Showing papers in "Molecular Crystals and Liquid Crystals in 1990"
TL;DR: In this article, the laser-induced reorientation was studied in absorbing nematic films and the optical Freedericksz threshold occured at an intensity level of 50 W/cm2 in contrast to the normally observed few KW/cm 2 value for transparent layers.
Abstract: Laser-induced reorientation was studied in absorbing nematic films. The optical Freedericksz threshold occured at an intensity level of 50 W/cm2 in contrast to the normally observed few KW/cm2 value for transparent layers. Thermomechanical coupling is considered as a possible explanation of the observed anomaly.
172 citations
TL;DR: Sulfonic acid ring-substituted polyaniline has been synthesized and characterized by elemental analysis, FTIR, UV-vis and electron spin resonance spectroscopy.
Abstract: Sulfonic acid ring-substituted polyaniline has been synthesized and characterized by elemental analysis, FTIR, UV-vis and electron spin resonance spectroscopy. Approximately 50% of the total number of phenyl rings in the polymer are mono-substituted by -SO− 3 groups. Without external doping, the ring-sulfonated polyaniline has a conductivity of ∼0.03 S/cm; it is therefore a “self-doped” conducting polymer. The water soluble sodium salt of the ring-sulfonated polyaniline is an insulator and can be reversibly converted back to the self-doped conducting form by treatment with aqueous acid.
111 citations
TL;DR: The nonresonant quadratic molecular hyperpolarizabilities of several classes of Organometallic aromatic compounds were studied with DC electric-field-induced second-harmonic generation (EFISH) experiments using fundamental radiation at 1.91 μm as mentioned in this paper.
Abstract: The nonresonant quadratic molecular hyperpolarizabilities of several classes of Organometallic aromatic compounds were studied with DC electric-field-induced second-harmonic generation (EFISH) experiments using fundamental radiation at 1.91 μm. Our goal is to survey and assess various strategies by which electron densities from metal centers can be exploited for quadratic nonlinear optics. Relying on optimized experimental techniques, systematic studies on structure-property relations concerning metal centers, bonding patterns, conjugations, and effects of ligands were conducted. Results on some arene metal carbonyl π-complexes, metal carbonyl pyridine derivatives, square-planar metal aromatics, and metallocene derivatives are included.
79 citations
TL;DR: In this paper, the cyclotetramerisation product of 4,5-bis(alkoxy)-phthalonitriles in lithium pentanolate with iron(II) acetate was treated with bidentate bridging ligands (e.g. pyrazine, 1,4-diisocyanobenzene) to obtain bridged complexes 8a and 9a.
Abstract: (μ-Oxo)bis[octakis(alkoxy)phthalocyaninatoiron (III)] 6a-c are obtained by treatment of the cyclotetramerisation product of 4,5-bis(alkoxy)-phthalonitriles in lithium pentanolate with iron(II) acetate. Compounds 6a-c are reduced to bisaxially coordinated octaalkoxyphthalocyaninatoiron(II) in the presence of ligands such as pyridine and t-butylisocyanide. Reaction of 6a with bidentate bridging ligands (e.g. pyrazine, 1,4-diisocyanobenzene) yields the bridged complexes 8a and 9a. The Mosbauer spectroscopic data are described and compared with the analogous unsubstituted phthalocyaninatoiron derivatives.
74 citations
TL;DR: In this article, the effects of THG interference between a film sample and substrate, and of the THG in air, were evaluated for several types of monomeric and polymeric materials.
Abstract: Third-order optical nonlinearities have been evaluated for organic materials in powder, solution, and film forms, by third-harmonic generation (THG) measurement. Considerations of the effects of THG interference between film sample and substrate, and of the effect of THG in air, are made for an accurate x(3) evaluation. Several types of monomeric and polymeric materials are examined by this method.
74 citations
TL;DR: In this paper, a novel method of inducing conductivity in polyaniline photochemically or by electron-beam exposure was described, which is accomplished with the use of onium salts which are a class of materials that decompose upon irradiation generating protonic acids.
