Photoisomerization and mesophase formation in azo-ionic liquids

Ionic liquids present a versatile, highly tunable class of soft functional materials. Aside from being low melting salts, they can be endowed with additional functionalities. In N-alkylimidazolium halides, which are a prominent class of ionic liquids (ILs), the imidazolium cation was linked via an ether-bridge to an azobenzene unit in order to obtain photoresponsive materials through photoinduced trans-cis isomeration. The azobenzene unit, in turn, was modified with electron donating or withdrawing groups such as methyl-, tert-butyl-, methoxy-, N,N-dimethylamino and nitro groups to study their influence on the photoisomerization and phase behavior. Endowing the imidazolium additionally with a long alkyl chain allows the materials to potentially form liquid crystalline (LC) mesophases before melting into the isotropic liquid. All, studied compounds qualify as ionic liquids; and all, except for the nitro-compound, show the formation of smectic mesophases melting to the isotropic liquid. The compounds with t...