Meta-Dimethoxy-Substituted Difluoroboron Dibenzoylmethane Poly(Lactic Acid) Nanoparticles for Luminescence Anisotropy

Difluoroboron β-diketonates derivatives are dyes with tunable fluorescence and room temperature phosphorescence when embedded in a rigid matrix such as poly(lactic acid) (PLA). Both fluorescence and phosphorescence are present in solid-state PLA, enabling a variety of applications such as bio-imaging and oxygen sensing. Here, a meta-dimethoxy-substituted difluoroboron dibenzoylmethane [BF₂dbm(m-OMe)₂OH] is prepared, and two PLA polymers [BF₂dbm(m-OMe)₂PLA] with different dye loadings are produced. Optical properties are studied in solution, and the emissions are environment sensitive. This is supported by density functional theory (DFT) calculations where intramolecular charge transfer is present and related to solvatochromism. Nanoparticles are fabricated with solvents of varied polarities via nanoprecipitation. Dynamic light scattering indicates dimethylformamide generates the smallest nanoparticles and tetrahydrofuran the largest. Luminescence polarization establishes that the absorbing and emitting dipoles are single axis and collinear. Förster resonance energy transfer within the nanoparticles is important and depends strongly on dye loadings.