Crystal structures of ferro- and antiferroelectric mesogens with a 1-methylalkoxycarbonyl group

Crystal structures have been determined for 4-[(S)-1-methylpentyloxycarbonyl]phenyl, 4-([S)-1-methylhexyloxycarbonyl]phenyl 4'-octyloxybiphenyl-4-carboxylates (1 and 2, respectively) and (R)-1-methylheptyl 4-(4'-octyloxybiphenyl-4-yloxymethylene)benzoate (3), which have S_CA*, S_C* and S_CA* phases, respectively. All the crystals have a common packing mode with the previously determined structure of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC). Each crystal forms a smectic-like layer structure composed of largely bent molecules with the long alkyl chain of the chiral group almost perpendicular to the core moiety. Differential scanning calorimetry showed that the crystals of 1, 2, and MHPOBC, which have a carbonyloxy group as the central linkage between the biphenyl and phenylene moieties, transform to higher temperature solid phases in a similar temperature range (around 60°C). For 3, which has an oxymethylene linkage between the biphenyl and phenylene moieties, three kinds of solids were distinguished.     

New liquid crystals containing the benzothiazol unit: amides and azo compounds

Two series of calamitic liquid crystals containing a benzothiazole ring within the central core and two different linkage groups (amide and azo) have been prepared and their liquid crystalline properties studied and compared with those of the analogous series of imines. The influence of the linkage group within the central core has been proven to determine the variety of mesomorphism displayed by the compounds. The compounds with imine and azo linkages behave in a similar way and exhibit typical nematic and smectic C mesophases. Compounds incorporating an amide linkage show a poorer mesomorphism and mainly present a smectic C mesophase.     

New mesogens with a fluoro-substituted bent core

Ferroelectric properties in liquid crystals are no longer restricted to materials with a chiral molecular structure; ferroelectricity has been observed in a smectic phase formed by bent achiral molecules. Accordingly, two homologous series possessing a central biphenyl methane core have been synthesized, the central core having two lateral fluoro substituents. Both the series have six-ring structures and exhibit smectic mesophases of high thermal stability. The flexible biphenyl methane core imparts a slight curve to the molecules, giving them a bent shape.     

New mesogens with a fluoro-substituted bent core

Ferroelectric properties in liquid crystals are no longer restricted to materials with a chiral molecular structure; ferroelectricity has been observed in a smectic phase formed by bent achiral molecules. Accordingly, two homologous series possessing a central biphenyl methane core have been synthesized, the central core having two lateral fluoro substituents. Both the series have six-ring structures and exhibit smectic mesophases of high thermal stability. The flexible biphenyl methane core imparts a slight curve to the molecules, giving them a bent shape.     

Theoretical investigations on electronic structures and photophysical properties of N-heteroaryl carbazole derivatives as host materials

The carbazole-endcapped host molecules with tailoring different heteroaryl core and meta-position linkage mode have great potential on phosphorescent organic light-emitting diodes. To provide a profound view on structure?Cproperty relationships, new linear-shaped counterparts have been designed based on the existing molecular composition and the linkage at para-position (p-type molecules). A series of studies about the influence of the linkage mode on optical and electronic properties of these carbazole derivatives have carried out via density functional theory and time-dependent density functional theory calculations. The geometric and the electronic structure of these molecules in the ground states, ions states, and lowest triplet states have been calculated especially focusing on the analysis of highest occupied molecular orbitals, lowest unoccupied molecular orbitals, energy gaps, triplet energies, ionization potentials, electron affinities, reorganization energies, triplet exciton-formation fraction, and absorption spectra. These optoelectronic properties can be effectively tuned by the chemical modifications of different linkage pattern. The good coordination between our calculated results and the available experimental data has been observed. The study reveals that the designed p-type molecules show great promise as new high-performance red host materials with large triplet energy, narrow energy gap, good electron and hole-transport properties, and high triplet exciton-formation fraction.     

Synthesis and mesomorphic properties of 4-n-alkoxy 4'-[4-((4-n-alkoxy-2,3,5,6-tetrafluoro-phenyl)ethynyl)benzyloxy]benzoates

Two series of tolane-based liquid crystals have been prepared that incorporate a tetrafluorophenyl moiety and a flexible methyl ether bond into the core structure. The mesomorphic properties have been studied by polarizing microscopic textural observation and DSC measurements. By comparison with their non-fluorinated analogues, the effect of tetrafluorophenylene on mesomorphic behaviour has been discussed in this paper.     

