Poly(thiophene) nanoparticles prepared by Fe³⁺-catalyzed oxidative polymerization: A size-dependent effect on photoluminescence property

Poly(thiophene) (PTh) nanoparticles with various sizes were directly prepared by Fe³⁺-catalyzed oxidative polymerization of thiophene with varying hydrogen peroxide (H₂O₂) concentrations. In the polymerization, the FeCl₃/H₂O₂ (catalyst/oxidant) combination system was used as an initiator couple. Under the optimized reaction condition, percentage monomer conversions were >90%. With increasing H₂O₂ molar concentration from 2.35 to 5.88 M, the average sizes of the PTh nanoparticles decreased from. 51 to 12 nm, and their photoemission wavelengths shifted from red to blue color at the maximum excitation wavelength (λ^UV_max = 400 nm). However, the molecular weights of all PTh nanoparticles were ∼3500 g/mol. As a result, we could tune the emitting colors that resulted from variations of the effective conjugation chain length by manipulating the size of PTh nanoparticles.