Soluble conjugated polymeric nanoparticles were synthesized through Sonogashira polycondensation between different combinations of multifunctional alkynes and aryl halides in structurally well-defined mesoporous reactors. The growth of the polymeric nanoparticles was controlled by the spatial confinement of the nanoreactors, giving conjugated polymeric nanoparticles with narrow size distribution centered at 5 nm. All the obtained polymers are freely soluble in common solvents and can be fabricated into thin film. Both of the solution and thin film prepared from these polymeric nanoparticles were highly fluorescent, endowing them potential applications in light emitting and other optoelectronic fields. (C) 2016 Wiley Periodicals, Inc.