FCE - Trabajos de Titulación Post-Grado

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Examinando FCE - Trabajos de Titulación Post-Grado por Autor "Arratia Pérez, Ramiro"

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    Calculated optical properties of polypyridine complexes and its possible use in solar cells
    (Universidad Andrés Bello, 2013) Schott Verdugo, Eduardo; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas
    A senes of polypyridyl complexes with tris-(2,2'-Bipyridine) and 2,2':6',2"-terpyridine substituted dyes and Ru(II) or Os(II) as central metal were studied. The influence on the variation of the substituents over the composition of the molecular orbitals, electronic transitions and reactivity of these compounds was studied. A good agreement with tbe previously reported experimental data, of the geometrical parameters and of the UV-Vis transitions, was found for the complexes which have previous experimental reports. In these theoretical calculations the -COOH anchor group to get attached to the semiconductor surface was included. Using the charge transfer analysis and the orbitals that are involved in the transitions, it was observed that the complexes that have electron-donor substituents might be more efficient to donate electrons when they are attached to a semiconductor surface than those complexes that have electron-acceptor substituents. Therefore the results suggest that these dyes with electron-donor substituents will give better yields in photocurrent generation. Also, the localization of the LUMO over the ligand that has the anchor will help to improve electron injections into the TiO2 nanoparticles. We propase here severa! not yet synthetized dyes, which could be used in this kind of devices, due to their interesting molecular properties. l
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    Description of the optical and molecular properties in lanthanide macrocyclic complexes using quantum chemical relativistic methods
    (Universidad Andrés Bello, 2015) Rabanal León, Walter A; Arratia Pérez, Ramiro; Facultad de Ciencias Exactas
    The lanthanides or most commonly known as .. rare earths" have attracted the interest of thc scic11tific comrnunity i11 thc last 30 ycars, duc to their uniquc and appealing characteristics. Probably, one of the most interesting is their f-f inherent spectroscopic properties in thc nea.r infra-red rcgion of the spectra prescnting charactcristic narrow "line-like" emission bands. Additionally, these f-f transitions are parity (and sornetimes also spin) forbidclen, rcsulting in vcry long livcd excited states. Unfortunately, as another consequence of the parity (Laporte) forbidden nature of the 4f transitions, the direct absorption of Ln(III) cations is quite poor, and they hence have very low molar absorption coefficients which limits their practical usage. For that reason, the use of molecular antennas, which absorbed highly effi.ciently the light and then promete a charge/energy transfer to the lanthanide center (populating their excited states), was proposed as a simple and useful way to sensitize and enhance the lanthanide luminescence. In this way, this doctoral dissertation entitled: "Description of the Optical and Molecular Properties in Lanthanide ::Ylacrocyclic Complexes Using Quantum Chemical Relativistic Methods", is a study based on the relativistic density functional and the wave-function theory of a series of poly-aza and poly-oxo lanthanide macrocyclic complexes, whose purpose is to characterize: i) the ground and excited states, ii) the lanthanide-macrocycle interaction, and iii) the nature of the main electronic transitions involved in optical applications. During the development of this work, we found interesting results on the characterization of the bond interaction, energetics and optical properties, that show the potential use of 1r-conjugated macrocyclic systems as molecular antennas which could sensitize the lanthanide luminescence throughout a charge transfer phcnomena, which is favoured by a dativc covalcnt intcraction betwccn thc macrocyclic ligand and the lanthanide center. Moreover, it was achieved an extensivc knowledge of thc clectronic structurc, cspecially the multi-coufigurational naturc of the ground and excited states, as a consequence of the low-lying character of the lanthanidc 4f-shcll ancl thc strong statc rnixiug possibility due to the low sy111rnetry and the spin-orbit coupling effect.
