beta-Phase Formation in Poly(9,9-dioctylfluorene) Promoted by Natural Lecithin Liposomes

The neutral polyfluorene poly(9,9-dioctylfluorene) has been enclosed in natural lecithin liposomes, one from Soy bean (Soybean PC) and two from egg yolk (Egg1 PC and Egg2 PC), and the effect of increase in polymer concentration on the photophysical properties of the polymer followed by absorption and emission (stationary and time-resolved) spectroscopies. The characteristic narrow absorption band at 435 nm of the planar beta-phase polymer conformation, together with vibronically structured emission band (with peaks at similar to 440, 465 and 500 nm), are observed with all the phosphatidylcholines studied. From de-convolution of the absorption spectra, the beta-phase contribution to the total absorption is estimated and found to increase with polymer concentration in a similar fashion to the synthetic lecithin 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholin, DMPC. A comparison of the effectiveness of the two natural lecithins in promoting beta-phase formation has been performed based on the saturation of the main fatty acid components of the two lecithins and its consequences on the inter-bilayer free volume which controls the polymer location.