A Long‐Lived Halogen‐Bonding Anion Triple Helicate Accommodates Rapid Guest Exchange

Abstract Anion‐templated helical structures are emerging as a dynamic and tractable class of supramolecules that exhibit anion‐switchable self‐assembly. We present the first kinetic studies of an anion helicate by utilizing halogen‐bonding m ‐arylene‐ethynylene oligomers. These ligands formed high‐fidelity triple helicates in solution with surprisingly long lifetimes on the order of seconds even at elevated temperatures. We propose an associative ligand‐exchange mechanism that proceeded slowly on the same timescale. In contrast, intrachannel anion exchange occurred rapidly within milliseconds or faster as determined by stopped‐flow visible spectroscopy. Additionally, the helicate accommodated bromide in solution and the solid state, while the thermodynamic stability of the triplex favored larger halide ions (bromide≈iodide≫chloride). Taken together, we elucidate a new class of kinetically stable helicates. These anion‐switchable triplexes maintain their architectures while accommodating fast intrachannel guest exchange.