Polymer dots of DASA-functionalized polyethyleneimine: Synthesis, visible light/pH responsiveness, and their applications as chemosensors

Visible light/pH dual-responsive polymer dots (PDs) were facilely prepared from branched polyethyleneimine (PEI) functionalized with donor-acceptor Stenhouse adducts (DASAs). The synthesized polymer dots were characterized by X-ray photoelectron spectroscopy, 1 H NMR spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), UV–vis absorption spectroscopy and fluorescence spectroscopy. The emission peak of the DASA-PEI polymer dots changed as the excitation wavelength varied from 360   nm to 520   nm. The strongest fluorescence emission was located around 522   nm upon 420   nm excitation. Moreover, the DASA-PEI polymer dots exhibited a typical photo-responsive behavior. After visible light irradiation, the triene of DASAs isomerized to the cyclopentenone form. Interestingly, the DASA-PEI polymer dots also responded to acid and alkali and showed a reversible transition between the triene and cyclopentenone isomers. It is demonstrated that the prepared DASA-PEI polymer dots could be applied as a turn-off chemosensor for the rapid and selective detection of Fe 3+ and Cu 2+ in aqueous solutions with detection limits of 10.1   nM and 1.3   nM, respectively.