Showing papers in "Molecular Crystals and Liquid Crystals in 1975"
TL;DR: In this paper, the electric permittivity of nematic 44′ n-pentylcyanobiphenyl has been measured in the presence of electric and magnetic fields.
Abstract: The electric permittivity of nematic 44′ n-pentylcyanobiphenyl has been measured in the presence of electric and magnetic fields. Values of the permittivity components for the aligned state have been obtained and analysed in terms of the statistical theory of Maier and Meier. The behaviour of bulk samples of the material in electric and magnetic fields has been investigated, and yielded a mean permittivity for the non-aligned state. The macroscopic behaviour is discussed in terms of the continuum theory. Variable frequency measurements have shown the presence of a dispersion region in e∥ at about 5 MHz.
126 citations
TL;DR: In this paper, the authors reported the observation of electroluminescence in pyrene single crystals by contact injection using CuI and Na-Hg amalgam electrodes as hole and electron injectors, respectively.
Abstract: The observation of electroluminescence in pyrene single crystals is reported. Holes and electrons were introduced into the samples by contact injection using CuI and Na-Hg amalgam electrodes as hole and electron injectors, respectively. The radiation-recombination light intensity is found to be directly proportional to the current through the crystal. The yield for light emission is about 2 × 10−3 photons per injected electron-hole pair. The electroluminescence spectrum differs from the fluorescence spectrum of pyrene (excimer emission) by the appearance of fine structure, the relative heights of the various peaks being functions of the injecting current.
53 citations
TL;DR: In this article, the total free energy of these distorted linear systems, in which the electronic energy results from an elementary one-dimensional split band model, leads to a temperature dependent band gap and band width and readily predicts these structural changes, induced by the electronic system.
Abstract: Spin susceptibility measurements in crystalline alkali+ TCNQ− salts reveal the occurrence of continuous changes and first-order phase transitions in these salts, except Li+TCNQ−. A consideration of the total free energy of these distorted linear systems, in which the electronic energy results from an elementary one-dimensional split band model, leads to a temperature dependent band gap and band width and readily predicts these structural changes, induced by the electronic system. The outlines of the theory are given first on a more symmetrical model, which leads to first- and second-order semiconductor-to-metal transitions. Calculations were performed in detail on the basis of the accurately known crystal structure of Rb+TCNQ−, which lead to first-order semiconductor-to-semiconductor transitions, as observed. The experimental absolute susceptibility data, arising from the low temperature as well as from the high temperature phase, are compared successfully with predictions from the theoretical model.
48 citations
TL;DR: In this paper, the orientational order parameters of MBBA from two sources (clearing temperatures 317.5° and 318.9°K) as functions of temperature were obtained from optical anisotropy (birefringence) measurements of orientated thin films by a variable wave-length method.
Abstract: The orientational order parameters of MBBA from two sources (clearing temperatures 317.5° and 318.9°K) as functions of temperature were obtained from optical anisotropy (birefringence) measurements of orientated thin films by a variable wave-length method. The formula proposed by Vuks for the polarization field associated with strongly anisotropic organic molecules was used as the basis for the development of new expressions used in our evaluation of the order parameter. The order parameters versus temperature reported in this paper are in very good agreement with recent NMR and Raman scattering measurements reported in the literature.
42 citations
TL;DR: In this paper, Raman spectra were recorded for (p-methoxy) benzylidene aniline (MBBA) in the solid, nematic, and isotropic liquid states.
Abstract: Les spectures RAMAN de la (p-methoxy) benzylidene (p-n-butyl) aniline (MBBA) ont ete enregistres dans les phases solide, nematique et liquide isotrope. L'evolution du spectre avec la temPerature permet de distinguer les bandes correspondant aux mouvements du noyau rigide benzilidene-aniline central de celles caracteristiques des mouvements de chaines laterales aliphatiques. L'attribution aux modes du groupement benzylidene-aniline a ete effectuee a l'aide d'un calcul a priori des frequences de vibration de ce compose. L'attribution aux modes des chaines alcoyles est basee sur les courbes de dispersion du polymethylene. Les transitions de phase n'affectent essentiellement que les mouvements des groupements alcoyles terminaux. Raman spectra were recorded for (p-methoxy) benzylidene (p-n-butyl) aniline (MBBA) in the solid, nematic, and isotropic liquid states. A clear differece has been observed in the temperature-dependent behaviour of Raman bands of rigid benzylidene aniline group and those of the...
