Made available in DSpace on 2014-06-12T15:51:55Z (GMT). No. of bitstreams: 2 arquivo872_1.pdf: 4987624 bytes, checksum: fe10b068072d15ab53986d95b266443d (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2010 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Cálculos de orbitais moleculares usando a Teoria do Funcional de Densidade (DFT) em nível BLYP com funções de base LanL1mb e LanL1dz foram executados para os supercondutores: Nb3Ge, MgB2, LaBa2Cu3Oy, La2-xSrxCuO4, YBa2Cu3Oy, TlBa2Ca2Cu3O8+δ, HgBa2Ca2Cu3O8+δ, LaO1-xFxFeAs e o Ba1-xKxFe2As2. Utilizamos modelos de cluster (aglomerado) baseados na célula unitária com os átomos de fronteira saturados com hidrogênio, o que minimiza o excesso de elétrons no cluster devido às ligações flutuantes. O cluster foi considerado diamagnético. Foram avaliados a distribuição de cargas atômicas e o gap de energia HOMO-LUMO (Highest Occupied Molecular Orbital - Lowest Unoccupied Molecular Orbital: Orbital Molecular de Mais Alta Energia Ocupado - Orbital Molecular de Mais Baixa Energia Desocupado). Os resultados foram interpretados à luz da teoria da ressonância não-sincronizada das ligações covalentes (RVB), como originalmente proposta por Linus Pauling. Uma característica de todos os sistemas investigados neste trabalho é a existência de um gap HOMO-LUMO da ordem de meV e uma distribuição de cargas compatível com a RVB. Apesar de não ser clara sua relação com a supercondutividade, o gap de energia HOMO-LUMO é da mesma ordem de magnitude do gap supercondutor medido experimentalmente. Em adição, verificou-se que os metais presentes nos sistemas investigados se encontram nos três estados de oxidação e na proporção requerida pelo princípio da eletroneutralidade de Pauling. Estes resultados reforçam o modelo RVB e convalidam esta proposta como uma teoria alternativa para a compreensão da supercondutividade. A coerência entre os argumentos da RVB e os resultados dos cálculos para a distribuição de cargas são discutidos

Synthesis of antiaromatic polycyclic hydrocarbons (PHs) is challenging because the high energy of their highest occupied molecular orbital and low energy of their lowest unoccupied molecular orbital cause them to be reactive and unstable. In this work, two large antiaromatic acene analogues, namely, cyclopenta[pqr]indeno[2,1,7-ijk]tetraphene (CIT, 1a) and cyclopenta[pqr]indeno[7,1,2-cde]picene (CIP, 1b), as well as a curved antiaromatic molecule with 48 πelectrons, dibenzo[a,c]diindeno[7,1,2-fgh:7′,1′,2′-mno]-phenanthro[9,10-k]tetraphene (DPT, 1c), are synthesized on the basis of the corona of indeno[1,2-b]fluorene. These three antiaromatic PHs possess a narrow energy gap down to 1.55 eV and exhibit high kinetic stability under ambient conditions. Moreover, these compounds display reversible electron transfer processes in both the cathodic and anodic regimes. Their cation and anion radicals are characterized by in situ vis−NIR absorption and electron paramagnetic resonance spectroelectrochemistry. The X-ray crystallographic analysis confirms that while CIP and CIT manifest planar structures, DPT shows a curved πconjugated carbon skeleton. The synthetic strategy starting from ortho-substituted benzene units to construct five-membered rings in this work provides a unique entry to novel pentagon-embedding or curved antiaromatic polycyclic hydrocarbons. In addition, besides the detailed chemical and physical investigations, microscale single-crystal fiber field-effect transistors were also fabricated.

