Bis(4-alkoxyphenyl) Viologen Bis(triflimide) Salts: Synthesis, Thermotropic Liquid-crystalline and Light-emitting Properties

Extended viologens with different organic counterions are an important class of ionic liquid crystals that combine the properties of ionic liquids and with those of liquid crystals. Here, we describe a series of extended viologen with such properties. A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1H and 13C Nuclear Magnetic Resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-SmA transitions, Tms, and SmA-to-isotropic transitions, Tis. Those of high length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330-370 C. Their light-emitting properties in methanol were also included.