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We report the synthesis of a new homologous series of symmetric bent-shaped liquid crystal dimers bearing oxybiphenylcarboxylate mesogens linked by a pentamethylene spacer. The dimers were characterised by optical, thermal, X-ray diffraction and computational techniques. Shorter dimers showed an I-N-SmA-SmC phase sequence with strong first-order phase transitions. For the longer dimers, the unconventional uniaxial SmA phase present in shorter members collapsed. A 9:1 binary mixture of a bent dimer with a non-mesogenic dimer exhibited upon the SmA-SmC phase transition a maximum layer contraction of 1%.

Lipophilic linear semirigid side arms containing two or three successive phenyl rings separated by carboxylate spacers have been connected to the 5 or 6 positions of bent aromatic terdentate 2,6-bis(benzimidazol-2-yl)pyridine binding units to give extended V-shaped (L11) and I-shaped receptors (L12, L12b, and L13). The carboxylate spacers limit the flexibility of the side arms and provide crossed arrangements of the successive aromatic rings in the crystal structure of L12b (C63H61N5O10; triclinic, P1̄, Z = 2) in agreement with semiempirical calculations performed on optimized gas-phase geometries. Moreover, the carboxylate spacers in L11−L13 prevent efficient electronic delocalization between the connected aromatic rings and act as weak π acceptors producing a slight increase of the energy of the 1ππ* and 3ππ* levels centered on the terdentate binding unit. Intermolecular π-stacking interactions observed in the crystal of L12b are invoked to rationalize (i) the peculiar excimer emission of L11 in the solid state and (ii) the rich and varied calamitic (I-shaped L12, L12b, and L13) and columnar (V-shaped L11) mesomorphism observed at high temperature. The ColR mesophase detected for L11 demonstrates that V-shaped bent terdentate binding units are compatible with liquid-crystalline behavior. Complexation of L11 with lanthanide(III) produces I-shaped complexes [Ln(L11)(NO3)3] (Ln = La, Eu, Gd, Tb, and Lu) possessing a large axial anisometry as found in the crystal structure of [Lu(L11)(CF3CO2)3(H2O)] (LuC81H87N5O17F9; triclinic, P1̄, Z = 2), which exists in the solid state as H-bonded dimers. No mesomorphism is detected for the complexes as a result of the large perpendicular expansion brought by the metallic coordination site, but the high energy of the ligand-centered 3ππ* prevents Eu(5D0) → L11 back transfer in the Eu(III) complex, which thus exhibits sizable red luminescence at room temperature, a crucial point for the design of luminescent materials.

Synthesis and characterization of new hexabenzocoronene (HBC) derivatives bearing perfluoroalkylated chains are described. These disc-shaped polycondensed aromatic hydrocarbons are known to self-assemble by π-stacking into columnar architectures. The peripheral decoration with perfluorinated chains, well-known for their low van der Waals forces, leads as expected to reduced intercolumnar interactions. Powder X-ray diffraction and differential scanning calorimetry of these perfluoroalkylated HBCs proved liquid crystalline (LC) properties whose transition temperatures, mesophase stability, and nature depend on the detailed structure of these side chains, i.e., the ratio between aliphatic and perfluorinated parts. On the other hand, the insertion of a phenyl spacer between the aromatic core and the lateral chains increases the LC transition temperature and, surprisingly, switches the mesophase structure from columnar to smectic.

The mesomorphic behavior, shape shifting, and shape-memory types of two homologous series of main-chain liquid-crystalline co-elastomers (MC-LCEs) with composition-tunable transition temperatures and mesophases structures are reported. The weakly cross-linked macromolecules were prepared in a one-step procedure by the versatile platinum-catalyzed hydrosilylation reaction between siloxane oligomers (linear spacers and netlike point molecules) and liquid-crystalline binary mixtures, composed of defined proportions of divinylic monomeric mesogens. First, the two sets of alternated, linear copolymers with disiloxane or trisiloxane chain extender, respectively, were investigated. They either exhibit both smectic C (SmC) and nematic (N) phases or a single SmC phase, the nature of which being dictated by the length of the inserted siloxane moieties, and the temperatures ranges regulated by the composition of the mesogenic mixture (mesogens ratio). As anticipated, the thermal behavior of the corresponding co-elas...

