Assembly of (l+d)‐Tryptophan Derivatives Containing an Imidazole Group Selectively Forms a Rare Purple Ni(2+)‐Hydrogel

Design of metal‐selective hydrogels is attractive due to potential applications in materials and biological sciences. Although much progress has been made, assembly of both l‐ and d‐amino acid derivatives was less explored for design of metallohydrogels. In this study, we synthesized a facile and small tryptophan derivative containing an imidazole ligand with both l‐ and d‐ configurations (denoted as l/d‐ImW). Intriguingly, the assembly of (l+d)‐ImW gelators was found to selectively form a Ni(2+)‐hydrogel in aqueous medium at room temperature, which shows a rare purple color and exhibits excellent multi‐responsiveness. In addition to insights into the gelation mechanism, this study provides a novel approach to the design of metallohydrogels, by the assembly of (l+d)‐amino acid derivatives containing both aromatic rings and multiple metal coordination sites.