Estudo teórico da fluorescência dupla em 9-antril oligotiofenos e da adsorção de moléculas orgânicas em uma superfície de grafite

Orientador: Maria Cristina dos SantosTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: O objetivo desta tese é o de aplicar métodos de Química Quântica e de Mecânica Molecular a fim de entender dois fenômenos observados experimentalmente: a fluorescência dupla em 9-antril-oligotiofenos e a adsorção de moléculas orgânicas em uma superfície de grafite. No estudo da fluorescência dupla em 9-antril-oligotiofenos, utilizamos o método Hartree-Fock para otimizar a geometria do estado fundamental e o método semiempírico ZINDO/S para obter os espectros de absorção e as propriedades dos estados excitados. As geometrias dos estados excitados foram obtidas utilizamos o método CI-Singles. Os espectros de emissão foram então simulados, a partir da geometria dos estados excitados, novamente utilizando o método ZINDO/S. Os resultados teóricos obtidos para os espectros de absorção e emissão dos 9-antril-oligotiofe-nos concordam muito bem com a absorção experimental e a fluorescência no azul, apresentada por estes sistemas. Com os métodos utilizados chegamos a encontrar um estado excitado com características semelhantes às encontradas experimentalmente para a emissão no vermelho, mas a posição em energia não é compatível com o experimento. Para este problema, concluímos que a técnica CI-Singles, quando aplicada em conjunto com o método ZINDO/S, pode fornecer resultados precisos para o espectro de emissão. Com relação aos espectros de absorção, mais uma vez confirmamos, para as moléculas estudadas, a confiabili-dade da técnica Hartree-Fock combinada com o método ZINDO/S. A impossibilidade de levarmos em conta o solvente em nossos cálculos impediu-nos de avaliar o efeito deste em um estado excitado que, aparentemente, está conectado à emissão no vermelho mas, analisando os resul-tados obtidos com os métodos citados, pudemos excluir algumas possibilidades e sugerir quais mecanismos estão envolvidos nesta emissão. No estudo da absorção de moléculas orgânicas numa superfície de grafite, utilizamos o método de Monte Carlo para gerar configurações compatíveis com o ensemble NVT. As configurações foram analisadas utilizando parâmetros geométricos específicos para cada problema. Concluímos que esta simulação pode nos ajudar a entender os mecanismos de auto-montagem mas, para que tenhamos resultados confiáveis, precisamos encontrar parâmetros empíricos para o nosso potencial que melhor modelem o experimento, além de relaxarmos o vínculo de molécu-las rígidas, impostas nestas primeiras simulaçõesAbstract: This thesis was devoted to the application of methods of Quantum Chemistry and Molecular Mechanics to study two experimentally observed phenomena: the dual fluorescence of 9-anthryl-oligothiophenes and the adsorption of organic molecules in a graphite surface. The investigation of the dual fluorescence was carried out employing a combination of the-oretical techniques. Ground state geometries were optimized thought the Hartree-Fock method and the first excited state geometries were obtained thought the CI-Singles method. Absorption and emission spectra were then simulated using the semi-empirical ZINDO/S method, adopting the ground state conformation in the former and the excited state geometry in the later. The theoretical results for the absorption and emission spectra of 9-anthryl-oligothiophenes agree very well with the experimental absorption spectra and the blue component of the flu-orescence. We also found an excited state with similar characteristics to the one found from experiment, related to the emission in the red, but the position in energy is not compatible with the experiment. We concluded that the CI-Singles technique, when applied together with ZINDO/S method, can yield precise results for the emission spectra. The simulated absorption spectra were also in agreement with experiments, thus confirming the reliability of the combination of theoretical methods Hartree-Fock and ZINDO/S. The impossibility of including solvent effects in our calcu-lation hindered us from obtaining a good characterization of the excited state responsible for the red emission. However, the analysis of our results led to the exclusion of some mechanisms invoked to explain the red emission and allowed us to suggest more reliable mechanisms. In the study of the adsorption of organic molecules in a graphite surface, we used the Monte Carlo method to generate compatible configurations in the NVT ensemble. The configurations have been analyzed using specific geometric parameters for each problem. We concluded that this simulation can helpful in the understanding of the self-assembly mech-anisms. However, in order to improve the theoretical description of the adsorption, a better parametrization and the inclusion of terms in the classical potential to account for torsions are necessaryDoutoradoFísicaDoutor em Ciência

