Hierarchical Gelation of a Pd12L24 Metal-Organic Cage Regulated by Cholesteryl Groups.

The creation of supramolecular assemblies by assembly of structurally simple components via supramolecular interactions provides an opportunity to develop functional materials with hierarchical complexibility. Herein, we report an assembly approach to supramolecular gels based on metal-organic cages with tunable hierarchical structures and properties. A Pd12L24 cage (L is cholesteryl-functionalized 3,5-bis(4-pyridyl)benzene) bearing 24 cholesteryl groups is used as a supramolecular building unit and molecular platform for functionalization with tunable functional behaviors. The Pd12L24 cage motifs spontaneously self-assemble into gels where orthogonal metal-organic coordination and cholesteryl-cholesteryl interactions are involved in the gelation. The Pd12L24 cage exhibits a reversible transition between solution and aggregated gel states in response to temperature. The gelation and the mechanical property are rarely regulated by deuterated solvents and tetramethylsilane. The mechanical property of the gel materials is tunable by varying the content of cholesteryl groups of Pd12L24. Functional moieties (e.g., luminescent TPE group) can be introduced on the cage, and the luminescent property changes while the structure is maintained. The Pd12L24 gel shows visible anion-responsive behaviors arising from the hierarchical structure.