35 citations
TL;DR: In this article, a simple phenomenological theory is presented for the dependence of the surface tension γ at the nematic-vapor interface in terms of the order parameter Qij.
Abstract: A simple phenomenological theory is presented for the dependence of the surface tension γ at the nematic-vapor interface in terms of the order parameter Qij. Account is taken of the observations that γ is often discontinuous at the nematic-isotropic transition, and that there is usually a preferred orientation at the free surface. The derived γ is anisotropic and depends on the angle between the normal to the surface. The derived γ is anisotropic and depends on the angle between the normal to the sufrace and the orientation at the surface. Two simple examples of possible distortions in the surface and the orientation at the surface. Two simple examples of possible distortions in the orientation are considered. Since γ depends upon the scalar order parameter S it is possible to have an excess order near the surface. The value of the excess order and its decay depth are calculated.
28 citations
TL;DR: In this paper, the chemical and crystallographic requirements for utilizing solid-state photodimertization reactions in the medium of chiral single crystals to realize asymmetric syntheses have been considered.
Abstract: The chemical and crystallographic requirements for utilizing solid-state photodimertization reactions in the medium of chiral single crystals to realize asymmetric syntheses have been considered. Asymmetric syntheses are possible from a variety of reactions in the monocomponent or two-component crystals which have been considered and in favorable cases quantitative optical yields are anticipated. These principles can be extended to other reactions including the formation of chiral cyclobutane photopolymers.
27 citations
TL;DR: In this paper, the hexagonal phase of the system C7D15COONa-H2O-CCI4 has been studied by deuterium magnetic resonance and the order parameters range from 0.02 to 0.13.
Abstract: The hexagonal phase of the system C7D15COONa-H2O-CCI4 has been studied by deuterium magnetic resonance. Order parameters for the different CD2-groups have been determined from the observed deuterium splittings in powder spectra. The order parameters range from 0.02 to 0.13. The order parameters decrease when CCI4 is solubilized, implying an increased motional freedom of the alkyl chain. For some samples a central, unsplit peak is observed originating from isotropic metastable aggregates.
25 citations
TL;DR: The dependence of the molecular Kerr constant on concentration and temperature was studied in this article, where the anomalous optical properties manifested by pure MBBA in the isotropic phase were also found to be present in the solutions.
Abstract: The molecular Kerr constant has been measured for undiluted N-(p-Methoxybenzylidene)-p-n-butylaniline (MBBA) in the isotropic phase and also for MBBA in solution in benzene and carbon tetrachloride. The dependence of the molecular Kerr constant on concentration and temperature was studied. The anomalous optical properties manifested by pure MBBA in the isotropic phase were also found to be present in the solutions. De Gennes' theory was obeyed for undiluted MBBA and for concentrated solutions of MBBA in carbon tetrachloride. The infinite dilution molecular Kerr constant for MBBA in solution in benzene or carbon tetrachloride was readily interpreted in terms of modest anisotropies in the polarisability of the individual molecules.
22 citations
TL;DR: Using tetracene crystals provided with hole injecting contacts (CuI(s) and Ce(SO4)2(aq)) the position of the virtual anode xm (potential maximum) within the crystal and have studied its voltage dependence as discussed by the authors.
Abstract: Using tetracene crystals provided with hole injecting contacts (CuI(s) and Ce(SO4)2(aq)) we have located the position of the virtual anode xm (potential maximum) within the crystal and have studied its voltage dependence. For this purpose, we used the triplet and singlet excitons as tracers, making particular use of the characteristic response of these excitons to an external magnetic field. The voltage dependence of xm follows that predicted by the simplified form of the exact theory of Sinharay and Meltzer. It appears that xm lies within the crystal for all voltages up to the saturation voltage. It is shown that a photoenhanced current will be produced not only by detrapping deep in the interior of the crystal, but by detrapping in the vicinity of the virtual anode xm.
22 citations
TL;DR: Many molecules and macromolecules present in the living systems are known to exhibit the mesomorphic or the so-called liquid crystalline state under appropriate conditions as mentioned in this paper, which is characterized by relative mobility when compared with true solids and by association and alignment in one crystallographic axis or in one plane.
