Ultrabright Fluorescent Polymeric Nanoparticles Made from a New Family of BODIPY Monomers

Four novel BODIPY derivatives (π-) functionalized by different polymerizable groups, styrene (S), phenyl acrylate (PhA), ethyl methacrylate (EtMA) and ethyl acrylate (EtA) have been synthesized. Following a formerly established one-pot RAFT miniemulsion polymerization process (Grazon et al. Macromol. Rapid Commun. 2011, 32, 699-705), the fluorophores were copolymerized in a controlled way at 2.6 mol% with styrene in water. Based on the polymerization-induced self-assembly (PISA) principle, the copolymers assembled during their formation into fluorescent nanoparticles. The distribution of the fluorescent monomers 2 along the polymer backbone was monitored by kinetic studies of the copolymerization reaction. Fluorescent stationary and time-resolved spectroscopy was then performed on both the monomers and the nanoparticles (NPs) and the observed differences are discussed in view of the distribution of the fluorescent monomers in the polymer chain. With two of the novel fluorescent monomers (πS and πPhA), the brightness of the NPs could be significantly improved (by a factor 2) compared to particles comprising the other BODIPY monomers. The obtained particles were 200 to 2000 times brighter than usual quantum dots and 40 to 300 times brighter than most of the fluorescent polymeric nanoparticles reported in the literature.