Showing papers in "Molecular Crystals and Liquid Crystals in 1989"
TL;DR: In this article, a liquid crystal-liquid crystal transition was observed by transmitted polarized light microscopy, small angle x-ray scattering and wide angle X-ray diffraction, and the transformation between the structures was achieved by a change in molecular tilt and the extent to which the molecules are interdigitated within each layer.
Abstract: Perfluorodecyl decane, F(CF2)10(CH2)10H, is shown to undergo a liquid crystal-liquid crystal transition above room temperature. The accompanying reversible structural reorganization is observed by transmitted polarized light microscopy, small angle x-ray scattering and wide angle x-ray diffraction. Both liquid crystalline phases have a layered structure; within the layers the molecules are interdigitated, tilted relative to the layer normal, and packed in a pseudo-hexagonal fashion. The transformation between the structures is achieved by a change in molecular tilt, together with a change in the extent to which the molecules are interdigitated within each layer.
93 citations
TL;DR: In this article, a table of ionization energies for 120 compounds is presented, and the trends in I g, I s, and Δ for various compounds are discussed, and information from I g and I s is surveyed for the energetics of ionized states and the electronic structure of binary systems.
Abstract: Gas phase ionization energies I g, for compounds of interest from electrical and electronic viewpoints can be determined using photoemission techniques. Also reasonably good estimation can be obtained from oxidation potential and energy of charge-transfer absorption in solution. Photoemission techniques are also used for determining ionization energies of molecular solids I s These methods are reviewed, and a table of ionization energies for 120 compounds are given. The difference Δ between I g and I s can be ascribed to the polarization of surrounding molecules and, in some cases, intermolecular band formation. The trends in I g, I s, and Δ for various compounds are discussed. Finally, information from I g and I s is surveyed for the energetics of ionized states and the electronic structure of binary systems.
77 citations
TL;DR: Optically responsive films comprising birefringent nematic and chiral nematic liquid crystal microdroplets dispersed in electron beam cured polymeric reaction products are disclosed in this article.
Abstract: Optically responsive films comprising birefringent nematic and/or birefringent chiral nematic liquid crystal microdroplets dispersed in electron beam cured polymeric reaction products are disclosed.
77 citations
TL;DR: A brief history and review of all-aromatic liquid crystalline polyesters is given in this paper, with the classification based on the following monomers: 4,4′-biphenol; asymmetrically substituted monomers; 2,6-oriented naphthalene monomer; 3,4''-oriented benzophenone and di...
Abstract: This brief history and review of liquid crystalline polyesters (LCPs) is limited to all-aromatic LCPs except for a description of the discovery of the first thermotropic polymer to be injection molded or melt spun and characterized as being liquid crystalline: an Eastman PET/PHB (p-hydroxybenzoic acid) copolyester (first reported as being liquid crystalline in 1974). In the same year a Carborundum terephthalic acid/4,4′-biphenol/PHB all-aromatic copolyester was reported to be injection moldable, and later this polymer was shown to be liquid crystalline. In 1975 various Du Pont LCPs prepared with substituted hydroquinones were disclosed, and in early 1978 the first Celanese LCPs based on 2,6-oriented naphthalene monomers were disclosed. The development and characterization of all-aromatic LCPs up to 1987 are described, with the LCP classification based on the following monomers: 4,4′-biphenol; asymmetrically substituted monomers; 2,6-oriented naphthalene monomers; 3,4′-oriented benzophenone and di...
67 citations
64 citations
TL;DR: In this article, a series of 4-cyanophenyl 4-X-benzoates (X =pentyl, butoxy) has been prepared without fluoro-substitution and with monofluoro to tetra-fluoro substitution; all possible combinations of substitution patterns at the positions ortho-to the cyano group and ortho -to the carboxylate group have been obtained in an attempt to determine the structural features which are responsible for some members of these series showing very large positive values of dielectric anisotropy.
Abstract: A series of 4-cyanophenyl 4-X-benzoates and a series of 4-cyanobiphenyl-4′-yl 4-X-benzoates (X =pentyl, butoxy) have been prepared without fluoro-substitution and with mono-fluoro to tetra-fluoro-substitution; all possible combinations of substitution patterns at the positions ortho- to the cyano group and ortho- to the carboxylate group have been obtained in an attempt to determine the structural features which are responsible for some members of these series showing very large positive values of dielectric anisotropy. The synthesis of novel precursors required for the preparation of these esters is described and the melting points and transition temperatures of the esters are discussed and an explanation is provided for the variation of TN -1 values with position and extent of fluoro-substitution.