Abstract: Many molecules and macromolecules present in the living systems are known to exhibit the mesomorphic or the so-called liquid crystalline state under appropriate conditions. This state is characterised by relative mobility when compared with true solids and by association and alignment in one crystallographic axis or in one plane when compared with true liquids. It may be brought about by the variation of temperature yielding thermotropic liquid crystals or by the variation of amount and properties of the solvent giving rise to the lyotropic ones. Of these the former mechanism is obviously unimportant for the living systems, particularly for the homeothermic organisms, since there are but few compounds which undergo liquid crystalline transitions at the body temperature within the range of probable local temperature fluctuations in the tissues and body surfaces. However, many molecular species of biological relevance, including some which form thermotropic mesophases, are capable of associating in...
TL;DR: The pitch of cholesteryl 2-(2-ethoxyethoxy) ethyl carbonate (CEEC) is measured as a function of temperature and is shown to increase with increasing temperature, unlike the behavior of other single component cholesteric liquid crystals as mentioned in this paper.
Abstract: The pitch of cholesteryl 2-(2-ethoxyethoxy) ethyl carbonate (CEEC) is measured as a function of temperature and is shown to increase with increasing temperature, unlike the behavior of other single component cholesteric liquid crystals. We find that improved sample purification shifts the pitch horizontally on the temperature axis, while sample aging causes an increased disorientation of the sample domains themselves.
TL;DR: In this paper, the diamagnetic susceptibilities of th enematic phase and of the ordered solid state obtained by freezing a nematic “monocrystal,” were derived by measuring the dielectric and refractive indices anisotropics and elastic coefficients.
Abstract: In this paper, we relate how we have determined the order parameter by measuring the diamagnetic susceptibilities of th enematic phase, and of the ordered solid state obtained by freezing a nematic “monocrystal.” Moreover, we have measured dielectric and refractive indices anisotropics, and elastic coefficients; and we have verified the theories giving the relations between the order parameter and all this physical macroscopic coefficients.
TL;DR: In this article, the infrared and Raman spectra of crystal n-butane are reported and the packing in the triclinic low temperature form III has been studied by using atom-atom potentials.
Abstract: The infrared and Raman spectra of crystal n-butane are reported. Evidence has been found that n-butane exist in three crystal forms having disordered (form I), monoclinic (form II) and triclinic (form III) structure. The packing in the triclinic low temperature form III has been studied by using atom-atom potentials. The structure obtained satisfactorily reproduces the Raman lattice frequencies.
TL;DR: The potential of these esters to produce low melting eutectic compositions with a wide nematic range on admixture with simpler 4,4′-disubstituted phenyl benzoates is assessed in relation to requirements for electrooptical displays such as the twisted nematic type.
Abstract: Thirteen 4′, 4″-disubstituted phenyl biphenyl-4-carboxylates have been prepared and their liquid crystal transition temperatures measured. In each case, one of the substituents is a cyano-group and the nematic phases are of positive dielectric anisotropy. The potential of these esters to produce low melting eutectic compositions with a wide nematic range on admixture with simpler 4,4′-disubstituted phenyl benzoates is assessed in relation to requirements for electro-optical displays such as the twisted nematic type.
TL;DR: The linear additive law for pitch dependence in binary mixtures of cholesterics (or combinations of ingredients producing cholesteric) is extended to include first order interactive effects and the resulting expression is shown to effectively treat an apparently widely diverse collection of experimental data.
Abstract: The linear additive law for pitch dependence in binary mixtures of cholesterics (or combinations of ingredients producing cholesterics) is extended to include first order interactive effects. The resulting expression is shown to effectively treat an apparently widely diverse collection of experimental data. The knowledge of the functional form of any given system is of value in predicting pitch sensitivity to heat, vapor, etc.
TL;DR: The far-infrared and Raman spectra of CBOOA (Np-cyanobenzilidene-p-n-octyloxyaniline) have been studied above 30 cm−1.
