Spectral and Physicochemical Characterization of Dysprosium-Based Multifunctional Ionic Liquid Crystals

Abstract

We report on the synthesis and characterization of multifunctional ionic liquid crystals (melting points below 100 °C) which possess chirality and fluorescent behavior as well as mesomorphic and magnetic properties. In this regard, (1R,2S)- (−)-N-methylephedrine ((−)MeEph), containing a chiral center, is linked with variable alkyl chain lengths (e.g., 14, 16, and 18 carbons) to yield liquid crystalline properties in the cations of these compounds. A complex counteranion consisting of trivalent dysprosium (Dy3+) and thiocyanate ligand (SCN−) is employed, where Dy3+ provides fluorescent and magnetic properties. Examination of differential scanning calorimetry (DSC) and hot-stage polarizing optical microscopy (POM) data confirmed liquid crystalline characteristics in these materials. We further report on phase transitions from solid to liquid crystal states, followed by isotropic liquid states with increasing temperature. These compounds exhibited two characteristic emission peaks in acetonitrile solution and the solid state when excited at λex = 366 nm, which are attributed to transitions from 4F9/2 to 6H15/2 and 4F9/2 to 6H13/2. The emission intensities of these compounds were found to be very sensitive to the phase.