A set of liquid-crystalline polymeric systems, associating at once the regioregular polythiophene backbone and pending mesogenic triphenylenes, is reported. Two series, namely regular homopolymers and alternating copolymers, were prepared by adapting a Grignard metathesis-based methodology, allowing some of the relevant structural parameters to be sequentially and independently modified. The thermal and self-organization behaviors of these uncommon macromolecular systems were investigated by polarized-light optical microscopy, differential scanning calorimetry and temperature-dependent small-angle X-ray scattering. Most polymers self-organize into mesophases possessing intertwined lamello-columnar morphologies, resulting from the simultaneous coexistence of lamellar and columnar sublattices. The successful preparation of oriented thin films of several of these polymeric homologues allowed further investigations by atomic force microscopy, transmission electron microscopy, electron diffraction, and grazing-incidence SAXS, which provided a deeper insight of the intricate supramolecular organizational modes, including the complete elucidation of the structure of the lamello-columnar mesophases. This simple and versatile strategy provides a route to elaborate polymeric materials incorporating two intercalated separate pathways toward charge carrier transport, of paramount importance for future electronic and optoelectronic applications.

The thermotropic properties and self-assembly of two different series of hexa-peri-hexabenzocoronenes (HBC) bearing either linear or branched perfluoroalkylated side chains, each with a wide range of alkyl spacer and perfluorinated tail lengths, have been studied. Correlations between thermogravimetric analysis, differential scanning calorimetry, polarised optical microscopy and small-angle X-ray scattering experiments revealed, as expected, that the transition temperatures and phase stability are influenced by the determining roles of the aliphatic spacer length and odd/even nature, as well as the size and structure (linear vs. bifurcation) of the perfluorinated sections. Most of the investigated HBC derivatives showed a single-column hexagonal columnar phase, where the columns are structured by a double segregation process between HBC aromatic cores and aliphatic spacers, on the one hand, and between aliphatic spacers and fluorinated tails, on the other hand. For the derivatives with long linear spacers, cores of untilted or quasi-untilted HBC stacks are surrounded by a cylindrical aliphatic envelope segregated from the fluorinated periphery, whereas for those with shorter linear spacers, the same structure is kept, except that the aliphatic envelope deviates from cylindricality and causes a symmetry break to rectangular envelope for the first term of the series. Of the four HBC with branched spacers, two are amorphous, whereas a columnar phase is maintained for the other two derivatives, but with tilted HBC stacks. Consequently, the evolution of the polymorphism in the series could be correlated with the variation of both interface areas.

A new class of star-shaped, liquid crystalline, low-molecular weight compounds functionalized with photochromic azobenzene and mesogenic groups was investigated in terms of light-induced anisotropy. The behaviour of the materials under the action of light with simultaneous or subsequent thermal treatment was examined with respect to the induction of anisotropy. The unconventional UV light treatment prior to the irradiation with linearly polarized light allowed induction of very high values of anisotropy (D = 0.77) at room temperature. Moreover, the simultaneous action of light and temperature led to the induction of higher values of dichroism in comparison with anisotropy generated by the standard procedure. Subsequent thermal treatment led to dewetting and the formation of 3D macroscopic stripe- and dome-like structures for one of the investigated compounds. Despite photoinduction of anisotropy by a single beam, the formation of polarization and surface relief gratings by two-beam interference pattern was also investigated.

The synthesis and self-organizing behaviour into liquid-crystalline mesophases of two libraries of segmented block co-dendrimers are described. The overall structure of the dendritic supermolecules consists of two chemically incompatible molecular moieties, covalently connected by combinatory cross-coupling reactions. One block is composed of linear perfluorinated segments (2 generations, defining the two libraries), and the bulky dendritic compartment is formed by a lipophilic poly(benzyl ether)-based dendron (3 generations). The mesomorphic properties were studied as a function of the respective generations of both blocks and of the peripheral alkyl chains’ substitution pattern. The results of these investigations reveal the formation of unusual and highly segregated supramolecular liquid-crystalline mesophases, whose arrangements are subtly controlled by the lipophilic/fluorophobic balance and dendritic connectivity.