Abstract: The far-infrared and the Raman spectra of crystalline CBOOA (N-p-cyanobenzilidene-p-n-octyloxyaniline) have been studied above 30 cm−1. The temperature dependence of the farinfrared spectrum reveals the existence of a solid-solid transition at 65°C. The two solid modifications can be obtained, respectively, from solvent crystalization (Phase II) and solidification from the mesophase (Phase I). Differential scanning calorimetric results confirm that an endothermic change from Phase II to Phase I occurs at 65°C with an associated heat of transition of 2030 cal/mole. X-ray powder diffraction patterns establish that the structures of the two phases are different. Tentative vibrational assignments are made for the far-infrared and the Raman lines observed in the internal mode region. At frequencies below 120 cm−1, both the far-infrared and the Raman spectra of Phase II exhibit distinct modes whereas, Phase I exhibits nearly quasicontinuous spectra. The possible implications of this result for the stru...
TL;DR: In this article, a new interference method for the determination of refractive indices and briefringence as functions of wavelength is proposed, which uses a spectrophotometer and a specially constructed interferometer.
Abstract: A new interference method for the determination of refractive indices and briefringence as functions of wavelength is proposed. Application of a spectrophotometer and a specially constructed interferometer makes the measurements easier and enables the determination of refractive indices over a broad spectral region.
TL;DR: In this article, the Burgers vector of dislocations (i.e., those that glide on (001) planes) cannot be exclusively in either the [100] or [010] directions, and is very likely to be [110] and/or [120] directions.
Abstract: The preparation of thick, vapour-grown crystals of anthracene is described, and the characterization of basal dislocations in these crystals is discussed. It is demonstrated that the Burgers vector of dislocations (i.e. those that glide on (001) planes) cannot be exclusively in either the [100] or [010] directions, and is very likely to be [110] and/or [120]. There is some evidence for the occurrence also of a hitherto unknown slip system: (121) [210].
TL;DR: The existence of a metastable solid phase of p-azoxyanisole (PAA) influences the phase diagram of binary mixtures of PAA and PAP and the Schroder-van Laar equations describe the phase diagrams of both systems well using reasonable values of the solid nematic transition energies for the pure components as discussed by the authors.
Abstract: The existence of a metastable solid phase of p-azoxyanisole (PAA) influences the phase diagram of binary mixtures of PAA and p-azoxyphenetole (PAP). In addition to a stable binary system having a eutectic transformation to a nematic phase at 97°C for a PAA mole-fraction (XPAA) of 0.59, a metastable binary (eutectic point at 86°C for XPAA = 0.69) is also observed. The Schroder-van Laar equations describe the phase diagrams of both systems well using reasonable values of the solid-nematic transition energies for the pure components.
TL;DR: In this article, it was shown that the shape of the reflection spectrum is highly dependent on the polarization of the incident beam and the refractive index of a given liquid crystal for a given crystal.
Abstract: Reflection at the interface between glass and cholesteric liquid crystals in theoretically investigated for the case of normal incidence using Oseen-DeVries' model. Attention is focused on the case where the average index of refraction of the liquid crystal differs from the glass refractive index. It is then found that the general shape of the reflection spectrum is highly dependent on the polarization of the incident beam. Thus, for example, two incident waves which are linearly polarized in different directions will generally have their peak reflections at different wavelenghts. The shape of the spectrum also depends, for a given liquid crystal, on the refractive index of the glass.
TL;DR: The urethan (carbamate) linkage has been investigated as a central group in liquid crystal systems as mentioned in this paper, and cholesteryl N-para-substituted-phenyl carbamates exhibit cholesteric mesophases with mes...
Abstract: The urethan (carbamate) linkage (-NHCOO-) has been investigated as a central group in liquid crystal systems. Cholesteryl N-para-substituted-phenylcarbamates exhibit cholesteric mesophases with mes...
TL;DR: The state of ferrocenecarboxaldehyde between 43.5° and 123.5 degrees has been characterized as a non-birefringent, highly viscous phase having the following enthalpies and entropies of transition.
Abstract: The state of ferrocenecarboxaldehyde between 43.5° and 123.5° has been characterized as a non-birefringent, highly viscous phase having the following enthalpies and entropies of transition: 43.5°: 3.0 kcal/mole, 9.5 cal/deg.mole; 123.5°: 0.6 kcal/mole, 1.6 cal/deg.mole. Several p-substituted phenyl Schiff's bases of ferrocenecarboxaldehyde were synthesized and examined together with various other ferrocene derivatives. All exhibited normal crystal melting behavior.
