Gelation and luminescence of lanthanide hydrogels formed with deuterium oxide.

Gel formations and efficient lanthanide luminescence appeared in deuterium oxide (D2O) medium instead of light water (H2O), and their solvation possibilities by using luminescence lifetimes were discussed. The lanthanide ions in the hydrogel of 1 obtained by H2O (abbreviated as H2O-Ln1; Ln = Eu, Tb, and Gd) in our previous report act as the coupling part between neighbor molecules for the bundle structure. Here, D2O also acts as a medium to form the lanthanide-hydrogel of 1, and increases intensities of luminescence for Tb, because a soft crystalline state reducing resonance thermal relaxation is realized. The gel-formation and luminescence band positions of Ln1 in D2O corresponded to those in H2O. From the observation of luminescence lifetimes in H2O and D2O, the number of coordinating water molecules on Eu and Tb were estimated to be around 3 or 4 for both. The luminescence intensity of Eu1 did not increase even in D2O, due to a blue shift of the excited triplet state of 1, as compared to that in H2O.

Cation-tuned stimuli-responsive and optical properties of supramolecular hydrogels.

Hierarchical self-assembly of an amphiphilic tris-urea in aqueous media is shown. A mixture of the amphiphilic tris-urea and an alkaline solution gave a viscous solution composed of fibrous aggregates. This viscous solution transformed into supramolecular hydrogels, which are capable of hierarchically organizing into higher-order aggregates in response to several cationic triggers. The resulting supramolecular hydrogels were relatively stiff and their storage moduli attained over 10(3)  Pa. The stimuli-responsive and optical properties of the resulting hydrogels were influenced by the cationic trigger. Proton and calcium ion triggers gave pH- and chemical stimuli-responsive hydrogels, respectively. A terbium ion trigger also provided a highly luminescent hydrogel through energy transfer from the tris-urea to terbium.