Smectic Liquid-Crystalline Phases of Quaternary Group VA (Especially Phosphonium) Salts with Three Equivalent Long n-Alkyl Chains. How Do Layered Assemblies Form in Liquid-Crystalline and Crystalline Phases?

Abstract

The neat phase behavior of 28 phosphonium salts (nPmA), each with three equivalent long n-alkyl chains containing m carbon atoms and one shorter chain containing n carbon atoms or a benzyl group, have been examined. Eighteen form a liquid-crystalline smectic A2 (SmA2) phase, where the lipophilic chains assemble in bilayers that sandwich an “ionic plane” consisting of an array of anions and positively charged phosphorus atoms. Several analogous ammonium salts are examined as well. These are the first structures reported for liquid-crystalline amphiphiles containing three equivalent long n-alkyl chains and a single atom headgroup. In addition, the nPmA demonstrate how the steric interactions of lipophilic chains and electrostatic interactions among the ionic parts must be balanced in layered assemblies when the cross-sectional area of the chains is much larger than that of the headgroups. A model is proposed to explain the dependence of layer thicknesses in the liquid-crystalline phases of the nPmA on m, n, and the size of the anion. A comparison is made of the packing modes among analogous Group VA salts (N.B., N or P) with 1−4 long n-alkyl chains (and the remainder as methyl groups) in their neat crystalline and liquid-crystalline phases.

Pyrrolidinium Ionic Liquid Crystals

“…[10][11][12] Different types of ionic liquid crystals have been investigated, among others imidazolium, [13][14][15][16][17][18] pyridinium, [13,16,[19][20][21][22] quaternary ammonium [2][3][4]23] and quaternary phosphonium salts. [24,25] Recently, we reported on nematic ionic liquid crystals and a luminescent tetrakis b-diketonate lanthanidome-A C H T U N G T R E N N U N G sogen with mesogenic imidazolium cations. [26] The liquidcrystalline behaviour of the ionic salts strongly depends on the nature of both the cation and the anion, but also on the length of the alkyl chain of the organic cation.…”

Supramolecular Structures in the Presence of Ionic Liquids

“…The ionic conductivities and LC structures of the obtained 1-methylimidazolium ILs could be conveniently adjusted by anions, which would potentially be used as an on-off switch of ions ( Figure 17) (Yazaki et al, 2008b). Besides imidazolium ionic LCs, other thermotropic ionic LCs based on pyridinium (Bowlas et al, 1996;Cruz et al, 2000;Cui et al, 2002;Gordon et al, 1998;Neve et al, 2000;Neve et al, 2001;Taubert, 2004), quaternary ammonium (Alami et al, 1993;Arkas et al, 1999;Lu et al, 1997;Pott & Meleard, 2009;Tittarelli et al, 1997), quaternary phosphonium (Abdallah et al, 2000;Chen et al, 2002;Gowda et al, 2004), pyrrolidinium (Goossens et al, 2009), dithiolium (Artzner et al, 1997) and guanidinium ILs (Kim et al, 2005;Mathevet et al, 2005;Sauer et al, 2008) have also been explored. Two important phenomena should be especially noticed.…”

The quest for the simplest possible organogelators and some properties of their organogels

“…However, these LMOGs are unstable at elevated temperatures due, probably, to Hofman-type elimination reactions. Replacement of the nitrogen atom of the cationic head group with phosphorus, another Group VA atom, provided much more stable phosphonium salts 36 whose gelation efficiencies are somewhat different from the corresponding ammonium salts 37 .…”