63 citations
TL;DR: The electron affinity of a molecule is the definitive measure of its ability to act as an electron acceptor as discussed by the authors, and experimental methods for the determination of this quantity have been developed.
Abstract: The electron affinity of a molecule is the definitive measure of its ability to act as an electron acceptor. During the past twenty years, experimental methods for the determination of this quantity have been developed. While the magnetron procedure and the electron capture detector method were introduced in the 1960s, only recently have confirmatory gas phase measurements been made. In this review, the experimental procedures and their limitations will be summarized, the available experimental results (about 200 values) will be critically evaluated, and the gas phase measurements will be compared with half wave reduction potentials. A method for estimating electron affinities from substituent effects will be presented.
61 citations
TL;DR: In this paper, the synthesis of some liquid crystal polymers containing various degrees of cross linking units is described, and the properties over and above those observed either from low molecular weight liquid crystals, or from conventional rubbers.
Abstract: The synthesis is described of some liquid crystal polymers containing various degrees of cross linking units. Such materials show properties over and above those observed either from low molecular weight liquid crystals, or from conventional rubbers. Thus, though these compounds show simple rubber like elasticity in the isotropic phase, on cooling to the liquid crystal region, more complex behavior is observed, an example being the high levels of orientation produced at relatively low strain. Such materials also show unusual properties in that, when swollen with a low molecular weight liquid crystal, they undergo macroscopic shape changes in the presence of applied electric fields, in addition to the more usual electro-optic effects.
56 citations
TL;DR: In this paper, a survey of the structural and electronic properties of organic charge transfer (CT) crystals studied by optical spectroscopy methods is presented in the form of a short review.
Abstract: The aim of the present paper is limited to a survey of part of the prolonged research activity of the Padova group in Italy on the structural and electronic properties of organic charge transfer (CT) crystals studied by optical spectroscopy methods The presentation is given in the form of a short review, without attempting to comprehensively cover all the relevant literature Attention is focused here on semiconducting CT crystals, but it is worthwhile stressing that optical studies of CT organic conductors and superconductors share many of the concepts, experimental methods and theoretical models discussed here
51 citations
TL;DR: In this article, the series of thiophene oligomers from bithienyl to α-sexitienyl has been synthesized according to the methods reported in the literature and some variation introduced by us.
Abstract: The series of thiophene oligomers from bithienyl to α-sexithienyl has been synthesized according to the methods reported in the literature and some variation introduced by us. UV-visible, FT-IR, 13C-nmr and mass spectra of thiophene oligomers have been recorded and also cyclic voltammograms. Results are compared with data available in literature and are discussed in terms of conjugation length and coplanarity.
49 citations
IBM1
TL;DR: In this paper, the authors review the background to the commercial development of the aromatic polyesters of p-hydroxybenzoic acid and then describe some of their recent work on elucidating their structure-property relationships, the effect of the synthetic route, and the role of processing in optimizing properties.
Abstract: In this paper I would like to first review the background to the commercial development of the aromatic polyesters of p-hydroxybenzoic acid and then describe some of our recent work on 1) elucidating their structure-property relationships, 2) the effect of the synthetic route, and 3) the role of processing in optimizing properties
TL;DR: In this article, the number of semicarbazones of 4(4′-n-alkoxybenzoyloxy) benzaldehydes is synthesized and they are cyclized to respective amino-oxadiazoles.
Abstract: Number of semicarbazones of 4(4′-n-alkoxybenzoyloxy) benzaldehydes are synthesized. They are cy-clized to respective amino-oxadiazoles. Both the series of compounds exhibit mesomorphism. However, the decomposition is a major problem for semicarbazones. Compounds of both the series are characterized by elemental analysis, UV, IR spectra and NMR spectra.
TL;DR: In this paper, a brief overview is given on literature dealing with purification, purity assessment, and crystal growth methods which are applicable to organic photoconductors and semiconductors under the aspect of the required high purity.
Abstract: First, a brief overview is given on literature dealing with purification, purity assessment, and crystal growth methods which are applicable to organic photoconductors and semiconductors under the aspect of the required high purity. Then some recent examples are presented of purification, material handling and crystal growth of some selected compounds (perylene, naphthalene, phenanthrene, TTF:chloranil and bipyridylammonium: (TCNQ)2). Progress is reflected in greatly improved electrical properties of these materials which allowed detection of entirely new features, such as enhanced charge carrier scattering at phase transitions and non-Ohmic transport. Finally, some advanced crystal growth techniques are presented: Czochralski growth of organic molecular crystals under high purity conditions, flux growth of donor:acceptor crystals from a melt solution in one of the two components, oriented epitaxial growth “organic on organic” and epitaxial growth of organic materials on inorganic substrates.
