Modulating the properties of metal-organic hybrid systems by light-stimulus is highly desirable in view of designing switchable systems in catalysis, materials chemistry, supramolecular chemistry, and biological applications. Photoswitchable compounds, which can be reversibly switched between two distinct isomers by light, provide tremendous opportunities to manipulate the structure, properties and function of many molecular systems. Photo-responsive metallogels composed of self-assembling low molecular weight gelators (LMEGs) represent an emerging class of soft biomaterials with tunable properties. In this work, visible-light-responsive metallogels based on the coordination of divalent metal ions and arylazopyrazole-functionalized phenylalanine derivatives were prepared at room temperature within a few minutes. Although the phenylalanine derivative alone could not form a gel, addition of metal salts resulted in the facile formation self-supporting metallogels. We also screened different salts to explore the effect of anions on gelation. The results reveal that the gelation process of phenylalanine based amino acid gelator is largely independent of the type of counter ions used. The photo-responsive behavior of both the arylazopyrazole and the metallogels was studied by UV-vis spectroscopy. Upon irradiation with visible-light arylazopyrazoles undergo efficient reversible <i>trans</i>-to-<i>cis</i> photo-isomerization. However, only a partial light-induced reversible gel-to-sol transition of the metallogels was observed. These initial findings suggest the reversible photo-isomerization behavior of the photoswitch was blocked while in the gel state.

Visible-light responsive arylazopyrazole-tagged phenylalanine based metallogels

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