Multi-stimuli Control over Assembly and Guest Binding in Metallo-supramolecular Hosts Based on Dithienylethene Photoswitches.

It is difficult to assemble multi-component metallo-supramolecular architectures in a non-statistical fashion, which limits their development toward functional materials. Herein, we report a system of interconverting bowls and cages that are able to respond to various selective stimuli (light, ligands, anions), based on the self-assembly of a photochromic dithienylethene (DTE) ligand, L a , with PdII cations. By combining the concept of "coordination sphere engineering", relying on bulky quinoline donors, with reversible photoswitching between the ligand's open ( o - L a ) and closed ( c - L a ) forms, a [Pd2 ( o - L a )4 ] cage ( o - C ) and a [Pd2 ( c - L a )3 ] bowl ( c - B ) were obtained, respectively. This structural rearrangement modulates the system's guest uptake capabilities. Among three bis-sulfonate guests ( G1 , G2 , and G3 ), the cage can encapsulate only the smallest ( G1 ), while the bowl binds all of them. Bowl c - B was further used to synthesize a series of heteroleptic cages, [Pd2 LA 3 LB ], representing a motif never reported before. Additional ligands ( L c-f ), with short or long arms, tune the cavity size, thus enabling or preventing guest uptake. Addition of Br- /Ag+ makes it possible to change the overall charge, again triggering guest uptake and release, as well as fourth ligand de-/recomplexation. In combination, site-selective introduction of functionality and application of external stimuli lead to an intricate system of hosts with different guest preferences. A high degree of complexity is achieved through cooperativity between only a few components.