Motion Restricted by Hydration Shell: A Self-Reporting System for Visualizing Electrolyte Interactions

Electrolyte interaction is of pivotal importance for chemical, biochemical, and environmental processes, including cellular signal transduction, DNA attraction, and protein dynamics. Although its investigation has been at the focus of extensive research, direct visualization of electrolyte interaction at the molecular level is exceptionally challenging. Here, we report a highly sensitive and readily-accessible technique to visualize the electrolyte interactions in water through molecular design and fluorescence spectroscopy. Two water-soluble luminogens with either cationic or anionic groups are designed as electrolyte models. The hydration shell of isolated luminogens is able to restrict their intramolecular motion, which enhances the emission. Consequently, the occurred electrolyte interactions can be optically detected since they affect the reorientation dynamics of water molecules in the hydration shell and vary the restriction strength on the intramolecular motion of the luminogens. Moreover, this technology allows us to reveal how electrolyte interaction affects the internal motion of an electrolyte within its hydration shell, which has rarely been achieved through experimental approaches.