Aqueous Synthesis of Green Fluorescence Non-Conjugated Polymer Nanoparticles by In Situ Formation of Poly-Ionic Complexes

We present a novel method for synthesizing water-based non-conjugated polymer nanoparticles that possess green fluorescence. This synthesis involves the crosslinking of polyethyleneimine (PEI) with glutaraldehyde (GA), followed by in situ polymerization of an acrylic acid-based monomer. The nanoparticles are formed through self-assembly driven by in situ electrostatic complexation, resulting in unique photoluminescence properties. This process involves the negatively charged polymer, formed via graft and homo-polymerization, interacting with the pre-existing positively charged PEI. The nanoparticles consist solely of heteroatomic bonds like C−O, C−N, C=O, and C=N. The restriction of vibrational and rotational relaxation of these bonds within the nanoscale poly-ionic complex enhances their photoluminescence properties. For example, glutaraldehyde-crosslinked polyethyleneimine/poly(methacrylic acid) (gPEI/PMAA) nanoparticles produced by this method demonstrate outstanding properties including a narrow size distribution with an average diameter of 35 nm, excitation-dependent fluorescence with a green emission peak at 527 nm when excited at 480 nm, and a high quantum yield of up to 23.6 % (±1.2 %). The green fluorescence property of the nanoparticles can be used in the generation of white LED light through incorporating them with silicone and coating them onto a blue light LED chip. This study represents a significant improvement in the fluorescence properties of PEI-based materials and opens up new possibilities for their applications in various fields.