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Liquid Crystalline Phase (liquid + crystalline_phase)
Selected AbstractsDiastereoselectivity in [2, + 2,] Photocycloaddition of Cholesteryl Cinnamate to Methyl 9-Phenanthrenecarboxylate: Control of the Stereoselectivity in Liquid Crystalline Phase.CHEMINFORM, Issue 52 2004Hajime Maeda Abstract For Abstract see ChemInform Abstract in Full Text. [source] Electric-Field Triggered Controlled Release of Bioactive Volatiles from Imine-Based Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009Andreas Herrmann Dr. Abstract Application of an electric field to liquid crystalline film forming imines with negative dielectric anisotropy, such as N -(4-methoxybenzylidene)-4-butylaniline (MBBA, 1), results in the expulsion of compounds that do not participate in the formation of the liquid crystalline phase. Furthermore, amines and aromatic aldehydes undergo component exchange with the imine by generating constitutional dynamic libraries. The strength of the electric field and the duration of its application to the liquid crystalline film influence the release rate of the expelled compounds and, at the same time, modulate the equilibration of the dynamic libraries. The controlled release of volatile organic molecules with different chemical functionalities from the film was quantified by dynamic headspace analysis. In all cases, higher headspace concentrations were detected in the presence of an electric field. These results point to the possibility of using imine-based liquid crystalline films to build devices for the controlled release of a broad variety of bioactive volatiles as a direct response to an external electric signal. [source] Distinct Columnar and Lamellar Liquid Crystalline Phases Formed by New Bolaamphiphiles with Linear and Branched Lateral Hydrocarbon ChainsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2008Marko Prehm Dr. Abstract A universal building block for the convergent synthesis of a wide variety of different T-shaped ternary amphiphiles was developed and used for the synthesis of a series of new liquid-crystalline materials composed of a rigid biphenyl core with polar glycerol groups at both ends and linear or branched alkyl chains in a lateral position. In addition, compounds with bulky achiral (2,4,6-trimethylphenoxy, adamantane-1-carboxylate, benzoate) or chiral (menthyl or cholesteryl) substituents attached to the end of the lateral alkyl chain were also investigated. In all cases the lateral chains were connected to the aromatic core by an ether linkage. The effect of the ether linking unit on mesophase stability and mesophase type is discussed with respect to conformational effects. The liquid-crystalline phases were investigated by polarizing microscopy, calorimetry, and X-ray diffraction of surface aligned samples. Upon enlarging the lateral chains a series of different polygonal cylinder phases was observed, which were replaced by lamellar phases and a non-cylinder hexagonal columnar phase by further increasing the size of these substituents. Remarkably, only pentagonal, hexagonal, and giant hexagonal cylinder phases could be observed, whereas mesophases composed of cylinders with a smaller number of sides are missing. No distinct chirality effects were observed for the menthyl- and cholesteryl-substituted compounds. However, the rodlike shape of the polycyclic cholesteryl core leads to a unique phase structure combining an organization of the alicyclic cholesteryl cores perpendicular to the layer planes and the aromatic biphenyl cores parallel to the layer planes. [source] Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Zhijian Chen Abstract A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3,a,f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H,NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The ,,, aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted ,-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×104 and 30,M,1. The photoluminescence spectra of the dimers of PBIs 3,a,f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective ,,, stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the , systems on their ,,, stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3,a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H -type into strongly fluorescent J -type packing of the dyes. [source] Phase transition behavior and structure of the thermotropic liquid crystal 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyneCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2006Leijing Liu Abstract The phase transition behaviors and corresponding structures of 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X-ray diffraction (WAXD). In comparison with the published homologues, 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)oxy]carbonyl}- 1-pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5°C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69Å. Further lowering the