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.

Luminescent lanthanide hydrogels using the low-molecular weight gelator 1 in D₂O were developed and evaluated quantitatively.