An Aggregation-Induced Emission (AIE)-Active Molecular Light Switch for Perchlorate Sensing at the Parts per Billion Level in Aqueous Solutions

The identification of perchlorate (ClO 4 – ) in water is of great significance to environmental protection and public health. Ruthenium(II) polypyridyl complexes bearing the dipyridophenazine (dppz) ligand, such as [Ru(bpy) 2 dppz] 2+ and [Ru(phen) 2 dppz] 2+ (bpy = bipyridine, and phen = phenanthroline), are known as light switches for DNA biomacromolecules. Herein, we demonstrate that they can also function as light switches for small inorganic anion ClO 4 – . The critical determinants of their light-switch effect toward ClO 4 – are the phenyl substitutions on the ancillary ligand (bpy or phen). Additionally, methyl substitution on the dppz ligand modulates the sensitivity and selectivity for ClO 4 – . Anion exchange and aggregation were driven by C–H···anion hydrogen bonding, C–H···π interaction, and weak π–π interaction between ClO 4 – and the light-switch complex, which is identified by single-crystal structure analysis and 1 H NMR. This anion exchange-based aggregation-induced emission (AIE) of the Ru–dppz complex constitutes a powerful light-switching strategy, enabling luminescence-based ClO 4 – sensing with a detection limit of 2.6 nM (0.26 ppb) and high specificity in aqueous solutions. Furthermore, the effectiveness of the developed light-switch sensing was demonstrated by analyzing different real water samples. These findings propose an alternative, previously unexplored light-switching mechanism for Ru–dppz complexes and pave the way for new efficient probes for anion recognition in pure water.