Niels Holten-Andersen, Massachusetts Institute of Technology (MIT), Cambridge, USA, and colleagues have developed a light-emitting lanthanide metallogel with tunable colors whose emission is highly dependent on external stimuli. The researchers used polyethylene glycol (PEG), functionalized with terpyridyl ligands which coordinate lathanide ions (namely, Eu³⁺ and Tb³⁺).

Changing the ratio of europium to terbium allowed the team to modulate the color emitted under UV irradiation, including even white light. The bonds between the lanthanides and the ligand are dynamic and react to a wide range of stimuli. The researchers were able to effect color changes in the white-emissive gel with chemicals such as trifluoroacetic acid (TFA), with mechanical stress in an ultrasound bath, and with temperature changes.

The material can be used as a thin film coating and can indicate environmental conditions in solvents or the gas phase, opening up a wide range of potential practical uses, e.g., detecting pollutants, toxins, or pathogens, mechanical stress, and temperature.

• White-Light-Emitting Lanthanide Metallogels with Tunable Luminescence and Reversible Stimuli-Responsive Properties,
  Pangkuan Chen, Qiaochu Li, Scott Grindy, Niels Holten-Andersen,
  J. Am. Chem. Soc. 2015.
  DOI: 10.1021/jacs.5b07394