A turn-on fluorescence chemosensor for Al3+, F− and CN− ions, and its application in cell imaging

•A fluorescent chemosensor for Al3+, F− and CN− ions was designed and synthesized.•The sensing mechanism is based on inhibition of ESIPT.•The possible fluorescent species formed in the solutions were deduced.•The chemosensor can be used to detect Al3+ and F− in cells by bioimaging. A chemosensor 3-[(2-hydroxybenzylidene)-amino]-1H-pyridin-2-one (HL) for multi-ions was synthesized and characterized by single-crystal X-ray diffraction. HL is a turn-on fluorescence chemosensor for Al3+, F−, and CN− ions in DMSO. F− and CN− anions could be further distinguished by the ratiometric absorption spectrometry method. Job plot and 1H NMR data showed that the binding stoichiometries of HL with Al3+, F−, or CN− all were 1:1. Further observations of 1H NMR titration and ESI-MS showed that the possible fluorescent species of Al3+ with HL was [AlL(OH)(DMSO)2]+ in DMSO. The spectroscopic observations of the Al(III) complex showed that the two oxygen atoms and one imine nitrogen atom of HL were coordinated to the Al(III) ion. While the crystal structure of the Ni(II)-L complex confirmed the tridentate coordination mode of HL in the complexes. The experimental results revealed that HL and F− ion formed hydrogen bond in DMSO, while CN− attacked the carbon atom at –CN of HL to undergo a nucleophilic addition. The theoretical calculations confirmed that HL showed very weak fluorescence because of the excited-state intramolecular proton transfer (ESIPT). The turn-on sensing of HL to Al3+, F−, and CN− ions arose from the inhibition of ESIPT. MTT tests showed that HL was low toxic to cells. Also, HL could probe intracellular Al3+ and F− ions by bioimaging.