Metallo supramolecular assemblies of bis-squaraines by allosteric Ca²⁺ ion binding

Abstract

Alkyl chain tethered bis-squaraines bind to Ca²⁺ ions through the participation of the negatively charged oxygen of the central cyclobutene moiety to form folded H-type aggregates. The initially formed Ca²⁺ complex is preorganized to facilitate cooperative allosteric binding of Ca²⁺, resulting in the formation of extended supramolecular arrays. The electronic absorption, IR, and ESI-MS studies support the formation of metallo supramolecular architectures of the folded H-type dimers of the bis-squaraines.