Full text
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| Author(s): |
Valtencir Zucolotto
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2003-10-31 |
| Examining board members: |
Osvaldo Novais de Oliveira Junior;
Teresa Dib Zambon Atvars;
Maurício da Silva Baptista;
Elisabeth Andreoli de Oliveira;
Antonio Ricardo Zanatta
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| Advisor: | Osvaldo Novais de Oliveira Junior |
| Abstract | |
This thesis describes the fabrication and possible applications of layer-by-Iayer (LBL) nanostructured films for three distinct systems comprising i) azopolymers and azodyes, ii) organometallic molecules (phthalocyanines) and iii) luminescent polymers and azodyes. Optically induced birefringence and surface relief gratings (SRGs) were studied in the azobenzene-containing composites, using a side-chain azopolymer (Ma-co-DR13) and a commercially available azodye, viz. Brilliant Yellow (BY). Optical storage experiments showed that the writing time required to induce birefringence (up to the saturation) in LBL films of Ma-co-DR13 is ca. 30 min, which is considerably longer than the times required in cast films of azopolymers (tens of seconds). The long writing time was attributed to the electrostatic interactions between the layers in the LBL film, which preclude photoisomerization or the reorientational processes for the azobenzene molecules.ln addition, entrained water in the films was found to affect the writing time. For example, the characteristic writing time decreases from 8 min. for a dry film to ca.2 min. for a film immersed for some minutes in water. This effect was completely reversible. Surface relief gratings were inscribed on LBL films from BY and analyzed with micro-Raman spectroscopy. The Raman spectra revealed that the process for SRG inscription is not entirely light-driven, with the occurrence of photodegradation. Such photodegradation can be minimized upon the appropriate choice of the polycations as well as the experimental conditions used for film fabrication. The lowest level of photodegradation was observed for films of poly(allylamine hydrochloride) (PAH) and BY fabricated from pH 10 solutions. Organometallic supramolecular composites were built using iron tetrasulfonated phthalocyanine (FeTsPc) and P AH as polycation. The combination of electronic and vibrational spectroscopic techniques showed the presence of unusual specific interactions between the central atom of FeTsPc and non-protonated groups from P AH (NH2). These interactions are believed to occur due to the intimate contact between the materials in the very thin PAH/FeTsPc LBL films, whose thickness was 10 ?Angstron? per bilayer. In the poly(p-fenilene vinylene) (PPV) (donor) and BY (acceptor) system, the resonant energy transfer process was exploited to control luminescence. The quenching in luminescence could be controlled by varying the distance between the PPV and BY layers, similarly to what has been reported in the literature. The novelty in this work, however, was the fine-tuning of luminescence achieved with the photoalignment of the acceptor molecules (BY). For example, the intensity of the photoluminescence increased 4 times upon the photoalignment for 10 min. of the BY chromophores. (AU) | |