Anion-driven supramolecular gel: naked-eye detection of picric acid, facilitating <i>in situ</i> formation of gel nanocomposites and enabling solid-state anion exchange

The tripodal receptor GUA-IND was synthesized using guanidinium hydrazide as a core, and its three arms were prepared with three indole moieties. This Schiff base receptor formed an organohydrogel (GI-G) when triggered by the presence of SO₄^2-/HSO₄^- anions selectively, thus demonstrating the rarely observed anion-induced supramolecular gelation behaviour. The supramolecular gel (GI-G) was found to be stimuli-responsive towards picric acid (PA) among different nitro-aromatic compounds, enabling completely naked eye sensing of picric acid, circumventing the need for any instruments. Gel nanocomposites (GI-Cu-G and GI-Ag-G), formed from GI-G<i>via in situ</i> reduction of precious metal salts like Cu²⁺ and Ag⁺ into their nanoparticles inside the gel matrix without using any external reducing agents, demonstrated antioxidant and antimicrobial activities. Additionally, the receptor facilitated anion exchange in the solid state with diverse anions, emphasizing its versatility and innovative design. This research paves the way for the development of advanced materials with tailored functionalities.