Neste artigo, apresenta-se a experiência da Unicamp nos processos de avaliação institucional e de... more Neste artigo, apresenta-se a experiência da Unicamp nos processos de avaliação institucional e de planejamento estratégico, a partir dos anos 2000, sob duas perspectivas: das recomendações pelos comitês externos e da análise da percepção das comissões internas. Apresenta-se, também, uma análise do Sinaes e do modelo do Conselho Estadual de Educação de São Paulo. Documentos referentes aos cinco ciclos mostram que os processos se tornam mais abrangentes, mas há limitações operacionais, que restringem a amplitude da avaliação. As questões formuladas às comissões internas de cada órgão avaliado, nos processos AI/2009-20013 e AI/2014-2018, prospectou a percepção da comunidade sobre a importância da avaliação e do planejamento decorrente dela, mostrando gradativa integração entre os mesmos.
Herein, we report the synthesis and characterization of two Pt(II) coordination compounds, the ne... more Herein, we report the synthesis and characterization of two Pt(II) coordination compounds, the new platinum(II)[N,N′-bis(salicylidene)-3,4-diaminobenzophenone)] ([Pt(sal-3,4-ben)]) and the already well-known platinum(II)[N,N′-bis(salicylidene)-o-phenylenediamine] ([Pt(salophen)]), along with their application as guests in a poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) conjugated polymer in all-solution processed single-layer white organic light-emitting diodes. Completely different performances were achieved: 2.2% and 15.3% of external quantum efficiencies; 2.8 cd A−1 and 12.1 cd A−1 of current efficiencies; and 3103 cd m−2 and 6224 cd m−2 of luminance for the [Pt(salophen)] and [Pt(sal-3,4-ben)] complexes, respectively. The Commission Internationale de l’Eclairage (CIE 1931) chromaticity color coordinates are (0.33, 0.33) for both 0.1% mol/mol Pt(II):PFO composites at between approximately 3.2 and 8 V. The optoelectronic properties of doped and neat PFO films have been investigated, ...
Copper–iodide moiety is an alternative to increase the spin–orbit coupling and the phosphorescenc... more Copper–iodide moiety is an alternative to increase the spin–orbit coupling and the phosphorescence decay rate versus the classical [Cu(NN)(PP)]+ system, moving closer to an iridium(iii) complex.
Avaliação: Revista da Avaliação da Educação Superior (Campinas), 2021
O presente artigo busca apresentar alguns resultados objetivos decorrentes de ações planejadas e ... more O presente artigo busca apresentar alguns resultados objetivos decorrentes de ações planejadas e orientadas pelo processo de avaliação, demonstrando que a implantação da gestão estratégica, vinculada à avaliação institucional, produz resultados tangíveis para a instituição no curto, médio e longo prazos. Estes resultados são, na nossa concepção, a maneira objetiva de defesa institucional a ser apresentada aos stakeholders como forma de accountability da missão institucional. Alguns dos stakeholders típicos são o governo do Estado de São Paulo, a Assembleia Legislativa do Estado de São Paulo, o Conselho Estadual de Educação, o Tribunal de Contas Estadual, o Ministério Público, as agências de fomento públicas, os agentes privados, tais como os agentes sociais críticos da universidade pública, os competidores do mercado da educação superior, e a mídia em geral (meios de comunicação e outros formadores de opinião, entidades e organismos sociais). Para tanto, as interações metodológicas ...
Inorganic organic metal halide perovskite materials have been investigated for several technologi... more Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX3, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of...
The journal of physical chemistry. A, Jan 16, 2016
An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been inve... more An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation O) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pKa*) has been estimated to be ca. -3.4 in t...
Langmuir : the ACS journal of surfaces and colloids, Jan 18, 2007
The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent br... more The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostati...