temperature, it enters into a metastable monotropic smectic B (SmB) phase with a longer layer spacing d=34.22Å which has a tendency towards crystallization. The metastability of the liquid crystalline phase may associate to the linkage order of the ester bridge between the mesogenic core and the flexible spacer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Quest for Nanoscale Magnets: The example of [Mn12] Single Molecule MagnetsADVANCED MATERIALS, Issue 43 2009Guillaume Rogez Abstract Recent advances on the organization and characterization of [Mn12] single molecule magnets (SMMs) on a surface or in 3D are reviewed. By using nonconventional techniques such as X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM), it is shown that [Mn12]-based SMMs deposited on a surface lose their SMM behavior, even though the molecules seem to be structurally undamaged. A new approach is reported to get high-density information-storage devices, based on the 3D assembling of SMMs in a liquid crystalline phase. The 3D nanostructure exhibits the anisotropic character of the SMMs, thus opening the way to address micrometric volumes by two photon absorption using the pump-probe technique. We present recent developments such as µ-SQUID, magneto-optical Kerr effect (MOKE), or magneto-optical circular dichroism (MOCD), which enable the characterization of SMM nanostructures with exceptional sensitivity. Further, the spin-polarized version of the STM under ultrahigh vacuum is shown to be the key tool for addressing not only single molecule magnets, but also magnetic nano-objects. [source] Formation of Lipid Emulsions and Clear Gels by Liquid Crystal EmulsificationINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1 2007T. Suzuki Recently developed emulsion technologies for the formation of fine emulsions, lipid emulsions and clear gels by liquid crystal emulsification were reviewed. As a basic information on liquid crystal emulsification, the structures and characteristic behaviours of lyotropic liquid crystals were summarized. Formation of a liquid crystalline phase was often seen in emulsions and biological systems. The significance of liquid crystal formation during emulsification was analysed by comparing the states and stabilities of emulsions prepared by different processes. Then uses of liquid crystals for formation of the characteristic emulsions and gels were also discussed. In liquid crystal emulsification, an oil phase is dispersed directly into the lamellar liquid-crystalline phase composed of surfactant, glycerol and water to prepare a gel-like oil-in-liquid crystal emulsion. This is followed by dilution with the remaining water to produce an emulsion. From the phase behaviour during emulsification and analysis of the local motion of the liquid crystal membrane by fluorometry, it was confirmed that the interaction between surfactant and a polyol molecule such as glycerol promotes hydrogen bonding and enhances the strength of the lamellar liquid crystal membranes, which results in the formation of oil-in-liquid crystal emulsions. The interaction between the liquid crystal and oil was analysed from the changes in molecular motion of the membrane at the oil-liquid crystal interface using the spin label technique of electron spin resonance (ESR). The fluidity of the liquid crystal membrane did not change when oil was added, and therefore oil-in-liquid crystal emulsions of various oils were prepared by the identical process. This lack of dependence of the liquid crystal membrane on oil results in the unique properties of liquid crystal emulsification, which can be used for oils of various polarity and different molecular constituents. When a self-organizing artificial stratum corneum lipid containing pseudo-ceramide was used as a principal component of the oil, a multilamellar emulsion of concentric lamellar structure was formed. The multilamellar emulsion supplements the physiological function of stratum corneum by the identical mechanism as natural intercellular lipids. High-pressure treatment of the lipid emulsion produced a gel-like emulsion crystal, in which the homogeneous nanoemulsion droplets were arranged in a hexagonal array. This review paper was presented at the Conference of the Asian Societies of Cosmetic Scientists 2005 in Bangkok. [source] An investigation into the mechanism of dissolution rate enhancement of poorly water-soluble drugs from spray chilled gelucire 50/13 microspheresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2010Sheng Qi Abstract The production and physicochemical characterisation of spray chilled Gelucire 50/13 microspheres is described with a view to improving the dissolution of a poorly water-soluble drug, piroxicam, and understanding the fundamental mechanisms associated with the improved drug release. Thermorheological testing was developed as a fast screening method for predicting the processability of dispersions for spray chilling preparation. Spray