Ionic liquid Crystals constitute highly versatile materials that have drawn much interest these past few years in the fields of academic research and industrial development. In this respect, the present article is intended as an update of K. Binnemans review published in 2005, but focusing exclusively on the imidazolium cation - the most widely studied. Herein, imidazolium-containing thermotropic liquid crystalline materials will be sorted by molecular structure (mono-, bis-, poly-imidazolium compounds, with symmetrical and non-symmetrical structures) and discussed. Their physico-chemical properties will be exposed in order to adduce the relevancy and potential of the imidazolium platform in various fields of research.

A new kind of side-chain liquid crystal semiconducting polymer where the backbone is a π-conjugated polymer and the side groups are π-conjugated discotic mesogens self-assembles in a peculiar lamello-columnar mesophase where a 2D oblique columnar lattice and the lamellar piling coexist in the same structure.

Gold nanoparticles offer the possibility of creating metamaterials; however, such nanoparticles are not particularly stable. Conversely, liquid crystals offer the possibility of creating self-organizing and self-assembling materials, which can be designed to be relatively stable. Potentially, combining these two concepts could provide materials that can be induced to assemble in a controlled way and that would have unique optical properties. This article describes some of the groundwork made in the preparation of stable liquid-crystalline metamaterials and the investigation of their structures and physical properties. In particular, spherically substituted materials are found to be deformed into tactoids with anisotropic properties, most notably their dielectric anisotropies.

The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe(3-x)O(4), i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x = 1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization M(s) and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.

Poly(4-vinylpyridine)s (P4VPs) fully and partially quaternized with dialkyloxyterphenyl groups were synthesized and characterized. These new polymers developed both liquid-crystalline (LC) properties and a light emission (luminescence) in the blue region. The mesomorphic behavior of the polymers was initially characterized by differential scanning calorimetry and polarizing optical microscopy and was further corroborated by X-ray diffraction analyses. The X-ray diffraction patterns showed in the low-angles region several equidistant diffraction peaks (d001, d002, d003, …) and in the wide-angles region a broad peak typical of nonordered mesophases. From d001 and the length of the monomers, we deduced that the molecular arrangement in the mesophase corresponded to a double-layered stacking of molecules with mesogens tilted with respect to the smectic plane and the backbones sandwiched between. In this arrangement, the different parts of mesogens are segregated from one another in layered domains. The longer smectic periods observed for copolymers indicated that the nonsubstituted pyridine cycles were sandwiched between two smectic layers. The emission spectra of these polymers were characterized by a broad signal centered at 365 nm. The combination of LC properties with luminescence in the polymers is interesting for the preparation of thin films with aligned emitters, particularly for linearly polarized light emission. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Molecular and polymeric liquid crystals bearing bipyridinium and pentaphenylene groups were synthesized and characterized. These new ionic liquid crystals develop single layer smectic-type mesophases with molecules tilted or orthogonal with respect to the smectic planes as a function of temperature. A high tendency to develop a homeotropic behavior was observed for the molecular liquid crystals. A molecular arrangement was proposed in which the different parts of molecules are fully segregated from one another with the ionic groups stabilizing the smectic order. These molecules show a luminescence in the blue region that combined with the liquid–crystalline behavior could be interesting for the fabrication of light emitting thin films with ordered molecular emitters.

A fluid nematic-like phase is induced in monodisperse iron oxide nanoparticles with a diameter of 3.3 nm. This supramolecular arrangement is governed by the covalent functionalization of the nanoparticle surface with cyanobiphenyl-based ligands as mesogenic promoters. The design and synthesis of these hybrid materials and the study of their mesogenic properties are reported. In addition, the modifications of the magnetic properties of the hybridized nanoparticles are investigated as a function of the different grafted ligands. Owing to the rather large interparticular distances (about 7 nm), the dipolar interaction between nanoparticles is shown to play only a minor role. Conversely, the surface magnetic anisotropy of the particles is significantly affected by the surface derivatization.

