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 (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.