Langmuir : the ACS journal of surfaces and colloids, Jan 21, 2006
In the present work, we studied the role of an anionic surfactant, sodium dodecyl sulfate, and a ... more In the present work, we studied the role of an anionic surfactant, sodium dodecyl sulfate, and a cationic surfactant, dodecyltrimethylammonium chloride, in the sorption of 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers. Fluorescence spectroscopy was used to quantify the amount of sorbed Tinopal CBS on the fiber surface. Differences in the spectral properties and the efficiency of sorption of the whitener/surfactant/fiber system are explained in terms of electrostatic interactions. Our results also show that the sorption efficiency is greater for solutions containing cationic surfactants only below the critical micelle concentration, while anionic surfactants show a smooth influence on the sorption process.
Renewable Energy and the Environment Optics and Photonics Congress, 2012
ABSTRACT We present the synthesis and the characterization of a series of conjugated D-A copolyme... more ABSTRACT We present the synthesis and the characterization of a series of conjugated D-A copolymers, where the molecular structure, in which the changes of dipole moments by photoexcitation facilitate the electronic transitions and increase the photovolatic efficiency.
The absorption, fluorescence and fluorescence-excitation spectra of concentrated toluene solution... more The absorption, fluorescence and fluorescence-excitation spectra of concentrated toluene solutions of selected para substituted trans-stilbene derivatives provide strong evidence for aggregation. A red-shifted fluorescence spectrum peaking at 420 nm gains in intensity as the stilbene concentration is increased. The excitation spectrum of this new emission is well to the red of the normal stilbene absorption spectrum, consistent with the appearance
POLYMERIC LIGHT EMITTING DEVICES. Here we present an overview of electroluminescent devices that ... more POLYMERIC LIGHT EMITTING DEVICES. Here we present an overview of electroluminescent devices that use conjugated polymers as the active media. The principal components of the devices are described and we show some examples of conjugated polymers and copolymers usually employed in polymeric light emitting devices (PLED). Some aspects of the photo and electroluminescence properties as well as of the energy transfer processes are discussed. As an example, we present some of the photophysical properties of poly(fluorene)s, a class of conjugated polymers with blue emission.
Static and dynamic fluorescence of pyrene has been used to study the polarity of microenvironment... more Static and dynamic fluorescence of pyrene has been used to study the polarity of microenvironments of ethyleneco-(vinyl acetate) copolymers of varying compositions. The polarity of these copolymers, defined by the Py-scale, has been compared with low-density polyethylene and poly(vinyl acetate). Linear correlations between vinyl acetate content and either the vibronic ratio, I/III, of the pyrene fluorescence spectra or the fluorescence decay constants, τ F , have been obtained. We have also studied the photophysical properties of pyrene sorbed on the polymer surface by vapor deposition or incorporated within the polymer by swelling with a solvent. The photophysical parameters determined by both experiments are virtually the same, demonstrating that pyrene senses the same type of environment throughout the polymer film. Furthermore, in each of the copolymers, the probes experience an average polarity rather than one from domains enriched in either ethylene or vinyl acetate.
This article reports a study of the thermal relaxation in cast films of two polyfluorene based po... more This article reports a study of the thermal relaxation in cast films of two polyfluorene based polymers, poly{9,9-dioctylfluorenyl-2,7-diyl} (BE329) and poly{(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene]} (GE108). The relaxation processes were identified by Dynamical Mechanical Thermal Analysis (DMTA), which revealed three processes in both samples:  process at lower temperatures and two relaxations at higher temperatures (named as˛A and˛B). The relaxations mechanics were elucidated by Solid-State Nuclear Magnetic Resonance (NMR) methods. The results revealed that the  relaxation is related to molecular motions in the side-groups, while the second and third relaxations can be attributed to local rotations in the backbone and to a glass transition. The molecular relaxations were also identified by the temperature dependence of the fluorescence spectra, which were also associated with their molecular nature.
