Figure 4.

Reversible response of Ln–Man–Geln hydrogels upon Fe²⁺/EDTA. a) Illustration of the Ln–Man–Geln hydrogels as matrices for reversible fluorochromic “On/Off” switch upon Fe²⁺ ions. b) Photographs of the fluorescence “On/Off” of Tb–Man–Geln and Eu–Man–Geln upon UV light (312 nm) irradiation. Gradual decrease in the fluorescence intensity of c) Tb–Man–Geln and d) Eu–Man–Geln by increasing the concentration of Fe²⁺. Fluorescent spectra of the hydrogel, the hydrogel treated with Fe²⁺, and the recovered hydrogel treated with EDTA about e) Tb–Man–Geln and f) Eu–Man–Geln. Fluorescence quenching and recovery cycles of g) Tb–Man–Geln and h) Eu–Man–Geln.