Shape of acid–base fluorescence emission titration curves in the presence of buffer and quenching effects

Abstract

New theoretical expressions to account for adiabatic and diabatic excited-state proton transfer in water, as well as the effect of the presence of added buffers, have been deduced for steady-state fluorescence emission measurements. These expressions are easy to manipulate and adequate for the calculation of rate constants by fitting of experimental data. A systematic procedure to obtain kinetic parameters of the several excited-state processes involving proton transfer is also proposed. Finally, the expressions have been tested on the parametrization of the titration curves followed by steady-state fluorescence emission of phenol, β-naphthol, α-naphthol and acridine. In the particular case of α-naphthol and acridine we were able to describe and characterize for the first time, the diabatic quenching effect of a buffer.