Multi-stimuli control over assembly and guest binding in metallo-supramolecular hosts based on dithienylethene photoswitches

Abstract

It is difficult to assemble multi-component metallo-supramolecular architectures in a non-statistical fashion, whichlimits their development toward functional materials. Herein, wereport a system of interconverting bowls and cages that are able torespond to various selective stimuli (light, ligands, anions), basedon the self-assembly of a photochromic dithienylethene (DTE)ligand,La, with PdIIcations. By combining the concept of“coordination sphere engineering”, relying on bulky quinolinedonors, with reversible photoswitching between the ligand’s open(o-La) and closed (c-La) forms, a [Pd2(o-La)4] cage (o-C) and a[Pd2(c-La)3] bowl (c-B) were obtained, respectively. This structuralrearrangement modulates the system’s guest uptake capabilities.Among three bis-sulfonate guests (G1,G2, andG3), the cage canencapsulate only the smallest (G1), while the bowl binds all of them. Bowlc-Bwas further used to synthesize a series of heterolepticcages, [Pd2LA3LB], representing a motif never reported before. Additional ligands (Lc‑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 guestuptake and release, as well as fourth ligand de-/recomplexation. In combination, site-selective introduction of functionality andapplication of external stimuli lead to an intricate system of hosts with different guest preferences. A high degree of complexity isachieved through cooperativity between only a few components.