Photochemical & Photobiological Sciences, 2002
Micromorphology is an important factor in determining polymer properties and uses. Here, steady-s... more Micromorphology is an important factor in determining polymer properties and uses. Here, steady-state and dynamic fluorescence from covalently attached 1-alkylpyrenyl groups are used to investigate the micromorphology of several random ethylene-co-vinyl acetate (EVA) copolymers with defined compositions of vinyl acetate monomer. The results are compared with those from homopolymers of high-and low-density polyethylenes and poly(vinyl acetate). Selective attachment of pyren-1-yl groups to polymer chains was accomplished by irradiation of pyren-1yldiazomethane sorbed into polymer films. Steady-state fluorescence spectra and fluorescence decay rates of attached pyrenyl groups in films of the polymers have been compared with those from films with sorbed pyrene. I 1 /I 3 intensity ratios from vibrational bands in the fluorescence spectra and the fluorescence decay rates of attached 1-alkylpyrenyl groups are much less sensitive to changes in the copolymer composition than are those of pyrene. These observations suggest that attachment occurs selectively to the olefinic segments (rather than to the acetate-rich regions) of polymer chains of EVA copolymers. This conclusion is consistent with the known preferences for reaction by pyren-1-ylcarbene in solution.
The intermolecular interactions of the bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) have been ... more The intermolecular interactions of the bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) have been studied as a function of concentration in aqueous solution and in cellophane using UV-visible absorption, NMR, and resonance Raman spectroscopy. UV-visible spectroscopy indicates that dimerization occurs in aqueous solution (K dim ≈ 77 000 dm 3 mol-1 at I) 0.01) and that it occurs more readily at higher ionic strength, where trimerization also occurs (K dim ≈ 580 000 dm 3 mol-1 and K trim ≈ 2700 dm 3 mol-1 at I) 0.1); the driving force is enthalpic rather than entropic (∆H dim ≈-53 kJ mol-1 and ∆S dim ≈-90 J K-1 mol-1 at I) 0.01). Dimerization occurs much less readily in cellophane (K dim ≈ 42 dm 3 mol-1) than in aqueous solution, indicating that strong dye-cellulose interactions compete effectively with dye-dye interactions. NMR spectroscopy indicates that Direct Blue 1 molecules interact by π-stacking at the central biphenyl group, while resonance Raman spectroscopy indicates that the internal structure and bonding of the monomers is essentially retained on stacking. The UV-visible spectra are consistent with this interpretation, and the application of exciton theory indicates that stacking results in angles between adjacent molecules which are different in the dimer (θ ≈ 84°) and trimer (θ ≈ 58°); they are attributed to geometries which minimize the repulsion between charged naphthylsulfonate groups.
Neste trabalho as isomerizações térmica e fotoquímica do 4-dimetilaminoazobenzeno e do ditizonato... more Neste trabalho as isomerizações térmica e fotoquímica do 4-dimetilaminoazobenzeno e do ditizonato de mercúrio foram estudadas tanto em solventes quanto em matrizes poliméricas. A cinética destas reações foi estudada usando-se funções exponenciais para o cálculo das constantes aparentes de velocidade. Observou-se que o comportamento cinético em soluções pode ser descrito por uma função mono-exponencial, enquanto que em sistemas poliméricos têm-se que empregar funções bi-exponenciais. As constantes de velocidades são fortemente influenciadas pelas interações soluto/solvente (ou polímero) além de, também, serem influenciadas pelos processos de tratamento térmico dos filmes poliméricos. Observou-se que, em geral, as reações são mais rápidas em meios mais polares (solventes e polímeros) devido a estabilização de diferentes tautômeros. Thermal and photo-isomerization reactions of mercury dithizonate and 4-dimethylaminoazobenzene were studied in solutions and in polymer matrices. We used exponential functions to calculate the rate constants for both processes. The kinetic behavior was well described by monoexponential functions for these dyes dissolved in solvents, although bi-exponential functions are required when these dyes are dissolved in polymers. The rate constants are strongly influenced by dye/solvent and dye/polymer interactions, as well as by the aging processes of the polymer matrix. In general, the reaction is faster in more polar mediums, solvents or polymer matrices, since stabilization of different tautomers takes place. We also showed that larger molecules isomerize slowly and slower isomerization has also been observed for annealed samples. Both results are attributed to the importance of free-volumes in polymeric matrices.
