Tris(triazolyl)triazine via Click-Chemistry: A <i>C</i>₃ Electron-Deficient Core with Liquid Crystalline and Luminescent Properties

The synthesis of a novel core based on tris(triazolyl)triazine has been accomplished by a one-pot procedure that combines a 3-fold deprotection of alkyne groups and “click chemistry” of the aromatic alkyne and azide precursors. The procedure is straightforward for the preparation of functional materials for organic electronics. Indeed, compounds with low reduction potential are obtained. These compounds also show liquid crystalline behavior, displaying columnar mesophases at room temperature, and are luminescent in the visible region both in solution and in thin films

Propeller-like Hydrogen-Bonded Banana−Melamine Complexes Inducing Helical Supramolecular Organizations

The results of the study presented here show a new example of the use of liquid crystals and the interactions involved in the mesomorphic state to build up complex molecular organizations. We have pursued a design strategy in which hydrogen bonding allows the combination of the π-stacking tendency of melamine and the lateral interaction capability of V-shaped molecules, which has been extensively demonstrated through nematic, smectic, or columnar mesophases. This combination addresses the formation of columnar arrangements with inherent helical organization. In this work, nonmesomorphic as well as mesomorphic V-shaped acids, with a structure similar to banana liquid crystals, have been complexed to a 2,4,6-triamino-1,3,5-triazine derivative in a proportion 3 to 1, respectively. Hydrogen-bonded supramolecules whose formation and stability in solution have been proven by infrared and NMR techniques have been thus obtained. DOSY experiments have allowed us to assess in solution the presence of the complexes and their tetrameric composition. All the complexes display mesogenic ability, and their mesomorphic organization has been studied by X-ray diffraction and CD spectroscopy. Results allow us to propose a helical columnar model for the mesophase originated from a propeller-like conformation of the supramolecular complexes

Supramolecular Helical Mesomorphic Polymers. Chiral Induction through H-Bonding

The work described here concerns a challenge of general interest in supramolecular chemistry:  the achievement of chiral helical organizations with controlled structures. This work provides a strategy to obtain supramolecular polymers in which a chiral helical conformation has been induced by a noncovalent association, that is, through hydrogen bonding. Polycatenar 2,4,6-triarylamino-1,3,5-triazines, which organize into columnar mesophases and are susceptible to H-bonding interactions, were chosen as a starting point to build up the chiral supramolecular structure. The stacking of these mesogens has been forced to wind in a helical way by means of H-bond association with (R)-3-methyladipic acid, within the mesophase. The optically active columnar organization has been studied in depth by optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction, and circular dichroism. Formation of stable complexes between the triazine units and (R)-3-methyladipic acid has also been investigated by means of NMR diffusion-ordered spectroscopy (DOSY) experiments in chloroform

Chiral ferroelectric nematic liquid crystals as materials for versatile laser devices

We present a liquid-crystal laser device based on the chiral ferroelectric nematic phase (NF*). The laser medium is obtained by mixing a ferroelectric nematic material with a chiral agent and a small proportion of a fluorescent dye. Notably, in the NF* phase very low electric fields perpendicular to the helical axis are able to reorient the molecules, giving rise to a periodic structure whose director profile is not single harmonic but contains the contribution of various Fourier components. This feature induces the appearance of several photonic bandgaps whose spectral ranges depend on the field, which can be exploited to build tunable laser devices. Here we report the characterization of home-made NF* lasers that can be tunable under low electric fields and present laser action in two of the photonic bands of the material. The obtained results open a promising route for the design of new and more versatile liquid-crystal based lasers

Long-Range Chiral Induction in Chemical Systems with Helical Organization. Promesogenic Monomers in the Formation of Poly(isocyanide)s and in the Organization of Liquid Crystals

The preparation of optically active poly(isocyanide)s derived from chiral promesogenic monomers is reported. Remarkably, the stereogenic carbon atom in the monomer is able to pass its chiral “information” to the growing polymer backbone which is at least 14 atoms (approximately 16 Å) remote from it. The sense of helical induction in these conformationally rigid polymers is compared to 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. Both relate to the odd−even rules for chiral sense changes in liquid crystalline phases. The role of noncovalent interactions in the polymerization has been proven by performing the reactions at various concentrations and in different solventsthe chiral induction from monomer to polymer is greatest in most concentrated reactions and in solvents with a balance between high dipolarity−polarizability and low hydrogen bond accepting and cavitational terms, as determined by an LSER analysis

