Ultraviolet absorption and fluorescence spectra were collected for para-substituted N,N-dimethylanilines in aqueous solution at various pH conditions. Two fluorescing forms were observed for all studied compounds, one protonated (ANsH(+)) and the second unprotonated (ANs) each of them with specific spectroscopic properties. Changing pH of solution results in the displacement of the equilibrium between two forms. It was found that protonated aniline derivatives in aqueous solutions undergo very fast excited-state proton dissociation and the pK(a) values obtained from absorption and fluorescence spectra are similar. The excited state pK(a)* values were calculated using the Forster cycle method. (C) 2013 Elsevier B. V. All rights reserved.