Synthesis and characterisation of ionic liquid crystals based on substituted pyridinium cations

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Abstract

Novel ionic liquid crystals based on pyridinium and methylpyridinium cations with a dodecyl chain and bromide as anion have been prepared and characterised. [C12Pyr][Br] and [C12-n-Pic][Br] (n = 2, 3 or 4) were studied in order to understand the influence of the methyl group position in the mesomorphic behaviour. Neat microwave-assisted reactions were carried out to synthesised [C12Pyr][Br], [C12-3-Pic][Br] and [C12-4-Pic][Br] as a sustainable approach, leading to significantly reduced reaction times (35 min vs. 48 h in conventional method). All prepared compounds were characterised by spectroscopic techniques (1H and 13C-NMR; ATR-FTIR), Elemental Analysis, Differential Scanning Calorimetry (DSC), Polarised Optical Microscopy (POM) and X-Ray Powder Diffraction (XRD). It was observed that the presence of water highly influences the phase transformations. Nevertheless, thermotropic smectic phases were detected for all materials with a layer spacing between 20 and 35 Å, compatible with a bilayer interdigitated or tilted lamellar arrangement of the cation’s alkyl chain. This work also indicates new routes for preparing ionic liquid crystals with various functionalities ruled by the synthesis design.

Original languageEnglish
JournalLiquid Crystals
DOIs
Publication statusAccepted/In press - 2022

Keywords

  • Differential Scanning Calorimetry (DSC)
  • ionic liquid crystals
  • microwave-assisted reactions
  • Polarised Optical Microscopy (POM)
  • Substituted pyridinium
  • X-Ray Powder Diffraction (XRD)

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