Study of temperature transitions in solid poly(oxymethylene) by thermal analysis methods

Poly(oxymethylene)s with different molecular mass and chemical structure were studied using DSC, dynamic mechanical relaxation, thermomechanical analysis, and thermogravimetry.Molecular mobilities of two types were found in the amorphous phase of poly(oxymethylene). Unconstrained chains of poly(oxymethylene) soften at –70°C and then amorphous chains with different restraints from the crystalline phase are successively activated in a wide temperature interval.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThis work has been supported by DuPont Company     

Inorganic oxide core, polymer shell nanocomposite as a high K gate dielectric for flexible electronics applications

Organic/inorganic core shell nanoparticles have been synthesized using high K TiO(2) as the core nanoparticle, and polystyrene as the shell. This material is easy to process and forms transparent continuous thin films, which exhibit a dielectric constant enhancement of over 3 times that of bulk polystyrene. This new dielectric material has been incorporated into capacitors and thin film transistors (TFTs). Mobilities approaching 0.2 cm(2)/V.s have been measured for pentacene TFTs incorporating the new TiO(2) polystyrene nanostructured gate dielectric, indicating good surface properties for pentacene film growth. This novel strategy for generating high K flexible gate dielectrics will be of value in improving organic and flexible electronic device performance.     

Influence of the structure of the mesogenic core on the thermotropic properties of ω-unsaturated fluorinated liquid crystals

Three series of calamitic liquid crystals have been prepared, consisting of a mesogenic core attached to which is a perfluorinated chain via a thioester linkage, and a hydrocarbon chain containing a terminal double bond. The rigid core is either a monophenyl, biphenyl or phenyl benzoate group. The mesomorphic properties were characterized by polarizing optical microscopy and differential scanning calorimetry. The influence of the structure of the mesogenic core and of the hydrocarbon chain length on mesomorphic behaviour was studied. Increasing the length of the alkyl chain strongly reduces the mesomorphic behaviour while increasing the number of aromatic rings in the core increases the transition temperatures, with the widest LC range observed for derivatives with the phenyl benzoate core. The introduction of a single ring as the mesogenic core is considered of great interest in the development of low cost liquid crystal materials.     

The transacetalization reaction during the etherification of poly(oxymethylene)diol [α-hydro-ω-hydroxypoly(oxymethylene)] with orthoesters in the presence of lewis acids

A transacetalization reaction occurs during the etherification of poly(oxymethylene)diol [α-hydro-ω-hydroxypoly(oxymethylene)] with orthoesters and an important modification of molecular structure takes place. The intermediates formed during the transacetalization reaction are emphasized. The connection between this reaction and the other reactions during the etherification of poly(oxymethylene)diols is discussed.     

Mechanical properties and structure relationships in drawn fibers of elastomer–polyoxymethylene blends

Superdrawn fibers of an elastomer–poly(oxymethylene) (POM) blend have been prepared and investigated in terms of the structure and mechanical properties. The development of the mechanical properties along the fiber axis and the formation of a higher order structure during drawing were slightly retarded by blending, but the loop tenacity increased greatly with the elastomer content. The blend microtextures had an immiscible and phase-separated morphology in which the elastomer was dispersed in the form of streaks between the oriented POM layers, which allowed the fiber to split into smaller filaments on bending. The high loop tenacity of the blend fibers is due to an increase in the radius of curvature resulting from the filament splitting on bending, because the shear stress at the bending corner becomes higher as the radius of curvature increases. © 1997 John Wiley & Sons, Inc.     

Syntheses of heparin - like pentamers containing “opened” uronic acid moieties

The syntheses of four analogues of pentasaccharide Ia, which corresponds to the minimal AT III binding region of heparin, are presented and the biological activities of these analogues will be discussed. Three of these analogues (i.e. compounds II, III and IV) contain an R-glyceric acid oxymethylene residue (i.e. B in fig.3) instead of -L-iduronic acid and in the other analogue (i.e. compound V) the β-D-glucuronic acid unit has been replaced by an s-glyceric acid oxymethylene residue (i.e. A in fig3). The R and S-glyceric acid oxymethylene residues represent an “opened” iduronic acid unit and an “opened” glucuronic acid unit, respectively, containing the essential carboxylate function in the appropriate configuration. The crucial step in the syntheses of these “opened” uronic acid pentamer analogues, was the preparation of the required glyceric acid oxymethylene residues 8a, 8b and 8c.