Long-Range Chiral Induction in Chemical Systems with Helical Organization. Promesogenic Monomers in the Formation of Poly(isocyanide)s and in the Organization of Liquid Crystals

The preparation of optically active poly(isocyanide)s derived from chiral promesogenic monomers is reported. Remarkably, the stereogenic carbon atom in the monomer is able to pass its chiral “information” to the growing polymer backbone which is at least 14 atoms (approximately 16 Å) remote from it. The sense of helical induction in these conformationally rigid polymers is compared to 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. Both relate to the odd−even rules for chiral sense changes in liquid crystalline phases. The role of noncovalent interactions in the polymerization has been proven by performing the reactions at various concentrations and in different solventsthe chiral induction from monomer to polymer is greatest in most concentrated reactions and in solvents with a balance between high dipolarity−polarizability and low hydrogen bond accepting and cavitational terms, as determined by an LSER analysis

Control of Self-Assembly of a 3-Hexen-1,5-diyne Derivative: Toward Soft Materials with an Aggregation-Induced Enhancement in Emission

The supramolecular architectures of a fluorophore are controlled through the design of a conjugated polycatenar molecule, the self-assembly of which can be addressed toward a columnar liquid-crystalline phase and organogels. Thus, depending on the environmental conditions for self-assembly, compound CA9 organizes into an unprecedented hexagonal columnar mesophase in the condensed state, in which half a molecule constitutes the slice of the column, or into a rectangular mesomorphic-like organization in the presence of apolar solvents such as cyclohexane and dodecane, at a concentration in which fibers form and gelling conditions are fulfilled. In this Colr-type arrangement, the organization within the columns depends on the solvent. All of the materials prepared show luminescence, and moreover, a remarkable 3-fold increase in fluorescence intensity was observed in going from the solution to the gel state

Control of Self-Assembly of a 3-Hexen-1,5-diyne Derivative: Toward Soft Materials with an Aggregation-Induced Enhancement in Emission

The supramolecular architectures of a fluorophore are controlled through the design of a conjugated polycatenar molecule, the self-assembly of which can be addressed toward a columnar liquid-crystalline phase and organogels. Thus, depending on the environmental conditions for self-assembly, compound CA9 organizes into an unprecedented hexagonal columnar mesophase in the condensed state, in which half a molecule constitutes the slice of the column, or into a rectangular mesomorphic-like organization in the presence of apolar solvents such as cyclohexane and dodecane, at a concentration in which fibers form and gelling conditions are fulfilled. In this Colr-type arrangement, the organization within the columns depends on the solvent. All of the materials prepared show luminescence, and moreover, a remarkable 3-fold increase in fluorescence intensity was observed in going from the solution to the gel state

Supramolecular Helical Stacking of Metallomesogens Derived from Enantiopure and Racemic Polycatenar Oxazolines

The present report undertakes a challenge of general interest in supramolecular chemistry:  the achievement of helical organizations with controlled structure. To achieve this target we considered the possibility of inducing supramolecular chirality using molecules that were designed to organize into columnar mesophases. The use of oxazoline-derived ligands and metal coordination served as tools to prepare molecules with a phasmidic-like structure, which show columnar organization in the liquid crystalline state. To ensure the formation of chiral mesophases, these complexes bear stereogenic centers in the rigid coordination environment of the metal. X-ray and circular dichroism experiments have revealed that chirality transfer does indeed take place from the chiral molecule to the columnar liquid crystal organization. This chiral columnar organization appears as a helix consisting of stacks of molecules that rotate with respect to one another along the column while maintaining their mean planes parallel to each other. In fact, it has been concluded that packing of these polycatenar molecules must be more efficient upon rotation of a molecule with respect to the adjacent one along the column. Furthermore, the same type of helical supraorganization has been found to be present in the mesophase of the racemic mixture and the mixture of diastereomers prepared from the racemic ligand. In this case, segregation of the optical isomers is proposed to occur to give rise to both types of helix (right-handed and left-handed)

Ferroelectric Liquid Crystals for Nonlinear Optics: Orientation of the Disperse Red 1 Chromophore along the Ferroelectric Liquid Crystal Polar Axis^†

Ferroelectric Liquid Crystals for Nonlinear Optics:  Orientation of the Disperse Red 1 Chromophore along the Ferroelectric Liquid Crystal Polar Axis†</sup