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.