A novel water-soluble colored polymer, based on 1,8-naphthalimide, was synthesized through a series of easy reactions with high yields. It emitted green fluorescence both in an aqueous solution and in a solid state. Fluorescence characteristics of the polymer as a function Of pH were investigated in aqueous solutions. The polymer solution showed weaker fluorescence in a more acidic medium. When the pH of the solution was higher than 5, stronger fluorescence could be seen with a pK(a) value of 3.5. The presence of metal cations (Mn2-, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+) could quench the fluorescence intensity of an aqueous solution of this polymer to different levels. It was highly sensitive to Cu2+ and Fe3+ present in the studied system. The results suggest that this newly synthesized compound could work as a polymeric sensor responding to water polluted by Cu2+, Fe3+, and protons. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1931-193-5, 2009