Self-assembly induced ferromagnetic interaction in magnetic polymers with terphenyl linkers

Abstract

Self-assembly is a universal method to prepare block copolymers with ordered structures, which is very important in organic magnets to align the magnetic centres to enhance ferromagnetic interaction. The amphiphilic magnetic polymers (PTMTBDI[FeCl₄]) with para-terphenyl group in the cations and high spin FeCl₄⁻ as single spin carrier are prepared by ring-opening metathesis polymerization (ROMP) and post-modification. Due to the strong π–π stacking interaction between terphenyl groups, magnetic polymers are self-assembled into macromolecular mono-layer structures with hydrophilic FeCl₄⁻ on the two sides and the polymer main chain and side group in the middle in aqueous solution. Fe(III) atoms are arranged in lattice fringe with domain spacing of ca. 2.6 Å. Magnetic property studies show that the polymers are changed from paramagnetic to ferromagnetic with hysteresis loops after self-assembly. The ferromagnetic interaction is induced by the close packing and ordered alignment of the Fe(III) atoms. This work unveils a new method to generate ordered structures in angstrom periodicity and thus improve ferromagnetic interaction in organic magnets.