Deciphering the Blinking Mechanisms of Dye-Loaded Organic Nanoparticles

This study investigates the blinking behavior of dye-loaded organic nanoparticles (NPs) and elucidates the role of energy transfer (EET) and dye aggregation. Using spectrally resolved single-molecule microscopy, we characterize the optical properties of NPs composed of poly(lactic-<i>co</i>-glycolic acid) (PLGA) and poly(methyl methacrylate) (PMMA) with varying dye loadings. At high dye concentrations, the NPs exhibit intensity fluctuations that are attributed to transient species quenching the emission. Temperature dependent studies evidence that the quenching disappears at 77 K, highlighting the role of dye diffusion in the polymer matrix. Spectral analysis confirms the formation of red-shifted emissive aggregates and nonemissive aggregates as major contributors to the blinking mechanism. Computational studies support these findings, identifying stable crossed J-dimers responsible for red-shifted emission and nonemissive H-dimers associated with fluorescence quenching. This work improves our understanding of the collective behavior of dyes embedded in polymeric NPs, paving the way for the development of brighter and more efficient fluorescent nanomaterials.