Macroscopic Structural Transition of Nickel Dithiolate Capsule with Uniaxial Magnetic Anisotropy in Water

Abstract Meeting the Internet of Things (IoT) demand for flexible organic spintronics requires dynamically flexible, “soft” organic magnetic materials. These materials should be capable of reordering their macroscopic assemblies in response to external stimuli. Unlike conventional rigid, “hard” crystalline organic paramagnets, that are typically composed of open‐shell π‐ or d/π‐conjugated planar molecules and rely on intermolecular interactions in the ordered, assembled structures, soft paramagnets necessitate a delicate balance between long‐range structural order (essential for controlling magnetic properties) and dynamic flexibility a challenge previously unmet for open‐shell planar molecules. In this study, an amphiphilic d/π‐conjugated nickel dithiolate radical anion salt is presented that self‐assembles into ordered membranes, forming capsule‐like macrostructures with exceptional stability in aqueous environments. This design achieves the desired balance. These assemblies exhibit uniaxial magnetic anisotropy driven by significant spin–spin interactions and undergo temperature‐dependent macroscopic structural transitions representing, to the knowledge, the first observation of such behavior for assemblies of open‐shell planar molecules. This well‐defined, single‐molecular‐weight system provides critical structural and mechanism insights for soft matter design and a versatile platform for spintronic applications. The findings advance the development of flexible, tunable molecular soft paramagnets, expanding their potential for innovative applications in flexible devices and beyond.