Guest-Triggered Charge Transfer for Magnetic Change in Redox-Active MOF Magnets

A frameworks that support multiple, closely spaced electronic states. Because these states lie in delicate energetic balance, subtle structural perturbations such as guest adsorption can trigger charge transfer and reorganize magnetic ground states. To enable guest-induced magnetic switching, we have developed two key mechanisms: (1) on-host charge transfer (CT), where neutral guests modulate the electronic state of the host framework, and (2) host-guest CT, where redox-active guests directly exchange electrons with the framework. Whereas host-guest CT is limited to strongly redox-active guests, on-host CT exploits the intrinsic energetic competition between donor and acceptor units, amplified by lattice electrostatics. The central question addressed in this Account is how to rationally design D/A-MOFs poised at electronic instability, such that minor external stimuli can tip the balance between competing charge states. We outline two guiding strategies: positioning donor-acceptor pairs at the boundary of multiple electronic states and targeting systems that display emergent electronic configurations beyond initial predictions. Guided by these principles, five representative systems showing guest-induced on-host CT have been discovered. We hope this Account will encourage continued investigation into these multifunctional materials at the interface of magnetism, electronic regulation, and host-guest chemistry.