Controlling the Size of Glassy Organic Dots Exhibiting Thermally Activated Delayed Fluorescence for Bioimaging

Luminescent glassy organic dots (g-Odots) are emerging as promising nanoparticles for bioimaging, exhibiting excellent brightness and photostability attributed to their glassy, rigid matrix. Emission color tuning in g-Odots is also easily accessible, since different hydrophobic fluorophores can be encapsulated within the glassy matrix of the particle. g-Odots are particularly useful when combined with dyes exhibiting phosphorescence or thermally activated delayed fluorescence (TADF), facilitating time-gated fluorescence imaging while the glassy core shields the emitters from oxygen. Despite their potential usefulness, strategies for controlling size in g-Odots remain unexplored─a critical parameter affecting cellular uptake and metabolism. Here, we investigate methods to control g-Odot size while retaining the glassy interior of the nanoparticles. Annealing of the glassy host material was explored as a postsynthetic step to promote the glass transition of the particles. Host-to-surfactant ratios were also investigated as a simple route to tunable particle sizes. Centrifugation and size exclusion chromatography were also examined as methods to fractionate g-Odots by size after synthesis. While established for other nanoparticle types, these methods have yet to be explored for g-Odots. Our findings provide strategies to control the size of g-Odots, which we anticipate will broaden their applicability in bioimaging applications.