We have prepared a series of thermotropic liquid-crystalline oligopeptide dimers based on dendritic oligo(glutamic acid)s. The synthesized oligopeptide dimers form thermally stable columnar liquid crystals. Self-assembled structures of the columnar liquid crystals varied with the spacer length and molecular chirality of the oligopeptide residues.

A series of discotic octa- and tetra-alkylthio substituted phthalocyanines containing four Cl, Br, I atoms or twelve fluorine atoms have been prepared. All compounds display columnar mesomorphism as confirmed by polarized optical microscopy, thermal analysis, and variable temperature X-ray diffraction. Phthalocyanines containing halide atoms do not crystallize but form glassy or partially crystalline hexagonal columnar phases. Glass transition temperatures increase with increasing size of the halide atoms and with decreasing length of the alkyl chains. In contrast, all octa- and tetra-alkylthio substituted phthalocyanines crystallize and octa-substituted derivatives with aliphatic chain lengths of C5–7 exhibit tilted (rectangular) columnar mesophases. Cyclic and differential pulse voltammetry, UV-Vis spectroscopy, and quantum chemical calculations at the DFT level have been employed to determine frontier orbital energies of all synthesized and some reference phthalocyanines. Octa- and tetra-alkylthio substituted phthalocyanines are typical p-type semiconductors and the introduction of four Cl, Br, or I atoms lowers frontier orbital energies by only up to 0.1 eV and the optical gap by up to 0.03 eV. A significant decrease in LUMO energy by 0.5 eV to about −4 eV is observed for the fluorinated phthalocyanine, which is a value right at the border of organic n-type semiconductors that may be stable in air.

Molecules containing a terphenylene core, two alkyl chains and a pyridinium ring associated with its bromine counterion were synthesised and their liquid crystalline properties were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results were compared with those of chemical intermediates, which also develop a liquid crystalline behaviour. Both intermediates and pyridinium salts showed a rich polymorphism at temperatures ranging from around 100 to 200°C and 115 to 220°C, respectively. X-ray results indicate that both intermediates and pyridinium salts develop tilted smectic mesophases with molecules stacked in single and double layers, respectively. The tilt angle of some of these compounds decreases so markedly upon cooling that molecules attain almost an orthogonal position. The stacking of molecules in the smectic layers was explained in terms of the mutual repulsion interactions between the terphenylene core, the alkyl chains and the ionic species ...

New liquid-crystalline protodendritic oligomers with dimesogenic side arms are reported. These “starlike” tetrapedes were obtained by modular synthesis involving the sequential association of different anisotropic promesogenic units within the molecular architecture. This synthetic methodology allowed to prepare tetrapedal oligomers with homolithic (all identical blocks) and conjugated heterolithic (different blocks) structures. The mesomorphism was largely influenced by the peripheral aliphatic chain substitution and to a lesser extent by the chemical nature of the primary constitutive building bricks (tolane and/or stilbene fragments). Indeed, depending on the number of terminal chains grafted onto the terminal mesogens, either columnar phases, resulting from the one-dimensional stacking of supramolecular disks of ∼3−6 supermolecules in fan conformation, or smectic phases, induced by the lateral two-dimensional registry of the supermolecules in cylindrical conformation, were induced. Some of the branche...

Hybrid organic−inorganic supramolecular aggregates displaying liquid crystal properties at room temperature have been synthesized by linking equimolar amounts of 2,4,6-triarylamino-1,3,5-triazine a...

