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

Abstract

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 (Colhex)–micellar cubic (CubI/Pm3n) was found for the ether based imidazolium salts; while only SmA and Colhex 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.