Columnar Liquid-Crystalline Imidazolium Salts. Effects of Anions and Cations on Mesomorphic Properties and Ionic Conductivities

Two series of l-methyl-3-[3,4,5-tris(alkyloxy)benzyl]imidazolium salts (1(n/X - ); n = 8, 12, 16, and 18) and 1,2-dimethyl-3-[3,4,5-tris(dodecyloxy)benzyl]imidazolium salts (2(12/X - )) containing anions (X - ), such as tetrafluoroborate, hexafluorophosphate, trifluoromethylsulfonate, and bis(trifluoromethylsulfonyl)imide, have been synthesized. The thermal properties of these salts were characterized by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The salts form hexagonal columnar liquid-crystalline phases except for 1(8/X - ) and 1(12/ X - ) containing CF 3 SO 3 - and (CF 3 SO 2 ) 2 N - , and 2(12/(CF 3 SO 2 ) 2 N - ) which melt directly to isotropic ionic liquids. The clearing points show a decreasing trend with an increase in the size of anions. The ionic conductivities of 1(16/X - ) forming columnar phases have been measured by using an alternating current impedance method. The conductivities depend on the nature of anions, suggesting that the predominant conduction mechanism is hopping and/or diffusion of anions in the columnar structures.