Counterion Dynamics in Chiral Supramolecular Polymerization

Counterions have been studied in a broad range of chemical and biological systems, and their effects are typically evaluated by comparing different ionic species. However, the dynamic effects of a single counterion within a given system remain poorly understood. In this study, we demonstrate that counterion dynamics governs assembly pathways and chirality in supramolecular polymerization. To investigate this phenomenon, we designed dicationic tetrapyridyl Pd(II) complexes bearing two BF₄ ^- counterions, amide groups for hydrogen bonding, and either S- or R-chiral side chains, and studied their supramolecular polymerization in nonpolar media. Under kinetic conditions, the S-chiral complex initially self-assembles into nanoparticle-like metastable aggregates (AggI), which over time evolve into thermodynamically controlled supramolecular polymers (AggII) with inverted chiroptical signal through a competitive pathway. Spectroscopic, microscopic, and computational studies indicate that subtle changes in the position of the BF₄ ^- counterions modulate the packing of the π-extended pyridine ligands and the hydrogen-bonding arrangement, giving rise to distinct asymmetry amplification behavior and supramolecular chirality. These findings demonstrate that a single counterion can direct pathway-dependent supramolecular polymerization into distinct helical states, highlighting the crucial role of charge desolvation and dynamics in governing supramolecular self-assembly.