The knowledge on the conformations of amino acids is essential to understand the biochemical behaviors and physical properties of proteins. Comprehensive computational study is focused to understand the conformational landscape of three aromatic amino acids (AAAs): tryptophan, tyrosine, and phenylalanine. Three different density functionals (B3LYP, M06-2X and wB97X-D) were used with two basis sets of 6-31G(d) and 6-31+G(d,p) for geometry optimizations of the conformers of AAAs followed by the vibrational frequencies. The goal was to identify the right choice of density functional theory (DFT) level for conformational analysis of amino acids by comparing the computational data against the available experimental results. Calculated infrared (IR) frequency values indicated that wB97X-D/6-31+G(d,p) level is less favorable than other DFT levels in case of O-H and N-H stretching frequencies for the conformers of AAAs. The C=O stretching frequencies at different computational levels were in good agreement with the experimental results. Interactions of AAAs (tryptophan, tyrosine, and phenylalanine) and two cyclic amino acids (histidine and proline) individually with two finite-sized graphene sheets (C62H20 and C186H36) were explored using M06-2X/6-31G(d) level. Computational investigations of the binding of amino acids with graphene provide knowledge for designing of new graphene-based biological/biocompatible materials. Selected conformers for each amino acid with different orientations on the surface of graphene were examined. The purpose of computational study on graphene-amino acids interactions was to identify the preferred conformer of amino acid to bind on graphene as well as to find the influence of amino acid binding on the band gap of graphene. Different conformers of AAAs generally prefer parallel orientation through π-π interactions to bind with graphene. However, bent orientation is more preferred over parallel to bind on the surface of graphene in case of conformer having relative energy approximately equal to 5 kcal/mol for all three AAAs. Histidine generally exhibits higher binding affinity than proline to form complex with graphene. The binding energies in the aqueous medium were slightly lower than those obtained in the gas phase with some exceptions. The adsorption of amino acids did not affect the band gap of graphene.

Submitted by Etelvina Domingos (etelvina.domingos@ufpe.br) on 2015-03-12T18:57:13Z No. of bitstreams: 2 TESE Marconi Bezerra Costa.pdf: 4071497 bytes, checksum: 5ff606ff53fab5504c1ac18294e33669 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-12T18:57:13Z (GMT). No. of bitstreams: 2 TESE Marconi Bezerra Costa.pdf: 4071497 bytes, checksum: 5ff606ff53fab5504c1ac18294e33669 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2014-02 / CNPq / Baseados em cálculos DFT (Density Functional Theory) B3LYP/LANL1dz e na análise da distribuição de cargas atômicas para cupratos, metálicos e pnictídeos, demonstramos a ocorrência de ressonâncias não-sincronizadas de ligações covalentes no estado supercondutor, conforme prevê a teoria RVB (Resonating-Valence-Bond). Os modelos de cluster com as dangling bonds saturadas com hidrogênio nos átomos de fronteira, mostraram-se bastante apropriados para descrever os sistemas investigados. Para caracterizar o estado supercondutor, usamos como critério o gap de energia HOMO-LUMO, que deve ser da mesma ordem de grandeza do gap supercondutor. Para os cupratos, os resultados confirmam as previsões da RVB para a transferência de carga dos elementos hipereletrônicos para os hipoeletrônicos e o efeito da vacância de oxigênio na indução do estado supercondutor. Nos sistemas metálicos, encontramos a separação e o ordenamento de cargas em planos distintos, conforme previsto qualitativamente por Pauling. Nos pnictídeos, o gap HOMO-LUMO só é da mesma ordem de grandeza do gap experimental para os clusters dopados, e a dopagem induz uma separação de cargas no plano em que o dopante é inserido. Baseados nestes resultados, propomos combinações de elementos hipo e hipereletrônicos visando a obtenção de novos sistemas supercondutores que podem apresentar temperaturas críticas maiores do que as conhecidas atualmente. Estes resultados reforçam a teoria RVB como uma alternativa para descrever o fenômeno da supercondutividade.

