Host-Guest Synergistic Regulation of Multi-Step Spin-Crossover Behavior in a Hofmann-Type Complex

Abstract

Spin-crossover (SCO) materials hold promising application prospects in fields such as information storage and molecular switches; however, achieving multi-step transitions and controllable regulation of hidden spin states remains challenging. In this study, a host-guest coordination polymer based on a Hofmann-type framework was synthesized, and its magnetic behavior, photo-response, and structural evolution were systematically investigated. The compound exhibits notable thermal stability and asymmetric multi-step SCO behavior, with its transition process accompanied by a significant kinetic trapping effect. Upon photoexcitation, the material demonstrates reversible light-induced excited spin-state trapping and reverse trapping effects, enabling stable cyclic switching between the high-spin state and the hidden low-spin state. Variable-temperature single-crystal structural analysis reveals that the spin transition occurs synergistically with conformational changes of the guest molecules. Through host-guest lattice strain transmission, a structural basis for the multi-step spin transition is established. This work achieves multi-state spin regulation via a dynamic host-guest coupling strategy, offering a new pathway for the development of novel stimulus-responsive SCO materials.