Showing papers in "Molecular Crystals and Liquid Crystals in 1993"
TL;DR: In this paper, it was shown that [Fe(ox)3]3- as the building block can be synthesized by using [Fe (ox)2]3]-3 as a building block.
Abstract: Hetero-metal assemblies, (NBu4=tetra(n-butyl)ammonium ion; ox=oxalate ion; M(II)=Ni(1), Fe(2), Mn(3), Zn(4)) have been synthesized by the use of [Fe(ox)3]3- as the building block. 1 and 2 are ferri...
114 citations
TL;DR: The mesomorphic properties of homologous series of 2,5-bis(4-alkoxybenzylidene)cyclopentanones, 2,6-bis (4-hexhexanone) cyclohexanones and 2,7-bis cycloheptanones have been compared with each other as mentioned in this paper.
Abstract: The mesomorphic properties of homologous series of 2,5-bis(4-alkoxybenzylidene)cyclopentanones, 2,6-bis(4-alkoxybenzylidene)cyclohexanones, and 2,7-bis(4-alkoxybenzylidene)cycloheptanoneshave been compared with each other. The clearing point is markedly depressed by increasing the size of the cycloalkanone ring. The cyclopentanone derivatives carrying the methoxy to pentyloxy groups are purely nematogenic, the next member exhibits a smectic A phase as well as a nematic phase. Smectic A and C phases are observed for the heptyloxy and octyloxy homologues, and only a smectic C phase for the later members. In both the cyclohexanone and cycloheptanone derivatives, the methoxy to decyloxy homologues exhibit a nematic phase and the higher members exhibit a smectic C phase. In addition, a smectic A phase appears in the nonyloxy and decyloxy homologues of the cyclohexanone series.
70 citations
TL;DR: In this paper, the rational step-by-step construction of molecular solids useful for the field of molecular electronics is described, and the chain stiffness as a structural principle leads to the design of molecular circuits.
Abstract: This contribution describes the rational step-by-step construction of molecular solids useful for the field of molecular electronics. Chain stiffness as a structural principle leads to the design o...
70 citations
TL;DR: In this article, the NBMOs of a non-Kekule hydrocarbon are classified as disjoint or non-disjoint to predict the spin of the ground state and the magnitude of the energy difference between it and the lowest excited state.
Abstract: Classification of the NBMOs of a non-Kekule hydrocarbon as being disjoint or non-disjoint can be used to predict the spin of the ground state and the magnitude of the energy difference between it and the lowest excited state. If the NBMOs are non-disjoint, the bonding in the lowest excited states will be more localized than that in the ground state. The nature of the localized pi bonding in the lowest excited states allows one to predict qualitatively which will be most stabilized by hetero-atom substitution and whether it is possible that the attendant stabilization, relative to the ground state, is capable of giving the substituted molecule a ground state of different spin multiplicity. The same predictions can also be made using VB theory.
64 citations
TL;DR: In this paper, a review on the experimental aspects of the alignment of NLC in the pretilted homogeneous form in the sandwich cells is provided, and most of the contents of this paper are the results of research done by the authors in these few years.
Abstract: This article provides a review on the experimental aspects of the alignment of nematic liquid crystal (NLC) in the pretilted homogeneous form in the sandwich cells; most of the contents of this paper are the results of research done by the authors in these few years. For simplicity and convenience, we used nematic liquid crystal (5CB) only; however, we have explored several polymer orientation films such as alkylbranched or alkylbranchless polyimide (PI), PI-Langmuir-Blodgett (LB) films, and those of polypyrrole. All these films were rubbed prior to assemble the cells except for some cases of PI-LB films. These films were characterized in terms of the atomic force microscope (AFM) observation and the optical retardation that are induced by the rubbing or unidirectional pulling up of the substrates in the LB process. Aligning capabilities of these orientation films for 5CB have been evaluated in terms of the texture of the NLC media, generation of pretilt angles, and temperature dependence of the ...
56 citations
TL;DR: In this paper, a new type of photochromic compounds, diarylethene derivatives, was developed for optical data storage media, which had read-out stability more than 106 times, and write/erase cycles could be repeated 3 × 103 times without loss of performance.