in several concentrations (10-8 mol L-1 to 10-4 mol L-1) and films produced by casting, showing t... more in several concentrations (10-8 mol L-1 to 10-4 mol L-1) and films produced by casting, showing that chloroform and toluene solvate the polymer chain differently. Diluted solutions (10-8 mol L-1) in chloroform exhibit broader fluorescence spectra. A red-shift of the fluorescence spectra was observed for concentrations higher than 10-6 mol L-1 that can be explained using Kasha's rule for the sandwich anti-parallel orientation of the transition moments of the two chromophores. The conformations observed in solutions are partially retained in the solid films in addition to the broader red-shift spectra attributed to aggregated forms of the macromolecular segments. Annealing of the polymer films at the glass transition temperature eliminates the more stressed conformations, erases the memory and leads to sharper fluorescence spectra.
Journal of Photochemistry and Photobiology A: Chemistry, 2011
The photophysical properties of a fluorescent silicone prepared by a hydrosilylation reaction fro... more The photophysical properties of a fluorescent silicone prepared by a hydrosilylation reaction from poly(dimethylsiloxane-co-methylhydrogensiloxane) terminated by dimethylhydrogensilyloxy groups, poly(dimethylsiloxane-co-methylvinylsiloxane) terminated by dimethylvinylsilyloxy groups and 9vinylcarbazole, as the luminescent group, have been studied under steady-state fluorescence and time-resolved conditions. At low temperature both steady-state fluorescence and phosphorescence spectra of isolated species are observed. Phosphorescence is quenched at temperatures higher than 150 K indicating that the environments where the carbazolyl moieties are located are very flexible, as expected for silicones. Fluorescence decays and phosphorescence (at 77 K) showed typical carbazolyl lifetimes and no rise-time was observed, which is consistent with the absence of excimer emission. The temperature dependence of the emission can be used to determine the polymer relaxation processes and transitions (T ␥ = 80-100 K, T g = 130-150 K and T m = 220 K), these last two comparable with those observed by differential scanning calorimetry.
Neste artigo, apresenta-se a experiência da Unicamp nos processos de avaliação institucional e de... more Neste artigo, apresenta-se a experiência da Unicamp nos processos de avaliação institucional e de planejamento estratégico, a partir dos anos 2000, sob duas perspectivas: das recomendações pelos comitês externos e da análise da percepção das comissões internas. Apresenta-se, também, uma análise do Sinaes e do modelo do Conselho Estadual de Educação de São Paulo. Documentos referentes aos cinco ciclos mostram que os processos se tornam mais abrangentes, mas há limitações operacionais, que restringem a amplitude da avaliação. As questões formuladas às comissões internas de cada órgão avaliado, nos processos AI/2009-20013 e AI/2014-2018, prospectou a percepção da comunidade sobre a importância da avaliação e do planejamento decorrente dela, mostrando gradativa integração entre os mesmos.
Herein, we report the synthesis and characterization of two Pt(II) coordination compounds, the ne... more Herein, we report the synthesis and characterization of two Pt(II) coordination compounds, the new platinum(II)[N,N′-bis(salicylidene)-3,4-diaminobenzophenone)] ([Pt(sal-3,4-ben)]) and the already well-known platinum(II)[N,N′-bis(salicylidene)-o-phenylenediamine] ([Pt(salophen)]), along with their application as guests in a poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) conjugated polymer in all-solution processed single-layer white organic light-emitting diodes. Completely different performances were achieved: 2.2% and 15.3% of external quantum efficiencies; 2.8 cd A−1 and 12.1 cd A−1 of current efficiencies; and 3103 cd m−2 and 6224 cd m−2 of luminance for the [Pt(salophen)] and [Pt(sal-3,4-ben)] complexes, respectively. The Commission Internationale de l’Eclairage (CIE 1931) chromaticity color coordinates are (0.33, 0.33) for both 0.1% mol/mol Pt(II):PFO composites at between approximately 3.2 and 8 V. The optoelectronic properties of doped and neat PFO films have been investigated, ...
