Examinando por Autor "Facultad de Ciencias Exactas."

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    Ítem
    DFT study of the optical properties and substituent effects in macrocyclic systems formed by metalloporphyrins for their potential application in solar cells
    (Universidad Andrés Bello, 2012) Zárate Bonilla, Ximena del Pilar.; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas.
    Dye-sensitized solar cells (DSCs) were designed by Michael Griitzel. They have become as a promising inexpensive alternative to light-current conversion. Basically, DSCs are constituted by nanocrystalline films of a semiconductor oxide, a !ayer of dye adsorbed to the oxide surface, solution of iodide/triiodide redox couple that by its reduction regenerates the dye after the electron-injection to the semiconductor. Nowadays, continuous researches are being carried out because of the variety of elementary components present in these cells. The process of current generation starts with the photo-excitation of the dye molecules, being this, the most important topic that has attracted a considerable experimental and theoretical interest. Studies point to different kind of dyes that allow tuning the properties and then to optimize their overall performance in assembled devices. The dyes show interesting properties useful in the design of a DSC, namely light absorption in the UV-Visible region of the electromagnetic spectrum, chemical stability, sensitization, effective adsorption on the semiconductor surface, electron-separated states, etc. Among the wide amount of dyes employed, porphyrinic systems have shown to be efficient light­harvesting. In this sense, properties of different families constituted by monomers, dimers and trimers of porphyrinic macrocycles coordinated to metals like Ti, Ni and Zn were studied. The structural modification consists in changing the peripheral 13-substituents in the rings with the proposal to predict the geometrical and electronic properties of new complexes which can be good candidates as sensitizers in solar cells. In addition, the study of electron-injection mechanisms from dyes to a TiO2 nanoparticle was performed since a theoretical point of view. In general, the results show that complexes with electron donor peripheral substituents are very promising to provide good performances as sensitizers and they could act as light-harvesting for DSCs. On the other hand, it was found a theoretical tool which allows differentiation of the direct and indirect photo electron-injection mechanisms in a DSC.
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    Ítem
    Phenomenological chemical reactivity theory for mobile electrons
    (Universidad Andrés Bello, 2009) González Suárez, José Mauricio.; Renato Contreras.; Facultad de Ciencias Exactas.
    We present herein a model to
  • Miniatura
    Ítem
    Relativistic study of the luminescent properties in systems containing lanthanide and actinide ions : a view of the antenna effect
    (Universidad Andrés Bello, 2017) Cantero López, Plinio de los Santos Plinio de los Santos.; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas.
    In the recent decades, the synthesis and the theoretical study of new compounds containing Lanthanide and Actinide ions have become in a very interesting topic of research. Ali this due to the potential use ofthis systems as materials for biological immunoassays, lasers, cathode ray tubes, lighting systems, electroluminescent devices, sensors, dosimeters, imaging agents, display applications, decoration purposes and light-emitting diodes (LEDs). These unique spectroscopic properties are attributed to the characteristic f-f transitions in their inner ( 4f/5f) shell, which is shielded from the influence of the environment by the outer (5s,5p/6d,7s) shells. These transitions are Laporte-forbidden with low absorption coefficient, which makes the direct excitation of the Ln/ An ion inefficient. For this purpose, over the years have been preved that the complexation by certain organic and organometallic ligands favored and enhances the luminescence intensity ofthese ions (Antenna effect), due to the ligand absorb highly efficiently the light in the ultraviolet region and transfers energy from its excited level to the resonant level of the Ln/An center (charge/energy transfer process), which can ernit light or decay non­radiatively. In this context, this doctoral thesis entitled: "Relativistic Study of the Luminescent Properties in Systems Containing Lanthanide Ions and Actinide" we study the Antenna effect and the electronic structure of the Ln/An systems using quantum chemical relativistic methods (relativistic density functional). In a first step, we investigated heterobimetallic systems of Actinide and transition metals unsupported by bridging ligands. Our aim was to research the role of the [CpM(C0)2r (M= Fe, Ru, Os) chromophore in the optical properties of the [Cp2ThMCp(C0)2]+ complexes. In the next stage, was shown the possibility of tuning the molecular antenna effect in these molecules by means of structural modifications in the peripheral ligands. Finally, were synthesized new luminescent Eu(III) complexes, based on dypiridophenazine (dppz) derivatives ligands. Apart from the Relativistic DFT, these compounds were also theoretically studied by means of ab initio methods that allows excited states in Lanthanide complexes to be analyzed, and energy transfer pathways from the antenna to Lanthanide ion.