Thermo‐Guest Programmable Structural Adaptability with Bistable Empty States and Photothermal Conversion in a Coordination Framework

Abstract

Stimuli‐responsive programmable materials exhibit remarkable potential for smart applications due to their ability to attain multi‐stable states through structural adaptability upon guest molecule removal or exchange. However, achieving designability remains challenging, particularly in maintaining the crystallinity for single‐crystal‐to‐single‐crystal (SCSC) transformations and ensuring tunable activation. In this study, it is demonstrated that programmable SCSC transformations between an empty monoclinic framework and an empty triclinic framework can be manipulated through the stimuli combining various activations and guest molecules. Reversible empty framework switching is facilitated by MeOH adsorption and heating‐induced SCSC transformations, whereas H₂O adsorption alone cannot directly induce structural transformation. Instead, the empty monoclinic framework must first adsorb N,N‐Dimethylformamide (DMF) molecules to form a new DMF‐adsorbed framework and subsequently undergoes H₂O adsorption and mild activation to yield the empty triclinic framework. These interconvertible frameworks differ in their photothermal conversion performance and selectively cause discoloration of CuSO₄·5H₂O due to dehydration. Photothermal temperatures ultimately induce the transformation to the empty monoclinic framework, attaining temperatures up to 640 K within 15 s under 808 nm laser irradiation (1.7 W cm⁻²). Potential energy calculations and single‐crystal data reveal that the programmable structural adaptability is driven by the varying affinities of pore environments for different guest molecules.