Stress-coupled spin state switching in a spin crossover composite modulates current in an organic semiconductor

Abstract

The combination of spin-crossover (SCO) complexes with electrically conducting materials offers a promising route for developing stimuli-responsive electronics, yet the mechanism of charge transport modulation remains unexplored. Here, we investigate a bilayer heterostructure comprising silica-coated SCO nanoparticles [Fe(Htrz)₂(trz)](BF₄)@SiO₂ within a polyvinylpyrrolidone (PVP) matrix and organic semiconductors (OSCs), where mechanical stress generated by spin-state switching within the PVP:SCO layer modulates the conductance within the OSC layer. Through in situ piezo-resistivity characterization, we reveal a reversible conductance modulation in the OSC layer under hydrostatic pressure, providing a quantitative evaluation of pressure-induced stress sensitivity with the OSC layer. Crucially, the intrinsic properties of the SCO nanoparticles dictate key characteristics of the switching device such as the spin transition temperature and hysteresis width, enabling tunable and non-volatile memory behavior. Demonstrating robust switching over multiple thermal cycles—rooted in the intrinsic thermal stability of the SCO and validated by X-ray diffraction/optical spectroscopy analysis at elevated temperatures—this work lays the groundwork for a new class of stress-coupled spin-electronic systems, offering a potential route for the development of piezo-resistive sensors and adaptive memory devices.