Oriented quasi-domain structure of helical spin polymers prepared by electrochemical polymerization in a cholesteric liquid crystal under a magnetic field, showing a helical stripe magnetic domain

Abstract

We report the synthesis and alignment of organic radicals with helical structures. Helical spin π-conjugated polymers bearing organic radicals were synthesized by electrochemical polymerization in cholesteric liquid crystals under a magnetic field, using several types of oligothiophenes containing phenoxy radicals in the side chain as the monomers. Under the magnetic field, the polymerization proceeded in the helical liquid crystal matrix oriented in the direction of the magnetic field. These polymers were aligned with its helical axis perpendicular to a magnetic field of 6.0 T. In addition, electrochemical measurements showed that phenoxy radicals in the side chain and polarons as charge carriers in the main chain were respectively produced. The phenoxy radical with a g value of 2.00415 was confirmed from the electron spin resonance spectroscopy measurements. Superconducting quantum interference device magnetometry measurements revealed that these polymers thus obtained are paramagnetic materials. The optical texture and magnetic spectroscopy measurements indicate that the films thus prepared are helical spin polymers with an oriented quasi-domain structure, showing magneto-electro-optical activity. The optical texture corresponds to the helical stripe magnetic domain of the polymer. This method provides a novel approach for the fabrication of chiral magnets and molecular spin electronics.