Joaquín Barberá

Breaking the Mold of Discotic Liquid Crystals

Small molecules of the indene and pseudoazulene type like 1 and 2 form columnar mesophases! These compounds do not possess peripheral flexible chains like conventional columnar liquid crystals. Instead, polarizable chlorine and sulfur atoms, as well as the polar cyano group, function as unusual soft regions between the rigid columns.

Dendromesogens: Liquid Crystal Organizations versus Starburst Structures

Poly(amidoamine) starburst dendrimers which contain peripheral mesogenic ester units were found to exhibit a smectic A mesophase. A structural model is proposed that is valid for several generations of dendrimers. The mesogenic units form parallel aggregations that give rise to the smectic structure (shown schematically).

Liquid crystalline phthalocyanine–fullerene dyads

Two phthalocyanine–C60 dyads 1 and 2 incorporating either a rigid or a flexible spacer between the phthalocyanine and fullerene units, respectively, have been prepared. Indeed, the nature of the spacer has proven to play an important role in the liquid crystalline properties of these compounds. Phthalocyanine–C60 dyad 2, containing a flexible spacer, self-organizes in columnar stacks within a rectangular arrangement. On the other hand, dyad 1 does not present mesomorphic properties on its own, but forms columnar hexagonal mesophases when blended with equimolar amounts of an intrinsically mesomorphic phthalocyanine.

Luminescent ionic liquid crystals from self-assembled BODIPY disulfonate and imidazolium frameworks

A series of modular mesogenic salts based on the combination of anionic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (F-BODIPY) 2,6-disulfonate dyes and trialkoxybenzyl-functionalised imidazolium cations has been designed and synthesised. Each salt contains a rigid dianionic BODIPY core associated with two imidazolium cations functionalised by 1,2,3-trialkoxybenzyl (alkyl=n-C(8), n-C(12) or n-C(16)) units or, in one case, with imidazolium cations functionalised by a trialkylgallate (3,4,5-trialkoxybenzoate) unit in which the 3,5-dialkyl groups are terminated with a polymerisable acrylate entity. All these compounds were highly fluorescent in solution with quantum yields ranging from 54 to 62%. In the solid state, the width of the emission band observed at around 650 nm is a clear signature of aggregation. With the trialkoxybenzylimidazolium cations, polarised optical microscopy (POM) and X-ray scattering experiments showed that columnar mesophases were formed. Differential scanning calorimetry (DSC) studies confirmed the mesomorphic behaviour from room temperature to about 130 degrees C for salts with alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of the BODIPY unit was maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The salt containing the gallate-functionalised imidazolium cations showed no mesomorphism but the acrylate terminal units could be used to engender photoinitiated polymerisation thereby allowing the material to be immobilised on glass plates. The polymerisation process was followed by FTIR spectroscopy and the fixed and patterned films were highly fluorescent with a solid-state emission close to that of the complex in the solid state.

Properties of thermotropic liquid crystals induced by hydrogen bonding between pyridyl‐1,2,4‐oxadiazole derivatives and benzoic acid, 4‐chlorobenzoic acid or 4‐methylbenzoic acid

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 3‐(4‐pyridyl)‐5‐(4‐n‐alkoxy)phenyl‐1,2,4‐oxadiazoles with benzoic acid, 4‐chlorobenzoic acid or 4‐methylbenzoic acid. Neither the oxadiazole derivatives nor the carboxylic acids are mesomorphic, but the H‐bonded complexes are. Their liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X‐ray diffraction.

Synthesis and mesogenic properties of novel board-like liquid crystals

The syntheses of novel octa- and tetra-substituted systems based on tetrabenz[a,c,h,j]anthracene are reported. The disc-shaped octa-substituted material exhibits a columnar mesophase, whereas the tetra-substituted material exhibits a lamellar phase. Binary mixtures of the two materials were examined in order to explore the change over from discotic to calamitic behaviour as a function of concentration. At the crossover point, the possibility of the formation of a biaxial phase was investigated.

Sugar-Coated Discotic Liquid Crystals

The constitutional marriage between a classical thermotropic discotic molecule and carbohydrate-based amphiphiles (e.g., see Figure) is shown to result in hybrid compounds, where, for example, a triphenylene unit serves as the central core from which oligomethyleneoxy chains terminated with sugar residues radiate, which have interesting liquid crystal properties

EIN NEUES BAUPRINZIP FUR DISKOTISCHE FLUSSIGKRISTALLE

Kleine Molekule vom Inden- und Pseudoazulentyp wie 1 bzw. 2 bilden kolumnare Mesophasen! Diese Verbindungen haben keine endstandigen flexiblen Ketten, wie sie sonst bei entsprechenden Mesogenen vorhanden sind, sondern polarisierbare Chlor- und Schwefelatome oder eine polare Cyanogruppe, die als ungewohnliche „weiche” Bereiche zwischen den saulenformigen Stapeln fungieren.

Structural study of metallomesogens derived from tris-[2-(salicylideneamino)ethyl]amine. A molecular meccano

The synthesis of new metal complexes based on imines derived from tris-(2-aminoethyl)amine (TREN) which exhibit different geometries depending on the metal [Cu(II), VO(IV), Pd(II), Ni(II), Ln(III)] has been carried out. TREN has three coordination positions which allow us to obtain different coordination complexes involving one, two or three metallic centres. The molecular structure and purity of these novel compounds have been verified by IR, 1H and 13C NMR and elemental analysis and electro-spray mass spectrometry. The phase behaviour was studied by polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction techniques. It was found that the transition metal complexes display a smectic C mesophase whereas the lanthanide complexes display an unidentified smectic mesophase.

Ionic Silver Amino Complexes Displaying Liquid Crystalline Behavior Close to Room Temperature

The liquid crystalline properties of a series of ionic silver complexes [Ag(NH2n-CnH2n+1)2]X (X = NO3, n = 6, 8, 10, 12, 14; X = BF4, n = 8, 10, 12, 14), derived from silver nitrate or tetrafluoroborate and aliphatic amines, have been investigated by optical microscopy, DSC, and X-ray diffraction. The materials exhibit a birefringent fluid phase identified as a smectic A mesophase by optical microscopy and X-ray diffraction. Some of the complexes are liquid crystalline at temperatures close to room temperature. The X-ray results are consistent with the existence in the mesophase of a bilayer organization. The silver cations adopt a U-shape, which allows for the adoption of this bilayer arrangement, with alternating ionic and apolar regions and a short-range square-planar array inside the cationic sublayers. The thermodynamic parameters suggest that the melting transition clearly involves only disorder (melting) of the chains, whereas the clearing transition implies breaking the anion-cation arrangement.