Molecular relaxations in polyfluorene based cast films

This article reports a study of the thermal relaxation in cast films of two polyfluorene based polymers, poly{9,9-dioctylfluorenyl-2,7-diyl} (BE329) and poly{(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene]} (GE108). The relaxation processes were identified by Dynamical Mechanical Thermal Analysis (DMTA), which revealed three processes in both samples: process at lower temperatures and two relaxations at higher temperatures (named as ˛A and ˛B). The\ud relaxations mechanics were elucidated by Solid-State Nuclear Magnetic Resonance (NMR) methods. The results revealed that the relaxation is related to molecular motions in the side-groups, while the second and third relaxations can be attributed to local rotations in the backbone and to a glass transition. The molecular relaxations were also identified by the temperature dependence of the fluorescence spectra, which were also associated with their molecular nature.FAPESPCNPqMCT/PADCT/IMM

Electroluminescence of (styrene-co-acrylic acid) ionomer/conjugated MEH-PPV blends

This work reports the electroluminescence of poly[2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and poly(styrene-co-acrylic acid-co-1-pyrenylmethyl methacrylate) (SAA) blends in ratios from 0 to 100 wt.% in mass of MEH-PPV. The styrene-co-acrylic copolymer was synthesized with 3 mol% of acrylic acid units to simultaneously enhance blend miscibility and charge transport in MEH-PPV. The morphology was studied using epifluorescence microscopy and scanning electron microscopy in which the pyrenyl-labeled copolymer is used to enhance microscopic contrast. Device performances were compared: those using MEH-PPV have a turn-on voltage of 3.5 V, luminance of 500 cd/m2 and current density of 430 mA/cm2 at 5 V, while MEH-PPV blended with 50 wt.% styrene–acrylic copolymer showed a turn-on voltage of 2.5 V, a luminance of 2300 cd/A and a current density of 640 mA/cm2 at 5 V

Study of solvent-conjugated polymer interactions by polarized spectroscopy: MEH-PPV and Poly(9,9′-dioctylfluorene-2,7-diyl)

Absorption, emission, and anisotropy measurements were performed on poly-[2-methoxy-5(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly-(9,9′-dioctylfluorene-2,7-diyl) (PF) solutions of various solvents, and in thin films deposited from them. The good correlation of MEH-PPV absorption and emission energy with Hildebrandt's dispersive parameter indicate that dispersive forces regulate the effective extent of the luminophore. The excitation and the emission spectra of α and β chains can be distinguished in PF solutions using the steady-state anisotropy. PF films show greater memory effect from the solutions from which they were spun than MEH-PPV. Anisotropy of MEH-PPV is very low, both in solutions and in films reflecting efficient energy migration. Anisotropy of PF in solutions and films demonstrates great differences in energy transfer efficiency within the α and β phases, while there is no energy transfer between these chain conformations.Fil: Cossiello, Rafael F.. Universidade Estadual de Campinas; BrasilFil: Susman, Mariano D.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Aramendia, Pedro Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Atvars, Teresa D. Z.. Universidade Estadual de Campinas; Brasi