Color Tunable Rare-earth Containing Supramolecular Gels with Improved Luminescent Properties Assembled in a Deep Eutectic Solvent

In this paper, a kind of environmentally friendly deep eutectic solvent (ChU) was obtained from chloline chloride and urea with a molar ratio of 1:2. As a low molecular weight gelator, sodium deoxycholate (NaDC) could form gel in ChU with a mass fraction even as low as 1%. With increasing NaDC concentration in ChU, such clear gel gradually became cloudy and then opaque, accompanied with the increasing mechanical strength revealed by rheological testing. The NaDC/ChU gel was formed by densely packed fiber aggregates with tens of microns in length under optical microscopic observations. The well-designed rare-earth complexes, i.e.[choline](3) [Ln(dpa)(3)] (Ln-dpa, Ln=Eu3+, Tb3+, dpa=2, 6-pyridinic acid)were fabricated, which had the same cationic group with ChU and excellent luminescent properties. Then, color tunable supramolecular gels were constructed through doping Eu-dpa or Tb-dpa into NaDC/ChU gels. The results showed that the introduction of deep eutectic solvent as well as the effective isolation and binding of gel matrix greatly improved the photophysical properties of such supramolecular gels compared with other solvent systems or powder states. This work develops a simple and universal strategy to prepare color tunable rare-earth containing supramolecular gel soft materials with highly luminescent efficiency and is also the first attempt in deep eutectic solvent.