Synthesis and characterisation of imidazolium-based ionic liquid crystals bearing a cholesteryl mesogenic group

Abstract

2014) Synthesis and characterisation of imidazolium-based ionic liquid crystals bearing a cholesteryl mesogenic group, Liquid Crystals, 41:12, 1843-1853, A series of cholesteryl-containing imidazolium chlorides and imidazolium tetrachloroaluminates were synthesised, and the chemical structure, liquid crystalline behaviour and ionic conductivity were characterised by several technical methods. Whereas the imidazolium chlorides show chiral smectic A (SmA*) phase on heating and cooling cycles, the imidazolium tetrachloroaluminates display chiral nematic (N*) phase, which is uncommon for ionic liquid crystals (ILCs). The imidazolium chlorides display similar phase transition temperature and entropy, indicating the cholesteryl component influence predominately on the phase transition rather than the different alkyl substituent groups. The imidazolium tetrachloroaluminates show lower melting point temperatures and lower clear point temperature than the imidazolium chlorides. The mesophases exist at rather moderate temperatures. Non-mesomorphic imidazolium tetrachloroaluminate(III) salts with short alkyl substituents have been known for a long time, and the synthesised imidazolium tetrachloroaluminates are the first examples of tetrahalogenoaluminate(III)-containing ILCs. For the imidazolium tetrachloroaluminates, imidazolium cations combine loosely with AlCl 4 − ions because AlCl 4 − ions are large and occupy more space in spite of the hydrogen bond and electrostatic attraction interaction, indicating that the layer structure can be destroyed easily to form N* phase on heating.

Current Topics in Ionic Liquid Crystals

“… [175] The occurrence of the N phase seems to be strictly limited to a maximum chain length of 8 C‐atoms. Besides these examples a few other non‐conventional ILCs displaying N phases have been reported [176–179] …”

Phase polymorphism and thermal stability of new cholesterol thioesters derivatives

“…[4,5] The studies of these substances have intensified during the last years. For example, imidazolium-based ionic liquid crystals bearing a cholesteryl mesogenic group were synthesised and characterised [6], effects of chain branching and lateral fluorine substitution on mesomorphism of cholesteryl benzoates has been investigated [7], as well influence of chemical structure on the optical properties of new side-chain polymers containing cholesterol was identified. [8] Cholesterol-based dimeric liquid crystals have also been studied in terms of mesomorphic properties of their frustrated phases.…”

Main‐chain ionic liquid‐crystalline polymers bearing quaternary phosphonium ions

“…Ionic liquid crystals (ILCs) have become an attractive functional soft material that combine the characteristics of ionic liquid and liquid crystal to exhibit anisotropic structure organization over a range of temperature . It has been reported that the liquid‐crystalline behavior of ILCs depends on the nature of the cations and anions that the ILCs have .…”