Paramagnetic supramolecular mesogens: A new paradigm in self-assembled magnetic materials

Abstract

Sterically crowded, shape-persistent star mesogens with three oligophenylenevinylene arms provide free space in which Blatter radical guests are incorporated by covalent bonds (esters) or supramolecular interactions (hydrogen bonds). The radical guests transform these compounds to paramagnetic liquid crystalline (LC) materials. The LC molecules are demonstrated to self-assemble into several types of columnar phases, a process that is controlled by the binding mode and the size of the star mesogen cavity. The conjugated scaffold remains stable in the presence of these radicals. Magnetic investigations by means of solid-state VT-EPR and SQUID experiments reveal that these materials are paramagnetic with weak antiferromagnetic interactions. In contrast to the covalent mesogens, the supramolecular systems do not only possess much lower clearing temperatures, but also radical guests exhibit mobility independent of the phase transition leading to soft paramagnetic materials with tunable magnetic properties.