Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones (original) (raw)
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Applied Sciences, 2021
The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts.
Journal of Materials Chemistry, 2012
The present work reports a simple and versatile pathway to incorporate redox-active 4,4 0 -bipyridinium (''viologen'') units with two, three, or six charges into dynamically ordered liquid crystalline structures by ionic interactions. A detailed analysis of the structure-property relationship was supported by molecular modelling experiments. Three redox-active 4,4 0 -bipyridinium (''viologen'') cores, 1,1 0dimethyl (4-pyridin-4-ylpyridinium) di-(MV 2+ ), 1,1 0 ,1 00 -[benzene-1,3,5-triyltris(methylene)]tris(4pyridin-4-ylpyridinium) tri-(V 3+ ), and 1,1 0 ,1 00 -[benzene-1,3,5-triyltris(methylene)]tris[(methyl) 4-pyridin-4-ylpyridinium] hexa-(MV 6+ ) cationic halides, were combined with an anionic caesium 3,4,5tris(dodecyloxy)benzene sulfonate (DOBS) under phase transfer conditions to yield complexes of constant stoichiometry. The formed complexes, MV 2+ (DOBS) 2 , V 3+ (DOBS) 3 and MV 6+ (DOBS) 6 , were characterized by NMR spectroscopy. Depending on the molecular structure, significantly different characteristics in electrochemical behaviour of ionic liquid crystals (ILCs) with two DOBS anions and a rod-like core (MV 2+ ) were observed compared with ILs with three and six DOBS anions and y-shaped cores (V 3+ ), and (MV 6+ ) cations respectively. We report for the first time a new electroactive thermotropic liquid crystal, MV 2+ (DOBS) 2 , which changes colour from yellow to blue-green above 75 C typically for redox units in the reduced state. The reduced states of the MV 2+ (DOBS) 2 complex at E ¼ À2 V exhibit reversible redox waves and have influence on molecular arrangement in the crystal structure as seen by polarisation microscopy. Our ionic liquid crystals have potential applications, due to their low melting temperature, wide temperature range, ionic conductivity, and thermal-and electrochromism, for instance, for the design of electrochromic displays.
New Pyrazolium Salts as a Support for Ionic Liquid Crystals and Ionic Conductors
Materials (Basel, Switzerland), 2018
Ionic liquid crystals (ILCs) are a class of materials that combine the properties of liquid crystals (LCs) and ionic liquids (ILs). This type of materials is directed towards properties such as conductivity in ordered systems at different temperatures. In this work, we synthesize five new families of ILCs containing symmetrical and unsymmetrical substituted pyrazolium cations, with different alkyl long-chains, and anions such as Cl, BF₄, ReO₄, -CH₃-₆H₄SO₃ (PTS) and CF₃SO₃ (OTf). We study their thermal behavior by polarized light optical microscopy (POM) and differential scanning calorimetry (DSC). All of them, except those with OTf as counteranion, show thermotropic mesomorphism. The observations by POM reveal textures of lamellar mesophases. Those agree with the arrangement observed in the X-ray crystal structure of [H₂pz][ReO₄]. The nature of the mesophases is also confirmed by variable temperature powder X-ray diffraction. On the other hand, the study of the dielectric properties...
A convenient method for preparing rigid-core ionic liquid crystals
Beilstein Journal of Organic Chemistry, 2009
An efficient, solvent free method for the N-arylation of imidazole by 1-(dodecyloxy)-4-iodobenzene using Cu(II)-NaY as catalyst and K 2 CO 3 as base is reported. By this synthetic approach, mesomorphic 3-[4-(dodecyloxy)phenyl]-1-methyl-1H-imidazol-3-ium iodide was synthesized in a two-step procedure, and its mesomorphism has been fully investigated by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. In addition its lamellar crystal structure, electrochemical behaviour and UV (absorption and emission) properties are reported.
Ester-Containing Imidazolium-Type Ionic Liquid Crystals Derived from Bio-based Fatty Alcohols
The need to take into account the life cycle of ionic liquids (ILs), from the sourcing of the raw materials involved in their synthesis to their disposal and degradation, has become paramount in the design of new IL-type molecular structures. In the case of 1-alkyl-3-methylimidazolium salts, one of the prominent IL families, there is an increasing demand for synthetic methods involving (i) the substitution of the petro-based alkyl derivatives by readily available bio-sourced surrogates, and (ii) the functionalization of the alkyl tail with hetero-functional groups enabling the (bio)degradation of the IL after use. Herein, a straightforward and industrially viable synthesis of lipidic imidazolium salts is reported, starting from different bio-sourced fatty alcohols, including oleic, stearyl and lauryl alcohols. The procedure is based on the acrylation of the fatty alcohol, followed by the aza-Michael addition of the imidazole group onto the acrylate moiety. Subsequent quaternization, using either methyl iodide or methyl tosylate, provides a library of 1-alkylpropionate-3-methylimidazolium salts with various alkyl chain length (C18, C12, C11) and incorporating different types of counter-anions (iodate, tosylate, tetrafluoroborate). These ester-containing analogs of classical 1-alkyl-3-methylimidazolium salts are all ILs, i.e., with a melting point below 100 °C. In addition, most of them exhibit a liquid crystal behavior and can be referred to as ionic liquid crystals (ILCs). The thermal stability, as well as the phase transitions of these ILs, have been investigated by thermogravimetric analysis and differential scanning calorimetry, respectively, while the molecular structure into the crystalline phase and the mesophase is studied by X-ray scattering. Interestingly, ILCs featuring unsaturated alkyl tails exhibit a low melting point, close to room temperature and the presence of the ester function is shown to provide an enhanced stabilization of the mesophase.
New ionic liquid crystals based on imidazolium salts
New Journal of …, 2006
The new ionic liquid crystal 1-(4-dodecyloxybenzyl)-3-methyl-1H-imidazol-3-ium bromide has been synthesized and its X-ray structure obtained; various salts containing BF 4 À , SCN À , PF 6 À , CF 3 SO 3 À , (CF 3 SO 2 ) 2 N À have been prepared by anion metathesis in water from bromide species as starting materials, and finally, the mesomorphism and electrochemical behavior have been investigated.