Abstract: In this paper we describe a novel method of inducing conductivity in polyaniline photochemically or by electron-beam exposure. This is accomplished with the use of onium salts which are a class of materials that decompose upon irradiation generating protonic acids. We find that the onium salt may be blended with the polyaniline and upon irradiation, the generated acid acts as an in situ dopant for the polymer. Conductivity on the order of ⋍0.1 S/cm has been attained. This system has significant applications in lithography since it allows patterns of conducting lines to be generated. The polyaniline/onium system represents the first electrically conducting photo and electron-beam resist. In addition, we find that this radiation induced doping technique is applicable to polythiophene systems as well.
70 citations
TL;DR: In this article, the effect of reversible shift of selective reflectivity band in induced cholesteric LC under the laser irradaition was investigated and the effect was shown to be reversible.
Abstract: The effect of reversible shift of selective reflectivity band in induced cholesteric LC under the laser irradaition is observed.
61 citations
TL;DR: In this article, a simulation of photoelectric conversion in the photosynthetic reaction center by monomolecular layer assemblies of a folded or a linear type A-S-D triad carried out in a laboratory is reviewed.
Abstract: Simulation of photoelectric conversion in the photosynthetic reaction center by monomolecular layer assemblies of a folded or a linear type A-S-D triad carried out in this laboratory is reviewed. The oriented triad molecule acts as a charge separation unit and is named a molecular photodiode. The combined system with the linear triad and an antenna pigment is also discussed in terms of the charge separation and the light harvesting.
57 citations
TL;DR: In this article, a modified chemical polymerization of aniline in the presence of a tailor-made polymeric surfactant is used as a steric stabilizer, resulting in the formation of sterically-stabilized polyaniline particles which have a non-spherical "rice-grain" morphology.
Abstract: Colloidal polyaniline has been prepared in acidic aqueous media by a modified chemical polymerization of aniline in the presence of a tailor-made polymeric surfactant. The surfactant which acts as a steric stabilizer used in this study is derivatized poly(vinyl alcohol-co-vinyl acetate). This surfactant contains pendant aniline units which participate in the aniline polymerization, resulting in the formation of sterically-stabilized polyaniline particles which have a non-spherical “rice-grain” morphology. It is shown that this novel form of polyaniline is more processable than the bulk powder that is normally obtained from a conventional chemical synthesis. The solid-state conductivity of solution-cast films or compressed pellets of these dispersions is surprisingly high (≃1 S/cm), despite the presence of the insulating outer layer of chemically-grafted stabilizer. We have characterized these polyaniline colloids by a wide range of techniques including electron microscopy, cyclic voltammetry and ...
52 citations
TL;DR: The development of all-solid-state rechargeable batteries has been a hot topic in the last few decades as discussed by the authors, due to their inherent advantages of negligible self-discharge, long cycle life, high reliability, and virtual absence of container corrosion.
Abstract: The dramatic proliferation of products based on semiconductor technology is a strong testament to the predictability and reliability of solid-state technology. In a similar vein, advances in materials exhibiting high levels of ionic conduction in the solid state has led to worldwide efforts in the development of all-solid-state rechargeable batteries. Although higher current densities are achievable with liquid electrolytes, all-solid-state cells offer inherent advantages of negligible self-discharge, long cycle life, high reliability, and virtual absence of container corrosion. Elegant work on polycrystalline and vitreous electrolytes has led to solid electrolytes with suitable ionic conductivities for battery development,1,2,3 however, the superior mechanical properties of elastomeric electrolytes combined with the simplicity of fabrication of thin separator films from these materials, has led to very active pursuit of solid-state cells based on solid polymeric electrolytes (SPE's). Although so...
52 citations
TL;DR: In this paper, the drift mobilities, their electric field dependence and the activation energies are investigated in films of solid solutions of N,N′-diphenyl-N,N€-bis(3-methylphenyl)-[1,1′-biphenYL]-4,4′-Diamine (TPD) and a structural variant of TPD in bisphenol A polycarbonate, polystyrene and phenoxy.