chilled piroxicam loaded microspheres were spherical in shape with a median diameter of circa 150,µm. DSC indicated no interaction between piroxicam and lipid matrix, while HSM studies performed in polarized light mode indicated that the spheres contained distinct drug crystals. Polarising light microscopy and small-angle XRD investigations on the hydration behaviour of the lipid and the spray chilled microspheres revealed the formation of liquid crystalline phases depending on the degree of hydration. The dissolution behaviour of the piroxicam loaded microspheres showed significant improvements compared to drug alone. The particle size, drug loading and aging of the microspheres were all found to have an influence on the release behaviour. It was proposed that Gelucire 50/13 microspheres release the entrapped piroxicam via formation of a lyotropic liquid crystalline phase, which allows dissolution of the drug particles in a finely divided, high surface area and well-wetted state. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:262,274, 2010 [source] Liquid crystalline conjugated polymers and their applications in organic electronicsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2009Sheng-Hsiung Yang Abstract This article describes the syntheses and electro-optical applications of liquid crystalline (LC) conjugated polymers, for example, poly(p -phenylenevinylene), polyfluorene, polythiophene, and other conjugated polymers. The polymerization involves several mechanisms: the Gilch route, Heck coupling, or Knoevenagel condensation for poly(p -phenylenevinylene)s, the Suzuki- or Yamamoto-coupling reaction for polyfluorenes, and miscellaneous coupling reactions for other conjugated polymers. These LC conjugated polymers are classified into two types: conjugated main chain polymers with long alkyl side chains, namely main-chain type LC polymers, and conjugated polymers grafting with mesogenic side groups, namely side-chain type LC conjugated polymers. In general, the former shows higher transition temperature and only nematic phase; the latter possesses lower transition temperature and more mesophases, for example, smectic and nematic phases, depending on the structure of mesogenic side chains. The fully conjugated main chain promises them as good candidates for polarized electroluminescent or field-effect devices. The polarized emission can be obtained by surface rubbing or thermal annealing in liquid crystalline phase, with maximum dichroic ratio more than 20. In addition, conjugated oligomers with LC properties are also included and discussed in this article. Several oligo-fluorene derivatives show outstanding polarized emission properties and potential use in LCD backlight application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2713,2733, 2009 [source] Phase behavior and photo-responsive studies of photoactive liquid crystalline hyperbranched polyethers containing benzylidene moietyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2009V. Srinivasa Rao Abstract Two sets of hyperbranched polyether epoxies were synthesized to study the effect of substituent, rigidity, and nature of photoactive unit on the thermal and photoresponsive properties. Each set was comprised of one molecule with an acyclic moiety in the repeating unit, and two molecules with a cyclic moiety of varying rigidity (cycle size) in the repeating unit. Two substituents on aromatic rings in the repeating unit were present in one set, and other set was without a substituent. The mesogenic and photoresponsive properties were studied and correlated to the varied structural parameters. The effects of varied molecular structural parameters on phase behavior and photoresponsive properties were very prominent. Out of six monomeric diols, only four have exhibited liquid crystalline phase while the polymers corresponding to all monomeric diols revealed mesophase. The findings in photoresponsive properties were further supported by molecular modeling studies. The changes in refractive index, photoviscosity, and fluorescence intensity with irradiation time substantiated the spectral pattern observed in UV-Vis spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2774,2786, 2009 [source] Hydrogen bond-directed self-assembly of peripherally modified cyclotriphosphazenes with a homeotropic liquid crystalline phaseJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008Jianwei Xu Abstract The synthesis and characterization of hydrogen-bonded star-shaped complexes consisting of stilbazolyloxy, azopyridyl, and Schiff base-substituted cyclotriphosphazenes (3a, 3b, and 3c, respectively) and monoalkyloxy, bis(dodecyloxy), and tris(dodecyloxy)benzoic acids are reported. The thermal behaviors of complexes are studied by the means of differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry. Only 3a and 3b with monoalkyloxybenzoic acids show a homeotropic smectic A mesophase. The effect of azo and ethylene linkage of mesogenic