Photoluminescence of 2,7-Poly(9,9-dialkylfluorene-co-fluorenone) Nanoparticles: Effect of Particle Size and Inert Polymer Addition

Stable nanoparticle dispersions of 2,7-poly(9,9-dialkylfluorene-co-fluorenone) (PFFO) and of PFFO/cellulose acetate butyrate (CAB) mixtures with particle size ranging between 5 and 500 nm were prepared by miniemulsification in the presence of a cationic surfactant. Photoluminescence spectra of nanoparticle dispersions showed that the decrease of particle size and of the PFFO/CAB mass ratio induced the progressive suppression of the PFFO excimer emission band at 535 nm. This behavior was associated with the limited ordered structure and π-stacking arrangement of PFFO molecules when confined within nanoparticles smaller than 150 nm or in the presence of CAB molecules. All nanoparticle dispersions displayed high dimensional stability; however, the relative intensity of the excimer emission band increased upon aging reflecting excimer formation due to the high mobility of PFFO chains (Tg −20 °C) or fluorene moiety oxidation.