Abstract: Hole transport has been investigated in films of solid solutions of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and a structural variant of TPD in bisphenol A polycarbonate, polystyrene and phenoxy. Rather than being ‘inert’ as previously assumed, the binder plays a major role in influencing the rate of charge exchange between molecules. It is found that the absolute values of the drift mobilities, their electric field dependence and the activation energies are strong functions of the binder polymer employed to cast the film. At equivalent molecular concentrations but with two different binder polymers, the mobilities can vary by as much as two orders of magnitude. In some instances mobility decreases as the electric field is increased. The role that binder plays is related to the dispersibility of the diamine molecules in the polymeric binders. It is concluded that the the best molecular dispersion is observed when polystyrene is employed.
TL;DR: In this paper, the formation process and phase behavior of a polyurethane-based polymer-dispersed liquid crystal system were investigated using calorimetry and scanning electron microscopy.
Abstract: Using calorimetry and scanning electron microscopy, we have investigated the formation process and phase behavior of a polyurethane-based polymer-dispersed liquid crystal system. We have measured the kinetics and energetics of the cure process during which liquid crystal microdroplets form by phase separation from the matrix as it cross-links. The greatest degree of cure occurs for sample cured at 375 K. For a given cure temperature, the heat of cure decreases more or less linerly with increasing liquid crystal concentration due to a dilution effect. The time constant for the cure process decreases rapidly with increasing temperature but is much less sensitive to liquid crystal content. Samples cured below 375 K are apparently not fully phase separated, but subsequent treatment at higher temperatures evidently increases the degree of cure. The highest nematic-isotropic transition temperatures were achieved for liquid crystal concentrations above 40 volume percent. The nematic-isotropic transition enthalpy, △H NI , is a measure of the amount of liquid crystal contained in the microdroplets. A model has been developed which explains the linear increase of △H NI with increasing liquid crystal concentration. Optimum microdroplet formation occurs at 375 K, but only for liquid crystal concentrations below about 53 volume percent. At higher concentrations a reversed phase ( polymer ball ) morphology is seen. For the lower concentration droplet size increases linearly with LC content. Droplet number density decreases with increasing droplet size in rough agreement with a simple model
TL;DR: In this article, 17 azobenzene derivatives were synthesized and their thermotropic properties were examined, and they were classified into three groups: 4-cyanobiphenyl moieties are attached t...
Abstract: Seventeen azobenzene derivatives were synthesized and their thermotropic properties were examined. They are classified into three groups. In the first group, 4-cyanobiphenyl moieties are attached t...
TL;DR: In this paper, the outstanding feature of liquid crystalline isothiocyanates is the possibility to make mixtures with a wide range of nematic phase low viscosity and weak temperature dependence of viscosities.
Abstract: Results referring to liquid crystalline isothiocyanates especially as components of liquid crystal mixture were summarized. The outstanding feature of liquid crystalline isothiocyanates is the possibility to make mixtures with a wide range of nematic phase low viscosity and weak temperature dependence of viscosity. The compounds exhibit good chemical stability; they are especially resistant to humidity and UV radiation. Their thermal stability is not extremely high but this disadvantage is overcome by a suitable selection of the mixture components.
TL;DR: In this article, the effects of various substituents including chromophores on the second harmonic generation (SHG) of Cyanovinylheteroaromatics were examined and the molecular polarizability was calculated by the PPP MO method to correlate SHG responsiveness with chemical structures.
Abstract: Effects of various substituents including chromophores on the second harmonic generation (SHG) of Cyanovinylheteroaromatics were examined. The molecular polarizability was calculated by the PPP MO method to correlate SHG responsiveness with chemical structures. 3-[(2-cyano-2-ethoxycarbonyl)ethenyl]indole 8b exhibited good SHG efficiency (PE = 25 U). The X-ray analysis of 8b showed that the crystals belong to novel and the most favorable P1 space group.
IBM1
TL;DR: In this paper, a novel process using polyaniline for plating through hole technology has been developed, which eliminates the necessity for expensive precious metal seeds and toxic electroless copper baths.
