Carboxylic acid functionalized imidazolium salts: sequential formation of ionic, zwitterionic, acid-zwitterionic and lithium salt-zwitterionic liquid crystals

Carboxylic acid functionalized imidazolium salts, their deprotonated carboxylate zwitterions and acid-zwitterion adducts have been studied, and are denoted as [N-C-n, N'-CO2H-Im][X] (C-n = CnH2n+1; X = Cl , Br , BF4 and PF6 ), [N-C-n, N'-CO2-Im] and [(N-C-n, N'-CO2-Im)(2)H][anion] (anion = NO3 and Br-), respectively. Crystal structures of [N-C-10, N'-CO2-Im]Br and [N-C-n, N'-CO2-Im]center dot 2H(2)O studied by single-crystal X-ray diffraction indicate that carboxylic acid and carboxylate groups provide rich C-H center dot center dot center dot Br and/or C-H center dot center dot center dot O hydrogen bonding interactions in the construction of helical architecture. Except the PF6- salts, all the other types of compounds with long alkyl chains exhibit wide range SmA mesophase. Zwitterions and adducts represent two new classes of imidazolium based liquid crystals. The adducts [(N-C-n, N'-CO2-Im)(2)H] Br display wider mesophase range than the other series of compounds. Mixtures of lithium salts with zwitterion of [N-C-10, N'-CO2-Im] form lithium containing liquid crystals at or near room temperature. A preliminary study of the mixtures of [N-C-10, N'-CO2-Im]/[LiClO4] (3 : 1) and [N-C-10, N'-CO2-Im]/[LiBF4] (3 : 1) placed between two ITO glasses shows that lithium ion conductivities increase upon increasing the temperature in the mesophase, yet decrease beyond the clearing temperature.