The design, synthesis, and some properties of magnetic nanocrystals of ferrite functionalized by luminescent prodendritic ligands are described. Multipotent hybrids resulting from the coupling of an inorganic nanocore (metallic, alloy, or oxide nanoparticle) embedded in an organic shell currently elicit sustained research activity in various areas of materials science and notably in the development of numerous, potential applications, for example, as relevant building blocks for self-assembled arrays of nanoparticles with magneto-luminescence properties, as magnetically movable luminescent probes, or as platforms for biomedical applications. In this study, we have essentially focused on the covalent functionalization of γ-Fe2O3 magnetic nanoparticles, with an average diameter of 40 nm by engineered luminescent, liquid-crystalline oligo(phenylene vinylene)-based prodendritic ligands. The grafting rate of the various ligands on the oxide surface and the thermal stability and behavior of the hybrids have bee...

The crystal structure of the title 1,1′-disubstituted ferrocene derivative was determined by X-ray diffraction using a single crystal. This compound exhibits a nematic phase only. The X-ray structure analysis revealed that the two substituents lie in the same direction (`U' shape) and the flexible spacer adopts agaucheconformation. These conformations are strongly related to the formation of a rod-like shape, which favors liquid crystalline behavior. In the crystal structure, C—H...π, π–π and T-stacking interactions were observed. It is considered that these interactions play a major role in stabilizing the molecular packing arrangement and the mesomorphism.

In this manuscript, a complete and comprehensive study on main-chain liquid crystalline dendrimers is reported. In order to be able to finely tune, and thus control, the mesomorphism of such multicomponent supermolecules, various structural parameters were systematically modified, such as the core nature and connectivity, the degree and topology of branching, the molecular architecture, the generation, and the chain substitution pattern of the peripherally grafted pro-mesogenic groups. The increase of the molecular complexity and the effects of the structural manipulations proved to be very interesting for the design of multifunctional molecular materials, and provided new types of mesophases, enlarging as such the diversity of liquid crystalline supramolecular organizations.

Two ferroelectric three‐ring chiral esters, one with a partially fluorinated alkyl chain and another with a cyano terminal group, were mixed with a structurally similar compound having an alkyl terminal chain. In their mixtures an antiferroelectric phase was induced. The phase behaviour, spontaneous polarisation, tilt angle, smectic layer spacing and helical pitch of both systems were determined. The mechanism of the induction of an antiferroelectric phase is different in both cases, with highly tilted phases in former system and less tilted phases in the latter.

The effect of surface inorganic−organic interactions on magnetic and structural properties of iron oxide magnetic nanoparticles functionalized by lipophilic stilbene molecules has been investigated. The molecules have been grafted through either phosphonate or carboxylate coupling agents. Mossbauer spectra recorded at 300 and 77K suggest a global composition of Fe2.82O4 for the two types of functionalization. Complementary in-field Mossbauer and SQUID measurements have demonstrated that the nanoparticles consist in a magnetite core surrounded by an oxidized layer. The oxidized shell exhibits a spin canting in the carboxylate case leading to a decrease of the net magnetization of the oxide nanoparticle. No canting occurs in the phosphonate case, and the magnetic properties are therefore preserved. The magnetic properties thus depend on the coupling agent, e.g., surface interactions. This result is of primary importance to tune the magnetic properties of functionalized nanoparticles for biomedical and high ...

In this study, we report on the design and synthesis of new main-chain liquid crystal elastomers (MC-LCEs), i.e., LCEs with the mesogenic groups inserted in the main-chain, and on their mesomorphic...

New imines (HL) containing substituted dibenzo-18-crown-6-ethers and their dinuclear ortho-palladated complexes, [Pd(μ-X)L]2 (X– = CH3COO–, Cl–), have been prepared. The free imine ligands are not liquid crystals, but the palladium complexes, including acetato-bridged derivatives, show liquid-crystal properties. The mesomorphic palladium complexes bear six or eight alkoxy chains. Although a columnar arrangement of these chains might be expected, a smectic arrangement is in fact preferred for half of the metallomesogens prepared, which show a smectic C mesophase. Complexation with potassium produces a significant increase in the mesophase range and stability. Moreover, both the free imines and the corresponding liquid-crystalline ortho-palladated complexes form stable Langmuir films at the air–water interface.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

