Optical activity and order in luminescent Langmuir-Blodgett poly(p-phenylene vinylene) films

Langmuir-Blodgett (LB) PPV films of poly(p-phenylene vinylene) (PPV) have been obtained using a mixture of a PPV precursor, poly(xylylidene tetrahydrothiophenium chloride) (PTHT), with the sodium salt of dodecylsulfonic acid (DBSA) as the spreading solution. Spin-coated films were prepared in order to compare their properties with those of LB films. A large circular dichroism was observed for LB films but not for spin-coated ones. Optical activity of PPV films was characterized by circular dichroism technique, while optical properties were evaluated by optical absorption and luminescence measurements at various temperatures. Overall, the results obtained allowed us to conclude that the layer-by-layer LB process yields a high degree of molecular order in the PPV films with low interchain interaction. Polarized absorption and circular dichroism measurements demonstrate a preferential chain orientation along the dipping direction in the LB processing. The origin of the CD in the PPV-LB can be ascribed to convenient packing of individual monolayers given by the Z-type deposition.