Synthesis, characterization, and energy transfer studies of dye-labeled poly(butyl methacrylate) latex particles prepared by miniemulsion polymerization

Poly(butyl methacrylate) (PBMA) latex particles have been copolymerized with new fluorescent naphthalimide dyes by miniemulsion polymerization. A new pair of naphthalimide dye monomers was synthesized and copolymerized with butyl methacrylate (BMA) via miniemulsion polymerization, producing approximately 80 nm diameter particles with a narrow size distribution. We were able to prepare polymers with molecular weights in excess of 100,000 g/mol. We also prepared 30,000 g/mol polymers using 1-dodecanethiol as a chain transfer agent. GPC and UV characterization suggest that nearly all of the dye monomers were incorporated into the PBMA polymer chains. The polymerized naphthalimide dyes can be used as a donor-acceptor pair for fluorescence resonance energy transfer (FRET) experiments. The analysis of FRET experiments is complicated by the slightly non-exponential decay of the donor naphthalimide dye. We propose a simple method to deal with this non-exponential behavior in the data analysis. Using our approach, we find that the Förster radius (Ro) between the donor and the acceptor dyes incorporated in the PBMA latex is 3.8 nm. This value is similar to the 3.6 nm Förster radius of a comparable model dye pair in ethyl acetate obtained by a different method.