Silver coordination-directed double-stranded polyrotaxanes with supramolecular isomerism and dual stimuli-responsiveness

Abstract

Hierarchical assembly provides a rational procedure to acquire complex supramolecular architectures from basic building blocks. In this work, a novel kind of double-stranded polyrotaxane motif was reported by Ag⁺-directed coordination-driven assembly following the preassembly of a four-connected pseudorotaxane (cpb)₂CB8 linker. Moreover, supramolecular isomerism is observed in crystalline compounds based on double-stranded polyrotaxane motifs due to differences in lattice stacking mode. Interestingly, the resultant supramolecular isomers, cross-Ag-DSP-1 and para-Ag-DSP-1, show dual thermo- and anion-responsiveness. Benefiting from high crystallinity of these coordination assemblies, a combination of characterization techniques, especially X-ray diffraction, was used to unveil precise molecular mechanisms related to the inherent dynamic behavior of these assemblies, which can be attributed to remarkable lattice rearrangement and crystal transformations as temperature increases or after anion exchange, reflecting the adaptive adjustment ability of these supramolecular architectures in response to external stimuli. Based on the anion exchange capability, these two supramolecular materials show fast removal kinetics and high sorption capacity for perrhenate (ReO₄^-) anion, a surrogate of radioactive pertechnetate (TcO₄^-) in nuclear waste eluents. This work provides a feasible way to supramolecular assemblies with customized structures and stimuli-responsiveness, and is helpful to design and synthesize more functional supramolecular systems with complex structures and tailored functions.