Figure 1.

UV–vis absorption spectra of 1 at constant total concentration c = 5.01 × 10^–5 M in 0.5 M NaCl recorded at 0.7 ≤ pH ≤ 9.8. The spectra have been grouped into three sets of curves arbitrarily shifted along the vertical axis for easier lecture. The three sets correspond to the three equilibria involved (vide ultra and the SI).