Ionic liquid crystals formed by self-assembly around an anionic anthracene core

We have designed and synthesised a series of modular, mesogenic complexes based on anthracene-2,6-di-sulfonate and trialkoxybenzyl-functionalised imidazolium cations. Each complex contains a central, rigid, dianionic anthracene core and two flexible monocations bearing paraffin chains anchored on imidazolium rings. Anthracene-2, 6-disulfonate can be crystallised with various simple alkylammonium ions and, in the case of ⁺N(CH ₃)₂-(C₁₆H₃₃)₂, a crystal structure determination has shown that the long paraffinic chains are intercalated between the anthracene moieties. The dianion forms columnar mesophases with trialkoxy-benzylimidazolium cations, as identified by polarising optical microscopy and X-ray scattering measurements. Differential scanning calorimetry studies confirmed mesomorphic behaviour from room temperature to about 200 °C for alkyl chains containing 8, 12 and 16 carbon atoms. The strong luminescence of anthracene is maintained in the mesophase and fluorescence measurements confirmed the presence of J aggregates in all cases. The new functional materials described herein provide an easy access to stable and luminescent mesomorphic materials engineered by an ionic self-assembly process.