Phosphine-Functionalized Squaramides as Responsive Organogelators: Structure, Gelation, and Metal-Ion Sensing

Phosphine-functionalized squaramides represent a promising class of low-molecular-weight gelators (LMWGs) capable of forming supramolecular organogels in a variety of organic solvents, including alcohols. In this work, a series of phosphine-containing squaramides was designed and evaluated, revealing that subtle structural differences critically influence gelation ability. Molecular dynamics simulations demonstrate that the phosphine functionality plays a key role in directing self-assembly, promoting the formation of fibrillar networks responsible for gel stabilization. The resulting organogels exhibit a selective response toward metal ions, with gold precursors inducing rapid and complete gel collapse even at low concentrations, while other cations produce only minor or no macroscopic effects. Experimental observations, supported by molecular dynamics simulations, indicate that Au³⁺ cations strongly interact with the phosphine moieties, promoting a reorganization of the supramolecular aggregates into more compact structures that disrupt the percolating fibrillar network. This coordination-driven restructuring highlights the sensitivity of phosphine-containing supramolecular assemblies to specific metal-ligand interactions. These findings demonstrate how the incorporation of metal-binding sites into squaramide-based gelators enables the development of responsive soft materials whose structure and stability can be selectively modulated by external chemical stimuli.