Copper–iodide moiety is an alternative to increase the spin–orbit coupling and the phosphorescenc... more Copper–iodide moiety is an alternative to increase the spin–orbit coupling and the phosphorescence decay rate versus the classical [Cu(NN)(PP)]+ system, moving closer to an iridium(iii) complex.
Avaliação: Revista da Avaliação da Educação Superior (Campinas), 2021
O presente artigo busca apresentar alguns resultados objetivos decorrentes de ações planejadas e ... more O presente artigo busca apresentar alguns resultados objetivos decorrentes de ações planejadas e orientadas pelo processo de avaliação, demonstrando que a implantação da gestão estratégica, vinculada à avaliação institucional, produz resultados tangíveis para a instituição no curto, médio e longo prazos. Estes resultados são, na nossa concepção, a maneira objetiva de defesa institucional a ser apresentada aos stakeholders como forma de accountability da missão institucional. Alguns dos stakeholders típicos são o governo do Estado de São Paulo, a Assembleia Legislativa do Estado de São Paulo, o Conselho Estadual de Educação, o Tribunal de Contas Estadual, o Ministério Público, as agências de fomento públicas, os agentes privados, tais como os agentes sociais críticos da universidade pública, os competidores do mercado da educação superior, e a mídia em geral (meios de comunicação e outros formadores de opinião, entidades e organismos sociais). Para tanto, as interações metodológicas ...
Inorganic organic metal halide perovskite materials have been investigated for several technologi... more Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX3, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of...
The journal of physical chemistry. A, Jan 16, 2016
An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been inve... more An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation O) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pKa*) has been estimated to be ca. -3.4 in t...
Langmuir : the ACS journal of surfaces and colloids, Jan 18, 2007
The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent br... more The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostati...
Langmuir : the ACS journal of surfaces and colloids, Jan 21, 2006
In the present work, we studied the role of an anionic surfactant, sodium dodecyl sulfate, and a ... more In the present work, we studied the role of an anionic surfactant, sodium dodecyl sulfate, and a cationic surfactant, dodecyltrimethylammonium chloride, in the sorption of 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers. Fluorescence spectroscopy was used to quantify the amount of sorbed Tinopal CBS on the fiber surface. Differences in the spectral properties and the efficiency of sorption of the whitener/surfactant/fiber system are explained in terms of electrostatic interactions. Our results also show that the sorption efficiency is greater for solutions containing cationic surfactants only below the critical micelle concentration, while anionic surfactants show a smooth influence on the sorption process.
Renewable Energy and the Environment Optics and Photonics Congress, 2012
ABSTRACT We present the synthesis and the characterization of a series of conjugated D-A copolyme... more ABSTRACT We present the synthesis and the characterization of a series of conjugated D-A copolymers, where the molecular structure, in which the changes of dipole moments by photoexcitation facilitate the electronic transitions and increase the photovolatic efficiency.
The absorption, fluorescence and fluorescence-excitation spectra of concentrated toluene solution... more The absorption, fluorescence and fluorescence-excitation spectra of concentrated toluene solutions of selected para substituted trans-stilbene derivatives provide strong evidence for aggregation. A red-shifted fluorescence spectrum peaking at 420 nm gains in intensity as the stilbene concentration is increased. The excitation spectrum of this new emission is well to the red of the normal stilbene absorption spectrum, consistent with the appearance
POLYMERIC LIGHT EMITTING DEVICES. Here we present an overview of electroluminescent devices that ... more POLYMERIC LIGHT EMITTING DEVICES. Here we present an overview of electroluminescent devices that use conjugated polymers as the active media. The principal components of the devices are described and we show some examples of conjugated polymers and copolymers usually employed in polymeric light emitting devices (PLED). Some aspects of the photo and electroluminescence properties as well as of the energy transfer processes are discussed. As an example, we present some of the photophysical properties of poly(fluorene)s, a class of conjugated polymers with blue emission.
