Tuning of the Self-Threading of Ring-in-Ring Structures in Aqueous Media

A series of aryl-extended N-monoalkyl-4,4′-bipyridinium salts L (aryl=1,4-phenyl, 4,4′-biphenyl, 2,6-naphthyl and 9,10-anthracenyl) have been implemented by Pd^II/Pt^II-directed self-assembly into constitutionally dynamic systems (CDSs). As a result, the intended processes produced not only (en) M ₂ L ₂ (en=ethylenediamine) metallacyclic species but also (en) M ₄ L ₄ ring-in-ring aggregates, in equilibrium with the former, as a consequence of the hydrophobic nature of the aryl rings within the 4,4′-bipyridinium scaffold. The key feature of the obtained dynamic systems is the possibility of modulating their response against external stimuli by modifying the hydrophobic character of the ligand. While the different dynamic libraries follow the same trends upon changes in concentration, temperature, polarity of the medium, or addition of an aromatic chemical effector, subtle changes in the ligand hydrophobic core results in a fine-tuning of the speciation when applying a certain degree of the different stimulus. The exception is the anthracene-containing derivative, which does not form inclusion complexes or self-threaded structures.