Chemical Defects in the Highly Fluorescent Conjugated Polymer Dots

We present strong evidence for the oxidation of conjugated polymers in the formation of conjugated polymer dots (CPdots) using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Although recent studies show that folding of the polymer chain into a compact 3D structure is involved in the formation of these nanoparticles, the process by which these intrinsically hydrophobic nanoscale particles circumvent aggregation in water is still not well understood. Zeta potential results show that these dots have a negatively charged surface at neutral pH, with a zeta potential and surface charge density of approximately -40 mV and (1.39 - 1.70) x 10(-2) C/m(2), respectively. In addition, quantitative elemental analysis of CPdots indicates that oxygen composes 7-13% of these nanoparticles. The overall results support the presence of chemical defects in forming a hydrophilic surface of CPdots. As a consequence, the charged surface contributes to inhibiting the aggregation of CPdots in water, leading to colloidal stability.