Eralci Therézio | Universidade Federal de Mato Grosso (UFMT) (original) (raw)

Papers by Eralci Therézio

Optical Materials, 2015

Herein a useful methodology to study optical properties of cholesteric liquid crystals (Ch-LC) is... more Herein a useful methodology to study optical properties of cholesteric liquid crystals (Ch-LC) is proposed by using the Fourier decomposition ellipsometry technique to calculate the Stokes parameters of transmitted and reflected light in the UV-Vis spectral range. Combining Bragg reflection and optical activity we were able to obtain $100% of linear or circular light polarization from the Ch-LC sample using achromatic and non-polarized light source. The photonic bandgap and the polarization components can be controlled with the temperature as a result of alterations in the helix pitch of the cholesteric phase. Finally, it is demonstrated the correlation between the dissymmetry factor (g) calculated via the Stokes parameter S 3 and the reflection spectrum. The data revealed that the maximum value of S 3 is not coincident with the peak of maximum reflection. The reflected or transmitted light analysis via Stokes parameters obtained by ellipsometry showed an alternative and low cost method for optical characterization in Ch-LC.

Scanning Probe Microscopy-Physical Property Characterization at Nanoscale, 2012

The Journal of Physical Chemistry C, 2013

The emission ellipsometry technique was applied to the donor−acceptor structure, poly[9,9′-diocty... more The emission ellipsometry technique was applied to the donor−acceptor structure, poly[9,9′-dioctyl-2,7-fluorenevinylene-alt-4,7-(di-2,5-thienyl)-2,1,3-benzothiadiazole], to quantify the energy transferred from the donor (fluorene) to the acceptor (thiophene−benzothiadiazole−thiophene). The relative contributions to the total emission from both donor and acceptor were determined and also the amount of the emitting species that lost coherence with the polarization of the excitation light. The results were discussed in terms of energy transfer via multiphonon processes.

Physical Chemistry Chemical Physics, 2014

The incorporation of dyes in liquid crystal matrices has been exploited to produce enhanced displ... more The incorporation of dyes in liquid crystal matrices has been exploited to produce enhanced displays, but it can also be used to probe ordering in liquid crystals and to assess intermolecular interactions and dye aggregation. In this study, we investigated polarized absorption and emission of the luminescent dyes 4,7-bis(2-(4-(decyloxy)phenyl)ethynyl)-[2,1,3]-benzothiadiazole (1A) and 4,7-bis{2-[4-(4-decylpiperazin-1yl)phenyl]ethynyl}-[2,1,3]-benzothiadiazole (5A) in the E7 s liquid crystal. The electronic structures of both 1A and 5A dyes were affected by the matrix and by the analysis of the line shape of emission we could determine that the dyes form J aggregates. This achievement is significant because obtaining this type of information for small molecules requires ordered matrices, which is difficult to obtain for these dyes.

Journal of the Serbian Chemical Society, 2013

In this work, poly (3-methylthiophene) (P3MT) and poly (3-octylthiophene) (P3OT) films were elect... more In this work, poly (3-methylthiophene) (P3MT) and poly (3-octylthiophene) (P3OT) films were electrochemically synthesized in non-aqueous media through the oxidation of the monomers, (3-methylthiophene and 3-octylthiophene) using a standard three-electrode cell in acetonitrile with 0.100 mol L -1 LiClO 4 . The polymeric thin films were deposited on platinum plates for optimal quality control of the process. It was observed that the material asprepared by anodic electropolymerization undergoes a natural process of deprotonation as a function of time. Moreover, the partial de-doped form obtained in NH 4 OH solution presents a good chemically stable form but becomes unstable again when radiated with blue light. Films obtained by these methods were characterized by cyclic voltammetry, Raman and photoluminescence spectroscopy. Both Raman and photoluminescence (PL) spectra led to the characterization of two structures (pristine and non-pristine forms of the thiophene rings), which formed the P3MT and P3OT polymer chains. These results were associated with the stabilization of pristine chains and mixed chains (nonpristine structures), radical cation and dication forms, in the polymeric film. Their bands in the Raman and PL spectra were broad and asymmetric and their adjustments by Gaussian functions indicated that there were three distinct contributions to the vibration and two to the emission spectra in the formed polymeric material.

Journal of Polymer Science Part B: Polymer Physics, 2011

The fabrication of controlled molecular architectures is essential for organic devices, as is the... more The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV)/ dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 C had a dichroic ratio d ¼ 2.3 and order parameter r ¼ 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with d ¼ 1.0 for a 75-layer LbL PPV þ DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the selfcovariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000-000, 2010

Journal of Physical Organic Chemistry, 2011

In this work, poly(3-octylthiophene) (P3OT) films were synthesized electrochemically in non-aqueo... more In this work, poly(3-octylthiophene) (P3OT) films were synthesized electrochemically in non-aqueous media through the oxidation of the monomer, (3-octylthiophene), using a standard three-electrode cell in acetonitrile with 0.05 mol L S1 LiClO 4 or 0.05 mol L S1 Et 4 NBF 4 . The polymeric films were deposited on fluorine tin oxide (FTO). The partial dedoping was obtained in NH 4 OH solution, providing a good chemical stability of the formed material. The films obtained through this method have been characterized by Fourier-transform infrared spectroscopy (FT-IR), electron paramagnetic resonance (EPR), UV-Vis absorption, and photoluminescence (PL) spectroscopy. The FT-IR and EPR spectra together gave the results that led to characterization of two structures (pristine and non-pristine forms of thiophene rings) while forming the P3OT polymer chain. These results were associated with the stabilization of pristine chains and mixed chains (non-pristine structures) in the polymeric film. Their bands in the PL spectra are wide and asymmetric and their adjustments by Gaussian functions was necessary; this was the main indication that there are two distinct contributions to the emission spectra. These two contributions are attributed to the emission by mixed chains (Gaussian centered at higher energy) and by pristine chains (Gaussian of lower energy) present in the formed polymeric material.

