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 Zn-II complexes, [(Zn4L3X6)-L-II] and [(Zn4L4)-L-II], respectively, which were found to form in equilibrium from porphyrin-based ligand L and Zn-II ions with different stoichiometry. Specifically, this interconversion was induced by four distinct external stimuli: exogenous ligands, Bronsted 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.