Discotic 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.

Metallic nanostructures with low dimensionality (one-dimension and two-dimension) possess unique structural characteristics and distinctive electronic and physicochemical properties including high aspect ratio, high specific surface area, high density of surface unsaturated atoms and high electron mobility. These distinctive features have rendered them remarkable advantages over their bulk counterparts for surface-related applications, for example, electrochemical water splitting. In this review article, we highlight the recent research progress in low-dimensional metallic nanostructures for electrochemical water splitting including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Fundamental understanding of the electrochemistry of water splitting including HER and OER is firstly provided from the aspects of catalytic mechanisms, activity descriptors and property evaluation metrics. Generally, it is challenging to obtain low-dimensional metallic nanostructures with desirable characteristics for HER and OER. We hereby introduce several typical methods for synthesizing one-dimensional and two-dimensional metallic nanostructures including organic ligand-assisted synthesis, hydrothermal/solvothermal synthesis, carbon monoxide confined growth, topotactic reduction, and templated growth. We then put emphasis on the strategies adopted for the design and fabrication of high-performance low-dimensional metallic nanostructures for electrochemical water splitting such as alloying, structure design, surface engineering, interface engineering and strain engineering. The underlying structure–property correlation for each strategy is elucidated aiming to facilitate the design of more advanced electrocatalysts for water splitting. The challenges and perspectives for the development of electrochemical water splitting and low-dimensional metallic nanostructures are also proposed.

Metallic nanostructures with low dimensionality for electrochemical water splitting

Guanidinium-functionalized poly(arylene ether sulfone) anion exchange polymer electrolytes were synthesized via activated fluorophnyl-amine reaction, followed by the methylation with dimethyl sulfate. The activated fluorine-amine reaction gives precise control of cation functionality without the deleterious side reactions and allows the direct connection of guanidinium into stable phenyl rings.

Guanidinium-FunctionalizedAnionExchangePolymerElectrolytesvia Activated Fluorophenyl-Amine Reaction

https://onlinelibrary.wiley.com/doi/pdf/10.1002/solr.201900546

Photocatalytic Reduction of CO2 by Metal‐Free‐Based Materials: Recent Advances and Future Perspective

https://onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201806054

Front Cover: In Celebration of the International Year of the Periodic Table 2019 (Chem. Eur. J. 1/2019)

Triphenylbenzenes with different substitution patterns at the outer phenyl rings have been successfully synthesised. Sixfold n-alkoxy substitution was insufficient for mesomorphism, but already increasing the number of side chains by three methoxy groups led to liquid crystalline behaviour and mesophase formation. Symmetrical triphenylbenzenes with nine n-alkoxy side chains (≥C9) formed broad enantiotropic mesophases. The symmetry of the liquid crystalline phases was unambiguously determined by X-ray diffraction measurements as Colh and Colho for symmetry-reduced methoxy–alkoxy derivatives and symmetrical nona-alkoxy-triphenylbenzenes, respectively. Based on X-ray diffraction data a stacking model was proposed in which the single molecules aggregate to helical columns forming a mesophase.

/pdf/columnar-propeller-like-1-3-5-triphenylbenzenes-the-missing-5bo6gpkp4v.pdf

Columnar propeller-like 1,3,5-triphenylbenzenes: the missing link of shape-persistent hekates.

https://pubs.rsc.org/en/Content/ArticlePDF/2016/CC/C5CC09110A

Phosphorescent columnar hybrid materials containing polyionic inorganic nanoclusters

Meta-alkyloxyguanidinium salt-based ionic liquid crystals 3–5, 7 and 9 were synthesised and investigated with respect to the influence of meta-substitution of the cation on the mesomorphic properties. As expected, bending of the mesogenic cation in ion pairs with simple counterions (3–5) decreased melting points irrespective of the anion, but clearing points were influenced by the anion radii. SmA mesophases were formed in all cases. The mesophase formation in guanidinium sulphonates 7 and 9, however, depended not only on meta-substitution but also on the anion, the respective difference between alkyl chain lengths in cation and anion and the number of alkyloxy substituents on the sulphonate, for which a change of mesophase type from smectic to columnar phases was observed. For two derivatives, 7e and 9b, room temperature SmA and Colh mesophases could be obtained that were stable for a temperature range of 91 K and 55 K, respectively. A packing model for both smectic and columnar phases based on powder XR...

Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core

The influence of the molecular shape on the charge transport in the columnar mesophases of bi-centred crown ether based mesogens is studied. Even though a bent shaped bridging of two aromatic cores promotes the stability and the width of the columnar liquid crystal phase, the quality of the intra-columnar packing and thus the charge carrier mobility are reduced. Keeping instead a linear arrangement of the cores and increasing the molecular flexibility by enlarging the crown is detrimental to the liquid crystal phase stability while the charge carrier mobility is only slightly affected. This leads to the conclusion that the optimal molecular geometry for crown ether based mesogens providing a stable mesophase with good charge transport properties is achieved by using small crown ether bridges connecting two π-systems as linear as possible. We used discotic mesogens based on 12-crown-4, 15-crown-5, 18-crown-6 and 21-crown-7 moieties linking two triphenylene cores. The inter- and intra-columnar structure is studied by detailed small- and wide-angle X-ray scattering experiments, respectively. To study the electronic properties temperature dependent photoconductivity and mobility measurements in the organic field effect transistor setup are carried out.

Stuart J. Beardsworth

Papers

Front Cover: In Celebration of the International Year of the Periodic Table 2019 (Chem. Eur. J. 1/2019)

Columnar propeller-like 1,3,5-triphenylbenzenes: the missing link of shape-persistent hekates.

Phosphorescent columnar hybrid materials containing polyionic inorganic nanoclusters

Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core

Design of conductive crown ether based columnar liquid crystals: impact of molecular flexibility and geometry