2-Aryl-substituted imidazo[4,5-f]-1,10-phenanthrolines were used as building blocks for metal-containing liquid crystals (metallomesogens). Imidazo[4,5-f]-1,10-phenanthrolines are versatile ligands because they can form stable complexes with various d-block transition metals, including platinum(II) and rhenium(I), as well as with lanthanide(III) and uranyl ions and they can easily be structurally modified by a judicious choice of benzaldehyde precursor. None of the ligands designed for this study were liquid-crystalline. However, mesomorphism could be induced by their coordination to various metallic fragments. The thermal behavior of the metal complexes depended on the metal-to-ligand ratio and the substitution pattern of the coordinating ligands. Complexes with a metal-to-ligand ratio of 1:1 [ML, with M = Pt(II), Re(I)] were not liquid-crystalline. The lanthanide(III) complexes with a metal-to-ligand ratio of 1:2 [ML2, with M = Ln(III)] formed an enantiotropic cubic mesophase or were not liquid-crystall...

The design and the functionalisation of nanoparticles is a promising way to elaborate new functional materials, with combined or coupled properties (magnetic, optical, optoelectronic …). In this context, the direct binding of functional organic conjugated molecules (stilbene derivative) onto the surface of monodisperse Fe 3 O 4 magnetic nanoparticles has been studied. Monodisperse Fe 3 O 4 nanoparticles have been synthesized by adjusting the conditions of precipitation and growth and then stilbene derivatives have been grafted onto the surface of these nanoparticles using either phosphonate or carboxylate groups as coupling agents. The functionalised nanoparticles have been characterized before and after grafting by several techniques (XRD, UV, TEM). Studies have demonstrated that the phosphonate coupling agent allows a higher grafting rate than with the carboxylate coupling agent. The nanoparticles functionalised via carboxylate groups are less stable than those functionalised with phosphonate groups mainly due to a strong P–O–Fe bonding. The coated magnetite nanoparticles retain their intrinsic magnetic properties.

Janus-type liquid−crystalline fullerodendrimers were synthesized via the 1,3-dipolar cycloaddtition of two mesomorphic dendrons and C60. By assembling poly(aryl ester) dendrons functionalized with cyanobiphenyl groups, displaying lamellar mesomorphism, with poly(benzyl ether) dendrons carrying alkyl chains, which display columnar mesomorphism, we could tailor by design the liquid−crystalline properties of the title compounds as a function of each dendron size. The liquid−crystalline properties were examined by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Depending on the dendrimer generations, smectic (SmC and/or SmA phases) or columnar (Colr-c2mm or Colr-p2gg phases) mesomorphism was obtained. The supramolecular organization is governed by (1) the adequacy of the cross-sectional area of the dendrons, (2) the microsegregation of the dendrimer, (3) the deformation of the dendritic core, and (4) the dipolar interactions between the cyanobiphenyl groups. Comparison of the mesomorphic properties of two fullerodendrimers with those of model compounds (fullerene-free analogues) indicated that the C60 unit does not influence the type of mesophase that is formed. Molecular properties determined in solution (permanent dipole moment, specific dielectric polarization, molar Kerr constant) confirm that microsegregation persists in solution and strengthen the models proposed for the structure of the mesophases.

The structure of hexacatenar bent-shape molecules has been systematically modified in order to determine the main molecular factors responsible for the appearance of the axially polar columnar mesophase. It was found that the stability of the polar phase is very sensitive to the subtle modifications of the molecular shape: the phase is solely preserved if the modification is made at the terminal parts of the mesogenic core, whilst any other modifications destabilize the phase. It can be concluded that the main factor driving the transition between the phase made of flat supramolecular discs and the axially polar phase made of the cone-like units is the ability to fulfill close packing conditions in order to eliminate voids between neighboring molecular rigid cores.

Great balls of fire: C60 and Y3 N@C80 were connected to the same oligo(phenyleneethynylene) unit to investigate their structural and photophysical properties. NMR investigations revealed a fulleroid structure for the Y3 N@C80 derivative, and both dyads gave rise to columnar phases with core-shell cylinders. The black and gray spheres represent the fullerene core units of the Y3 N@C80 derivative, which is an ideal candidate to be involved in energy and electron transfer processes.

