Morphology and photoluminescence of colloidal polypyrrole nanoparticles

In order to elucidate the origin of the photoluminescence (PL) of polypyrrole (PPy) colloids, several PPy colloidal samples were prepared under various emulsifying conditions and their PL properties were correlated with the particle morphologies. While highly aggregated fibril- or sheet-like PPy particles were obtained when a cationic surfactant [decyltrimethyl ammonium bromide (DeTAB)] and metal halide oxidant (CuCl2) were used, employment of anionic surfactant and non-metallic oxidant [sodium di(2-ethyl-1-hexyl)sulfosuccinate (DEHSNa) and ammonium persulfate (APS)] afforded spherical PPy nanoparticles with more regularity. PL measurements of these samples indicated that the highest PL intensity is obtained from the less aggregated and smaller PPy nanoparticles. It was presumed that the smaller particles generate more localized excitons due to shorter π-conjugation length, thereby resulting in stronger PL intensity.