Polyethylenimine-Derived Fluorescent Nonconjugated Polymer Dots with Reversible Dual-Signal pH Response and Logic Gate Operation

Abstract

A kind of nonconjugated polymer dot possessing autofluorescence was synthesized by hyperbranched polyethylenimine and salicylaldehyde via environmentally friendly imine cross-linking and self-assembly in the aqueous phase. Both fluorescence and ultraviolet–visible (UV–vis) absorption of the polymer dots showed a sensitive and reversible response to pH. The mechanism of pH-dependent optical properties was investigated. The existence of two proton-responsive functional groups (phenolic hydroxyl groups and amine groups) on the polymer dot surface is crucial. The pH-dependent fluorescence is ascribed to electron transfer, which is controlled by the protonation degree of amine groups, while the pH-dependent UV–vis absorption is induced by ionization of phenolic hydroxyl groups. Based on the pH-mediated optical properties, a colorimetric and fluorescent dual-signal pH sensor and multiple logic gates were developed. The fluorescent nonconjugated polymer dots with easy preparation and sensitive response to pH are...