Light-Induced Dramatic Enhancement of Magnetization in Methylviologen-Prussian Blue Hybrids
The dynamic modulation of magnetic properties by external stimuli represents a paradigm shift in materials science, enabling non-contact, reversible control of spin states for applications in optical switching, sensing, and low-power spintronics. Prussian blue analogues (PBAs) are versatile platforms for photo-responsive magnetism, yet their photomagnetic response is highly sensitive to transition metal selection, alkali ions, vacancies, and water content, complicating targeted synthesis. Here, we introduce a generalizable strategy by incorporating the photo-responsive organic cation methyl viologen (MV2+) into PBA frameworks, yielding hybrids MVPB, MVPB-Co, and MVPB-Ni. Upon Xe lamp irradiation, MV2+ undergoes reduction to the radical cation MV+•, which acts as a spin carrier coupling to the magnetic moments of the metal ions. This mechanism decouples the photomagnetic response from the inorganic lattice, overcoming stoichiometric limitations. Irradiation leads to a substantial enhancement of magnetization, followed by partial relaxation under prolonged exposure, attributed to the generation and accumulation of MV+• radicals. These radicals function as dynamic magnetic modifiers, distinct from conventional light-induced charge transfer in PB frameworks. The approach is applicable across diverse cyanide-bridged metal pairs, irrespective of alkaline cations, vacancies, or water content, establishing a robust route for designing light-responsive magnetic materials.