A multifunctional fluorescent probe based on Schiff base with AIE and ESIPT characteristics for effective detections of Pb, Ag and Fe.

In this work, three Schiff-based fluorescent probes with aggregation-induced emission (AIE) and excited intramolecular proton transfer (ESIPT) characters were synthesized by grafting 2-aminobenzothiazole group onto 4-substituted salicylaldehydes. More important, a rare tri-responsive fluorescent probe (SN-Cl) was developed by purposeful variation of substituents in the molecule. It could selectively identify Pb, Ag and Fe in different solvent systems or with the help of masking agent and show complete fluorescence enhancement without interference of other ions. Meanwhile, the other two probes (SN-ON and SN-N) could only recognize Pb in DMSO/Tris-HCl buffer (3: 7, v/v, pH = 7.4). According to Job's plot, density functional theory (DFT) calculations and NMR analysis, coordination between SN-Cl and Pb/Ag/Fe was determined. The LOD values for three ions were as low as 0.059 μM, 0.012 μM and 8.92 μM, respectively. Ideally, SN-Cl showed satisfactory performance in real water samples detection and test paper experiments for three ions. Also, SN-Cl could be used as an excellent imaging agent for Fe in HeLa cells. Therefore, SN-Cl has the ability to be a "single fluorescent probe for three targets".