The title compounds were synthesized by applying the 1,3-dipolar cycloaddition reaction of aldehyde-based poly(benzyl ether) dendrimers and sarcosine (N-methylglycine) to [60]fullerene (C60). The dendritic building blocks used to functionalize C60 displayed cubic and hexagonal columnar phases. The fullerene derivatives showed rectangular columnar phases of c2mm symmetry.

The synthesis of 3,4-dialkoxy and 3,4,5-trialkoxy derivatives of 2- and 3-stilbazole are reported along with their related complexes with silver dodecylsulphate and silver triflate. The single crystal structures of one ligand and two complexes are reported. While none of the complexes of the 2-stilbazoles is liquid-crystalline, several complexes of the 3-stilbazoles show columnar mesophases as characterised by polarised optical microscopy and X-ray diffraction. The liquid crystal phase behaviour is compared with that of the parent 4-stilbazole derivatives.

A new iron–terpyridine complex based on a 3,5-diacylaminotoluene platform bearing two phenyl rings appended with aliphatic chains provides robust and transparent organo-gels and liquid-crystalline materials. The LC mesophase was characterized by small-angle X-ray diffraction, and is described as a columnar phase with a rectangular lattice symmetry. Based on the measured parameters, a molecular packing model is suggested in which two complexes aggregate together to form a pseudo elliptical plateau; the latter then pile up to form the columns.

The Schiff base LH3 obtained by condensation of 3-formyl4-hydroxyphenyl-3,4,5-tris(tetradecyloxy)benzoate with 1,3diamino-2-propanol reacts with lanthanide(III) acetate salts to form dinuclear complexes of the type Ln2L2 with the trivalent ions from the first half of the lanthanide series (Ln =

Liquid-crystalline complexes of rhenium(I), yttrium(III), lanthanum(III), neodymium(III), samarium(III), europium(III), erbium(III), and ytterbium(III) were obtained by coupling mesogenic 4-cyanobiphenyl groups via a long alkyl spacer to a substituted imidazo[4,5-f]-1,10-phenanthroline, which acts as the coordinating group. In the case of the rare-earth complexes, 2-thenoyltrifluoroacetonate was used as the coligand. The rhenium(I) complexes contain the bromotricarbonylrhenium(I) moiety. All the rare-earth complexes exhibit a nematic phase, whereas the rhenium(I) complexes and the imidazole-bearing phenanthroline derivatives show a nematic or a lamellar columnar phase, depending on the number of attached mesogenic groups. The phase structures of the lamellar columnar phases are discussed and described on the basis of both X-ray diffraction data and dynamic molecular modeling. The lanthanide complexes are highly luminescent in the solid phase and as a solution in a nematic liquid-crystal host (5CB). The ap...

A new amphiphilic hexasubstituted [60]fullerene bearing 10 cholesterol units and a polar head made of two carboxylic acid functions has been prepared and its aptitude to film forming (Langmuir and Langmuir–Blodgett) evaluated. The results show that this amphiphile has the prerequisite qualities for its incorporation into the cellular membranes of living organisms.

The liquid-crystalline behaviour of copper(II) and nickel(II) complexes of a mesogenic Schiff-base ligand derived from N,N'-disalicylidene-1,2-phenylenediamine (salophenH2) and of the corresponding trinuclear mixed copper(II)/lanthanum(III) and nickel(II)/lanthanum(III) complexes was investigated. High-temperature X-ray diffraction studies revealed that both the parent transition metal complexes and the mixed f-d complexes exhibit a hexagonal columnar phase (Colh) over an extended temperature range. Complex formation with lanthanum(III) nitrate resulted in an increase of the transition temperatures. The geometrical parameters (lattice parameters and column cross-section) of all the metal complexes are very similar, which indicates that the local organisation in the mesophase is the same despite their structural differences. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The columnar mesophases of two series of hexacatenar palladium(II) mesogens have been studied in detail by a combination of X-ray diffraction on aligned and unaligned samples and dilatometry. The results of these studies, combined with the results of two single crystal structure determinations, have allowed a model of the molecular arrangement in the columnar phases to be proposed. This model differs in detail from that generally accepted for the arrangement of polycatenar mesogens in columnar phases, and a new model is proposed which accounts for both new and existing data.

