RCAAP Repository

The combination, enhancement or development of new properties in molecular architectures of π-conjugated systems can be strategically exploited in the construction of optoelectronic devices and producers of energy. This work is based on the results of a multidisciplinary collaboration and focuses on the synthesis, characterization and application of π-conjugated systems derivated of thienylene-phenylene units. The aim was to highlight the relationships between the chemical structure of the synthesized materials and their optoelectronic and photovoltaic properties. Thus, our studies were focused on two specific cases. The first case was the production of solar cells based on a polymer as theelectron donor and a fullerene derivative as the electron acceptor. Physical parameters were correlated to morphological, structural and optoelectronic properties of each polymer applied, demonstrating the importance of optimizing physicochemical parameters for the performance of photovoltaic devices. The second case consisted of the controlled investigation of stable aqueous dispersions of carbon nanotubes into single conjugated molecules functionalized with imidazole groupments. Optimization of experimental conditions and quantification of the dispersions were performed by absorption spectroscopy in the UV-Vis-NIR range. Dispersability, individualization and stability of the dispersions were estimated using transmission electron microscopy, Raman spectroscopy and photoluminescence techniques. Nuclear magnetic resonance results have provided direct evidence for a possible cation-π interaction between conjugated polymer and carbon nanotubes. Finally, we present in this work, the synthesis of various organic materials, as well as their first characterizations for possible technological applications, such as our proposal, the organic materials as the active layer in photovoltaic devices and as dispersing materials of carbon nanotubes.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

In the present work, new polymers based on thiophene-phenylene were designed, synthesized, and their properties were studied by physicochemical characterization. In particular, interaction of gamma radiation and the polymer 5-(5-(10-chlorodecyloxy)-2-methoxy-4-(5- methylthiophen-2-yl)phenyl)-5\'-(2-(2-ethylhexylo-xy)-5-methoxy-4-(5-methylthiophen-2-yl) phenyl)-2,2\'-bithiophene (PTBT-46) was performed. Linking phenylene and thiophene rings in a polymer chain is known to improve, in general, optical, electrochemical, and transport properties and then, considering this, several chemical routes have been used and different dialkoxy side chains were attached to it in order to develop such materials. For such alkyl chains, halogens groups, which have a bigger cross section for gamma radiation, have been inserted. The polymers were characterized by nuclear magnetic resonance spectroscopy (1H NMR, 13C NMR), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), optical absorption (AO), spectroelectrochemistry (in situ UV-Vis), photoluminescence (PL), photoluminescence excitation (PLE) and dc electrical conductivity measurements. Some compounds were characterized by cyclic voltammetry (CV) to compare the electronic band gap with the optical one. The monomers obtained showed interesting optical properties and one of them (TBT-25) was able to form films. Polymers of different sizes and emissions in the range that goes from green to red in the spectral region of the UVVis were synthesized. The PTBT-46 presented a unique property in the interaction with gamma radiation: the doping of the chain. This effect was observed mainly by color change, by optical measurements and the conductivity increase with increasing of radiation dose. We also checked the influence of solvent type, material concentration, and dose rate. Blue shifts with increasing of radiation dose were observed in optical measurements and were attributed to the breaking of conjugation by molecular conformational changes. This statement comes from the fact that FTIR measurements showed no break in the chain and this process was claimed to be reversible. Therefore, new luminescent conjugated polymers were obtained with great technological interest in optoelectronic area and the use of the new phenomena, semiconductor extrinsic doping processes, is promissory in detection on the ionizing radiation area.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

In this work, we performed an ab initio study of interaction between several molecules with SiC nanotubes and SiC Sheets, with focus on benzene molecule. performed too a study the mechanical and electronic properties of SiC nanowires(SiCNWs). For study the interaction of molecules with SiCNTs and SiCSheets, we considered two possibilities, (1) molecules adsorbed on SiCNT/SiCSheet surface, and (2) molecules encapsulated by SiCNT. We have considered several geometries for adsorption and dierent nanotube chiralities. For study of mechanical and electronics properties of SiCNWs, we considered 3C-, 2H, 4H and 6H-SiCNW, analyzing the eects of the diameter on these properties. All calculations were performed by using the Density Funcional Theory, using de the Local Density Approximation (LDA). The electron-ion interaction was describe by using norm-conserving pseudopotentials. For the benzene adsorption on the SiCNT, we nd an exothermic process, with binding energies between 0.3 and 0.4 eV/molecule, and for benzene encapsuladed we nd binding energies of 0.6 eV/molecule, revealing a preference for the benzene encapsulated systems. For both cases, we verify that there are not chemical bonds at the benzene- SiCNT/SiCSheet interface, and the interaction of benzene molecule with nanotube and Sheet is mediated by pi stacking interactions, similar to the benzene-CNT systems. For both cases, we verify that SiCNTs are more reactive than the carbon nanotube (CNTs) For nanowires study, our results show that all nanowires investigated exhibit direct band gaps, in contrast with the indirect band gap observed in Bulk SiC. The study of eect of unixial stress on the electronic properties of nanowires, reveal that band-gap dependence on the strain is dierent for each nanowire type. For the mechanicals properties, our results revels that Youngs moduli of nanowires show strong dependece on the diameters, and the 2H-SiCNWs are stier than than other nanowires with similar diameter. The values for Youngs moduli of dierent SiCNWs, revels that they are more stifer than nanowires of other elements, for example Si, InAs and Ge.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Universidade Federal de Uberlândia

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Spin states of an electron trapped in a quantum dot is a strong candidate for qubit implementation in solid-state systems. Here we use a sequence of polarized laser pulses to coherent manipulate the spin degree of freedom of one electron trapped in a quantum dot. To achieve that we use an external magnetic eld, and manipulate dierent parameters as pulse duration, relative pulse polarization and phase. Moreover, we show that one approximation frequently used in this system is not valid, neglecting one of the levels and making it a lambda system cannot be applied when a trion is created.

Universidade Federal de Uberlândia

Universidade Federal de Uberlândia

Fundação de Amparo a Pesquisa do Estado de Minas Gerais