Comment on “Excited-State Intermolecular Proton Transfer of Lumazine”

Abstract

A critical comment on excited-state intermolar proton transfer of lumazine was discussed. In their article, Hupper and co-researchers reported the emission properties of lumazine (Lum) using steady-state and time-resolved emission techniques. They also reported the absorption spectra at different pH and they evaluated the pKa value in water to be about 10.5. Hupper do not mention how the pH was measured. The critic´s results on emission of Lum indicate that the fluorescence of Lum is quenched by hydroxide anions, and consequently, a decrease of the fluorescence is observed at pH higher than 10.5. Hupper and co-researchers did not refer the tautomerism of Lum, which implies different atoms participating in proton transfer they also postulate. Indeed, they discuss the inter-molecular proton transfer in the excited state of Lum, but they analyzed the tautomeric forms of Lum neither in the ground state nor in the excited state.