Navegando por Palavras-chave "Copolymers"

Agora exibindo 1 - 2 de 2
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Novel blue emitters based on pi-conjugated block copolymers
    (Elsevier B.V., 2009-03-01) Peres, L. O. [UNIFESP]; Wang, S. H.; Wery, J.; Froyer, G.; Faulques, E.; Universidade Federal de São Paulo (UNIFESP); Universidade de São Paulo (USP); Inst Mat Jean Rouxel
    A series of new phenyl-based conjugated copolymers has been synthesized and investigated by vibrational and photoluminescence spectroscopy (PL). the materials are: poly( 1,4-phenylene-alt-3,6-pyridazine) (COP-PIR), poly(9,9-dioctylfluorene)-co-quaterphenylene (COP-PPP) and poly[(1,4-phenylene-alt-3,6-pyridazine)-co-(1,4-phenylene-alt-9,9-dioctylfluorene)] (COP-PIR-FLUOR), with 3.5% of fluorene. COP-PPP and COP-PIR-FLUOR have high fluorescence quantum yields in solution. Infrared and Raman spectra were used to check the chemical structure of the compounds. the copolymers exhibit blue emission ranging front 2.8 to 3.6 eV when excited at E(exc)=4.13 eV. Stokes-shift Values were estimated on pristine samples in their condensed state from steady-state PL-emission and PL-excitation spectra. They suggest a difference in the torsional angle between the molecular configuration of the polymer blocks at the absorption and PL transitions and also in the photoexcitation diffusion. Additionally, the time-resolved PL of these materials has been investigated by using 100 fs laser pulses at E(exc)=4.64 eV and a streak camera. Results show very fast biexponential kinetics for the two fluorene-based polymers with decay times below 300 ps indicating both intramolecular, fast radiative recombination and migration of photogenerated electron-hole pairs. By contrast, the PL of COP-PIR is less intense and longer lived, indicating that excitons are confined to the chains in this polymer. (C) 2008 Elsevier B.V. All rights reserved.
  • Nenhuma Miniatura disponível
    Item
    Somente Metadadados
    Pf/clay hybrid materials: a simple method to modulate the optical properties
    (Assoc brasil polimeros, 2016) Chen Em, Marcio Chao [UNIFESP]; Barbosa, Camila Gouveia [UNIFESP]; Peres, Laura Oliveira [UNIFESP]; Faez, Roselena
    The aim of this work was modulate the emission properties and improve thermal stability of a conjugated polymer incorporated into an inorganic matrix. Hybrid material was prepared based on poly(9,9-dioctylfluorene-co-phenylene (PF) and montmorillonite (Na(+)Mt) clay using wet impregnation of 10, 30 and 50 wt.% of PF into Na(+)Mt and Na(+)Mt intercalated with ammonium quaternary salts (hexadecyltrimethylammonium - HDTMA) in a different proportions (OMt-1 and OMt-2). The materials were characterized by infrared and UV-Vis spectroscopy, fluorescence, X-ray diffratometry and thermogravimetry analysis. The results show that the presence of the clay alters the photoluminescent and thermal properties. Nevertheless, the degree of the clay organophilization and the clay content influences the luminescent properties due to the diverse interaction behavior between the polymer and clay. The sodium clay acted only as dispersing agent since no intercalation process occurs and the emission displacement is assigned to this behavior. In this case the PF emission displace from 402 to 395 nm. A nonlinear displacement is observed for PF/OMt-2 due the difficulties to conclude if the intercalation of the polymer occurs (379, 403 and 412 for hybrid with 10, 30 and 50%, respectively). For PF/OMt-1 a higher displacements for lower wavelength is observed due to intercalation of polymer chains and subsequent isolation in the interlamellar space, especially with material with 10 and 30% of PF in the hybrid material, whose displacement reached to 360 nm. All these results show that is possible to try to control the emission of the conjugated hybrid material changing the rate of the material.