Propriedades fotofísicas do copolímero polifluoreno-carbazol e aplicações eletro-ópticas

Abstract

The edge emission in waveguides of thin films of conjugated copolymer poly [(9,9-diexilfluoreno-2,7-diyl) -co- (9-ethylcarbazole-2,7-diyl)] (PDHF - ECZ) a strip-excited laser is obtained for different distances x from a region not illuminated by the laser to the edge of the film. These measures have allowed us to study the formation of vibronic bands in the photoluminescence spectra in different conditions of scattering and / or self-absorption of the emitted light. The photoluminescence spectra were also obtained at different temperatures in the optical configuration 45O excitation-emission before and after thermalization of the films. The Franck-Condon analysis of the vibronic bands, these two experimental settings, allowed us to obtain the Huang-Rhys factors of the effective vibrational modes involved. Our studies show that the higher the scattering process and / or self-absorption in the material is greater electron interaction with the vibrational modes of lower energy. A green band appears in the photoluminescence spectra of the samples after thermalization. The same green band was observed in electroluminescence spectra. The issuance of this band saturates faster with increasing laser power the natural emission in blue PDHF-ECZ. Considering the green band comes from the final states of emission due to the segments of greater conjugation length in a more ordered structure of aggregates, their faster saturation would be expected. Besides, different vibrational modes within this aggregate region could contribute as non-radiative pathways for relaxation of optically excited electrons. Another fact which confirms the formation of aggregates of the sample after heat treatment is shift to longer wavelengths (red-shift) observed in the green emission band with the temperature and also decreased with increasing tension in the electroluminescence. A larger absorption coefficient is observed for the film after thermalization. In our understanding we consider a power transfer mechanism is due to the migration through the excimers states within the aggregates formed after annealing of the film. Our results favor the assumption that the origin of the green band is more related to the issuance of excimers delocalizados states within the cleanest aggregate, than the issue of localized states due to the formation of the fluorenone defects in type monomers polyfluorene.