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| Author(s): |
Raquel Aparecida Domingues
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Química |
| Defense date: | 2013-09-26 |
| Examining board members: |
Teresa Dib Zambon Atvars;
Marian Rosaly Davolos;
Marcelo Henrique Gehlen;
Pedro Luiz Onófrio Volpe;
René Alfonso Nome Silva
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| Advisor: | Teresa Dib Zambon Atvars |
| Abstract | |
In this work, the influence of substrate on the photophysical properties of two polyfluorene derivatives, F8BT and PFO-MEHPPV was studied. The films were prepared by spin-coating solutions of the polymers, using glass and ITO coated glass as the substrates. The thickness was varied from 50 nm to 600 nm. A cast film with a thickness of 50 ìm was also prepared using both polymers. The photophysical properties of the two polyfluorene derivatives, F8BT and PFO-MEHPPV were studied using their emission spectra, the full width at half maximum (FWHM) of the spectra, the temperature dependence of the peak position of the 0-0 emission band and the vibronic progression of the emission spectra. For both polymers, F8BT and PFO-MEHPPV, as the film thickness decreased the glass transition temperature decreased. Below a film thickness of 450 nm, a deviation from bulk behavior was observed. It is also importante note that the substrate type did not affect the relaxation temperature. It was possible to classify the F8BT films into two groups. Those with thicknesses between 52 nm to 185 nm have shown greater inhomogeneous broadening and very heterogeneous cybotatic environments for the fluorophores, while those with film thicknesses greater than 450 nm have shown higher Tg values which induce lower inhomogeneous broadening. PFO-MEHPPV also has shown a similar trend. As the thickness of the film increased, a higher Tg was observed. However, thicker films of PFO-MEHPPV were observed to be less locally organized, in contrast to the F8BT films of the same thickness. This might be due to the substrate, which would favor some degree of organization in the films in comparison to the bulk material. Time-resolved PL measurements have also been used to characterize the interface interactions between the polymer film and ITO (polymer/ITO) or aluminum (polymer/aluminum). The aluminum layer acted as a quencher through an interference effect, energy transfer to the metal and excitonic diffusion. The interference effect was determined by using a model described in the literature however, it has a minimal effect in thinner films. The evidence gained from the photophysical measurements indicates that these films with thicknesses above 450 nm do not show thin film behavior (AU) | |