Metallo Supramolecular Assemblies of Bis-squaraines by Allosteric Ca2+ Ion Binding

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.