Photophysical properties of tyrosine at low pH range

The global analysis of the fluorescence intensity decays of tyrosine across the emission spectrum at pH=0 revealed that its fluorescence intensity decay is bi-exponential with fluorescence lifetimes equal to 63±7 ps and 1.030±0.009 ns, whereas, the global analysis of the fluorescence intensity decays of tyrosine at different pH revealed that the quenching of tyrosine fluorescence by H3O+ ions is connected with the presence of protonated carboxyl group. The lack of acid–base equilibrium in the excited state or disturbance of this equilibrium by an additional quenching process caused the discrepancy between experimental points and Hendersson–Haselbalch relationship.