Achieving high-performance room-temperature organic ferromagnetic semiconductor films via topochemical reduction

Abstract The development of high-performance organic ferromagnetic semiconductors has been hampered by the intrinsic coupling of radical formation and structural organization during synthesis, which makes it difficult to achieve long-range magnetic coupling in highly conjugated systems. Here, we report an effective topochemical reduction strategy that decouples radical formation from structural organization, enabling unprecedented control over intermolecular arrangements in organic ferromagnetic materials. Using perylene diimide as a model system, this approach preserves the highly ordered structure of thermally evaporated precursor films during reduction, resulting in a shortened π-π stacking distance of 3.26 Å and exceptional long-range molecular order. The resulting films exhibit remarkable room-temperature ferromagnetism, as evidenced by X-ray magnetic circular dichroism, with a saturation magnetization of 10.5 emu g⁻ 1 —nearly an order of magnitude higher than conventional organic magnetic materials—while retaining semiconducting properties. Generality of this strategy has also been demonstrated in naphthalene-based systems, underscoring its broad applicability. Theoretical calculations reveal that this enhanced performance originates from optimized ferromagnetic coupling between adjacent radicals through controlled twisted stacking configurations. This work provides a practical route to high-performance ferromagnetic semiconductors.