Understanding of cooperative effects in molecule-based spin transition materials

Spin transition (ST) materials, exhibiting spin state conversions by external stimuli, have been studied for over a half-century and have been continuing research interests owing to their promising applications in switching and memory devices. In manipulating the spin transition and related properties, cooperative interactions are deemed high responsibility for the abrupt STs with a wide room-temperature thermal hysteresis loop, which is required for practical applications. This review focuses on the recent advances in ST systems, especially concerning the cooperative effects on the transition properties. The factors that influence the cooperative interactions, including ligand substitution, crystal size, metal dilution, counter anion, lattice solvent, crystal packing, and matrix, are systematically discussed to demonstrate how they affect the solid-state structural arrangements and spin transition behavior. Besides, further external perturbations are also illustrated. The challenges and perspectives of multifunctional ST materials are also discussed in conclusion. This review provides valuable insights into this field and enriches its future applications.