Host-Host Interactions Control Self-assembly and Switching of Triple and Double Decker Stacks of Tricarbazole Macrocycles Co-assembled with anti-Electrostatic Bisulfate Dimers.

Abstract

Hierarchical assembly provides a route to complex architectures when using building blocks with strong and structurally well-defined recognition elements. These rules are traditionally expressed using cationic templates with reliable metal-ligand bonding but use of anions is rare on account of weak anion-host contacts. We investigate an approach that relies on host-host interactions to fortify assemblies formed between bisulfate anion dimers, [HSO4⋅⋅⋅HSO4]2- , and shape-persistent macrocycles called tricarbazole triazolophanes. These macrocycles have significant self-association. In chloroform, they form high fidelity, triple-decker stacks with bisulfate dimers. The strength of host-host interactions allows for preferential formation of the 3:2 tricarb:bisulfate architecture over an ion-paired architecture seen with analogous macrocycles with much weaker self-association. Solvent was expected and found to tune host-host contacts enabling formation of a 2:2 complex and solvent-driven switching between triple- and double-stacked structures. Crystallography of the 2:2:2 complex supports the idea that significant host-host interactions with tricarb arises from dipole-stabilized π-stacking. Computational studies were also conducted further highlighting the importance of host-host interactions in stacked complexes of tricarb. These findings unambiguously verify the importance of host-host interactions in the assembly and stability of discrete, responsive anion-templated architectures.