β-Phase transformation and energy transfer induced photoluminescence modulation of fluorene based coploymer mono-dispersive nanoparticles

9,9-Dioctylfluorene (DOF) copolymer nanoparticles (NPs) aqueous suspensions were prepared by a simple reprecipitation method. The copolymer comprises 99% 9,9-dioctylfluorene (DOF) and 1% 2,3-dimethyl-5,8-dithien-2-yl-quinoxalines (DDQ) in the polymer backbone. Transmission electron microscopy (TEM) images of NPs show mono-dispersive size distribution of 1-3 nm, among the smallest fluorescent polymer NPs reported in literature. Several NPs aqueous suspension samples are prepared by controlling polymer concentrations in the reprecipitation method. The photophysical properties of NPs were studied by UV-vis absorption spectroscopy and photoluminescence (PL) spectroscopy. The UV-vis absorption peaks at 402 and 435 nm indicate formation of the β-phase in the PFO while the 390 nm peak is attributed to the disordered PFO glassy phase. PL spectra of the NPs, as determined by the energy transfer between glassy phase PFO, β-phase PFO and narrow band gap DDQ segments, can be controllably tuned from blue to white by controlling the initial concentration of the copolymer solution. © 2013 The Royal Society of Chemistry.