groups in the cyclotriphosphazenes and the length of the flexible chain in monoalkyloxybenzoic acids on mesophase transition behaviors are investigated, revealing that the linkages in mesogenic groups governs the phase transition temperatures, and the length of flexible chain in proton donors plays an important role in controlling the magnitude of enthalpy and entropy of mesophase transitions in this supramolecular liquid crystal system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4691,4703, 2008 [source] Effect of stoichiometry on liquid crystalline supramolecular polymers formed with complementary nucleobase pair interactionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006Kelly A. Burke Abstract We report herein studies on the liquid crystalline behavior of a series of supramolecular materials that contain different ratios of two complementary symmetrically-substituted alkoxy-bis(phenylethynyl)benzene AA- and BB-type monomers. One monomer has thymine units placed at either end of the rigid mesogenic core, while the other has N6 -(4-methoxybenzoyl)-adenine units placed on the ends. Differential scanning calorimetric and polarized optical microscopy studies have been carried out on these systems. These studies show that the material's behavior is strongly dependent on its thermal history. As a result, the materials can exhibit, on heating, either a liquid crystalline phase, a crystalline phase, or the coexistence of crystalline and liquid crystalline regions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5049,5059, 2006 [source] Photoinduced Microphase Separation in Block Copolymers: Exploring Shape Incompatibility of Mesogenic Side GroupsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 11 2010Yi Zhao Abstract Photoinduced microphase separation in block copolymers (BCP) was achieved for the first time, using a rationally designed diblock copolymer composed of two side-chain liquid crystalline polymers (SCLCP). The miscibility of the two blocks was promoted by the miscibility between the two types of mesognic side groups, while upon UV exposure inducing the trans,cis isomerization of azobenzene mesogens on one SCLCP, the shape incompatibility of bent cis isomers with an ordered liquid crystalline phase drove the separation of the two blocks resulting in a microphase separated morphology. This result shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner. [source] Nature of water molecules in hydrogels based on a liquid crystalline cellulose derivativePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2003P. Wojciechowski Abstract The status and nature of water molecules in hydrogels with a liquid crystalline organization of the polymer network based on a biopolymer were investigated. Liquid crystalline (LC) hydrogels were obtained in situ by the photopolymerization of acrylic acid into the lyotropic liquid crystalline phase of (2-hydroxypropyl)cellulose in a solvent mixture of water and acrylic acid. The photopolymerization of acrylic acid in the lyotropic liquid crystalline phase at room temperature gives a hydrogel in which liquid crystalline order and water are retained. The liquid crystalline hydrogel contains water, which originates from the composition of the lyotropic liquid crystalline phase, and may also contain water after immersion in liquid water. The water molecule characteristics were examined by means of differential scanning calorimetry, dielectric relaxation spectroscopy, and differential scanning calorimetry coupled with thermo-optical measurements. The swelling data were obtained by using a weighing method. The investigations reveal the different nature of the two above-mentioned water types. For the water from the composition of the lyotropic liquid crystalline phase, the phase transitions,typical for the bulk water,were not observed, in contract to the water after swelling of the liquid crystalline hydrogel in the liquid water. The results of the measurements suggest that water, which comes from the composition of the lyotropic liquid crystalline phase, forms,together with a polymer network,a microstructure, stabilized by this water. The water, after swelling of the LC hydrogel in the liquid water, is separated in the pores of the hydrogel and exhibits the phase transitions of the bulk water. Copyright © 2003 John Wiley & Sons, Ltd. [source] Short wavelength light reflecting films from side-chain liquid crystal homopolymers with chiral spacersPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2001J. M. G. Cowie Abstract A series of acrylate monomers with alkoxy tails of varying lengths are synthesised and polymerised. The butoxy analogue had a stable enantiotropic cholesteric liquid crystalline phase which formed a grandjean texture when prepared as a thin film between glass slides. The polymer was mixed with a low molar mass nematic liquid crystal in various proportions and the pitch of the chiral nematic phases were determined using a cano-wedge