Semiconducting aromatic-boron carbide composite/alloyed films formed by plasma enhanced chemical vapor deposition from carborane and aromatic precursors have been demonstrated to be excellent detectors for thermal neutrons because of the large 10B cross section. The electronic properties of these films derived from XPS show that the properties of boron carbide can be tuned by co-deposition of aromatic compounds and carborane. Aromatic doping results in narrower indirect band gaps (1.1 - 1.7 eV vs ~3 eV for orthocarborane-derived boron carbide without aromatics) and average charge transport lifetimes (as long as 2.5 ms for benzene-orthocarborane and 1.5 - 2.5 ms for indole-orthocarborane) that are superior to those of boron carbide (35 µs). The films also show enhanced electron-hole separation that is also superior to those of boron carbide where the states at the top of the valence band is made of aromatic components while states at the bottom of the conduction band is a combination of aromatic and carborane moeities. These properties result in greatly enhanced (~850%) charge collection, relative to films without aromatic content, in thermal neutron exposures at zero-bias, and are gamma-blind. Such films are therefore excellent candidates for zero-bias neutron detector applications. These properties also show little variation with increasing aromatic content beyond a critical concentration, indicating that at some point, excess aromatic results in the formation of regions of polymerized aromatic within the film, rather than in additional carborane/aromatic linkages. While previous studies on these aromatic-boron carbide materials indicate the potential for neutron detection due to the narrowed band gap, enhanced electron-hole separation and charge transport lifetimes compared to the boron carbide counterpart, the mechanisms of charge transport and photoconductivity (important for photovoltaic applications) of these materials have remained unexplored. Properties such as narrowed band gap, efficient electron-hole separation and long charge transport lifetimes, are also desirable in photovoltaic applications. This, plus ease of fabrication and environmental robustness makes aromatic-boron carbide films promising candidates for photovoltaic applications. Plasma enhanced chemical vapor deposition (PECVD) has been used to synthesize these aromatic-boron carbide composite films by co-deposition of pyridine, aniline or indole with orthocarborane/metacarborane. Film chemical composition and bonding were characterized by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), variable angle spectroscopic ellipsometry (VASE) and (in collaboration with Dowben Group at UNL) charge transport and photoconductivity measurements. Results show narrowed band gaps (indirect) where the top of the valence band is made up of the aromatic moiety and the conduction band minimum us made of aromatic and carborane moeities, improved charge carrier mobilities that is stoichiometry and frequency dependent (aniline-orthocarborane films). Photoconductivity measurement results obtained from ~2.6:1 indole-orthocarborane film show fourth quadrant conductivity. I(V) curves indicate a photocurrent of 2.36 µA at zero bias, with an appreciable open-circuit voltage of 1V. The ability for these aromatic-boron carbide films to operate at zero bias for both neutron detection and photovoltaic applications is an excellent advantage that indicates low cost of operation of these materials.

Yes / Pharmaceutical salt, nitrofurantoin–4-dimethylaminopyridine (NF-DMAP), along with its native components NF and DMAP are scrutinized by FT-IR and FT-Raman spectroscopy along with density functional theory so that an insight into the H-bond patterns in the respective crystalline lattices can be gained. Two different functionals, B3LYP and wB97X-D, have been used to compare the theoretical results. The FT-IR spectra obtained for NF-DMAP and NF clearly validate the presence of C33–H34⋅⋅⋅O4 and N23–H24⋅⋅⋅N9 hydrogen bonds by shifting in the stretching vibration of –NH and –CH group of DMAP+ towards the lower wavenumber side. To explore the significance of hydrogen bonding, quantum theory of atoms in molecules (QTAIM) has been employed, and the findings suggest that the N23–H24⋅⋅⋅N9 bond is a strong intermolecular hydrogen bond. The decrement in the HOMO-LUMO gap, which is calculated from NF → NF-DMAP, reveals that the active pharmaceutical ingredient is chemically less reactive compared to the salt. The electrophilicity index (ω) profiles for NF and DMAP confirms that NF is acting as electron acceptor while DMAP acts as electron donor. The reactive sites of the salt are plotted by molecular electrostatic potential (MEP) surface and calculated using local reactivity descriptors. / SERB, DST, India, for providing the National Post-doctoral Fellowship (Project File Number: PDF/2016/003162); Central Facility for Computational Research (CFCR), University of Lucknow; Newton-Bhabha Ph.D. placement award (2017); Royal Society seed corn research grant (2018-19)

In the presented work, first principle studies on electronic structure, stability, and magnetic properties of metal chalcogenide, CrnTem clusters have been carried out within a density functional framework using generalized gradient functions to incorporate the exchange and correlation effects. The energetic and electronic stability was investigated, and it was found that they are not always correlated as seen in the cluster Cr6Te8 which has smaller gap between its HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) and a high electron affinity of 3.39 eV indicating lower electronic stability whereas higher fragmentation energy indicating energetic stability. The high electron affinity shows that the stability of Cr6Te8 cluster can be enhanced by adding charge donating ligands including PEt3 to form stable Cr6Te8(PEt3)6 clusters as seen in experiments. The other cluster of interest was Cr4Te6 in which energetic stability was accompanied with electronic inertness marked by its large HOMO-LUMO gap, non-magnetic ground state and high fragmentation energy.