Electronic couplings and rates of excited state charge transfer processes at poly(thiophene-co-quinoxaline)-PC71BM interfaces: two- versus multi-state treatments

Electronic coupling between adjacent molecules is one of the key parameters determining the charge transfer (CT) rates in bulk heterojunction (BHJ) polymer solar cells (PSCs). We calculate theoretically electronic couplings for exciton dissociation (ED) and charge recombination (CR) processes at local poly(thiophene-co-quinoxaline) (TQ)-PC71BM interfaces. We use eigenstate-based coupling schemes, i.e. the generalized Mulliken-Hush (GMH) and fragment charge difference (FCD) schemes, including 2 to multiple (3-11) states. Moreover, we study the effects of functionals, excited state methods, basis sets, surrounding media, and relative placements of TQ and PC71BM on the coupling values. Generally, both schemes provide consistent couplings with the global hybrid functionals, which yield more charge-localized diabatic states and constant coupling values regardless of the number of states, and so the 2-state schemes may be sufficient. The (non-tuned and optimally tuned) long-range corrected (LRC) functionals result in more notable mixing of the local components with the CT states. Employing multiple states reduces the mixing and thus improves the LRC results, although the method still affects the GMH CR couplings. As the FCD scheme is less sensitive, we recommend combining it with the multi-state treatment for polymer-fullerene systems when using the LRC functionals. Finally, we employ the 11-state FCD couplings to calculate the ED and CR rates, which are consistent with the experimental rates of the polymer-fullerene systems. Our results provide more insight into choosing a suitable eigenstate-based coupling scheme for predicting the electronic couplings and CT rates in photoactive systems.Funding Agencies|Academy of FinlandAcademy of Finland [251823, 298182, 310489]; Graduate School of Tampere University of Technology (TUT); Finnish Cultural FoundationFinnish Cultural Foundation; Faculty of Engineering and Natural Sciences of Tampere University; Swedish e-Science Research Center (SeRC)</p

Structural Study of Diketopyrrolopyrrole Derivative Thin Films: Influence of Deposition Method, Substrate Surface, and Aging

We report the morphology and microstructure of n-dialkyl side-chain-substituted thiophene DPP end-capped with phenyl groups (Ph-TDPP-Ph) thin films and compare the influence of deposition method and substrate surface using thermally oxidized Si and graphene substrates as well as monolayer graphene surfaces with an underlying self-assembled octadecyltrichlorosilane monolayer, complemented by an aging study of spin-coated films over a 2 weeks aging period. A distinct difference in morphology was observed between spin-coated and vacuum-deposited thin films, which formed a fiber-like morphology and a continuous layer of terraced grains, respectively. After an initial film evolution, all combinations of deposition method and substrate type result in well-ordered thin films with almost identical crystalline phases with slight variations in crystallinity and mosaicity. These findings point toward strong intermolecular forces dominating during growth, and the templating effect observed for other oligomer films formed on graphene is consequently ineffective for this material type. Upon aging of spin-coated films, a noticeable evolution involving two different morphologies and crystalline phases were observed. After several days, the thin film evolved into a more stable crystal phase and a fiber-like morphology. Moreover, slight variation in optical spectra were elucidated on the basis on density functional theory calculations. These results demonstrate that thin-film properties of DPP derivatives can be tailored by manipulating the film formation process

Structural study of Diketopyrrolopyrrole derivative thin films : influence of deposition method, substrate surface, and aging

