Design and synthesis of a solvent-dependent fluorescent probe for dual selective detection of Mg2+ ion and Zn2+ ion

A solvent-dependent fluorescent probe QC for the dual detection of Mg2+ ion and Zn2+ ion has been constructed based on a Schiff base compound, in which 8-hydroxyquinoline served as not only a fluorophore but also a recognition group. Among the various tested metal ions, this probe exhibited high sensitivity and good selectivity toward Mg2+ ion in acetonitrile and Zn2+ ion in EtOH-H2O (9:1, v/v), respectively. With the treatment of Mg2+ ion or Zn2+ ion, 1:2 complex was formed between QC and Mg2+ ion, which inhibited the PET processes caused by the lone pair electrons from the nitrogen atom of the -C = N group and the nitrogen atom of quinoline moiety, resulting in the fluorescence enhancement for Mg2+ ion. Whereas a 1:1 complex was formed between QC and Zn2+ ion, which inhibited the PET process only caused by the lone pair electrons from the nitrogen atom of the -C = N group, resulting in the fluorescence enhancement at a shorter wavelength. The detection limit was calculated as low as 6.28 x 10(-8) M for Mg2+ ion and 2.36 x 10(-7) M for Zn2+ ion. DFT analysis further supported this concept to design the probe.