Analogues II and III, containing an “opened” iduronic acid moiety, display a significant AT III mediated Xa activity. Compound III contains two extra sulphate groups at unit 2. Removal of the contributing O-sulphate groups at position 3 and 6 of unit 6 of compound II (i.e. compound IV) results in a seven-fold drop in Xa activity. Replacement of the β-D-glucuronic acid unit by an S-glyceric acid oxymethylene residue (i.e. compound V) leads to almost a complete loss of Xa activity, notwithstanding the fact that all the essential and contributing charged groups are present in the molecule.     

Chirality Transfer in the Formation of Poly(oxymethylene) Helices by Anionic Polymerization

In this article, we present the synthesis of a series of oligo(oxymethylenes) capped with 1‐phenylethanol and MeOH. The anionic condition affords enantiomerically pure oligo(oxymethylene) oligomers, while the cationic oligomerization leads to a racemic mixture of the oligo(oxymethylene) chain.     

Discotic liquid crystals: a new generation of organic semiconductors

Discotic (disc-like) molecules typically comprising a rigid aromatic core and flexible peripheral chains have been attracting growing interest because of their fundamental importance as model systems for the study of charge and energy transport and due to the possibilities of their application in organic electronic devices. This critical review covers various aspects of recent research on discotic liquid crystals, in particular, molecular design concepts, supramolecular structure, processing into ordered thin films and fabrication of electronic devices. The chemical structure of the conjugated core of discotic molecules governs, to a large extent, their intramolecular electronic properties. Variation of the peripheral flexible chains and of the aromatic core is decisive for the tuning of self-assembly in solution and in bulk. Supramolecular organization of discotic molecules can be effectively controlled by the choice of the processing methods. In particular, approaches to obtain suitable macroscopic orientations of columnar superstructures on surfaces, that is, planar uniaxial or homeotropic alignment, are discussed together with appropriate processing techniques. Finally, an overview of charge transport in discotic materials and their application in optoelectronic devices is given.     

Theoretical studies of some nonbenzenoid hydrocarbons—IV : Pleiadiene and related compounds

Pleiadiene and other similar compounds have been studied by the semi-empirical SCFMO method of Pariser, Parr and Pople using the core resonance integral value developed by Lo and Whitehead, Dewar et al. and Yamaguchi et al. It has been found that π^*←π transitions predicted by the methods of Lo and Whiteheadand Dewar et al. suitable for the prediction of ground state properties are also in good agreement with experimental results where available and comparable to those predicted by the method of Yamaguchi et al. developed for the prediction of spectral transitions. The resonance stabilization of the molecules 3,4.5,7,8 and 9 have also been studied. It is found that ethylinic linkage across the naphthalene moity in pleiadiene increases the resonance energy of the final compound, in contrast to our previous observation, i.e. ethylinic linkage across the naphthalene moiety reduces the resonance energy of the final compound.     

Lateral substituted phenyl biphenylcarboxylates ‒ non-chiral analogues of ferroelectric liquid crystals

ABSTRACT

We report mesomorphic properties of non-chiral liquid crystalline molecules and study the effect of lateral halogen (fluoro, chloro) substitution in the molecular core and the length of terminal chains. We have prepared nine homologue series with the molecular core substituted at different positions with respect to the ester linkage group. Additionally, we have modified the length of both terminal alkyl chains (hexyl, octyl, decyl and dodecyl) symmetrically for both terminal chains. The effects of the lateral substitution and the chain length are analysed with respect of the possibility to reduce the transition temperatures and tune the properties of presented liquid crystalline molecules.     

