Switchable Columnar Metallomesogens

Abstract

Chiral columnar liquid crystals have recently appeared as a promising new type of ferroelectric materials. To date, all the columnar liquid crystals that have been reported to show ferroelectric switching consist of organic compounds. However, metal-containing liquid crystals open this field to a significant number of new structures and offer the possibility of adding to the ferroelectric behavior other properties inherent to the presence of metals in the structure, such as magnetism, as well as the use of new methods of characterization (EPR, synchrotron radiation, etc.). The potential of columnar metal-containing liquid crystals as ferroelectric materials has been demonstrated even though only a few organic columnar ferroelectric liquid crystals have been described. As a first approach to this type of material, this concepts article describes the results obtained with chiral metal beta-diketonates that show ferroelectric switching in the columnar mesophase. It has been shown that these materials have a helical columnar arrangement in the mesomorphic state, and a chiral superstructure has been proposed from circular dichroism studies. This type of supramolecular structure plays a fundamental role in the ferroelectric properties of these compounds. The discussion is mainly focused on the strategy employed for the molecular design, and on the interpretation of the mesophase structure and the electrooptic effect. The use of a diverse range of techniques, both those commonly used in the field of liquid crystals and those that are more specific will be highlighted, and the principles of these specific techniques are summarized together with a justification of their applicability to this study.

Chiral Discotic Molecules: Expression and Amplification of Chirality

“…35,36 These compounds form rectangular columnar mesophases with helical order within the columns. A spin-coated sample of 32 showed a positive exciton-splitted signal in the CD spectra, which was interpreted as a left-handed (M) helix.…”

“…Finally, ferroelectricity has been shown for columnar metallomesogens. 35 Serrano and co-workers have shown that metal β-diketonates, provided with chiral side chains (e.g., 32), form helical columns (vide supra), which can also be switched under an alternating electric field.…”

A Monte Carlo study of the chiral columnar organizations of dissymmetric discotic mesogens

“…8 Chiral columnar mesophases are however particularly interesting, 9 also because of their ferroelectric 10 properties, and a number of these chiral columnar systems have now been prepared and their properties studied. [11][12][13][14][15][16] From the theory and modelling point of view the relation between a discotic and its chirality and the mesophases formed is certainly not clear. This is partly due to the complexity of the molecular structures that can give chiral columns and the difficulty in identifying a precise relation between some key molecular features and observable properties.…”

Structure of tetrakis(μ-decanoato-κ2 O:O′)bis[(4-methylpyridine-κN)copper(II)], a dimeric copper(II) complex

“…Carboxylate anions are versatile ligands capable of existing as counteranions or as ligands coordinating to the metal ions in different modes (Deacon & Philips, 1980;Tao et al, 2000;Smithenry et al, 2003). Copper complexes containing aliphatic/aromatic carboxylic acid anions as ligands with the general formula [Cu 2 (O 2 CR) 4 ] have been known to adopt a paddle-wheel structure where four bidentate carboxylato ligands bridge the Cu II centres (Baruah et al, 2015;Serrano & Sierra, 2000). Complexes having R = a long-chain alkyl group can make the resultant dimeric carboxylates more soluble in organic solvents and hence can be more effective as catalysts in certain reactions (Baruah et al, 2015).…”