Abstract: A novel process using polyaniline for plating through hole technology has been developed. Polyaniline was dip-coated onto printed circuit boards and in turn acted as a thin conducting electrode for the electrolytic metallization of Cu on the through holes. This eliminates the necessity for expensive precious metal seeds and toxic electroless copper baths. This process offers simplification, cost reduction, and performance enhancement over current methods used in the industry. Spontaneous deposition of noble metals, e.g. Pd, Ag, occurred on polyaniline coated epoxy substrate by simply immersing the substrate in an aqueous solution containing the corresponding metal salt, e.g., CH3-C6H4-SO3Ag, PdCl2. The thin metallic layer so plated was then used as an electrode for subsequent electroplating of Cu.
TL;DR: In this paper, the first BEDO-TTF-mXn charge transfer salt was characterized and a 2:1 stochasticity was obtained for the AuBr2− salt.
Abstract: Charge transfer salts of bis(ethylenedioxy)tetrathiafulvalene, BEDO-TTF, namely (BEDO-TTF)2AuBr2, and charge transfer salts (BEDO-TTF)mXn where X− is I3, AuI2 −, Au(CN)2−, ClO4 −, BrO4 −, BF4 −, PF6 −, AsF6 −, NO3 −, C(CN)3 −, and HgBr3− have been synthesized. The AuBr2− salt is the first BEDO-TTF salt to be structurally characterized. Crystallographic investigations of several of the other (BEDO-TTF)mXn salts have shown that (with the exception of the I3− salt) these new synmetals are structurally very similar to (BEDO- TTF)2AuBr2. Therefore, a 2:1 stoichometry is expected for BEDO-TTF salts. The observation of similar ESR linewidths for all the BEDO-TTF salts reinforces this conclusion. While (BEDO-TTF)2PF6 is semiconducting and the AuBr2−, Au(CN)2−, and ClO4− salts are metallic only near room temperature and semiconducting at low temperatures, (BEDO-TTF)2AuI2 shows metallic conductivity to low temperatures. RF penetration depth measurements on crystals derived from BEDO-TTF/KSCN/CuSCN show the...
TL;DR: In order to obtain polydiacetylenes having π-conjugation between polymer backbone and side chains, many of unsymmetrical diphenylbutadiyne derivatives with trifluoromethyl substituents on one of the phenyl rings have been synthesized as mentioned in this paper.
Abstract: In order to obtain the polydiacetylenes having π-conjugation between polymer backbone and side chains, many of unsymmetrical diphenylbutadiyne derivatives with trifluoromethyl substituents on one of the phenyl rings have been synthesized. Among them, 1-(3-(methylamino) phenyl)-4-(3, 5-bis (trifluoromethyl)-phenyl) butadiyne (MADF) was found to be topochemically polymerized with complete conversion into the polymer single crystals. Spectroscopies and X-ray crystal structure analysis revealed that the π-conjugation of this polymer are more extended than those of the so-far prepared poly(diphenylbutadiyne)s, with smaller dihedral angles between π-conjugation planes of polymer backbone and phenyl rings. The extended π-conjugation was also confirmed by larger X(3) values.
TL;DR: In this paper, a comparative study of the chromoionophoric and fluoroion-ophoric behavior of 1 and 2, which both consist of an aza-crownether-ionophore integrated with a twisted 9-aryl-acridinium chromophore, is presented.
Abstract: A comparative study is presented of the chromoionophoric and fluoroion-ophoric behaviour of 1 and 2, which both consist of an aza-crownether-ionophore integrated with a twisted 9-aryl-acridinium chromophore. In 2 the degree of ground state twisting in the chromophore is enhanced relative to that in 1. While the cation induced spectral shifts (i.e. chromoionophoric effect) in 2 are not significantly different from those in 1, the cation binding properties of 2 are enhanced significantly. This is explained in terms of better preorganisation of 2 and higher charge density of the anilino nitrogen in 2 as supported by X-ray data. In addition to their chromoionophoric properties, the non-fluorescing 1 and 2 show an acridiniumtype of fluorescence upon binding of H+ and Ag+ ions. This fluoroionophoric effect is also significantly enhanced in 2 where restricted internal rotational freedom allows for a higher fluorescence quantum yield of the complex.
TL;DR: In this paper, Galfi and Racz predicted that the reaction boundary will propagate as t 1/2 (the more numerous particles penetrating the less numerous antiparticles domain) and the width of the reaction front should increase as t 2 1/6 and the rate of reaction as t −2/3.
