Low-temperature liquid-crystalline nitroxide radical†

Abstract

Liquid-crystalline (LC) radicals have been considered promising as metal-free paramagnetic soft materials, but those reported so far are not easy to use because of their stability and LC temperature range. Here, we report a paramagnetic LC nitroxide radical (NR) that shows durability and tractability. The new compound shows a low melting point, high chemical stability, and high vacuum and synchrotron radiation resistance. The coexistence of the four properties enables us to take photographs of the magnetic structures of the compound on a ferromagnetic iron film using photoemission electron microscopy (PEEM). We discuss the origins of these properties. The fluorine substitution near the NR moiety significantly alters the conformational ensemble to decrease the entropy in the crystal phase. It seems beneficial to focus on conformational ensembles to incorporate bulky functional moieties into LC molecules together with durability and tractability.