TL;DR: In this article, the authors derived the structure factor Sm(Q) of the fully deuterated para-azoxyanisole (d 14-PAA) in both liquid and isotropic liquid phases.
Abstract: Neutron diffraction patterns of the fully deuterated para-azoxyanisole (d 14-PAA) were obtained in the liquid crystalline phase and the isotropic liquid phase. The momentum transfer range extends from 0.5 A−1 to 15 A−1. The structure factors Sm(Q) of d 14-PAA in both phases were deduced. Sm(Q) is separated into two terms of intramolecular and intermolecular contributions. The former term S intra(Q) is calculated on the assumption of a rigid molecule. The comparison of S inter(Q) in both the liquid crystalline state and the isotropic liquid state shows that the information near Q ∼ 6.0 A−1 ∼ 8.0 A−1 plays an important part in understanding the structure of the nematic liquid crystalline state of PAA.
TL;DR: In this paper, the Davydov splitting of the abosrption spectra of molecular crystal is considered from the standpoint of the law of conservation of the first spectrum moment.
Abstract: Davydov splitting of the abosrption spectra of molecular crystal is considered from the standpoint of the law of conservation of the first spectrum moment. Various models of states of crystal excitations are applied to the analysis of the law: Davydov one-particle model of rigid lattice, Rashba two-particle model of vibron states of rigid lattice, The model based on exciton-phonon and vibron-phonon interactions The analysis, based on exciton-phonon and vibron-phonon spectra of benzene crystals, naphthalene and anthracene crystals, shows that it is feasible to determine both values of parameters of exciton-phonon and vibron-phonon interactions and Davydov splittings in the exciton and vibron regions of spectrum.
TL;DR: A classification of all possible groups of rigid transformations, namely rotations, reffections, translations, screw axes and glide planes, is presented in this paper, which can be used to describe the symmetry of crystals, liquids, amorphous solids, powders, and liquid crystals.
Abstract: A classification of all the possible groups of rigid transformations, namely rotations, reffections, translations, screw axes and glide planes, is presented. These groups are the subgroups of the centrosymmetric Euclidean group. They may be used to describe the symmetry of crystals, liquids, amorphous solids, powders, and liquid crystals. They may also be used to describe the symmetry of systems of lower dimensionality, as surfaces, thin layers, etc.
TL;DR: In this paper, the internal and external zero-wave vector phonon frequencies have been calculated using interaction potential functions between non-bonded atoms, which can also be used to predict some internal properties of molecules.
Abstract: Calculations of some internal and external zero-wave vector phonon frequencies have been carried out using interaction potential functions between nonbonded atoms. It is shown that potential functions obtained from crystal data can also be used to predict some internal properties of molecules. Experimental data and calculated results are compared for Durene crystal.
TL;DR: In this article, the temperature dependence of the dielectrice of a dielectric constant, δ, and die-lectric loss, was studied in the case of metal acetylacetonate compounds.
Abstract: During the study of the temperature dependence of the dielectrice of the dielectric constant, δ, and dielectric loss, tan δ of some metal acetylacetonate compounds, anomalous behaviour in Na(acac) ...
TL;DR: In the polar host crystal benzophenone, the nonpolar guest naphthacene exhibits different dipole moments in its ground and first excited state, as measured by low-temperature Stark techniques as mentioned in this paper.
Abstract: In the polar host crystal benzophenone, the nonpolar guest naphthacene exhibits different dipole moments in its ground and first excited state. The dipole moment changes upon excitation for three guest sites are 1.2, 0.35, and 0.61D, as measured by low-temperature Stark techniques. The dipole moments are attributed to the polarizability of the guest in the electrostatic crystal field of the host, which is estimated to be ∼ 107 V/cm.
TL;DR: In this article, the p-alkoxyphenylazo-p'-phenyl esters have been prepared for methoxy, ethoxy, butoxy and methoxy-butoxy.
Abstract: The compounds methoxy, ethoxy, butoxy of three series of p-alkoxyphenylazo-p'-phenyl esters have been prepared: these are the acrylates, β chloropropionates and β bromopropionates. The transition temperatures were determined by microscopy.