Polymerization-Induced Emission and Specific Detection to Cu2+ Ions of Polyacrylates with Morpholine Structure

In this investigation, the fluorescent poly(N-hydroxyethyl morpholine acrylate) (PHEMA) and poly(N-hydroxypropyl morpholine acrylate) (PHPMA) are prepared and applied as fluorescent probes for the specific detection of Cu²⁺ ions. Far different from the non-fluorescent monomer, PHEMA and PHPMA emit a strong fluorescence at 410 nm due to the intramolecular aggregation of morpholine structures along macromolecular chains in the polymerization, indicating polymerization-induced emission (PIE). The fluorescent emission of PHPMA shows the dependence on external factors including solution concentration, excitation wavelength, solvent, and pH value. PHPMA specifically detects Cu²⁺ ions even in the presence of 16 common metal ions and 6 anions, with an LOD of 0.077 µM. In the fluorescent quenching, the O atom from ─C═O and N atom from morpholine moiety on the PHPMA chain participate in the complexation with Cu²⁺ ions with the ratio of the structural unit and Cu²⁺ ion of 2:1, leading to the dynamic quenching of PHPMA solution. As for the application, PIE-active PHPMA is easily made into a portable semi-quantitative filter paper with recyclability. In brief, the PIE-active PHPMA synthesized in this study can be used as a promising material for the specific detection of Cu²⁺ ions in industry, agriculture, and medicine fields.