We report the morphology and microstructure of n-dialkyl side-chain-substituted thiophene DPP end-capped with phenyl groups (Ph-TDPP-Ph) thin films and compare the influence of deposition method and substrate surface using thermally oxidized Si and graphene substrates as well as monolayer graphene surfaces with an underlying self-assembled octadecyltrichlorosilane monolayer, complemented by an aging study of spin-coated films over a 2 weeks aging period. A distinct difference in morphology was observed between spin-coated and vacuum-deposited thin films, which formed a fiber-like morphology and a continuous layer of terraced grains, respectively. After an initial film evolution, all combinations of deposition method and substrate type result in well-ordered thin films with almost identical crystalline phases with slight variations in crystallinity and mosaicity. These findings point toward strong intermolecular forces dominating during growth, and the templating effect observed for other oligomer films formed on graphene is consequently ineffective for this material type. Upon aging of spin-coated films, a noticeable evolution involving two different morphologies and crystalline phases were observed. After several days, the thin film evolved into a more stable crystal phase and a fiber-like morphology. Moreover, slight variation in optical spectra were elucidated on the basis on density functional theory calculations. These results demonstrate that thin-film properties of DPP derivatives can be tailored by manipulating the film formation process

Interfacial versus Bulk Properties of Hole-Transporting Materials for Perovskite Solar Cells: Isomeric Triphenylamine-Based Enamines versus Spiro-OMeTAD

International audienc

Randomized Trial of Machine Perfusion Versus Cold Storage in Recipients of Deceased Donor Kidney Transplants With High Incidence of Delayed Graft Function

Background. This study compared the use of static cold storage versus continuous hypothermic machine perfusion in a cohort of kidney transplant recipients at high risk for delayed graft function (DGF). Methods. In this national, multicenter, and controlled trial, 80 pairs of kidneys recovered from brain-dead deceased donors were randomized to cold storage or machine perfusion, transplanted, and followed up for 12 months. The primary endpoint was the incidence of DGF. Secondary endpoints included the duration of DGF, hospital stay, primary nonfunction, estimated glomerular filtration rate, acute rejection, and allograft and patient survivals. Results. Mean cold ischemia time was high but not different between the 2 groups (25.6 +/- 6.6 hours vs 25.05 +/- 6.3 hours, 0.937). The incidence of DGF was lower in the machine perfusion compared with cold storage group (61% vs. 45%, P = 0.031). Machine perfusion was independently associated with a reduced risk of DGF (odds ratio, 0.4995% confidence interval, 0.26-0.95). Mean estimated glomerular filtration rate tended to be higher at day 28 (40.6 +/- 19.9 mL/min per 1.73 m(2) vs 49.0 +/- 26.9 mL/min per 1.73 m(2)P = 0.262) and 1 year (48.3 +/- 19.8 mL/min per 1.73 m(2) vs 54.4 +/- 28.6 mL/min per 1.73 m(2)P = 0.201) in the machine perfusion group. No differences in the incidence of acute rejection, primary nonfunction (0% vs 2.5%), graft loss (7.5% vs 10%), or death (8.8% vs 6.3%) were observed. Conclusions. In this cohort of recipients of deceased donor kidneys with high mean cold ischemia time and high incidence of DGF, the use of continuous machine perfusion was associated with a reduced risk of DGF compared with the traditional cold storage preservation method.Univ Fed Sao Paulo, Hosp Rim, Sao Paulo, SP, BrazilEscola Paulista Med, Org Procura Orgaos, Sao Paulo, SP, BrazilUniv Sao Paulo, Fac Med, Hosp Clin, Sao Paulo, SP, BrazilHosp Israelita Albert Einstein, Kidney Transplant Unit, Sao Paulo, SP, BrazilHosp Samaritano, Sao Paulo, SP, BrazilSanta Casa Sao Paulo, Sao Paulo, SP, BrazilHosp Bandeirantes, Sao Paulo, SP, BrazilHosp Servidor Publ Estadual, Sao Paulo, SP, BrazilHosp Beneficencia Portuguesa, Sao Paulo, SP, BrazilHosp Dante Pazzanese, Sao Paulo, SP, BrazilHosp Base Sao Jose do Rio Preto, Sao Jose Do Rio Preto, SP, BrazilUniv Estadual Paulista, UNESP, Dept Internal Med, Rubiao Jr S-N, Sao Paulo, BrazilSanta Casa Ribeirao Preto, Ribeirao Preto, SP, BrazilHosp Alemao Oswaldo Cruz, Sao Paulo, SP, BrazilHosp Santa Marcelina, Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Hosp Rim, Sao Paulo, SP, BrazilEscola Paulista Med, Org Procura Orgaos, Sao Paulo, SP, BrazilWeb of Scienc