A facile route of polythiophene nanoparticles via Fe³⁺-catalyzed oxidative polymerization in aqueous medium

We have demonstrated that unsubstituted thiophene can be polymerized by Fe³⁺-catalyzed oxidative polymerization inside nanosized thiophene monomer droplets, that is, nanoreactors, dispersed in aqueous medium, which can be performed under acidic solution conditions with anionic surfactant. Besides, we proposed a synthetic mechanism for the formation of the unsubstituted polythiophene nanoparticles in aqueous medium. This facile method includes a FeCl₃/H₂O₂ (catalyst/oxidant) combination system, which guarantees a high conversion (ca. 99%) of thiophene monomers with only a trace of FeCl₃. The average particle size was about 30 nm, within a narrow particle-size distribution (PDI = 1.15), which resulted in a good dispersion state of the unsubstituted polythiophene nanoparticles. Hansen solubility parameters were introduced to interpret the dispersion state of the polythiophene nanoparticles with various organic solvents. The UV-Visible absorption and photoluminescence (PL) spectrum were measured to investigate the light emitting properties of the prepared unsubstituted polythiophene nanoparticle emulsions. According to nonnormalized PL analysis, the reduced total PL intensity of the polythiophene nanoparticle emulsions can be rationalized by self-absorption in a wavelength range less than 500 nm.