cell technique. The polymer prepared from (S)-2-(4-butoxyphenyl-4,-benzoyloxy)-1-methyl ethyl acrylate had a pitch length of 113,nm which indicates that the polymer film could be employed in optical devices requiring selective reflection of light with short wavelengths in the region of 170,nm. Copyright © 2001 John Wiley & Sons, Ltd. [source] Electric-Field Triggered Controlled Release of Bioactive Volatiles from Imine-Based Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009Andreas Herrmann Dr. Abstract Application of an electric field to liquid crystalline film forming imines with negative dielectric anisotropy, such as N -(4-methoxybenzylidene)-4-butylaniline (MBBA, 1), results in the expulsion of compounds that do not participate in the formation of the liquid crystalline phase. Furthermore, amines and aromatic aldehydes undergo component exchange with the imine by generating constitutional dynamic libraries. The strength of the electric field and the duration of its application to the liquid crystalline film influence the release rate of the expelled compounds and, at the same time, modulate the equilibration of the dynamic libraries. The controlled release of volatile organic molecules with different chemical functionalities from the film was quantified by dynamic headspace analysis. In all cases, higher headspace concentrations were detected in the presence of an electric field. These results point to the possibility of using imine-based liquid crystalline films to build devices for the controlled release of a broad variety of bioactive volatiles as a direct response to an external electric signal. [source] An investigation into the mechanism of dissolution rate enhancement of poorly water-soluble drugs from spray chilled gelucire 50/13 microspheresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2010Sheng Qi Abstract The production and physicochemical characterisation of spray chilled Gelucire 50/13 microspheres is described with a view to improving the dissolution of a poorly water-soluble drug, piroxicam, and understanding the fundamental mechanisms associated with the improved drug release. Thermorheological testing was developed as a fast screening method for predicting the processability of dispersions for spray chilling preparation. Spray chilled piroxicam loaded microspheres were spherical in shape with a median diameter of circa 150,µm. DSC indicated no interaction between piroxicam and lipid matrix, while HSM studies performed in polarized light mode indicated that the spheres contained distinct drug crystals. Polarising light microscopy and small-angle XRD investigations on the hydration behaviour of the lipid and the spray chilled microspheres revealed the formation of liquid crystalline phases depending on the degree of hydration. The dissolution behaviour of the piroxicam loaded microspheres showed significant improvements compared to drug alone. The particle size, drug loading and aging of the microspheres were all found to have an influence on the release behaviour. It was proposed that Gelucire 50/13 microspheres release the entrapped piroxicam via formation of a lyotropic liquid crystalline phase, which allows dissolution of the drug particles in a finely divided, high surface area and well-wetted state. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:262,274, 2010 [source] Influence of the intermediate digestion phases of common formulation lipids on the absorption of a poorly water-soluble drugJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2005Greg A. Kossena Abstract The influence of different model intestinal phases (modelled on those likely to be produced in vivo after the digestion of commonly used formulation lipids) on the absorption profile of cinnarizine has been studied. Combinations of C8, C12, or C18:1 fatty acid and monoglyceride and simulated endogenous intestinal fluid were formulated to provide examples of liquid (L1), lamellar (L,), and cubic (C) liquid crystalline phases. Phases containing cinnarizine were dosed intraduodenally and absorption was assessed in an anesthetized rat model. Bile duct ligation was performed to inhibit the effects of digestion/dilution on the phase structure. Absorption from the L, phases (C8 and C12 lipids) was statistically higher (p,<,0.05) than a cinnarizine suspension: however, a statistically significant difference was not observed from the L1 and C phases. The rigid C18:1 C phase showed evidence of providing for sustained drug absorption. Experiments in bile intact rats with the C8 L, and C18:1 C phase highlighted that the absorption-modifying properties of these phases were influenced by dilution in the endogenous bile milieu, with absorption from L, phase reducing (possibly through precipitation of solubilized drug) and increasing in the case of the C18:1 C phase, possibly through the coexistence of L1 and C upon dilution permitting more efficient transfer of solubilized drug. