Room-Temperature and Low-Ordered, Amphotropic-Lyotropic Ionic Liquid Crystal Phases Induced by Alcohols in Phosphonium Halides

Abstract

Tri- n-decylmethylphosphonium chloride and bromide ( 1P10X) salts are not liquid crystalline. However, mesophases are induced by adding very small amounts of an alcohol or water. The temperature ranges of the induced smectic A 2 (SmA 2) liquid-crystalline phases can be very broad and the onset temperatures can be below room temperature depending upon the concentration of the alcohol or water and the structure of the alcohol. At least one molar equivalent of hydroxyl groups is necessary to convert the 1P10X completely into a liquid crystal. Strong association between the hydroxyl groups of an alcohol or water and the head groups of the 1P10X is indicated by spectroscopic, diffraction, and thermochemical data. Unlike many other smectic phases, those of the 1P10X/alcohol complexes are easily aligned in strong magnetic fields and the order parameters of selectively deuterated alcohols as measured by (2)H NMR spectroscopy, approximately 10 (-2), are much lower than the values found when the host is a commonly employed thermotropic liquid crystal. The dependence of the specific values of the order parameters on temperature, the nature of the halide anion, and the structure and concentration of the alcohol are reported. In sum, a detailed picture is presented to explain how and why an alcohol or water induces liquid crystallinity in the 1P10X salts. The data also provide a blueprint for designing media with even lower order parameters that can be hosts to determine the conformations and shapes of guest molecules.

Ionic Liquid Crystals: Versatile Materials

“…572 In this context, it is noteworthy that the Weiss group found that addition of at least 1 molar equivalent of water or MeOH to P,P,P-tris(n-alkyl)-P-methylphosphonium halides induces LC properties in some cases, and enhances the mesophase temperature range and lowers the melting point in some other cases. [497][498][499]574 These general findings on the importance of hydrogen-bonding interactions for the induction and stabilization of ILC smectic phases will be further discussed in section 7. The transition temperatures in Figure 16b S2.…”

“…These findings are in good agreement with the idea of "molecular lubrication" that was proposed by Weiss and coworkers in relation to phosphonium-based ILCs. 385,[497][498][499]574 This concept will be dealt with more extensively in section 7. The compounds with the highest overall length (m + n) of the hydrophobic chains (149-Br-16/8, 149-Br-14/10, 149-Br-12/ 12, and 149-Br-10/14) show the highest clearing points.…”

“…2 The amphotropic LC behavior of several of the previously discussed phosphonium salts in the presence of different solutes (such as acetonitrile or DMSO, and the alcohols, which allow for Scheme 16. Phosphonium-Based ILCs Investigated by Weiss and Co-workers [496][497][498][499]574 Chemical Reviews "lubrication" as seen above) was extensively studied using quadrupolar 2 H NMR spectroscopy, besides the usual techniques of POM, DSC, and PXRD. 496−499 For oriented deuterated molecules in an aligned mesophase, splitting of the 2 H NMR peaks occurs because of quadrupolar interactions, whereas single sharp signals appear in the isotropic liquid state (because the quadrupolar interactions are orientationally averaged).…”

Supramolecular Structures in the Presence of Ionic Liquids

“…Su et al (Xiao et al, 2008) fabricated a new type of thermotropic liquid-crystalline photosensitive supramolecular ionic self-assembly of polyelectrolyte and functional unit azobenzene IL crystal (azo-ILC), where the thermal and phase behaviors can be modulated by changing the spacer length (methylene units in azo). Ma et al (Ma et al, 2008) found that the addition of very small amounts of an alcohol or water into tri-ndecylmethylphosphonium chloride and bromide salts (1P10X) induced the formation of liquid crystalline, where strong association between the hydroxyl groups of alcohol or water and the head groups of 1P10X is indicated. However, little attention has been given to the protein crystallization system where IL is added.…”

Sequential bromination reactions from beads with methyltriphenylphosphonium tribromide groups

“…Swellable (insoluble) solid support reagents are advantageous for some synthetic procedures,23 and bromination reactions have been exploited using quaternary ammonium24 and pyridinium25 tribromide polymer‐bound ions. Because P + is a larger cation and has lower binding energies with anions than N + ,26–35 3 is an attractive and interesting alternative to the other polymer‐bound tribromide reagents reported thus far. It is found to be quite robust.…”