Abstract: When electrons diffuse into a domain of holes, or defects into a domain of anti-defects, or molecules A meet molecules B with a reaction : A+B→C, what are the time characteristics of the reaction front and reaction rate? A scaling argument by Galfi and Racz predicts that the reaction boundary will propagate as t 1/2 (the more numerous particles penetrating the less numerous antiparticles domain). The width of the reaction front should increase as t 1/6 and the rate of reaction as t −2/3 . Monte Carlo simulations confirm the first prediction but suggest that the reaction boundary may be even more compact. Experiments were performed in round and square capillary domains, using colored reactant A molecules, colorless B molecules and a colorless product (C). Preliminary results support the t 1/2 reaction front propagation rate. This is the same as the Einstein diffusion law for a non-reacting dye (which we also confirmed experimentally with the same apparatus). However, the width of the reaction front is significantly more compact than that of a diffusion front
TL;DR: Nickel complexes of the dithiolenes type with broad but also intense electronic transitions in the NIR region of the electromagnetic spectrum have been synthesized as discussed by the authors, which are extremely useful in certain applications involving NIR lasers.
Abstract: Nickel complexes of the dithiolenes type with broad but also intense electronic transitions in the NIR region of the electromagnetic spectrum have been synthesized. These complexes are extremely useful in certain applications involving NIR lasers
TL;DR: In this paper, a partial answer to the asymmetric self-assembly question using intermolecular hydrogen bonds was found. But it is not a solution to the symmetry problem, since chiral molecules necessarily crystallize in acentric structures.
Abstract: Second order non-linear optical (NLO) effects, such as second harmonic generation, occur only in materials that are acentric. Finding ways to assure that a bulk material is acentric has been a serious hurdle in the design of new organic materials for non-linear optical uses.1 A trivial, albeit useful, solution to the symmetry problem is to use chiral molecules which necessarily crystallize in acentric structures.2 The general solution to the problem involves understanding how to promote self-assembly of molecules, regardless of their molecular symmetry, into acentric arrays. We have found a partial answer to the asymmetric self-assembly question using intermolecular hydrogen bonds.
TL;DR: In this paper, a series of ferroelectric liquid crystals with a fluorinated asymmetric frame were synthesized by utilizing optically active S-(-)-2-fluoroalkanols or S-( −)-2 -fluoralkanoic acids, and their mesomorphic and physical properties were studied.
Abstract: Two new series of ferroelectric liquid crystals with a fluorinated asymmetric frame were synthesized by utilizing optically active S-(-)-2-fluoroalkanols or S-(-)-2-fluoroalkanoic acids, and their mesomorphic and physical properties were studied. 5-Alkyl-2-[p-(2-fluoroalkyloxy)phenyl]pyrimidines (5, n ≧ 6, m = 12) exhibited enantiotropic chiral smectic C phase, and their spontaneous polarizations were more than 34nC/cm2 (except for n = 4). The values of response time were short (on the order of 10 μ sec) and were found to be shorter by decreasing the value of n. 5-Alkyl-2-[p-(2-fluoroalkanoyloxy)phenyl]pyrimidines (6) exhibited the monotropic chiral smectic C phase characterized by an extremely short response time of 4.2 μ sec.
TL;DR: Despite differences in molecular configuration and crystal symmetry, the crystal structures of the odd and even alkyl chain members of the N-(n-alkyl-D-gluconamides and the odd alkene-alkene chains of the 1-deoxy-(N-methyl alkanamido)-D-glucitols have closely related hydrogen-bond systems, which include a homodromic fourbond cycle as mentioned in this paper.
Abstract: Despite differences in molecular configuration and crystal symmetry, the crystal structures of the odd and even alkyl chain members of the N-(n-alkyl-D-gluconamides and the odd alkyl chain members of the 1-deoxy-(N-methyl alkanamido)-D-glucitols have closely related hydrogen-bond systems, which include a homodromic four-bond cycle. This is associated with the monolayer head-to-tail molecular packing common to these crystal structures.
TL;DR: In this article, the growth of a nematic wetting layer at a surface in an isotropic fluid close to the nematic-isotropic transition is discussed, using general principles.