Abstract: A new type of photochromic compounds, diarylethene derivatives, has been developed for optical data storage media. The photochromic dye - polymer media had read-out stability more than 106 times, and write/erase cycles could be repeated 3 × 103 times without loss of performance.
51 citations
TL;DR: In this article, the authors reviewed the recent studies on the ferromagnetic properties of β-phase of p-nitrophenyl nitronyl nitroxide (p-NPNN) and provided an example of the first organic bulk ferromagnet composed only of light elements.
Abstract: The search for bulk ferromagnetism in a genuine organic substance has long been one of the major subjects in the field of molecular magnetism. Recently, we have reported the successful results for orthorhombic β-phase crystal of p-nitrophenyl nitronyl nitroxide (abbreviated as p-NPNN). This provides an example of the first genuine organic bulk ferromag-net composed only of light elements. In this article, our recent studies on the ferromagnetic properties of β-Phase of P-NPNN are reviewed.
46 citations
TL;DR: In this paper, the electronic hyperpolarisabilities of a chiral 4-alkoxystilbazole and its complexes with Rh(I) and Ir(I), were discussed in terms of the acceptor properties of the metal fragment.
Abstract: The electronic hyperpolarisabilities of a chiral 4-alkoxystilbazole and its complexes with Rh(I) and Ir(I) are reported and discussed in terms of the acceptor properties of the metal fragment.
44 citations
TL;DR: The basic properties of conducting polymers which can be coloured by reversible electrochemical doping processes, are briefly described in this paper, and the application of these materials for the development of optical devices of technological importance, such as electrochromic displays and windows, is also illustrated and discussed.
Abstract: The basic properties of conducting polymers which can be coloured by reversible electrochemical doping processes, are briefly described. The application of these materials for the development of optical devices of technological importance, such as electrochromic displays and windows, is also illustrated and discussed.
42 citations
TL;DR: The 40-year old polymer poly-2,5-di(benzoyloxy)styrene has been restudied from the view point of the "mesogen-jacketed liquid crystal polymer".
Abstract: The 40 year old polymer, poly-2,5-di(benzoyloxy)styrene, has been restudied from the view point of the “mesogen-jacketed liquid crystal polymer.” This old polymer was synthesized in 1952 as a precursor of an electron exchange polymer and is now found to be thermotropically liquid crystalline, from which the characteristic banded texture of rigid and semi-rigid liquid crystal polymers may be obtained. The monomer of this polymer, 2,5-di(benzoyloxy)styrene, was then also not realized as liquid crystalline, is now found to be liquid crystalline forming too. This finding offers probably the first example of liquid crystal rigid rod-like molecules with lateral but without terminal substitutions. The synthesis and primary characterization of a series of the closely related polymers poly-2,5-bis[(4-substituted-benzoyl)oxy styrenes are also reported.
40 citations
TL;DR: In this paper, the first realization of a thermally addressed display is described, based on a user-friendly and reliable optical technique to characterize the spin transition phenomenon in iron II derivatives.
Abstract: After a presentation of a user-friendly and reliable optical technique to characterize the spin transition phenomenon in iron II derivatives, this paper describes the first realization of a thermally addressed display. This new technology, still at the beginning of its development, is promising for further recording or display applications.
TL;DR: A retrospective view from the first quasi one-dimensional superconductors (TMTSF salts) to quasi two-dimensional BEDT-TTF salts and recent three-dimensional fullerene complexes is presented in this article.
Abstract: Some structural and chemical approaches applied to the construction of organic superconductors are discussed. A retrospective view from the first quasi one-dimensional superconductors (TMTSF salts) to quasi two-dimensional BEDT-TTF salts and recent three-dimensional fullerene complexes is presented.
TL;DR: In this article, the properties of the Per2M(mnt)2 with α phases are reviewed taking into account recent experimental results, including perylene chains, responsible for electronic conduction.
Abstract: The properties of the compounds of the family Per2M(mnt)2 with α phases are reviewed taking into account recent experimental results. The perylene chains, responsible for electronic conduction unde...
TL;DR: In this paper, a strategy of how to endow organic molecules with many half-filled orthogonal orbitals has been studied systematically, where the radical centers are placed in phase with the spin polarization of the intervening π-bonds.
