Light and ferric ion responsive fluorochromic hydrogels with high strength and self-healing ability

Abstract

Here, light and ferric ion (Fe³⁺) responsive fluorochromic hydrogels with high strength and self-healing ability were designed and synthesized. The hydrogels were prepared via physical crosslinking of poly(vinyl alcohol) (PVA), in the presence of γ-cyclodextrin-spiropyran (γ-CD-SP) and tannic acid (TA). By utilizing the hydrogen bonding interaction between the γ-CD moiety and PVA chain, the fluorophore γ-CD-SP could be incorporated into the PVA gel successfully. Owing to photo-isomerization of the SP moiety, the hydrogel showed “on/off” fluorescence behavior upon ultraviolet/bright light irradiation. Moreover, the fluorescence emission of the hydrogel could also be turned off in the presence of Fe³⁺ by fluorescence inner filter effects, and then recovered by adding EDTA. The hydrogel possessed high tensile strength (i.e. 2.18 MPa) and self-healing ability. With the features of high strength, self-healing, and tunable fluorescence properties, the hydrogels would have potential applications in wearable devices, fluorescent sensors, and optical switches.