Luminescent Ionic Liquid Crystals Based on Naphthalene-Imidazolium Unit

In this article, we describe an efficient synthetic pathway and the characterization of liquid crystal luminescent imidazolium salts based on a naphthalene unit. The luminescent imidazolium-naphthalene rigid part is decorated with a benzyl group functionalized by two or three dodecyloxy chains. A crystalline structure shows unambiguously the segregation between the rigid ionic and flexible parts conducive to the emergence of mesomorphic properties. A complete thermotropic properties study of these salts has been carried out according to different anions. The alkyl tail number variation and therefore the amphipathic character (balance between hydrophilic/hydrophobic) makes it possible to induce liquid crystal state with different architectures of self-organization in layers (Smectic A) or columns (Columnar hexagonal). Finally, the photophysical properties were measured in solution and in the solid state at room temperature and showed photoluminescence quantum yields around 20 %.