Publications (19) View all
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Article: Investigation of ground- and excited-state photophysical properties of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin with ruthenium outlying complexes.
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ABSTRACT: The present work employs a set of complementary techniques to investigate the influence of outlying Ru(II) groups on the ground- and excited-state photophysical properties of free-base tetrapyridyl porphyrin (H(2)TPyP). Single pulse and pulse train Z-scan techniques used in association with laser flash photolysis, absorbance and fluorescence spectroscopy, and fluorescence decay measurements, allowed us to conclude that the presence of outlying Ru(II) groups causes significant changes on both electronic structure and vibrational properties of porphyrin. Such modifications take place mainly due to the activation of nonradiative decay channels responsible for the emission quenching, as well as by favoring some vibrational modes in the light absorption process. It is also observed that, differently from what happens when the Ru(II) is placed at the center of the macrocycle, the peripheral groups cause an increase of the intersystem crossing processes, probably due to the structural distortion of the ring that implies a worse spin-orbit coupling, responsible for the intersystem crossing mechanism.The Journal of Physical Chemistry A 12/2011; 116(1):18-26. · 2.95 Impact Factor -
Article: Controlling bandgap energy and multivibronic modes of a poly(2,5-thiophene-1,4-dialkoxyphenylene) derivative by gamma photons.
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ABSTRACT: In this work, the influence of γ radiation on electronic, structural, and vibrational properties of a poly(2,5-thiophene-1,4-dialkoxyphenylene) derivative is studied by optical absorption and photoluminescence. A Gaussian fit of emission spectra within Franck-Condon vertical transitions formalism was carried out in order to understand how vibronic coupling is affected by the dose, because an unexpected luminescence behavior was observed. Aiming to understand the ionizing radiation-matter interaction processes, we employed a molecular modeling procedure, through the use of a semiempirical method (AM1) applied to conjugated oligomers' conformational structure and equilibrium geometries, to clarify the defects induction for the used doses. From AM1 optimized structures, electronic transitions were calculated by ZINDO/S-CI semiempirical method to measure the chain scission degree. Moreover, with the results presented in this work, it is possible to come up with a new physical-chemical route to treat and increase conjugated polymers' efficiency. Finally, we believe that the present paper contributes to the literature about defects on conjugated polymers.The Journal of Physical Chemistry A 06/2011; 115(29):8288-94. · 2.95 Impact Factor -
Article: Thickness and annealing temperature effects on the optical properties and surface morphology of layer‐by‐layer poly(p‐phenyline vinylene)+dodecylbenzenesulfonate films
Journal of Polymer Science Part B Polymer Physics 12/2010; 49(3):206 - 213. · 1.53 Impact Factor -
Article: Exchange with temperature of the electron‐vibrational mode interaction between thienylene–phenylene copolymer rings
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ABSTRACT: Thienylene–dialkoxyphenylene copolymers with polar side chains are soluble in most organic solvents and exhibit excellent glass adhesion properties, allowing the formation of homogeneous thin films on glass, quartz, and other substrates by spin coating. The electrochemical and optical properties of thin films of this material are studied in this work. The calculated band gap derived from electrochemical data (2.34 eV) is in good agreement with that observed from the UV–vis spectrum edge (2.25 eV). The analysis of the emission properties reveals the strong dependence on temperature of the electron coupling with different vibrational modes in the formation of the vibronic bands. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 964–971, 2010Journal of Polymer Science Part B Polymer Physics 03/2010; 48(9):964 - 971. · 1.53 Impact Factor -
Article: Induced secondary structure in nanostructured films of poly(p-phenylene vinylene).
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ABSTRACT: The control of emission properties in luminescent polymers such as poly(p-phenylene vinylene) (PPV) is important for various applications, and may be achieved with suitable molecular architectures in nanostructured films. This paper reports on optical properties of PPV films, using ellipsometry measurements for emitted light in the scope of the Stokes' theory. Organized PPV films obtained with the Langmuir-Blodgett (LB) method exhibited high degree of polarization for the emitted light, while cast films emitted mainly non-polarized light. From ellipsometry data, a secondary structure was inferred for poly(xylylidene tetrahydrothiophenium) chloride (PTHT), a PPV precursor, in solution, which is retained only to a small extent in the PPV cast film as thermal conversion was performed close to the glass transition temperature of PPV. On the other hand, a higher intensity of emitted light with circular polarization was observed for the LB film, which is attributed to PPV molecular secondary structure that was enhanced during the LB film deposition. Circular dichroism experiments were performed to corroborate this hypothesis. It is suggested that such a secondary structure has not been predicted in theoretical models for PPV because possible conformational changes induced in the processing steps are not taken into account.Journal of Nanoscience and Nanotechnology 10/2009; 9(10):5981-9. · 1.56 Impact Factor
