Fluorescence of 9 in aqueous 3 × 10−4 M K3PO4 solution (pH = 8.0) in the presence of Mn(II), Co(II), Fe(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II)chlorides. The concentration of 9 was 2.5 × 10−5 M. The metal ion concentration was 1.0 ×10−4 M. Excitation wavelength: 390 nm. Emission wavelength: 470 nm.