Effect of counterions on the thermotropic and thermochromic properties of ionic liquid crystals

Novel liquid crystal materials based on 1-alkyl-4-[5-(dodecylsulphanyl)-1,3,4-oxadiazol-2-yl]pyridinium and bearing bromide, alkyl sulphate or bis(2-ethylhexyl)sulphosuccinate counterions were prepared. Their thermotropic and thermochromic properties were characterized and compared. It was established that the majority of these compounds exhibited SmA mesophases. The observation of thermochromic properties for certain of the compounds is considered to be the consequence of the existence of a charge-transfer complex between the pyridinium cation and its counterion.