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    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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    Estudio DFT para predecir la actividad catalítica de ftalocianinas metálicas sustituidas en procesos electroquímicos
    (Universidad Andrés Bello, 2012) Linares Flores, Cristian Antonio Cristian Antonio; Arratia Pérez, Ramiro; Facultad Ciencias Exactas
    En este trabajo de tesis. se han estudiado de forma teórica tres tópicos principales sobre electro-catálisis usando la teoría de los funcionales de la densidad (DFf) para predecir la actividad catalítica de una serie de ftalocianinas metálicas sustituidas. para la electro-oxidación o electro-reducción de sustancias. Este estudio propone una ruta para encontrar la estructura molecular adecuada. con el fin de diseñar el catalizador óptimo para procesos electroquímicos en una reacción química determinada. Los tópicos estudiados son los siguientes: 1.- Electro-reducción de oxígeno sobre electrodos modificados con ftalocianinas metálicas. Se ha hallado una correlación teórico experimental entre el índice de nucleofilicidad y el potencial redox de la cupla M( 11/l) de diferentes ftalocianinas metálicas con M=Cr, Mn, Fe, Co, Ni, Cu, utilizando un modelo descriptor de la nucleofilicidad, en el cual se analizaron las energías de los orbitales moleculares frontera ocupados (HOMO) obtenidos desde el esquema de Kohn-Sham fueron comparados con cálculos empíricos del índice de nucleofilicidad. Además, se ha realizado una correlación entre las energías re lativas de e nlace de los aductos formados entre las ftalocianinas metálicas y el oxigeno molecular con la actividad catalítica de estos sistemas.
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    Estudio teórico de las interacciones entre tinturas orgánicas derivadas de fenotiazinas y superficies de TiO2-anatasa
    (2015) Urzúa Leiva, Rodrigo Antonio; Arratia Pérez, Ramiro
    Entre los dispositivos diseñados para recolectar luz solar y transformarla en energía eléctrica, las celdas solares sensibilizadas por tinturas (DSSC) son las que presentan un mayor crecimiento en cuanto a eficiencia e investigación durante las últimas décadas. Dentro de este grupo de dispositivos, las DSSC orgánicas han ganado gran atención debido al bajo costo, simplicidad de diseño y síntesis, sumado al amplio conocimiento químico de algunas familias de tinturas orgánicas. Sin embargo, la complejidad de este tipo de celdas plantean aún grandes incógnitas en cuanto a su funcionamiento y eficiencia. En este contexto, el siguiente trabajo presenta un estudio teórico-computacional de las interacciones entre tinturas orgánicas derivadas de fenotiazinas (PTZ) y superficies de TiO2 en su morfología anatasa, que comúnmente son usados en DSSC. El estudio consiste en una detallada descripción de las superficies de anatasa a partir de su estructura cristalina fundamental, para posteriormente adsorber sobre dichas superficies dos conjuntos de PTZ funcionalizadas con los grupos de anclaje ácido cianoacrílico y ácido acético rodanina-3. Además, a partir de las diferencias encontradas en las geometrías de adsorción de estos dos conjuntos de PTZ, se realizó un estudio dinámico del mecanismo de trasferencia de energía resonante de Forster (FRET) cuando se utiliza como grupo antena dador de electrones el carbazol (CZ). En la primera etapa de este trabajo, se realizó un estudio del rendimiento de varios funcionales de la densidad (LDA, PW91 , PBE, HSE, PBE0 y B3L YP) en reproducir los parámetros de la red cristalina, el módulo de compresibilidad y el band- gap de la morfología anatasa, con la finalidad de establecer el(los) funcional( es) que mejor reproduce(n) la estructura geométrica y electrónica de los cristales de anatasa que serán usados para construir las superficies. Los resultados mostraron que la combinación de los funcionales PBE y HSE resultan en el mejor acuerdo entre exactitud y desempeño para determinar la morfología anatasa. De este modo, a partir de las estructuras cristalinas establecidas, se estudió la estabilidad teórica de las superficies de anatasa exponiendo las caras ( 1 O 1 ), ( 100) y (O 1 O), resultando la cara ( 1 O 1) como la más estable y en claro acuerdo con resultados