Tuning optical properties of poly(3-hexylthiophene) nanoparticles through hydrothermal processing

Poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) were prepared by a reprecipitation method. Hydrothermal processing applied external pressure to the pristine P3HT NPs at temperatures ranging from 60 to 150 degrees C. Optical absorption and photoluminescence (PL) spectra for the hydrothermally treated P3HT NPs varied markedly with the processing temperature. With increasing treatment temperature, the absorption peak broadened and the peak position shifted from 510 to 623 nm; moreover, the intensity ratio of the 0-1 to 0-0 emission varied. These changes were caused by interactions between the P3HT main chains and alkyl side groups and conformational modifications induced by the high pressure during the hydrothermal process. The evolution of the optical absorption spectra of the P3HT NPs during the hydrothermal processing was strongly correlated with the variation of PL excitation spectra and with the PL emission spectra of a single NP.