Multi-Stimuli-Responsive Interconversion between Bowl- and Capsule-Shaped Self-Assembled Zinc(II) Complexes.

Self-assembled metal-organic architectures have great potential to undergo major structural changes into different architectures. Such molecular transformation is widely applicable to responsive systems like drug delivery and allosteric catalysis. A great number of metal-organic architectures responsive to a specific stimulus have been reported so far. However, interconversion between a pair of distinct metal-organic structures in response to multiple stimuli is rarely reported despite its high versatility. Herein we report multi-stimuli-responsive interconversion between a bowl-shaped and a capsule-shaped self-assembled ZnII complexes, [ZnII4L3X6] and [ZnII4L4], respectively, which were found to form in equilibrium from porphyrin-based ligand L and ZnII ions with different stoichiometry. Specifically, this interconversion was induced by four distinct external stimuli: exogenous ligands, Brønsted base/acid, solvents, and guest molecules. The mechanisms of the interconversion system are discussed in detail focusing on the species included in the equilibria. Thus, these findings would provide a helpful clue to design principles for multi-stimuli-responsive systems with functional versatility.