Fluorescence enhancement of N2O2-type dipyrrin ligand in two step responding to zinc(II) ion

► The fluorophore ligand, N2O2-type dipyrrin (BB2), showed two step responses to zinc(II) ion. ► Addition of 0.2 equiv. of ZnCl2 to BB2 immediately increased the fluorescence intensity. ► Only micromolar concentrations of ZnCl2 were needed to achieve 3-fold fluorescence enhancement. ► Fluorescence response of the substituted dipyrrin dye upon zinc complex formation can be observed by the naked-eye. ► High optical brightness, high binding constant and very low detection limit values make BB2 as selective sensor for Zn(II) detection.