TL;DR: In this paper, the phase behavior and electro-optic phenomena observed in a new system of blue phase mixtures have been determined, which include both cyanobiphenyl and chiral ester components, have relatively high pitch values (∼0.3 μm) but nonetheless exhibit broad blue phase temperature ranges ( ∼2.5°C total).
Abstract: The phase behavior and electro-optic phenomena observed in a new system of blue phase mixtures have been determined. The mixtures, which include both cyanobiphenyl and chiral ester components, have relatively high pitch values (∼0.3 μm) but nonetheless exhibit broad blue phase temperature ranges (∼2.5°C total). On application of electric fields to samples of these materials, colour switches and phase transitions to both turbulent chiral nematic and homeotropic nematic states were induced in both BPI and BPII. Both of these electric field induced phenomena are described as functions of the applied voltage and frequency. The response times of these field effects were also determined with high accuracy and found in the case of the field transitions to be extremely fast (∼100 μs). The mechanism associated with the field induced colour switch was found to have two distinct response times associated with it, one fast (∼100 μs) and the second much slower (∼1–10 μs). Finally, the relaxation phenomena obs...
TL;DR: In this paper, the authors describe the reasoning underlying the design and synthesis of a range of cyanohydrin esters, specifically as high Ps dopants of host SC materials, for use in fast switching ferroelectric displays.
Abstract: This paper describes the reasoning underlying the design and synthesis of a range of cyanohydrin esters, specifically as high Ps dopants of host SC materials, for use in fast switching ferroelectric displays. Full synthetic details are given for the preparation of optically pure cyanohydrin esters from naturally occurring L-amino-acids; examples derived from (a) a D-amino-acid, (b) lactic acid are also given. Such materials provide excellent dopants which in suitable SC hosts provide mixtures with wide S*C ranges, good Ps values and long pitches, which switch rapidly at room temperature and may be multiplexed at video frame rates.
TL;DR: In this paper, the collective Cotton-Mouton (CM) technique was used to study phase transitions of aqueous suspensions of droplets of smectogens using two compounds: NPOOB and 8OCB.
Abstract: Phase transitions of aqueous suspensions of droplets of smectogens have been studied using the collective Cotton-Mouton (CM) technique. Two compounds were examined: NPOOB and 8OCB. A statistical model (previously developed for suspensions of nematogens) has been adapted to describe the collective CM effect in these systems. It was found that both the phase transitions and the changes of architecture within the droplets cause distinct changes in the CM effect. An attempt was made to investigate suspensions of theliquid crystalline germs created in the isotropic melts of nematic and smectic mesogens mixed with a chiral additive. In such mixtures, nematoids (the liquid crystal analogues of the whiskers of crystalline solids) are formed. It is usually found that nematoids arise as an extension of the tail of a monopole droplet or grow from a focal conic multipole droplet but “free” nematoids (without droplets at their ends) can also occur. The aspect ratio of nematoids varies with the composition, ra...
TL;DR: In this article, the synthesis, characterization and thermal behavior of several new series of copper (II) complexes derived from Schiffs bases are reported, and the complexes are of the type: [Cu{C6H3O(OR)
Abstract: The synthesis, characterization and thermal behavior of several new series of Copper (II) complexes derived from Schiffs bases are reported. The complexes are of the type: [Cu{C6H3O(OR)‒C(Z)=N‒R′}2] (R=n‒C n H2n+1+, R′=p-n-alkoxy-(C6H4)‒, p-n-alkyl‒(C6H4)‒, n-alkyl; Z˭H, CH3). Sehiffs base complexes of Copper (II) derived from an aldehyde show thermotropic mesophases (smectic discotic polymorphism), whereas complexes derived from a ketone do not. When the amine forming the imine ligand is an aromatic amine the complexes form liquid crystals, whereas if the amine is aliphatic the complexes do not give liquid crystals.
TL;DR: Viscosity coefficients analogous to the Miesowiez viscosities and to the Leslie coefficients were determined for an oriented nematic discotic liquid crystal in molecular dynamics computer simulations and compared with theoretical calculations as discussed by the authors.
Abstract: Viscosity coefficients analogous to the Miesowiez viscosities η1, η2, η3 and to the Leslie coefficients γ1 and γ2 are determined for an oriented nematic discotic liquid crystal in molecular dynamics computer simulations and compared with theoretical calculations.
TL;DR: In this article, a phenomenological elastic free energy concerned with layer distortion, c−director deformation, and their coupling is proposed to discuss the layer structure of the chevron.
