Electroluminescent polyelectrolyte-surfactant complexes

Polyelectrolyte complexes of poly(1,4-phenyleneethynylene carboxylate) (PPE) with 10 different cationic counterions were prepared. The counterions differed in their amphiphilicity, their headgroups (ammonium, pyridinium and sulfonium), and their alkyl chain lengths. It is shown that the optical properties of the PPE complexes depend on the nature of their counterions: the peak wavelength of the electroluminescence shifts from 430 to 515 nm for single-layer light-emitting diodes (LEDs) when the counterions were changed from tetraethylammonium to sulfonium ions. All the PPE complexes with amphiphile counterions displayed ordered mesophases. They are smectic A or smectic B-like in the solid state at room temperature with long periods of 2.38-4.27 nm. By contrast, no mesomorphous structures were found for the PPE complexes with nonamphiphilic counterions. All complexes were investigated by using differential thermal analysis, small- and wide-angle X-ray scattering techniques, and fluorescence spectroscopy