Nematic Ion-Clustomesogens from Surfactant-Encapsulated Polyoxometalate Assemblies

Ionic-surfactants-based thermotropic liquid crystals

Ionic surfactants can be combined with various functional groups through electrostatic interaction, resulting in a series of thermotropic liquid crystals (TLCs).

Thermal stability of mesoscopic compounds of cetyltrimethylammonium and Keggin metatungstates

A hybrid surfactant/polyoxometalate compound was synthesized by combining isopolytungstate anions with the cationic surfactant cetyltrimethylammonium bromide (CTA-Br) to produce a hierarchical compound that we identify as (CTA)₇[H₂W₁₂O₄₀]Cl·2H₂O. At room temperature the compound consisted of hexagonally ordered sheets of Keggin ions, with an intervening gallery containing alkyl-chains of the organic cations. The synthesis was highly dependent on solution pH, reaction time and the order in which the reactants were added. We examined the effect of temperature on the stability of (CTA)₇[H₂W₁₂O₄₀]Cl·2H₂O using thermal gravimetric analysis, differential scanning calorimetry, FT-IR spectroscopy and in situ synchrotron X-ray diffraction, and found a step-wise conversion to monoclinic WO_xvia a series of intermediates. Heating under nitrogen atmospheres accelerated transition events by ∼100 °C when compared to heating in air. During heating, the interplanar gallery at first expanded in a series of steps starting at 90 °C as the CTA⁺ amphiphiles changed orientation, before collapsing rapidly at 240 °C, a temperature coinciding with the removal of about 40% of the organic material. Between 240 and 320 °C, the material consisted of fragments of the Keggin ion cores, arranged in 2D hexagonally-packed sheets. At ∼330 °C, the Keggin ions were completely destroyed and replaced by bulk W₁₇O₄₇ which, upon further heating, transformed to bulk WO₂ or WO₃ depending on the environment.

Ionic Liquid Crystals: Versatile Materials

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.

Synthesis, characterization, and tuning of the liquid crystal properties of ionic materials based on the cyclic polyoxothiometalate [{Mo4O4S4(H2O)3(OH)2}2(P8W48O184)](36-)

A series of compounds resulting from the ionic association of a nanoscopic inorganic cluster of formula [K2NaxLiy{Mo4O4S4(OH)2(H2O)3}2(HzP8W48O184)]((34-x-y-z)-), 1, with several organic cations such as dimethyldioctadecylammonium DODA(+), trimethylhexadecylammonium TMAC16(+), alkylmethylimidazoliums mimCn(+) (n = 12-20) and alkyl-dimethylimidazoliums dmimCn(+) (n = 12 and 16) was prepared and characterized in the solid state by FT-IR, EDX, Elemental analysis, TGA and solid state NMR. The solid state NMR experiments performed on (1)H, (13)C and (31)P nuclei evidenced the interactions between the cations and 1 as well as the organization of the alkyl chains of the cations within the solid. Polarized optical microscopy, DSC and SA-XRD experiments implicated mesomorphic phases for DODA(+) and mimCn(+) salts of 1. The crystallographic parameters were determined and demonstrated that the inter-lamellar spacing could be controlled upon changing the length of the alkyl chain, a very interesting result if we consider the huge size of the inorganic cluster 1 and the simple nature of the cations.

Photosensitive polyoxometalate-induced formation of thermotropic liquid crystal nanomaterial and its photovoltaic effect

The photosensitive POM [PW₁₁O₃₉RhCH₂CO₂H]⁵⁻ was first introduced into the liquid crystal nanomaterial and simulated by theoretical calculations. It exhibits the photovoltaic effect with the character of a p-type material.

From metallic cluster-based ceramics to nematic hybrid liquid crystals: a double supramolecular approach

Luminescent bulky anionic inorganic species are directly integrated in a liquid crystalline material by a double supramolecular approach combining host–guest and electrostatic interactions.

Intelligent supramolecular assembly of aromatic block molecules in aqueous solution

The construction of supramolecular nanoscopic architectures has been intensively pursued because of their unique features for applications in nanoscience and biomimetic chemistry. Molecular self-assemblies of aromatic rod-coil amphiphiles consisting of rigid rod segments and hydrophilic flexible chains in aqueous solution provide a facile avenue into this area. This feature article highlights the recent progress regarding the construction of aqueous assemblies that result from the sophisticated design of aromatic rod-coils, with the aim to develop stimuli-responsive systems and bioactive materials. Important factors affecting the self-assembly morphologies are discussed and summarized. Dynamic structural changes triggered by temperature and guest molecules are demonstrated. Finally, the perspective of bioactive nanostructures originated from self-assembly of aromatic block amphiphiles is also introduced.