Journal of Luminescence, 2013

In the present paper the layer-by-layer self-assembly (LbL) technique was used to obtain poly(pph... more In the present paper the layer-by-layer self-assembly (LbL) technique was used to obtain poly(pphenylenevinylene) (PPV) films exchanging the counter-ion Cl of the poly(xylylidene tetrahydrothiophenium) (PTHT ) precursor polymer by Congo Red (CR) azodye. The objective of the present paper is to study the azodye photoisomerization trans-cis-trans process as a function of the PPV thermal annealing procedure. The LbL PTHT/CR films were thermally converted into LbL PPV/CR films at low (110 1C) and conventional (230 1C) temperatures, and characterized through both absorption and emission techniques. We found that the unexpected emission band above 650 nm, attributed to the azodye, for LbL PPV/CR film thermally converted at lower temperature (110 1C) is an evidence of the considerable decrease of CR degradation in the polymeric matrix. Emission anisotropy and selective photoluminescence were carried out to characterize qualitatively the exciton energy transfer.

Journal of Insect Behavior, 2014

Pigmentation patterns, ultraviolet reflection and fluorescent emission are often involved in mate... more Pigmentation patterns, ultraviolet reflection and fluorescent emission are often involved in mate recognition and mate quality functions in many animal taxa. We investigated the role of wing ultra-violet reflection, fluorescence emission, and pigmentation on age and sexual signals in the damselfly Mnesarete pudica. In this species, wings are sexually dimorphic in colour and exhibit age dependency: males and females show a smoky black colouration when young, turning red in mature males while it turns brown in females. First, we investigated wing UV patterns through reflectance and emission spectra. Second, behavioural experiments were undertaken to show male and female responses to manipulated wing pigmentation and experimentally reduced UV (UV-). Reflectance spectra of the wings of juvenile and mature males and females were used to show the differences between controls and individuals with manipulated colouration used in the behavioural experiment. UV-reduced, females with wings painted red, and control males and females were J Insect Behav tethered and presented to conspecific males and females, and their behavioral responses were recorded. The male red wing pigmentation and females with red wings elicited an aggressive response in territorial males and a sexual response in females. Both males and females showed neutral responses towards individuals with reduced UV. Wing signals of juvenile individuals also provoked neutral responses. These results suggest that UV, together with pigmentation, plays a role during mate recognition in males and females. Other than butterflies and spiders, it seems that fluorescence signals and UV reflectance can also be part of communication in odonates.

Journal of Applied Physics, 2011

The importance of interface effects for organic devices has long been recognized, but getting det... more The importance of interface effects for organic devices has long been recognized, but getting detailed knowledge of the extent of such effects remains a major challenge because of the difficulty in distinguishing from bulk effects. This paper addresses the interface effects on the emission efficiency of poly(p-phenylene vinylene) (PPV), by producing layer-by-layer (LBL) films of PPV alternated with dodecylbenzenesulfonate. Films with thickness varying from $15 to 225 nm had the structural defects controlled empirically by converting the films at two temperatures, 110 and 230 C, while the optical properties were characterized by using optical absorption, photoluminescence (PL), and photoluminescence excitation spectra. Blueshifts in the absorption and PL spectra for LBL films with less than 25 bilayers (<40-50 nm) pointed to a larger number of PPV segments with low conjugation degree, regardless of the conversion temperature. For these thin films, the mean free-path for diffusion of photoexcited carriers decreased, and energy transfer may have been hampered owing to the low mobility of the excited carriers. The emission efficiency was then found to depend on the concentration of structural defects, i.e., on the conversion temperature. For thick films with more than 25 bilayers, on the other hand, the PL signal did not depend on the PPV conversion temperature. We also checked that the interface effects were not caused by waveguiding properties of the excited light. Overall, the electronic states at the interface were more localized, and this applied to film thickness of up to 40-50 nm. Because this is a typical film thickness in devices, the implication from the findings here is that interface phenomena should be a primary concern for the design of any organic device.

Thin Solid Films, 2013

Emission ellipsometry technique was used as a tool to optimize the electrochemical synthesis of l... more Emission ellipsometry technique was used as a tool to optimize the electrochemical synthesis of luminescent poly 24 [3-alkylthiophenes] conjugated polymers. This methodology was applied to poly[3-octylthiophene] (P3OT) films. P3OT films were synthesized by the chronocoulometry technique, using tetraethylammonium tetrafluoroborate and lithium perchlorate, as supporting electrolytes to control empirically the polymer/polymer interaction. After excitation with polarized light, a partially polarized emission from these films was observed. The polarization degree of the light emitted by the polymer was calculated by Stokes theory. Emission of polarized light is attributed to the limitation of energy transfer and/or diffusion processes of the excited carriers. These energy transfer and/or diffusion processes are dependent on the concentration and on the chemical nature of the electrolyte in the polymer film. The best condition for synthesis of P3OT films is correlated with the maximum of the polarization degree. The proposed methodology can be applied to optimize the electrochemical synthesis of luminescent conjugated polymers.