The design of photoactive polymer substrates producing singlet oxygen under visible light irradiation has great technological potential. Aqueous dispersion of novel photoactive core-shell particles was synthesized by surfactant-free reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of n-butyl acrylate. The surface of the nanoparticles is directly decorated thanks to the polymerization-induced self-assembly process using a hydrophilic macromolecular chain transfer agent (macro-CTA) functionalized with the organic photosensitizer. The macro-CTA was synthesized by statistical copolymerization of acrylic acid and 2-Rose Bengal ethyl acrylate (RBEA) at 80 °C mediated with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid. Monitoring polymerization kinetics of RAFT polymerization highlights that increasing amount of RBEA induces retardation, still more pronounced when using the vinylbenzyl Rose Bengal comonomer. The present work provides insight into the quantum yield of singlet oxygen production in water (ΦΔ = 0.2-0.6) for the three types of synthesized polymers (hydrophilic polymer, latex particles, and polymer film). The photoactive core-shell latex particles enabled the easy preparation of photoactive polymer film by simple casting.