Magnetic Polymers

Abstract Discovery of doped polyacetylenes and the following extensive investigations of π‐conjugated conducting polymers also evoked the attempt creating magnetic organic polymers. In the last two decades, theoretical and experimental studies on π‐conjugated organic molecules bearing plural unpaired electrons have elucidated a clear correlation between the molecular connectivity or substitution positions of the radical groups on the conjugated skeleton and spin multiplicity or spin quantum number (S) at a ground state. A stabilized high‐spin state (spin alignment, S > 2/2) among the plural unpaired electrons was achieved based on an intramolecular and strong through‐bond spin‐exchange interaction through pi‐conjugation. Here we start with molecular structure‐S correlation of diradical model molecules as an example, and then extend the criteria for designing high‐spin organic polymers. The highest spin alignment (S) value of the polymers has been improved year by year through two main molecular design approaches: (i) π‐conjugated polymers bearing pendant radical groups, and (ii) cross‐conjugated, radical‐integrated polymers. Advantages and limitations of these two approaches are described, and the two‐dimensionally extended organic polyradical molecules (hyperbranched and/or cross‐conjugated network) are highlighted in this chapter. The molecular‐based, tunable magneto‐responsible polymer dots can lead to the potential application for the magnetic information storage, and the opto‐magnetic and electro‐magnetic properties of the polyradicals are promising field. The high‐spin organic polyradical molecules with chemical stability, flexibility, plasticity, and moldability will open a new field of magnetic organic materials.