A naphthalimide-based bifunctional fluorescent probe for the differential detection of Hg²⁺ and Cu²⁺ in aqueous solution.

A novel fluorescent probe NPM based on naphthalimide was designed and synthesized. Interestingly, NPM exhibited highly selective fluorescence turn-on for Hg(2+) and turn-off for Cu(2+) in aqueous solution (10 mM HEPES, pH 7.5). Its fluorescence intensity enhanced in a linear fashion with the concentration of Hg(2+) and decreased in a nearly linear fashion with the concentration of Cu(2+). Thus NPM could be potentially used for the quantification of Hg(2+) and Cu(2+) in aqueous solution. A series of model compounds were rationally designed and synthesized in order to explore the sensing mechanisms and binding modes of NPM with Hg(2+) and Cu(2+).