Ionic liquid crystals.

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

Ionic Liquid Crystals: Versatile Materials.

Since the discovery of the liquid-crystalline state of matter 125 years ago, this field has developed into a scientific area with many facets. This Review presents recent developments in the molecular design and self-assembly of liquid crystals. The focus is on new exciting soft-matter structures distinct from the usually observed nematic, smectic, and columnar phases. These new structures have enhanced complexity, including multicompartment and cellular structures, periodic and quasiperiodic arrays of spheres, and new emergent properties, such as ferroelctricity and spontaneous achiral symmetry-breaking. Comparisons are made with developments in related fields, such as self-assembled monolayers, multiblock copolymers, and nanoparticle arrays. Measures of structural complexity used herein are the size of the lattice, the number of distinct compartments, the dimensionality, and the logic depth of the resulting supramolecular structures.

Development of structural complexity by liquid-crystal self-assembly.

The study of metallomesogens has added several new dimensions to the wider field of liquid crystals. In this Account, just one family of complexes is considered, namely alkoxystilbazole complexes of various silver(I) salts. These complexes show an incredibly rich and diverse mesomorphism ranging from nematic and smectic to columnar phases; in particular, many complexes show the still rare thermotropic cubic phase. Through systematic structural variations, it has been possible to gain a good understanding of the factors influencing the behavior of these fascinating systems.

Calamitics, cubics, and columnars-liquid-crystalline complexes of silver(I).

Novel amphiphilic polyhydroxy compounds [N-(3,4-dialkoxybenzoyl)-1-amino-1-deoxy-d-glucitols (glucamides), N-(3,4-dialkoxybenzoyl)-1-deoxy-1-methylamino-d-glucitols, N-(3,4,5-trialkoxybenzoyl)-1-deoxy-1-methylamino-d-glucitols (N-methylgucamides), 1-benzoylaminopropane-2,3-diols, 2-benzoylaminopropane-1,3-diols, 2-(3,4,5-tridodecyloxybenzoylamino)-2-(hydroxymethyl)propane-1,3-diol and (3,4,5-tridodecyloxybenzoyl)bis(2,3-dihydroxypropyl)amine] have been synthesized. Their thermotropic liquid crystalline phases were investigated by means of polarizing microscopy, differential scanning calorimetry and X-ray diffraction. Depending on the chain length, and the size of the hydrophilic polyhydroxy units, different mesophases have been found: smectic A phases (SA), inverted bicontinuous cubic phases (CubV2 , Ia3d), hexagonal columnar phases (ColH2) and micellar cubic mesophases (CubI2 , Pn3m or P43n). In strong analogy to lyotropic systems, the type of thermotropic mesophase depends on the ratio between the volume of the lipophilic moiety and the surface area of the hydrophilic moiety at the hydrophilic–lipophilic interface. The crossing from zero interface curvature (SA phase) to the finite negative curvature of the inverted cylindrical aggregates of the columnar mesophase takes place via bicontinuous cubic mesophases. The cylindrical aggregates of the columnar mesophase are stable over a rather broad range of variation of the structural parameter. At a certain degree of the size of the lipophilic moiety in respect to the surface area of the hydrophilic group, however, the transition from the hexagonal columnar to a micellar cubic mesophase takes place. On the basis of proton conductivity measurements and from packing considerations we propose that this cubic lattice is built up by eight closed micelles per unit cell which have a rod-like shape and represent small segments of extended columns. Therefrom we can propose a model for the transformations between these different thermotropic mesophases.

Tailoring thermotropic cubic mesophases: amphiphilic polyhydroxy derivatives

Reaction of tran.s-4-alkyloxy-4′-stilbazoles (n-OPhVPy) with silver dodecylsulphate (AgDOS) led to the complexes [Ag(n-OPhVPy)2][DOS] which showed thermotropic mesomorphism. All homologues from met...

McDonald

Papers

Polymorphic Ionic Mesogens of Silver(l): Ionic Materials Exhibiting a Thermotropic Cubic Mesophase