Conjugation Length Distribution in Poly(p-phenylenevinylene) (PPV) Films.

We studied the absorption line-shape of poly(p-phenylenevinylene) (PPV) films deposited via spin coating and Langmuir-Blodgett techniques with the intent of identifying the conjugation length distribution in these two types of films, a key morphological aspect of conjugated polymer films. We treated the excitons in the polymer as independent oligomer excitons and modeled the absorption spectra of the individual oligomers using simple expressions for the oligomer size dependence of the gap energy, the line-broadening factor, the transition dipole moment and the Huang-Rhys parameter. We validated these expressions by independent measurements on phenyl-based oligomers and Density Functional Theory calculations.

Study of the catalytic behavior of montmorillonite/iron(III) and Mn(III) cationic porphyrins.

Two samples of montmorillonite (one of Brazilian origin, BNC1 clay, and the other STX-1, supplied by the Clay Mineral Society Repository (University of Missouri, USA) were allowed to react with biomimetic metalloporphyrins of Fe(III) and Mn(III) in cationic form. The compounds were characterized by several techniques, showing that the metalloporphyrins molecules were adsorbed at the surface of the clay platelet crystals. The catalytic activities of the intercalated complexes for the oxidation of alkane were dependent upon the concentration of the porphyrin immobilized in the clay and factors such as the metal ion species in the porphyrins, choice of solvent, and concentration of the iodosylbenzene oxidant.