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 pi-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 exeimer emission band Increased upon mum: reflecting excimer formation due to the high mobility of PFFO chains (T-g -20 degrees C) or fluorene moiety oxidation.