Synthesis and application of a highly selective copper ions fluorescent probe based on the coumarin group

A highly selective copper ions fluorescent probe based on the coumarin-type Schiff base derivative 1 (probe) was produced by condensation reaction between coumarin carbohydrazide and 1H-indazole-3-carbaldehyde. The UV-vis spectroscopy showed that the maximum absorption peak of compound 1 appeared at 439nm. In the presence of Cu²⁺ ions, the maximum peak decreased remarkably compared with other physiological important metal ions and a new absorption peak at 500nm appeared. The job's plot experiments showed that complexes of 1:2 binding mode were formed in CH₃CN:HEPES (3:2, v/v) solution. Compound 1 exhibited a strong blue fluorescence. Upon addition of copper ions, the fluorescence gradually decreased and reached a plateau with the fluorescence quenching rate up to 98.73%. The detection limit for Cu²⁺ ions was estimated to 0.384ppm. Fluorescent microscopy experiments demonstrated that probe 1 had potential to be used to investigate biological processes involving Cu²⁺ ions within living cells.