Transfer of Luminescent Radicals to the Aqueous Phase by Polymerization in a Miniemulsion

Luminescent radicals have recently emerged as a new class of open‐shell emitters with unique excited‐state properties and theoretical potential for 100% internal quantum efficiency. However, their application in aqueous environments and biological imaging remains severely limited by poor water dispersibility and aggregation‐induced quenching. Herein, we report an efficient strategy to transfer red‐emissive tris(2,4,6‐trichlorophenyl) methyl (TTM) based luminescent radicals into the aqueous phase via redox polymerization in a miniemulsion. A series of heterocyclic donor‐substituted TTM radicals were synthesized and systematically investigated. By encapsulating the radicals in poly(methyl methacrylate) (PMMA) latex particles, stable water‐dispersible luminescent radical miniemulsions were obtained. Notably, the aqueous radical‐loaded miniemulsion exhibits a photoluminescence quantum yield of 37.6%, which is significantly higher than that of the corresponding radical solution (7.5%), owing to the rigid microenvironment within the polymer matrix. The resulting miniemulsion particles display uniform size distribution, long‐term stability, and bright red emission in water. Furthermore, in vivo imaging experiments demonstrate that the luminescent radical miniemulsion enables stable red fluorescence in living mice. This work provides a general and facile approach for constructing water‐dispersible luminescent radical materials and opens new opportunities for their applications in bioimaging and aqueous photonic systems.