Static and dynamic fluorescence of pyrene has been used to study the polarity of microenvironment... more Static and dynamic fluorescence of pyrene has been used to study the polarity of microenvironments of ethyleneco-(vinyl acetate) copolymers of varying compositions. The polarity of these copolymers, defined by the Py-scale, has been compared with low-density polyethylene and poly(vinyl acetate). Linear correlations between vinyl acetate content and either the vibronic ratio, I/III, of the pyrene fluorescence spectra or the fluorescence decay constants, τ F , have been obtained. We have also studied the photophysical properties of pyrene sorbed on the polymer surface by vapor deposition or incorporated within the polymer by swelling with a solvent. The photophysical parameters determined by both experiments are virtually the same, demonstrating that pyrene senses the same type of environment throughout the polymer film. Furthermore, in each of the copolymers, the probes experience an average polarity rather than one from domains enriched in either ethylene or vinyl acetate.
This article reports a study of the thermal relaxation in cast films of two polyfluorene based po... more This article reports a study of the thermal relaxation in cast films of two polyfluorene based polymers, poly{9,9-dioctylfluorenyl-2,7-diyl} (BE329) and poly{(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene]} (GE108). The relaxation processes were identified by Dynamical Mechanical Thermal Analysis (DMTA), which revealed three processes in both samples:  process at lower temperatures and two relaxations at higher temperatures (named as˛A and˛B). The relaxations mechanics were elucidated by Solid-State Nuclear Magnetic Resonance (NMR) methods. The results revealed that the  relaxation is related to molecular motions in the side-groups, while the second and third relaxations can be attributed to local rotations in the backbone and to a glass transition. The molecular relaxations were also identified by the temperature dependence of the fluorescence spectra, which were also associated with their molecular nature.
Photochemical & Photobiological Sciences, 2002
Micromorphology is an important factor in determining polymer properties and uses. Here, steady-s... more Micromorphology is an important factor in determining polymer properties and uses. Here, steady-state and dynamic fluorescence from covalently attached 1-alkylpyrenyl groups are used to investigate the micromorphology of several random ethylene-co-vinyl acetate (EVA) copolymers with defined compositions of vinyl acetate monomer. The results are compared with those from homopolymers of high-and low-density polyethylenes and poly(vinyl acetate). Selective attachment of pyren-1-yl groups to polymer chains was accomplished by irradiation of pyren-1yldiazomethane sorbed into polymer films. Steady-state fluorescence spectra and fluorescence decay rates of attached pyrenyl groups in films of the polymers have been compared with those from films with sorbed pyrene. I 1 /I 3 intensity ratios from vibrational bands in the fluorescence spectra and the fluorescence decay rates of attached 1-alkylpyrenyl groups are much less sensitive to changes in the copolymer composition than are those of pyrene. These observations suggest that attachment occurs selectively to the olefinic segments (rather than to the acetate-rich regions) of polymer chains of EVA copolymers. This conclusion is consistent with the known preferences for reaction by pyren-1-ylcarbene in solution.
The intermolecular interactions of the bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) have been ... more The intermolecular interactions of the bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) have been studied as a function of concentration in aqueous solution and in cellophane using UV-visible absorption, NMR, and resonance Raman spectroscopy. UV-visible spectroscopy indicates that dimerization occurs in aqueous solution (K dim ≈ 77 000 dm 3 mol-1 at I) 0.01) and that it occurs more readily at higher ionic strength, where trimerization also occurs (K dim ≈ 580 000 dm 3 mol-1 and K trim ≈ 2700 dm 3 mol-1 at I) 0.1); the driving force is enthalpic rather than entropic (∆H dim ≈-53 kJ mol-1 and ∆S dim ≈-90 J K-1 mol-1 at I) 0.01). Dimerization occurs much less readily in cellophane (K dim ≈ 42 dm 3 mol-1) than in aqueous solution, indicating that strong dye-cellulose interactions compete effectively with dye-dye interactions. NMR spectroscopy indicates that Direct Blue 1 molecules interact by π-stacking at the central biphenyl group, while resonance Raman spectroscopy indicates that the internal structure and bonding of the monomers is essentially retained on stacking. The UV-visible spectra are consistent with this interpretation, and the application of exciton theory indicates that stacking results in angles between adjacent molecules which are different in the dimer (θ ≈ 84°) and trimer (θ ≈ 58°); they are attributed to geometries which minimize the repulsion between charged naphthylsulfonate groups.