Abstract: We discuss, using general principles, the growth of a nematic wetting layer at a surface in an isotropic fluid close to the nematic-isotropic transition. The effect of competition between the nematic anchoring at a wall and at the incipient isotropic surface can lead to effects which are particular to systems with orientational order. Such effects also change the Kelvin equation which governs the shift in the nematic-isotropic phase transition in a finite geometry.
TL;DR: The thermal behavior of several cis,cis-(35-dihydroxycyclohexyl)- 34-bis(alkoxy)benzoates is discussed in this paper.
Abstract: The thermal behaviour of several cis,cis-(35-dihydroxycyclohexyl)- 34-bis(alkoxy)benzoates is discussed
TL;DR: The dependence of the liquid-crystal transition temperatures of these new classes of compounds on diverse central linkages, chain lengths, alicyclic structural units and lateral substituents has been studied systematically as discussed by the authors.
Abstract: About 50 novel liquid crystalline 2,5-disubstituted 1,3,4-thiadiazole derivatives incorporating a carboxylic group or anoxymethylene unit have been prepared. The dependence of the liquid-crystal transition temperatures of this new class of compounds on diverse central linkages, chain lengths, alicyclic structural units and lateral substituents has been studied systematically. Most of the compounds exhibit broad smectic C mesomorphic ranges.
TL;DR: Methods for synthesis and properties of oxygen-, sulfur-, selenium-, and nitrogen-containing transition-metal 1,2-diheterolenes and polyheterotetrahetera-fulvalenes are described in this article.
Abstract: Methods for synthesis and properties of oxygen-, sulfur-, selenium-, and nitrogen-containing transition-metal 1,2-diheterolenes and polyheterotetrahetera-fulvalenes are described Also, the preparation and properties of some conducting salts based on these compounds are briefly discussed
TL;DR: In this paper, the electro-optic performance characteristics of PDLC films using two different polymers, namely, poly (methyl methacrylate) (PMMA) and poly (vinyl chloride:vinyl acetate 17%) (PVC:VAC-17) and liquid crystal mixture E-8 (BDH, England) have been studied.
Abstract: The electro-optic performance characteristics of PDLC films using two different polymers, namely, poly (methyl methacrylate) (PMMA) and poly (vinyl chloride:vinyl acetate 17%) (PVC:VAC-17) and liquid crystal mixture E-8 (BDH, England) have been studied. It is found that the PMMA-based PDLC films have more superior mechanical and electro-optical properties than the PVC:VAC-17-based PDLC films. The performance characteristics of PDLC films, in general, improve significantly with increasing temperature. An optimum weight fraction of liquid crystal mixture is to be added in the polymer for good performance of the PDLC films. The finite solubility of liquid crystal mixture in the polymer affects the properties of the polymer matrix and hence the electro-optic performance characteristics significantly.
TL;DR: In this article, the thermal properties of 4-Z-phenyl 4-(4-octyloxybenzoyloxy)benzoates have been examined, where the substituents (Z) are halogens, alkoxy, alkyl, formyl, acetyl, cyano, and nitro groups.
Abstract: Summary: The thermal properties of 4-Z-phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxy- phenyl 4-(4-Z-benzoyloxy) benzoates (2), 4-(4-octyloxybenzoyloxy) phenyl 4-Z-benzoates (3) and 4- octyloxyphenyl 4-(4-Z-phenoxycarbonyl)benzoates (4) have been examined, where the substituents (Z) are halogens, alkoxy, alkyl, formyl, acetyl, cyano, and nitro groups, etc. The smectic properties are strongly dependent on the orientation of the ester linkages. Compounds 1 and 4 having alkoxy and alkyl groups tend to show smectic A and C phases. Compounds 2 and 3 are intrinsically poor in smectic properties, and only a smectic C phase is formed by the long-alkoxy and alkyl derivatives. Throughout the compounds, the thermal stability of the smectic A phase is strongly dependent on the electrostatic nature of the substituents; that is, both electron-donating substituents such as the methoxy and methyl groups and electron-withdrawing ones such as the cyano and nitro groups, steeply lower the smectic A therma...