Two new quinoline-based regenerable fluorescent probes with AIE characteristics for selective recognition of Cu²⁺ in aqueous solution and test strips

Two novel highly selective quinoline-based fluorescent probes (1 and 2) with an aggregation induced emission (AIE) feature have been designed and synthesized for the rapid analysis of Cu²⁺ ions in aqueous media and on paper strips with a fluorescence quenching mechanism. Moreover, probes 1 and 2 exhibit excellent sensitivity and anti-interference for Cu²⁺ detection, and the detection limits are as low as 1.3 × 10^-8 M and 8.5 × 10^-8 M, respectively, which are much lower than the allowable standard of Cu²⁺ (∼20 μM) in drinking water (EPA). More importantly, these two probes were successfully applied for the determination of Cu²⁺ in real aqueous samples and fabrication of simple device test strips for rapid and on-site detection of Cu²⁺ ions. Interestingly, they can also be regenerated by adding an excess of S^2-. Additionally, the crystallographic structure of probe 1 was confirmed through a single crystal X-ray study. Job's plot analysis and ESI-MS spectroscopic studies reflect the 1:1 complexation of the 1-Cu²⁺ and 2-Cu²⁺ complexes. Furthermore, DFT/TDDFT calculations were performed in order to help in understanding the electronic properties of the complexes and the chelation-induced quenching mechanism.