Abstract: Strategy of how to endow organic molecules with many half-filled orthogonal orbitals has been studied systematically. In principle, parallel alignment of the two spins can become favored in π-conjugated diradicals, if the radical centers are placed in phase with the spin polarization of the intervening π-bonds. Studies of a wide variety of non-Kekule hydrocarbons and the heteroatom analogues by EPR spectroscopy and magnetic susceptibility/magnetization measurements have revealed, however, that only a part of them related in connectivity to trimethylenemethane have high-spin ground states. Some super-high-spin polycarbenes, polynitrenes and persistent trinitroxides from these laboratories will be discussed in some detail.
TL;DR: Magnetic properties and crystal structures of several derivatives of phenyl nitronyl nitroxide (abbreviated as PNN; 2-phenyl-4,4,5,5-tetramethyl-4-5-dihydro-lH-imidazol-l-oxyl-3-Noxide) are investigated in this paper.
Abstract: Magnetic properties and crystal structures of several derivatives of phenyl nitronyl nitroxide (abbreviated as PNN; 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-l-oxyl-3-N-oxide) are investigated. Some of them have the intermolecular interactions between the nitroxide group and the phenyl group, which are suggested to be favorable to ferromagnetic coupling. As a result of the coexistence of different types of magnetic interactions, anomalies in the temperature dependence of paramagnetic susceptibility are found for some compounds.
TL;DR: In this article, Seo et al. showed that in a PI film with alkylbranches there exist grooves owing to strong rubbing, while the branchless polyimide does not reveal grooves at the AFM resolution.
Abstract: Atomic force microscope (AFM) observation has been made on rubbed polymer films for liquid crystal (LC) molecular orientation such as those of alkylbranched and branchless polyimide (PI) together with polystyrene (PS); other characterizations such as Fourier analysis and roughness evaluation have also been made. It has been investigated how these results of the characterization relate to the LC aligning capabilities such as microscopic texture and pretilt angle. It is shown that in a PI film with alkylbranches there exist grooves owing to strong rubbing, while the branchless does not reveal grooves at the AFM resolution. However, both of them are shown to be capable of aligning nematic (N) LCs very well. Regarding PS film, the grooves run parallel to the rubbing direction but LC alignment is perpendicular to that of rubbing, in accordance with the previous report (D.-S. Seo et al., Jpn. J. Appl. Phys. 31, 2165C 1992)).
TL;DR: In this paper, three ways of inducing spin conversions are presented, i.e., a variation of temperature, an external perturbation, and an irradiation with light, for a number of transition metal complexes.
Abstract: High spin ↔ low spin electronic spin crossovers may be observed in a number of transition metal complexes when the ligand-field and electron-pairing energies happen to be comparable in magnitude. They are obtained under the effect of an external perturbation such as a variation of temperature, a variation of pressure or an irradiation with light. These three ways of inducing spin conversions are presented.
TL;DR: Magnetic ordering phenomena in mixed-metal assemblies were studied by using 57Fe Moessbauer spectroscopy, where NBu4 +=tetra(n-butyl)ammonium ion, ox2-=oxalate ion as discussed by the authors.
Abstract: Magnetic ordering phenomena in mixed-metal assemblies {NBu4[Fe(II)M(III)(ox)3]}3∞ (M=Cr (1), Fe (2)) were studied by using 57Fe Moessbauer spectroscopy, where NBu4 +=tetra(n-butyl)ammonium ion, ox2-=oxalate ion. Nuclear Zeeman splittings were observed in the Moessbauer spectra of both 1 and 2 at low temperatures (below 10 K for 1 and 41 K for 2), which indicated the occurrence of three-dimensional magnetic ordering in these complexes under zero applied field.
TL;DR: In this paper, nine kinds of ferrocene derivatives, [4]-(cholesteryloxy carbonyl)alkoxy carbonyl]phenyl] ferrocenes, were synthesized in a wide temperature range.
Abstract: Nine kinds of ferrocene derivatives, [4-[ω-(cholesteryloxy carbonyl)alkoxy carbonyl]phenyl] ferrocene, were synthesized. Polarizing microscopy observations and differential scanning calorimetry measurements of these compounds were made in a wide temperature range. The liquid crystallinity was observed in the derivatives containing 2,4,6, 10, and 11 carbon atoms in the flexible alkyl chain of the compounds. An appearance of the liquid crystallinity was discussed with a conformation of the flexible alkyl chain which exerted a great influence on the molecular shape.
