Room-Temperature Thermotropic Ionic Liquid Crystals: Viologen Bis(Triflimide) Salts

Several dicationic salts with bis(triflimide) as counterions—otherwise known as viologens—were prepared by metathesis reaction of the corresponding viologen dibromides (diiodides) with lithium triflimide in a polar solvent. They were characterized for their thermotropic liquid-crystalline properties with various experimental techniques. Two of them had low crystal-to-smectic phase transitions (Tm) at –4 and 28°C; the other two also had low Tm values, at 51 and 58°C. Each had a wide range of LC phase. Two had relatively low crystal-to-isotropic (Tm) transitions at 117 and 131°C. Each had excellent thermal stability in the temperature range of 327–396°C. They exhibited photoluminescence property in both nonpolar and polar solvents as well as in the solid state. Their emission spectra in the solid state exhibited hypsochromic shift when compared with those in solution of dimethoxyethane.