Abstract: In this work, a simple explanation is given for the chevron layer structure which has been observed in SmC* phase. A phenomenological elastic free energy concerned with layer distortion, c−director deformation, and their coupling is proposed to discuss the layer structure of them. It will be shown that there exists a soliton solution corresponding to the chevron structure. The transition layer thickness of the chevron is theoretically estimated as the penetration length (∼molecular length)/molecular tilt angle. In similar to the kinked layer structure, the c-director rotation angle is also found to show a soliton-like behaviour within the transition region. In addition, the existence of the selective pre-tilt at the bounding surface is explained in the relation with the chevron structure.
TL;DR: The mesomorphic properties of a series of bis-(4-alkyl- or 4-alkoxy-benzoyloxy)-trans-1,4-dioxanes 1, trans- 1, 4-dithianes 2 and trans-1-4-cyclohexanes 3 are reported and compared to the corresponding hydroquinone bis-esters 4 as mentioned in this paper.
Abstract: The preparation and mesomorphic properties of a series of bis-(4-alkyl- or 4-alkoxy-benzoyloxy)-trans-1,4-dioxanes 1, trans-1,4-dithianes 2 and trans-1,4-cyclohexanes 3 are reported and compared to the corresponding hydroquinone bis-esters 4. The 1,4-dithianes 2 do not show liquid crystalline properties and the 1,4-dioxanes 1 in their trans diaxial conformation are less favorable for nematic phases than the corresponding cyclohexanes 3 which are predominantly in the diequatorial conformation. However, owing to the cross-dipole moments they seem to be of advantage in stabilizing smectic phases.
TL;DR: In this article, it was shown that the triplet centers at the m,p′- and m,m′-positions interact ferro-and antiferromagnetically.
Abstract: Some polymer radicals have been proposed as potential organic magnetic materials. In order to determine where to place the doublet or triplet centers on the side chains of a conjugated polymer chain, we have studied model dimers, i.e., isomeric bis(nitrenophenyl)acetylenes and diacetylenes. They were generated by photolyses of the corresponding diazides in MTHF at 10 K in an ESR cavity. The m,p′-dinitrenes showed strong fine-structure signals characteristic of quintet states that obeyed Curie law in the range 12–85 K. The m,m′-dinitrenes showed fine-structure signals due to quintet states that had the maximum intensities at 50 and 28 K for the mono- and diacetylenes, respectively. It is concluded that the two triplet centers at the m,p′- and m,m′-positions interact, respectively, ferro- and antiferromagnetically. Efforts directed to the construction of ferromagnetic poly(acetylenes) are briefly discussed.
TL;DR: In this paper, the authors investigated the control of the dynamical motion of protons by using the excess a-electron effect on the hydrogen bonding in the CT-interaction system, which provided useful information in the design of a new molecular function using the H-bonded CT complexes.
Abstract: Our recent study of the proton transfer in the double-well potential of the H-bonded charge-transfer (CT) crystals is introduced together with several other related topics. Special attention is focused on our investigation into the control of the dynamical motion of protons by using the excess a-electron effect on the hydrogen bonding in the CT-interaction system, which provides useful information in the design of a new molecular function using the H-bonded CT complexes. In this process, optical transitions enhanced by the dynamical motion of protons has been identified as the proton-linked super-CT transitions.
TL;DR: In this article, a new method of evaluating the optical properties of stratified uniaxial media is proposed, within Berreman's 4 × 4 matrix formalism, the exact propagator of a homogeneous layer is used instead of the Taylor series expansion.
Abstract: A new method of evaluating the optical properties of stratified uniaxial media is proposed. Within Berreman's 4 × 4 matrix formalism, the exact propagator of a homogeneous layer is used instead of the Taylor series expansion. The calculation of the transmission and reflection matrices for a given propagator is performed. Examples are given to demonstrate the usefulness of the proposed method.
TL;DR: In this paper, the order parameters S xx, S yy and S zz of heptyl-cyanophenyl-cyclohexan (PCH7) were determined independently by analyzing three different benzene ring skeleton vibrations.
Abstract: The order parameter S zz and the molecular biaxiality parameter D = S xx - S yy have been evaluated for various nematic liquid crystal materials employing infrared dichroism measurements. The influence of the terminal group, the ring systems and an ester linkage group on S zz and D has been studied for various terminally polar and terminally non-polar liquid crystal materials. Our experimental results for the cyanobiphenyl CB5 are in agreement with NMR-studies, if we allow for a small local field correction which is nearly within our experimental measuring accuracy. For the first time, the order parameters S xx, S yy and S zz of heptyl-cyanophenyl-cyclohexan (PCH7) are determined independently by analyzing 3 different benzene ring skeleton vibrations. The existence of a weakly pronounced molecular biaxiality is demonstrated for most of the liquid crystal materials investigated. Moreover the variation of D as a function of S zz is found to be approximately of the form predicted by the molecular fi...
