Fig. 27. Fluorescence spectra of 119 (1 × 10⁻⁵ mol L⁻¹, λ_ex = 380 nm) after the amounts of Co²⁺ from 0–5 equiv. in CH₃CN/HEPES at Rt. (a) fluorescence titration curve (b) the color change of complex by UV light of 119 and on addition of cobalt ion (5 equiv.) pH = 7.