Neste trabalho as isomerizações térmica e fotoquímica do 4-dimetilaminoazobenzeno e do ditizonato... more Neste trabalho as isomerizações térmica e fotoquímica do 4-dimetilaminoazobenzeno e do ditizonato de mercúrio foram estudadas tanto em solventes quanto em matrizes poliméricas. A cinética destas reações foi estudada usando-se funções exponenciais para o cálculo das constantes aparentes de velocidade. Observou-se que o comportamento cinético em soluções pode ser descrito por uma função mono-exponencial, enquanto que em sistemas poliméricos têm-se que empregar funções bi-exponenciais. As constantes de velocidades são fortemente influenciadas pelas interações soluto/solvente (ou polímero) além de, também, serem influenciadas pelos processos de tratamento térmico dos filmes poliméricos. Observou-se que, em geral, as reações são mais rápidas em meios mais polares (solventes e polímeros) devido a estabilização de diferentes tautômeros. Thermal and photo-isomerization reactions of mercury dithizonate and 4-dimethylaminoazobenzene were studied in solutions and in polymer matrices. We used exponential functions to calculate the rate constants for both processes. The kinetic behavior was well described by monoexponential functions for these dyes dissolved in solvents, although bi-exponential functions are required when these dyes are dissolved in polymers. The rate constants are strongly influenced by dye/solvent and dye/polymer interactions, as well as by the aging processes of the polymer matrix. In general, the reaction is faster in more polar mediums, solvents or polymer matrices, since stabilization of different tautomers takes place. We also showed that larger molecules isomerize slowly and slower isomerization has also been observed for annealed samples. Both results are attributed to the importance of free-volumes in polymeric matrices.
in several concentrations (10-8 mol L-1 to 10-4 mol L-1) and films produced by casting, showing t... more in several concentrations (10-8 mol L-1 to 10-4 mol L-1) and films produced by casting, showing that chloroform and toluene solvate the polymer chain differently. Diluted solutions (10-8 mol L-1) in chloroform exhibit broader fluorescence spectra. A red-shift of the fluorescence spectra was observed for concentrations higher than 10-6 mol L-1 that can be explained using Kasha's rule for the sandwich anti-parallel orientation of the transition moments of the two chromophores. The conformations observed in solutions are partially retained in the solid films in addition to the broader red-shift spectra attributed to aggregated forms of the macromolecular segments. Annealing of the polymer films at the glass transition temperature eliminates the more stressed conformations, erases the memory and leads to sharper fluorescence spectra.
Journal of Photochemistry and Photobiology A: Chemistry, 2011
The photophysical properties of a fluorescent silicone prepared by a hydrosilylation reaction fro... more The photophysical properties of a fluorescent silicone prepared by a hydrosilylation reaction from poly(dimethylsiloxane-co-methylhydrogensiloxane) terminated by dimethylhydrogensilyloxy groups, poly(dimethylsiloxane-co-methylvinylsiloxane) terminated by dimethylvinylsilyloxy groups and 9vinylcarbazole, as the luminescent group, have been studied under steady-state fluorescence and time-resolved conditions. At low temperature both steady-state fluorescence and phosphorescence spectra of isolated species are observed. Phosphorescence is quenched at temperatures higher than 150 K indicating that the environments where the carbazolyl moieties are located are very flexible, as expected for silicones. Fluorescence decays and phosphorescence (at 77 K) showed typical carbazolyl lifetimes and no rise-time was observed, which is consistent with the absence of excimer emission. The temperature dependence of the emission can be used to determine the polymer relaxation processes and transitions (T ␥ = 80-100 K, T g = 130-150 K and T m = 220 K), these last two comparable with those observed by differential scanning calorimetry.
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Papers by Teresa Atvars