Fig. 1. (A) Chemical structures showing the reversible ionization of 1. (B) Photographs of aqueous solutions of protonated (1, left) and deprotonated (1′, right) (C) UV-vis absorbance spectra of 1 (8.7 mM) in water. (D) Chemical structures showing the reversible change in ionization state of 2. (E) Photographs of aqueous solutions of 2 in 9 : 1 DCM/MeOH while protonated (2, left) and deprotonated (2′, right) (F) UV-vis absorbance spectra of 2 in 9 : 1 DCM/MeOH (0.87 mM).
