Nematogens containing oxyethylene units at a lateral or terminal position and their mixtures with salts

Abstract

Short terminal polyoxyethylene chains may be introduced into mesogens containing lateral substituents such as two hexyloxy chains or a crown-ether fragment. These compounds have a large nematic range near room temperature and can dissolve large amounts of the salt LiBF 4 without destroying the nematic arrangment. In the nematic phase, the ions are ordered and the quadrupolar splitting associated with these ions can allow this ordering to be monitored. Increasing the salt concentration does not seem to change the ordering of the individual ions. The 13C thermal evolution of the eld-induced chemical shift in the oxyethylene (OE) units with or without salt does not show any real diOE erence, indicating that the interaction between the ions and the mesogen is small. This means that there is very little change in conformation in the OE unit when adding salt to the mesogen.

Ionic Liquid Crystals: Versatile Materials

“…495−499 It should be noted that Judeinstein and coworkers also monitored the local anisotropy in oriented ionic LC media (i.e., mixtures of neutral calamitic mesogens containing a crown ether moiety and/or oligo(ethylene oxide) chains with Li + and Na + salts, as well as pure [C n mim][BF 4 ] and [C n vim][BF 4 ] salts and their mixtures with LiBF 4 ) via 2 H, 7 Li, 11 B, 13 C, and 19 F NMR spectroscopy (see section 12.1). 448,450,560 The taper-shaped phosphonium-based mesogens 162-m/n that were reported by Kato and co-workers 674 have already been discussed in section 6.2.…”

“…This is not only due to the “straightening” of these chains by metal ion complexation; the stacking into columns also originates from the sequential electrostatic interactions between the ionic moieties in the direction of the columnar axes. Nevertheless, several examples of low molar mass thermotropic ILCs displaying a nematic phase, or a (not commonly observed) columnar nematic phase, can be found in the literature. ,,,,,− [Remark: The quaternary ammonium halide salts based on tris­( n -octadecyl)­amine that were originally claimed to show a nematic phase were later reported to show a SmA phase. , ] Veber and co-workers proposed that the formation of the N C phase by some tricatenar dithiolium salts can be rationalized by the fact that the columns in the lower-temperature Col hex and Col rec phases are stabilized by ionic interactions, so that the 2D hexagonal lattice can “melt” without complete destruction of the columns. , Several neutral nematogenic calamitic LCs with a crown ether moiety and/or short oligo­(ethylene oxide) chains were found to dissolve large amounts of LiBF 4 , NaOTf, or sodium picrate (with complexation of the alkali metal cations by the crown ether moiety if present) and still exhibit a nematic phase. − On the other hand, mesomorphism was lost upon addition of small amounts of LiBF 4 to some derivatives with a lower shape anisotropy . Yoshio et al mentioned a short-range nematic phase for an equimolar mixture of an IL ([C 2 mim]­[BF 4 ]) with a neutral, hydroxyl-terminated LC .…”

“…As will be further explained in section , such amphotropic LCs that can be oriented and that possess low order parameters (∼10 –2 –10 –3 ) can be used as partially ordered NMR solvents for structure studies of solute molecules of interest, such as small organic molecules but eventually also medium-sized biomolecules. − It should be noted that Judeinstein and co-workers also monitored the local anisotropy in oriented ionic LC media (i.e., mixtures of neutral calamitic mesogens containing a crown ether moiety and/or oligo­(ethylene oxide) chains with Li + and Na + salts, as well as pure [C n mim]­[BF 4 ] and [C n vim]­[BF 4 ] salts and their mixtures with LiBF 4 ) via 2 H, 7 Li, 11 B, 13 C, and 19 F NMR spectroscopy (see section ). ,, …”

Ionic Liquid Crystals

“…A calamitic molecule with a four-ring core and a lateral crown ether ( 134 ) can dissolve large amounts of lithium tetrafluoroborate and still exhibit a nematic phase. No induction of smectic phases was found . The ordering of the ions was explored by lithium-7 and boron-11 NMR, and it was noticed that especially the lithium ions are ordered in the nematic phase.…”

Liquid crystal engineering – new complex mesophase structures and their relations to polymer morphologies, nanoscale patterning and crystal engineering

“…to a loss of the organization in layers. 38,39 The loss of positional long range order is due to a steric distortion as well as to a mixing of the lateral chains with the terminal chains if there is no strong incompatibly between lateral and terminal chains. If the lateral chains are incompatible with the terminal chains, then smectic phases can be maintained, as demonstrated with rod-like molecules having terminal fluorinated chains and lateral alkyl groups 40 or terminal alkyl chains and polar lateral groups.…”