Magnetic properties of terminal iodinated nitroxide radical liquid crystals

We designed and synthesized terminal iodinated nitroxide radical liquid crystalline compounds (NR-LCs) with octyloxy side chain (+/-)-8-I and dodecyloxy side chain (+/-)-12-I to understand the substitution effects of an iodine atom on the phase transition behavior and on the magnetic properties in crystalline (Cr), liquid crystalline (LC) and isotropic (Iso) phases. These NR-LCs show monotropic nematic phases because the iodine atom is too short and apolar as a terminal group to stabilize LC phases. Furthermore, the SQUID magnetometry and electron paramagnetic resonance (EPR) spectroscopy indicate that the magnetic properties in the Cr phase depend on the length of the alkoxy side chain; antiferromagnetic interactions occur in (+/-)-8-I, whereas ferromagnetic interactions occur in (+/-)-12-I, and the paramagnetic susceptibility of (+/-)-8-I slightly decreases ((J) over bar < 0) and that of (+/-)-12-I abruptly increases (<(J)over bar> > 0) at each of the Cr-to-Iso phase transitions. These results suggest that the most frequent type of the magnetic interactions in LC and Iso phases is similar to those in the Cr phases among the various types of intermolecular magnetic interactions induced by the inhomogeneous intermolecular contacts. (C) 2017 Elsevier Ltd. All rights reserved.