experimentales. En la segunda etapa, se estudiaron ocho tinturas orgánicas derivadas de PTZ adsorbidas sobre superficies perfectas de anatasa (101). Dos tipos PTZ fueron consideradas: PTZl y PTZ2, ambas funcionalizadas con los grupos de anclaje ácido cianoacrílico o ácido acético rodanina-3. Además, se estudiaron tres tipos de sustituyentes en las PTZ tipo 1 (PTZ 1) con la finalidad de evaluar sus efectos en las propiedades de adsorción. En cada sistema estudiado se evaluaron detalladamente las energías de adsorción, la transferencia de carga (análisis de cargas de Bader) y las densidades de estado proyectadas (pDOS) sobre los átomos. Los resultados mostraron que el grupo de PTZ funcionalizadas con ácido cianoacrílico se adsorbe en una forma cercana a la perpendicular respecto de la superficie, a diferencia del grupo de PTZ funcionalizadas con el ácido acético rodanina- 3, que lo hacen en una forma más paralela a la superficie. Esta diferencia incide en el efecto que ejerce el sustituyente en las energías de adsorción de las PTZl, mostrado tendencias opuestas en cada subconjunto. Por otra parte las energías de adsorción y cargas de Bader indican que todas las PTZ se adsorben favorablemente sobre superficies de anatasa ( 1 O 1) y que ocurre una transferencia de carga desde la superficie hacia el adsorbato. Junto con esto, un análisis de las pDOS que componen la superficie y el adsorbato en el grupo de PTZ funcionalizadas con ácido cianoacrílico, mostraron que nuestro modelo de orbitales frontera HOMO-LUMO en la superficie y el adsorbato presentan un buen acuerdo con resultados experimentales acerca de las energías de excitación fundamental en estas tinturas. Finalmente, en un estudio dinámico de la tasa FRET sobre dos PTZ funcionalizadas con ácido cianoacrílico o ácido acético rodanina- 3, y sustituida con el grupo antena CZ, se estableció que en este tipo de sistemas resulta indispensable incluir las fluctuaciones térmicas cuando se intenta predecir teóricamente la tasa FRET. Además se mostró que la aproximación de esta tasa mediante los modelos estáticos e isotrópicos es inadecuada cuando se trata de reproducir resultados de FRET en DSSC funcionalizadas con derivados de CZ- PTZ.
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    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.
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    Theoretical study of molecular donor/acceptor semiconductors for tandem photovoltaic cells
    (Universidad Andrés Bello, 2013) Aparecida Barboza, , Cristina.; MacLeod-Carey, Desmond; Arratia Pérez, Ramiro
    In this Thesis quantum chemical tools have been used to gain more information about physicochemical properties of organic and inorganic molecules that could be used as semiconductors for photovoltaic ce lis of tandem type. Into this context, severa( levels of theory have been used to validate the methodologies chosen for the calculations, fron density functional have been used to validate the methodologies chosen for the calculations, f om density functional theory (DFT and time dependent-DFT) to post-Hartree-Fock methods (Coupled-Cluster Singles and Doubles - CCSD). Fluorene, a model molecule used as semiconductor for organic electronics was employed to carry out this benchmark study. Following an analysis of the structural and optical prope1ties of dimers of fluorenes, pentalenes and indenofluorenes (fluorenacenes and fluorenaphenes) derivatives were done. The electronic delocalization of these molecules were also evaluated, due to their importance in the processes of charge transfer that occur in photovoltaic devices. Besides on the organic molecules, properties of copper clusters were also calculated, in order to evaluate if those molecules could also be used as semiconductors. Our results suggest that is possible to modulate the electronic properties of the compounds studied, as well to combine them in order to get a better coverage of the solar spectrum, leading to a more efficient photovoltaic solar device. The strong directionality of the electronic transitions of the copper clusters indicates that them could be used as donor materia Is, while the organic small molecules could be used as acceptors, improving the charge transfer in photovoltaic solar devices.