Polymer dots with nonconjugated groups that are facile to synthesize and environmentally friendly generally attract substantial interest. However, their fluorescence-emitting mechanisms are not clear. In this paper, nonconjugated polymer dots (N-PDs) are synthesized by amidation reaction between polyethylenimine (PEI) and citric acid (CA), then self-assemble into rice-like dots in aqueous phase with a high fluorescence quantum yield. Such nitrogen-containing nonconjugated compounds N-PDs are believed to be inherently fluorescent, and the reported reasons for fluorescence-emitting are discussed. Importantly, these N-PDs can be used as an excellent fluorescent probe to detect Cu2+ and ClO- in aqueous solutions. Cu2+ could combine with the PEI moiety of the N-PDs to form a copper amine complex and then quench the fluorescence by an internal filtration effect. ClO- could oxidize the hydroxyl groups on the surface of the N-PDs to form a positive charge, blocking electron transfer between the hydroxyl groups and the chromophore groups. Finally, the sensor was successfully applied to the detection of Cu2+ and ClO- in environmental water samples.
Keywords: copper ions; fluorescent sensor; hypochlorite ions; nonconjugated fluorescent polymers; polymer dots.