Simple and double pyridinium salts with cyanobiphenyl groups as ionic liquids and ionic liquid crystals: synthesis and investigation of thermal behavior

A series of mono- and di-cationic pyridinium salts with one or two promesogenic cyanobiphenyl groups and different counterions, bromide, dodecylsulfate or dioctyl sulfosuccinate, were designed and prepared while their thermal properties were investigated by means of differential scanning calorimetry (DSC) and thermogravimetric analysis. The monocationic bromide pyridinium salt 3 tethered with only one cyanobiphenyl group behaves as an ionic liquid crystal displaying monotropic nematic and smectic phases at low temperatures, evidenced by polarizing optical microscopy observations and DSC analysis. Replacement of the bromide ion with dodecylsulfate or DOSS- (dioctyl sulfosuccinate) ions gave pyridinium salts with no mesogenic properties. Monocationic pyridinium salt with a DOSS- ion behaves as an ionic liquid with glass transition near - 16 A degrees C.