Highly oriented Langmuir-Blodgett films of poly(p-phenylenevinylene) using a long chain sulfonic counterion

Langmuir-Blodgett (LB) films of a poly(p-phenylenevinylene) (PPV) precursor were prepared using an amphiphilic precursor, poly(xylylidenetetrahydrothiophenium chloride) (PTHT), where the counterion chloride was replaced by a long chain dodecylbenzenesulfonate (DBS) ion. Stable PTHT-DBS monolayers were transferred onto quartz substrates in the form of LB films. Using DBS allowed PPV films to be converted under atmospheric pressure at temperatures as low as 80 degrees C, with conjugation length and optical properties better than for standard films converted at temperatures above 200 degrees C under controlled atmospheres. These LB-PPV films are highly anisotropic as demonstrated by linear dichroism experiments using linearly polarized optical absorption and emission. The dichroic ratio between the intensity of the emitted light parallel and perpendicular to the dipping direction was ca. 17, which is much higher than the dichroic ratio of 3.6 found in the polarized absorption experiment. This difference indicates an efficient excitation transfer between the low conjugated segments (disordered) and the highly conjugated (ordered) ones after excitation.