Effect of central linkages on mesophase behavior of imidazolium-based rod-like ionic liquid crystals

Two series of phenylbenzylether and benzanilide based rod-like imidazolium bromides and their nonionic precursors, the 1-phenyl-1H-imidazoles have been synthesized and the influence of the number and length of the alkyl chain(s) and the structure of the linking group in the aromatic core (-CH2O-, -COO-, -CONH-) on their mesophase self-assembly in ionic liquid crystalline phases were studied by POM, DSC and XRD. Upon decreasing the length of the N-terminal chain or by enlarging the number and length of the C-terminal chains, the sequence smectic (SmA)-hexagonal columnar (Col(hex))-micellar cubic (Cub(I)/Pm3n) was found for the ether based imidazolium salts; while only SmA and Col(hex) phases were observed for the related amides. The influence of the polarity of the central linkages, namely -CH2O- and -CONH-, on the mesophase structure and stability is discussed and compared with related -COO- connected ILC.