the translational self-diffusion relaxation mechanism dominates over a broad frequency range and that layer undulations are less relevant than the relaxation contribution associated with the diffusion process across the TGB structure. In the TGBC1* phase, the T1 dispersion presents a strong contribution of in-layer tilt direction fluctuations (T1(-1) proportional to ν(-1/2)), while, in the TGBC2* phase, the linear frequency dependence of T1 could be associated with a much stronger contribution of layer undulations than for the other TGB phases. This is at present the first molecular dynamics investigation on several TGB phases by means of 1H NMR relaxometry.

Dynamics of the l-phenylalanine-d(8) has been here investigated by analyzing the (2)H NMR spin-lattice relaxation times of this selectively deuterium enriched amino acid diluted in the cesium pentadecafluorooctanoate/water (CsPFO/H(2)O) lyotropic system both in the nematic (N(+)(D)) and in the lamellar (L(D)) phases. Information on the internal and overall molecular motions as well as on collective motions has been achieved by a global fitting procedure. The dynamic processes affecting this probe molecule reflect its particular conformational and interaction properties with respect to the lyotropic environment. The best reproduction of the experimental data is obtained by assuming free internal reorientations of the benzylic moiety, which results in diffusion constants of the same order of magnitude of the overall molecular spinning motion. Moreover, the contribution of collective motions (order director fluctuations and layer undulations) is estimated to be greater than that commonly observed by other techniques in lyotropic systems.

A complete Deuterium NMR study performed on partially deuterated liquid crystalline carbosilane dendrimer is here reported. The dendrimer under investigation shows a SmA phase in a large temperature range from 381 to 293 K, and its mesophasic properties have been previously determined. However, in this work the occurrence of a biphasic region between the isotropic and SmA phases has been put in evidence. The orientational order of the dendrimer, labeled on its lateral mesogenic units, is here evaluated in the whole temperature range by means of (2)H NMR, revealing a peculiar trend at low temperatures (T < 326 K). This aspect has been further investigated by a detailed analysis of the (2)H NMR spectral features, such as the quadrupolar splitting, the line shape, and the line-width, as a function of temperature. In the context of a detailed NMR analysis, relaxation times (T(1) and T(2)) have also been measured, pointing out a slowing down of the dynamics by decreasing the temperature, which determines from one side the spectral changes observed in the NMR spectra, on the other the observation of a minimum in the T(1).

In the present work, we analyze pulsed deuterium NMR experiments performed on the isotropic and nematic phases of the banana-shaped liquid-crystalline mesogen 4-chloro-1,3-phenylene bis{4-4'-(11-undecenyloxy) benzoyloxy} benzoate (ClPbis11BB) selectively deuterated on the central ring. Starting from a previous evidence of unusual slow dynamics in the isotropic phase (Domenici V. et al., J. Phys. Chem. B 2005, 109, 769), a quantitative and model-supported analysis of the deuterium NMR data is performed here by accounting for slow-motional modulation of the magnetic anisotropies through the full solution of the stochastic Liouville equation. Focusing on the quadrupolar echo experiments performed in the nematic phase, the analysis of the transverse relaxation rate has been carried out by considering single-molecule motions and fluctuations of the local director. The main conclusions are: (a) director fluctuations are not relevant on driving the signal relaxation; (b) molecular reorientations about transverse axes control the dynamic regime of the signal relaxation and impose a full slow-motional treatment; (c) the small amplitude tumbling of the molecule within the wells of orientational potential occurs with characteristic times up to the microsecond. The outcome of our analysis has to be taken as indicative of very slow dynamics concerning out-of-plane motions of the molecules. Besides the specific application, this paper also offers the methodological tools to treat the pulsed deuterium NMR experiment in the slow-motional regime of reorientational motions and provides a detailed comparison with the usually employed fast-motional approximation.

In this paper, the difficulty in orienting the B(2) phase of the banana mesogen 1,3-Phenylene-bis 4-[4-(10-undecenyloxy)-benzoyloxy] benzoate (Pbis11BB) in a relatively high magnetic field is reported based on some observations using both (13)C and (2)H NMR. (2)H NMR spectra recorded for the two labeled isotopomers of Pbis11BB in the isotropic and B(2) phases are shown here. Preliminary results on the deuteron spin-spin relaxation (T(2)) data are reported at 61 MHz in order to underline the peculiar slow dynamics of banana-shaped liquid crystals (BLC), and these results are discussed in the framework of recent studies on similar BLC. The molecular structure and dynamics in the B(2) and crystalline phases are also studied by (13)C solid-state NMR techniques. The results also point to the slow dynamics in the B(2) phase of Pbis11BB. In particular, two-dimensional MAS exchange experiment has been performed to shed light on the molecular conformation structure of the five-ring banana core in the crystalline phase of Pbis11BB, and to compare with that of quantum mechanical calculations reported in the literature.

In this work, the rotational-diffusion coefficients D(parallel) and D(perpendicular) for the ferroelectric smectogen (+)-(S)-4-[4'-(1-methylheptyloxy)] biphenyl 4-(10-undecenyloxy)benzoate have been studied by means of 2H NMR spectroscopy in the smectic C phase, using a new theoretical approach (Domenici,V.; Geppi, M.; Veracini, C. A. Chem. Phys. Lett. 2003, 382, 518). The analysis of spin-lattice relaxation times has been performed in terms of the diffusional constant and the activation energy of the internal and overall molecular-reorientational motions, and the results are compared to the smectic A (SmA) phase. Moreover, from the 2H NMR data in the SmA phase, the dielectric permittivity and the dielectric relaxation time functions are investigated using a theoretical approach. The longitudinal and transverse components of the real Rchigammaomega and imaginary chigammaomega (gamma = parallel, perpendicular) parts of the complex susceptibility tensor and the nematic-like rotational-viscosity coefficients, lambda2 and lambda5, are calculated.

In this work the first experimental observation of a peculiar behavior in the isotropic phase of liquid crystals by means of 2H NMR is reported. In particular, two five-ring banana-shaped mesogens, the 1,3-phenylenebis{4,4'-(11-undecenyloxy)benzoyloxy}benzoate (Pbis11BB) and its 4-chloro homologue (ClPbis11BB), selectively deuterium labeled on their central rings, are the subject of our investigation. The dynamic behavior of the two liquid crystals was studied in their isotropic phases and in the nematic phase of ClPbis11BB by means of 2H NMR line width and spin-spin relaxation time (T2) analysis. The results obtained reveal that the unusual line broadening observed in the 2H NMR spectra in the isotropic phase, even far above the isotropic phase-mesophase transition, has a homogeneous nature, thus indicating the presence of reorientational motions much slower than in conventional isotropic liquid-crystalline phases.