TL;DR: In this article, a strong boundary distortion of the director field near the boundary surface of nematics is evidenced and theoretically discussed in terms of elastic constants, and the sources of the distortion are the diffuse nature of the surface tension, the spontaneous splay, which is different from zero in a boundary layer of thickness comparable with the range of molecular interactions and the surface-like free energy term k 13 div([ncirc] div [ncirc]).
Abstract: A strong boundary distortion of the director field [ncirc](R) near the boundary surface of nematics is evidenced and theoretically discussed in terms of elastic constants. The sources of the distortion are the diffuse nature of the surface tension, the spontaneous splay, which is different from zero in a boundary layer of thickness comparable with the range of molecular interactions, and the surface-like free energy term k 13 div([ncirc] div [ncirc]). In the distorted layer a drastic change of [ncirc](R) with respect to the surface normal [kcirc] occurs. As a consequence, the surface alignment may appear homeotropic from a macroscopic point of view, even in the case where the short range nematic-substrate interactions give an obliquely oriented surface layer, as suggested by recent experiments of P. Guyot-Sionnest, H. Hsiung and Y. R. Shen.
TL;DR: In this paper, X-ray, miscibility and calorimetric studies of four homologous 2-(trans-4-n-alkylcyclohexyl)-propan-1,3-diols are reported.
Abstract: X-ray, miscibility and calorimetric studies of four homologous 2-(trans-4-n-alkylcyclohexyl)-propan-1,3-diols are reported. The specific intermolecular interactions lead to novel variants of smectic structures of types A and B, designated with A+ and B+. They are explained by a bi-molecular layer with intercalated alkyl chains. The hydrogen bonded molecular arrangement causes a well defined layer periodicity even in the A+ phases. Both phases A+ and B+ do not show a complete miscibility with conventional liquid crystals.
TL;DR: In this article, Goldmann and Kalandyk separated photoconduction from photoelectric emission, observing it in anthracene under U.V. irradiation, and also deduced the formula linking specific conductivity a with absolute temperature T, [sgrave] = [ sgrave]0,exp(-Eact/kT).
Abstract: The earliest studies concerned photoelectric emission of negative charges from dyestuff solutions,1,2 and anthracene layers.3 The negative charges were identified as electrons,4 then in 1911 Goldmann and Kalandyk5 separated photoconduction from photoelectric emission, observing it in anthracene under U.V. irradiation, while Pauli6 and Volmer7 studied photoconduction in anthracene in the visible. Petrikaln8 discussed gas effects on visible light photoconduction in dyestuffs, Koenigsberg and Schilling9 studied dark conduction in anthracene, naphthalene and alizarine and also deduced the formula linking specific conductivity a with absolute temperature T, [sgrave] = [sgrave]0,exp(-Eact/kT). Further dark conduction studies were carried out by Rabinowitsch.
TL;DR: In this article, a number of homologous series of three-ring esters containing a 5-membered heteroaromatic ring were synthesized in order to establish how a change in the position of the heterocyclic ring influences liquid crystal behavior when compared with corresponding all-benzenoid esters.
Abstract: Ninety compounds, over seventy of which are members of a number of homologous series of three-ring esters containing a 5-membered heteroaromatic ring, have been synthesized in order to establishhow a change in the position of the heterocyclic ring influences liquid crystal behavior when comparedwith corresponding all-benzenoid esters The liquid crystal properties of these esters, which showconsiderable variation, are discussed One group of compounds shows unusual phase behavior, involvingan unidentified (smectic?) phase and photomicrographs of optical textures of this phase are included
TL;DR: In this article, the lithium phthalocyanine π-radical compound is interpreted as resulting from two distinct spin species, one being delocalized and its behaviour may be interpreted in the frame of itinerant magnetism.
Abstract: The lithium phthalocyanine π-radical compound is a molecular semiconductor which exhibits exceptional magnetic properties. These latter are interpreted as resulting from two distinct spin species. One species is delocalized and its behaviour may be interpreted in the frame of itinerant magnetism. It is responsible of an extremely narrow ESR line. The other species is due to localization of the PcLi spins interacting with molecular oxygen. At low temperature this magnetic coupling is shown to stabilize a septet spin state which involves indirect ferromagnetic coupling between neighbouring π-spins. The experimental results obtained up to now on this unexpected spin state are presented and discussed.