Reversible On/Off Switching of Ferroelectricity in a Molecular FeCo Prussian Blue Analogue with Multiple Control

Polar molecule-based magnetic materials capable of multistate switching have garnered significant interest for their potential applications in next-generation memory devices, sensors, and energy conversion. Among such materials, Prussian blue analogs that exhibit electron transfer-coupled spin transition (ETCST) behavior stand out due to their unique switching properties. In this study, we report a trinuclear cyanide-bridged FeCo compound (1) that exhibits photo- and thermo-induced ferroelectric phase transition via ETCST mechanism. Notably, this FeCo complex also demonstrates a quenching effect, whereby a non-polar state is trapped as a metastable state at low temperature, allowing the polarization control via the cooling rate variations. In addition, reversible single-crystal-to-single-crystal transformation via the desorption and absorption of solvent molecules are observed. The EtOH-removed FeCo compound (1') loses its ferroelectricity, revealing that the ferroelectric phase transition can be modulated by dynamic desorption/adsorption of the guest molecule. These findings advance the design of functional ferroelectric materials with multistate switching capabilities, offering potential for future applications in contactless memory devices and beyond.