A novel family of highly functionalized molecules consisting of a central 4-methyl-3,5-diacylaminobenzene platform linked in close proximity to the methyl group by two lateral aromatic rings each equipped with two long alkoxy chains has been rationally designed. The presence of amide tethers and a chelating phenanthroline fragment connected via an ester dipole formed a new class of gelating reagents and mesomorphic materials. A few of these compounds have the tendency to form macromolecule-like aggregates through noncovalent interactions in hydrocarbon solvents and were found to exhibit thermotropic cubic mesophases. In light of the X-ray molecular structure of the methoxy ligand, an infinite network maintained by intermolecular hydrogen bonds as well as by pi-pi stacking of the phenyl subunits was evidenced. FT-IR studies confirm that the common driving force for aggregation in the organogels and microsegregation in the mesophase is the occurrence of a tight intermolecular H-bonded network that does not persist in diluted solution. This situation is switched when the ligands are interlocked by a copper(I) cation. A strong intramolecular H-bond confirmed by X-ray diffraction of a single crystal for the methoxy case provides very stable complexes but inhibits the gelation of the solvents. Heating the complexes bearing long paraffin chains (n = 12 and 16) in the dried state leads to a self-organization into a columnar liquid-crystalline phase in which the columns are arranged along a 2D oblique symmetry as deduced from powder XRD experiments. In this case, the complexes with the appended counteranions self-assemble in a specific way to form columns. A striking observation is that the intramolecular hydrogen bond persists in the mesophase as it does in solution without any evidence of an extended network. As far as we are aware, these ligands and complexes are rare examples in which organogelation and thermotropic mesomorphic behavior could be observed in parallel with molecules bearing a chelating platform. Due to the synthetic availability of the 4-methyl-3,5-diacylaminobenzene core and the simplicity by which the chelating platforms can be graphed, this methodology represents a practical alternative to the production of functionalized organogelators and mesomorphic materials.

We have studied the behavior of a low molecular mass organosiloxane ferroelectric liquid crystal at the air−water interface. Data obtained with Langmuir isotherms, surface potential measurements, and Brewster angle microscopy are presented and discussed. The compound forms films on the Langmuir trough, with phase transitions to multilayers upon compression. As seen with Brewster angle microscopy, the monolayers are optically isotropic whereas striking birefringent structures develop in the multilayer films. These periodic structures result from a surface elasticity phenomenon.

Two series of polymeric mixed-valent diruthenium (II,III) aliphatic carboxylates of formula Ru2[O2C(CH2) n−2CH3]4X (where X=dodecylsulfate (DOS) anion and n=8, 9, 16 and 18, or X=octylsulfonate (OS) anion and n=8, 10, 12, 14 and 18) were synthesized and characterized. Their liquid crystalline properties and crystalline (Cr) structures were analysed; the Cr phases are lamellar in all cases. For long chain DOS derivatives (n=16 and 18) hexagonal and rectangular columnar mesophases (Colh and Colr) with melting temperatures close to 140°C were observed. For long chain OS derivatives (n≥10) a Colh mesophase was observed, with melting temperatures between 140 and 190°C.

Several new enaminoketone mesogens were synthesized and coordinated to various metal salts to yield a variety of novel rodlike metal-containing liquid crystals. The mesophases were characterized by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). Whereas the free ligands display SmA and nematic mesophases, the NiII and PdII complexes give rise to SmC and nematic phases, and the paramagnetic CuII mesogens to a narrow temperature-range nematic mesophase only. The magnetic behaviour of the latter was studied by means of EPR and magnetic susceptibility (SQUID) measurements.