β-Phase formation of poly(9,9-dioctylfluorene) induced by liposome phospholipid bilayers

The well-structured β-phase emission of the neutral poly(9,9-dioctylfluorene) (PFO) is observed in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers, either as polydisperse aqueous liposomes or as the lamellar phase in thin films, and has been characterized by absorption, fluorescence (steady-state and time-resolved), and fluorescence anisotropy spectroscopy. Inclusion of PFO in DMPC liposomes provides a way of obtaining the ordered structure of this neutral polymer in aqueous suspensions. Quantification of the increase of the PFO β-phase in DMPC liposomes with the increase in polymer concentration is followed by deconvolution of the absorption spectra. In solid films, the presence of the phospholipids enhances the β-phase formation. In addition, the effect of the PFO concentration on the phospholipid phase transitions has been studied by differential scanning calorimetry (in liposome) and polarized light thermal microscopy (in solid film), confirming PFO/DMPC interactions in both liposome and films. The liposome size and structure in the presence and absence of polymer were characterized by dynamic light scattering and transmission electron microscopy, which showed relatively modest changes in liposome shape but a decrease in size upon incorporation of PFO.