A turn-on AIE sensor for nanomolar detection of perrhenate in aqueous media

The "light-switch" Ru(ii) polypyridine complexes have been developed as a novel fluorescent sensor for rapid and sensitive detection of ReO₄ ^- anions in pure aqueous media. When counterions (Cl^-) in aqueous solution are specifically exchanged by ReO₄ ^- anions, the "light-switch" Ru(ii) polypyridine complexes exhibit a significant fluorescence emission enhancement, accompanied by the formation of nanoaggregates. This aggregation is driven by weak interactions with electrostatic attraction, anion⋯π, C-H⋯anion hydrogen bonding and π-π stacking interactions between ReO₄ ^- anions and "light-switch" Ru(ii) polypyridine complexes, which is confirmed by single crystal structure analysis, density functional theory (DFT) and Energy decomposition analysis (EDA). The anion exchange-induced aggregation effect of the Ru(ii) polypyridine complexes demonstrate a potent "light-switch" strategy, capable of rapid response to ReO₄ ^- within 1 s and a limit of quantification of 1.5 nM, below the WHO guideline value for its radioactive analogue ⁹⁹TcO₄ ^- (1.6 nM), demonstrating potential for monitoring pertechnetate contamination. This work opens a new way for future research based on "light-switch" Ru(ii) polypyridine complexes as turn-on fluorescent sensing probes for ReO₄ ^-/⁹⁹TcO₄ ^- anions detection in aqueous media.