Abstract: Crystal structures of title compounds have been determined by single crystal x-ray analysis. Crystal data. 4′-Hexyloxy-4-cyanobiphenyl (6OCB), Molecular structures in both crystals are very similar with twisted biphenyl moieties and fully extended paraffin chains. Dimers are formed by close contacts of CN groups between neighboring molecules (C-N: 3.56 and 3.40 A for 6OCB and 3.55 and 3.39 A for 7OCB). The neighboring dimers in 6OCB are overlapped half-and-half, while those in 7OCB are arranged in a smectic-like layer structure.
TL;DR: The synthesis and mesomorphic behavior of 3,5-bis-(p-n-alkoxyphenyl)isoxazole (series I) and 3,7-bis-nalkoxymhenyl pyrazole(series II) are reported for the number of carbon atoms in the alkoxy chains varying from three to eight.
Abstract: The synthesis and mesomorphic behavior of 3,5-bis-(p-n-alkoxyphenyl)isoxazole (series I) and 3,5-bis-(p-n-alkoxyphenyl)pyrazole (series II) are reported for the number of carbon atoms (n) in the alkoxy chains varying from three to eight. Series I shows an enantiotropic nematic phase for all n and an enantiotropic smectic phase for n ⩾ 6. Series II shows one smectic phase SI for all n and an additional smectic phase SII for n ⩾ 6. From optical and X-ray data, the smectic phase of series I is identified as smectic C and in series II the SI phase is classified as smectic A and SII as a smectic C with a temperature dependent tilt angle. The 1-methyl substituted pyrazole was prepared and did not show mesophases.
TL;DR: In this article, a carboxypentonic acid was synthesized and characterized by x-ray diffraction, which is isomorphous with the CI and Br congeners.
Abstract: Cu9F2(cpa)6 xH2O (cpa = carboxypentonic acid) has been synthesized, and characterized by x-ray diffraction. It is isomorphous with the CI and Br congeners. Two coordinatively different Cu(II) ions ...
TL;DR: In this paper, an EL device was fabricated using poly(methyl methacrylate) (PMMA) molecularly doped with triphenyldiamine derivative and tris(8-quinolinolato)aluminum(III) complex (Alq).
Abstract: Electroluminescent devices were fabricated using poly(methyl methacrylate) (PMMA) molecularly doped with triphenyldiamine derivative and tris(8-quinolinolato)aluminum(III) complex (Alq). A cell structure of glass substrate/indium-tin-oxide/doped PMMA/Mg: Ag was employed. Green emission with luminance of 920 cd/m2 was achieved at a drive voltage of 17 V. The EL color was tuned to blue-green and yellow-orange by further doping the PMMA layer with suitable organic dyes.
TL;DR: In this paper, the relative widths of photoconductive current transients, obtained in molecularly doped polymers, are independent of the electric field and sample thickness, even when the current before the transit time is nearly time independent.
Abstract: It is shown that the relative widths of photoconductive current transients, obtained in molecularly doped polymers, are independent of the electric field and sample thickness, even when the current before the transit time is nearly time independent. Such a result has been termed universality in the Scher-Montroll theory of dispersive transport. The implications of these results for the field and temperature dependence of the mobility are considered.
TL;DR: In this article, a thermodynamically based model for phase separation in polymer-dispersed liquid crystals (PDLCs) is developed using Flory-Huggins theory and the lever rule.
Abstract: A thermodynamically based model for phase separation in polymer-dispersed liquid crystals (PDLCs) is developed. Using Flory-Huggins theory and the lever rule, it quantitatively describes liquid crystal (LC) solubility in a polymer matrix as a function of temperature. From the spinodal compositions, the model yields upper bounds for the solubility limits of LC in polymer and of polymer in LC. The solubility limits are related to the Flory-Huggins interaction parameter, χ, and hence to solubility parameters, δ. This model may prove useful in selecting materials for which maximum segregation of liquid crystal into microdroplets is desired.