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:481,492, 2005 [source] Long-range effects of chirality in aromatic poly(isocyanide)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006David B. Amabilino Abstract The preparation of optically active atropoisomeric polymers which present chiral backbones, thanks to induction during their synthesis from stereogenic centers, located far away from the skeleton is possible, thanks principally to semirigid conformations of the promesogenic spacers between them. The result is that chiral "information" can be passed as far as 21 Å from the asymmetric center to the carbon atom that forms the polymeric chain in poly(isocyanide)s. The sense of chiral induction in these conformationally rigid polymers parallels the helical sense of the cholesteric phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and smectic C phases, respectively. All these phenomena obey the odd,even rules proposed for chiral sense changes in these liquid crystalline phases. Noncovalent interactions play an important part in the induction process, in which steric arguments can be used to justify the inductions observed. The methodology can be used to prepare macromolecules, which display switching behavior upon thermal or electrochemical stimulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3161,3174, 2006 [source] Liquid Crystalline Ordering and Charge Transport in Semiconducting MaterialsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2009Wojciech Pisula Abstract Organic semiconducting materials offer the advantage of solution processability into flexible films. In most cases, their drawback is based on their low charge carrier mobility, which is directly related to the packing of the molecules both on local (amorphous versus crystalline) and on macroscopic (grain boundaries) length scales. Liquid crystalline ordering offers the possibility of circumventing this problem. An advanced concept comprises: i) the application of materials with different liquid crystalline phases, ii) the orientation of a low viscosity high temperature phase, and, iii) the transfer of the macroscopic orientation during cooling to a highly ordered (at best, crystalline-like) phase at room temperature. At the same time, the desired orientation for the application (OLED or field-effect transistor) can be obtained. This review presents the use of molecules with discotic, calamitic and sanidic phases and discusses the sensitivity of the phases with regard to defects depending on the dimensionality of the ordered structure (columns: 1D, smectic layers and sanidic phases: 2D). It presents ways to systematically improve charge carrier mobility by proper variation of the electronic and steric (packing) structure of the constituting molecules and to reach charge carrier mobilities that are close to and comparable to amorphous silicon, with values of 0.1 to 0.7,cm2,·,V,1,·,s,1. In this context, the significance of cross-linking to stabilize the orientation and liquid crystalline behavior of inorganic/organic hybrids is also discussed. [source] Effect of Core Twisting on Self-Assembly and Optical Properties of Perylene Bisimide Dyes in Solution and Columnar Liquid Crystalline PhasesCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2007Zhijian Chen Abstract A series of highly soluble and fluorescent core-twisted perylene bisimide dyes (PBIs) 3,a,f with different substituents at the bay area (1,6,7,12 positions of the perylene core) were synthesized and fully characterized by 1H,NMR, UV/Vis spectroscopy, MS spectrometry, and elemental analysis. The ,,, aggregation properties of these new functional dyes were investigated in detail both in solution and in condensed phase by UV/Vis and fluorescence spectroscopy, vapor pressure osmometry (VPO), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. Concentration-dependent UV/Vis measurements and VPO analysis revealed that these core-twisted ,-conjugated systems show distinct self-dimerization equilibria in apolar solvent methylcyclohexane (MCH) with dimerization constants between 1.3×104 and 30,M,1. The photoluminescence spectra of the dimers of PBIs 3,a,f exhibit bathochromic shifts of quite different magnitude which could be attributed to different longitudinal or rotational offsets between the dyes as well as differences in the respective ,,, stacking distance. In condensed state, quite a few of these PBIs form luminescent rectangular or hexagonal columnar liquid crystalline phases with low isotropization temperatures. The effects of the distortion of the , systems on their ,,, stacking and the optical properties of the resultant stacks in solution and in LC phases have been explored in detail. In one case (3,a) a particularly interesting phase change from crystalline into liquid crystalline could be observed upon annealing that was accompanied by a transformation from non-fluorescent H -type into strongly fluorescent J -type packing of the dyes. [source] | ||||||||||||||||