Hybridization of a Flexible Cyclooctatetraene Core and Rigid Aceneimide Wings for Multiluminescent Flapping π Systems

The hybridization of flexible and rigid π‐conjugated frameworks is a potent concept for producing new functional materials. In this article, a series of multifluorescent flapping π systems that combine a flexible cyclooctatetraene (COT) core and rigid aceneimide wings with various π‐conjugation lengths has been designed and synthesized, and their structure/properties relationships have been investigated. Whereas these molecules have a V‐shaped bent conformation in the ground state, the bent structure changes to a planar conformation in the lowest excited singlet (S₁) state irrespective of the lengths of the aceneimide wings. However, the fluorescence behavior in solution is distinct between the naphthaleneimide system and the anthraceneimide system. The former has a nonemissive S₁ state owing to the significant contribution of the antiaromatic character of the planar COT frontier molecular orbitals, thereby resulting in complete fluorescence quenching in solution. In contrast, the latter anthraceneimide system shows an intense emission, which is ascribed to the planar but distorted S₁ state that shows the allowed transition between the π‐molecular orbitals delocalized over the COT core and the acene wings. The other characteristic of these π systems is the significantly redshifted fluorescence in the crystalline state relative to their monomer fluorescence. The relationship between the packing structures and the fluorescence properties was investigated by preparing a series of hybrid π systems with different sizes of substituents on the imide moieties, which revealed the effect of the twofold π‐stacked structure of the V‐shaped molecules on the large bathochromic shift in emission.     

An insight into a novel class of self-assembled porphyrins: geometric structure, electronic structure, one- and two-photon absorption properties

We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibit large two-photon absorption (TPA) cross sections in the visible-IR range. The electronic structure, one-photon absorption (OPA), and TPA properties have been studied in detail. We found that the introduction of a butadiyne linkage and the increase of the molecular dimensionality from monomer to dimer determine the OPA intensities of Q band and Soret band, respectively. A most important role for the enhancement of the TPA cross section is played by introducing a butadiyne bridge. The complementary coordination and the combination of the terminal free base and the core zinc porphyrin are also two effective factors for the enhancement of the TPA efficiency. The dimer with two porphyrins linked at meso-positions by a butadiyne linkage results in a maximum TPA cross section (79.35 x 10(-48) cm4 s per photon). Our theoretical findings are consistent with the recent experimental observations. This series of porphyrin derivatives as promising TPA materials are the subject of further investigation.     

Peak area measurements of cross-polarization magic-angle-spinning 13C-NMR spectra of crosslinked polystyrenes

Cross-polarization magic-angle-spinning ¹³C-NMR spectra of polystyrenes crosslinked with 1–20% of methine vinyl carbon ¹³C-labeled p-divinylbenzene and of Friedel–Crafts crosslinked poly(chloromethylstyrene)s have been obtained with both glossy solid and CDCl₃-swollen gel samples. The spectra of natural abundance, uncrosslinked, glassy polystyrene, and the spectra of the solid labeled networks give aliphatic and aromatic peak areas only 0.7 times as large per ¹³C atom as that of poly(oxymethylene). Similarly the crosslinked poly(chloromethylstyrene) gave peak areas about 0.6 times that of internal poly(oxymethylene). The labeled gels give peak areas 0.2–0.6 times as large per ¹³C atom as glassy polystyrene, and the peak areas in spectra of gels increase with the divinylbenzene content     

Cationic grafting from carbon black. VII. Grafting of polyacetals by cationic ring-opening polymerization of trioxane and 1,3-dioxolane initiated by CO+ClO4− groups on carbon black

The cationic ring-opening polymerization of trioxane and 1,3-dioxolane was found to be initiated by CO⁺CIO₄^? groups on a carbon black surface, which were introduced by the reaction of COCI groups with AgCIO₄. The activation energy of the ring-opening polymerization of trioxane was estimated to be 15.5 kcal/mol. In the polymerization system, poly(oxymethylene) and poly(1,3-dioxolane) formed were effectively grafted onto carbon black depending upon the propagation of these polymers from the carbon black surface; for instance, the grafting ratio of poly(oxymethylene) onto carbon black increased with an increase in conversion and went up to about 180%. Although the grafted chain of poly(oxymethylene) was subject to stepwise thermal depolymerization from the chain ends, the thermal stability of poly(oxymethylene)-grafted carbon black was improved by acetylation of hemiformal end groups. The molecular weight of ungrafted poly(oxymethylene) formed in the polymerization was determined to be 1.8–2.0 × 10⁴. Furthermore, the copolymerization of trioxane with 1,3-dioxolane, styrene, and other comonomers initiated by CO⁺CIO₄^? groups and the thermal stability of these acetal copolymer-grafted carbon black were investigated.