No description available.

This thesis gives a detailed description of the design and synthesis of new organic sensitizers for Dye sensitized Solar Cells (DSCs). It is divided in 7 chapters, where the first gives an introduction to the field of DSCs and the synthesis of organic sensitizers. Chapters 2 to 6 deal with the work of the author, starting with the first publication and the other following in chronological order. The thesis is completed with some concluding remarks (chapter 7). The DSC is a fairly new solar cell concept, also known as the Grätzel cell, after its inventor Michael Grätzel. It uses a dye (sensitizer) to capture the incident light. The dye is chemically connected to a porous layer of a wide band-gap semiconductor. The separation of light absorption and charge separation is different from the conventional Si-based solar cells. Therefore, it does not require the very high purity materials necessary for the Si-solar cells. This opens up the possibility of easier manufacturing for future large scale production. Since the groundbreaking work reported in 1991, the interest within the field has grown rapidly. Large companies have taken up their own research and new companies have started with their focus on the DSC. So far the highest solar energy to electricity conversion efficiencies have reached ~12%. The sensitizers in this thesis are based on triphenylamine or phenoxazine as the electron donating part in the molecule. A conjugated linker allows the electrons to flow from the donor to the acceptor, which will enable the electrons to inject into the semiconductor once they are excited. Changing the structure by introducing substituents, extending the conjugation and exchanging parts of the molecule, will influence the performance of the solar cell. By analyzing the performance, one can evaluate the importance of each component in the structure and thereby gain more insight into the complex nature of the dye sensitized solar cell. / QC 20110505

Le domaine de la science des matériaux et plus particulièrement celui des matériaux hybrides suscite un intérêt croissant en raison de leurs nombreuses applications. Dans ce travail, deux stratégies synthétiques ont été considérées pour la synthèse de matériaux hybrides.Dans une première partie, nous nous sommes intéressés à une approche de synthèse directe en faisant réagir des ligands organiques de type oligophénylène avec de l’isopropoxyde de titane. Malheureusement, ces réactions ont conduit à la précipitation de solides amorphes ne permettant pas la caractérisation de ces produits.Dans une seconde partie, une approche de synthèse séquentielle qui consiste à synthétiser un objet précondensé pouvant s’auto-Assembler dans un second temps avec des ligands organiques a été proposée. Cette approche nous a conduits à synthétiser une nouvelle brique de formule Ti10O12(cat)8(pyr)8 et de trois dérivés de formules analogues Ti10O12(cat)8(pyr’)8 (pyr’ = pyridines substituées) obtenus par échange de ligands. Ces complexes, qui présentent des propriétés d’absorption dans le visible, ont été étudiés par spectroscopie d’absorption UV-Vis et grâce à des calculs théoriques. Puis nous avons utilisé le motif [Ti10O12(cat)8] pour générer des matériaux hybrides via des substitutions de ligands par des molécules polytopiques comme la 4,4’-Bipyridine et la poly(4-Vinylpyridine). / In the field of materials science, hybrid materials are of crucial importance due to their numerous applications. In this work, two strategies were considered to synthesize such hybrid materials.In a first part, we have tackled a one step synthetic approach by reacting resorcinol-Based oligophenylene organic ligands with titanium isopropoxide. Unfortunately, these reactions led to amorphous solids and no further structural information concerning these precipitates was obtained.In a second part, we have described a sequential approach which first concerns the preparation of pre-Ordered systems that are, in a second step, self-Assembled with organic linkers. Thus, our approach deals with the preparation of a new building block formulated as Ti10O12(cat)8(pyr)8 and three derivatives formulated as Ti10O12(cat)8(pyr’)8 (pyr’ = substituted pyridine) obtained by ligands exchange. These complexes exhibit visible light absorption properties that were studied through UV-Vis absorption spectroscopy and theoretical calculations. Then, the [Ti10O12(cat)8] motif was used to generate hybrid materials via ligands substitutions with polytopic ligands such as 4,4’-Bipyridine and poly(4-Vinylpyridine).