A facile approach to the design of stimuli-responsive supramolecular gels (SRSGs) termed double-metal-ion competitive coordination control is reported. By this means, the fluorescence signals and guest-selective responsiveness of the SRSGs are controlled by the competitive coordination of two different metal ions with the gelators and the target guest. To demonstrate this approach, a gelator G2 based on multiple self-assembly driving forces was synthesized. G2 could form Ca²⁺-coordinated metallogel CaG with strong aggregation-induced emission (AIE). Doping of CaG with Cu²⁺ results in AIE quenching of CaG and formation of Ca²⁺- and Cu²⁺-based metallogel CaCuG. CaCuG could fluorescently detect CN⁻ with specific selectivity through the competitive coordination of CN⁻ with the Cu²⁺ and the coordination of Ca²⁺ with G2 again. This approach may open up routes to novel stimuli-responsive supramolecular materials.

A highly selective chemosensor 1 based on an acylhydrazone group as binding site and naphthalene group as the fluorescence signal group were described, which could instantly detect CN⁻ in water with specific selectivity and high sensitivity. The detection of cyanide was performed via the nucleophilic attack of cyanide anion on the carbonyl group, which could be confirmed by ¹H NMR, ¹³C NMR, ESI-MS and DFT calculations. The addition of CN⁻ to sensor 1 induced a remarkable color change from colorless to yellow and generated a blue fluorescence, these sense procedure could not interfered by other coexistent competitive anions (F⁻, Cl⁻, Br⁻, I⁻, AcO⁻, H₂PO₄⁻, HSO₄⁻, ClO₄⁻, SCN⁻, S²⁻, NO₃⁻ and SO₄²⁻). The detection limits were 5.0×10⁻⁷ M and 2.0×10⁻⁹ M of CN⁻ using the visual fluorescent color changes and fluorescence spectra changes respectively, which is far lower than the WHO guideline of 1.9×10⁻⁶ M. Test strips based on sensor 1 were fabricated, which could act as a convenient and efficient CN⁻ test kit to detect CN⁻ in pure water for “in-the-field” measurement.