TL;DR: In this paper, the APUHF calculations are performed for radical pairs in the β and γ-phase crystals of para-nitrophenyl nitronyl nitroxide, and the magnetic transition temperatures are calculated by the use of Langevin-Weiss type mean-field theory combined with the calculated effective exchange integrals.
Abstract: Intermolecular spin alignment rules are derived on the basis of ab initio results obtained for clusters of triplet carbenes, free radicals, etc. Interrelationships between several theoretical models are also clarified. The APUHF calculations are performed for radical pairs in the β and γ-phase crystals of para-nitrophenyl nitronyl nitroxide. The magnetic transition temperatures are calculated by the use of Langevin-Weiss type mean-field theory combined with the calculated effective exchange integrals. The origins of ferromagnetic interactions in both the phases are discussed in relation to the intermolecular spin alignment rules.
TL;DR: The tilt bias angle dependence on the alkylene chain length of polyimides shows an anomalous odd-even effect as mentioned in this paper, which is due to the difference of surface structures between polyimide chains with odd-number lengths and those with even ones.
Abstract: Measurements of tilt bias angles of a nematic liquid crystal were carried out, by using several alkylene polyimides synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydrides and diamines with different chain lengths as alignment layers. The tilt bias angle dependence on the alkylene chain length of polyimides shows an anomalous odd-even effect. Small tilt bias angles, less than one degree, were observed with odd-number alkylene chain lengths. Relatively high tilt bias angles, however, were observed with even-number lengths. We have made an attempt to explain this effect from X-ray diffraction and scanning electron microscope measurements and molecular mechanics calculations of the polyimides with alkylene chain. As a result, this odd-even effect of the tilt bias angle is due to the difference of surface structures between alkylene polyimides with odd alkylene lengths and those with even ones.
TL;DR: In this paper, the authors studied the relationship between the morphology and the electro-optic properties of liquid crystal-polymer composite (LCPC) materials and showed that the maximum transmittance in the on state depends primarily on the polymer morphology and secondly on the solubility between the polymers and the liquid crystal in the network-type LCPC film.
Abstract: We have studied the relationship between the morphology and the electro-optic properties of liquid crystal-polymer composite (LCPC) materials. The materials consist of the liquid crystal (80° by weight) and the polymerizable mixture (20° by weight) composed of the monofunctional monomer, the oligomer, and the multifunctional acryl monomer. The results show that the electro-optic properties such as the driving voltage and the transmittance depend strongly on the polymer species used. When the solubility between the liquid crystal and the growing polymers formed during the polymerization process is low and the speed of phase separation is fast, the morphology shows a ‚Network’ type, the liquid crystal exhibits a continuous phase through the sample, and such a film scatters light strongly in the off state. The maximum transmittance in the on state depends primarily on the polymer morphology and secondly on the solubility between the polymers and the liquid crystal in the ‚Network’ type LCPC film. Th...
TL;DR: In this article, nine kinds of monosubstituted ferrocene derivatives, ω-[4-(methoxyphenoxy carbonyl)phenoxycarbonyllalkyl 4-ferrocenylbenzoate, were prepared.
Abstract: Nine kinds of monosubstituted ferrocene derivatives, ω-[4-(4-methoxyphenoxycarbonyl)phenoxycarbonyllalkyl 4-ferrocenylbenzoate, were prepared. The derivatives containing 4, 6, 10 and 11 carbon atoms in the flexible alkyl chain of the compounds showed liquid crystallinity, and multiple melting behavior was observed in the compounds containing 4, 6 and 11 carbom atoms. An appearance of the liquid crystallinity showed a carbon number dependence on the flexible alkyl chain.
TL;DR: In this article, the EPR technique is described as a valuable tool in order to probe the spin correlations in π-radical magnets and the peculiar features of low dimensional exchange coupled spin systems are recalled.
Abstract: The Electron Paramagnetic Resonance (EPR) technique is described as a valuable tool in order to probe the spin correlations in π-radical magnets. The peculiar features of the EPR response of low dimensional exchange coupled spin systems are recalled. The extreme sensitivity of the resonance field to both magnetic and dipolar interactions is emphasized. The example materials include phthalocyanine radical derivatives and nitronyl nitroxide radical derivatives. Both exhibit either anti ferromagnetic or ferromagnetic intermolecular interactions.