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Macrociclos tetrapirrólicos para células solares
Get PDFMestrado em Química - Química Orgânica e Produtos NaturaisA presente dissertação teve como principal objetivo sintetizar novos derivados porfirínicos com potencial aplicação em células solares sensibilizadas por corante (DSSCs) recorrendo a reações de acoplamento catalisadas por paládio em condições de Buchwald e a reações de ciclização oxidativa.
O presente documento encontra-se dividido em três partes. Na primeira parte, descrevem-se as caraterísticas gerais das porfirinas bem como as suas propriedades espetroscópicas, métodos de preparação e funcionalização de posições β-pirrólicas, nomeadamente via reações catalisadas por paládio. Neste capítulo também serão abordados alguns trabalhos relacionados com a potencialidade de porfirinas como corantes em DSSCs.
Na segunda parte, descreve-se a preparação de 2-(4-carboxiaminofenil)porfirinas formadas através do acoplamento catalisado por paládio entre (2-amino-5,10,15,20-tetrafenilporfirinato)níquel(II) e 4-iodobenzoato de metilo, seguido da hidrólise da função éster. A posterior reação de ciclização oxidativa redundou na formação de N-(4-carboxifenil)quinolino[2,3,4-at]porfirinas, moléculas comportando anéis fundidos. A extensão destas metodologias ao 5-bromoisoftalato de dimetilo resultou na obtenção de 2-(3,5-dicarboxiaminofenil)porfirinas e de uma N-(3,5-dicarboxifenil)quinolino[2,3,4-at]porfirina. As estruturas de todos os novos derivados porfirínicos foram confirmadas recorrendo às técnicas de ressonância magnética nuclear, espetrometria de massa e espetrofotometria de UV-vis. Em alguns casos algumas técnicas de RMN 2D, nomeadamente COSY, NOESY, HSQC e HMBC, foram também usadas.
Na terceira parte, descrevem-se os resultados já obtidos na aplicação de 2-(4-carboxiaminofenil)porfirinas como corantes em dispositivos DSSC. Estes resultados foram sempre comparados com os de uma célula contendo o corante N719, tendo-se verificado uma eficiência de cerca de 30% do valor obtido com o uso do corante de referência.The principal aim of this dissertation is related with the preparation of new porphyrinic derivatives with potential application as dyes in DSSCs through palladium-catalyzed coupling reactions and by oxidative cyclizations.
This document is divided into three main parts. In the first part, are described the general characteristics of porphyrins, their spectroscopic properties, some synthetic methodologies to prepare meso-tetraarylporphyrins and functionalization of their β-pyrrolic positions, namely using palladium-catalyzed coupling reactions. In this chapter a special emphasis will be also given to the potentiality of porphyrins as dyes in DSSCs.
In the second part is described the preparation of 2-(4-carboxyaminophenyl)porphyrins, obtained by the reaction of (2-amino-5,10,15,20-tetraphenylporphyrinato)nickel(II) with methyl 4-iodobenzoate in presence of palladium using Buchwald conditions, followed by ester function hydrolysis in basic medium. The oxidative cyclization of this class of compounds allowed the formation of N-(4-carboxyphenyl)quinolino[2,3,4-at]porphyrins, molecules bearing fused rings. The extension of these methodologies to dimethyl 5-bromoisophthalate gave rise to 2-(3,5-dicarboxyaminophenyl)porphyrins and one N-(3,5-dicarboxyphenyl)quinolino[2,3,4-at]porphyrin. All the new synthesized porphyrins were characterized by nuclear magnetic resonance, mass spectrometry and UV-vis spectrophotometry. In some cases, several 2D-NMR techniques were used, namely COSY, NOESY, HSQC and HMBC.
In the third part, are described the results accomplished by 2-(4-carboxyaminophenyl)porphyrins as dyes in DSSC devices. The performance of these derivatives was always compared with a reference cell, containing N719 and values of power conversion efficiencies of about 30% of the more conventional Ru(II)-sensitizer N719 was achieved
Síntese de derivados de tiazolotiazóis e de porfirinas e suas aplicações
No full textThe work described in this thesis had as the main objective the synthesis of new thiazolothiazoles (TzTz) and porphyrins and to evaluate the potential applications of these compounds as dyes in dye-sensitized solar cells (DSSC) and as metal ion sensors.
This document is divided into seven chapters. The first one describes the known methods for the synthesis and functionalization of thiazolothiazoles, their general characteristics as well as their spectroscopic properties. This introductory chapter also covers some work related to the applicability of thiazolothiazoles in organic light-emitting diodes (OLED), as photocatalysts, as probes for live cells imaging, as luminescent metal-organic frameworks (LMOF) and as chemosensors.
In the second chapter it is described the synthesis of 2,5-bis(6-methylpyridin-2-yl)thiazolo[5,4-d]thiazole and the synthetic approaches for its conversion into other TzTz derivatives. The efficiency of some prepared derivatives as metal ion sensors using spectrophotometric and spectrofluorimetric titrations is also discussed in this chapter. The most significant interactions were observed for the metal ions Zn²⁺ and Cu²⁺.
The third chapter discusses the synthesis of non-symmetrical thiazolothiazoles for use in dye-sensitized solar cells. These compounds, with a donor-acceptor character, have carboxy or pyridyl groups to allow them to be anchored to the TiO₂ surface. Derivatives with a carboxy group were obtained through the condensation reaction of dithiooxamide with methyl 4-formylbenzoate and other appropriate aldehydes, such as 4-(diphenylamino)benzaldehyde or 4-[bis(4-bromophenyl)amino] benzaldehyde, followed by hydrolysis of the ester function. The extension of these methodologies to pyridine-4-carbaldehyde resulted in TzTz derivatives with pyridyl groups. This chapter also describes the efficiency of dye-sensitized solar cells (DSSC) prepared with these TzTz. The efficiencies of these devices varying between 64% and 27% of the value achieved for the reference N719. The most relevant results were obtained with a TzTz bearing the carboxy group (1.89%) and a TzTz with a pyridyl group that presented the highest efficiency (2.37%).
In chapter 4 is discussed the reaction conditions used to obtain mono- and dicationic TzTz. These derivatives were obtained by quaternization of the pyridyl substituent with different alkylating agents. Their structures were confirmed using appropriate spectroscopic techniques. In chapter 5 is reported a brief overview of the structural characteristics of porphyrins, their importance, reactivity and potential applications, giving special focus to work related with their applicability as dyes in DSSC. This chapter also describes the synthetic approaches to porphyrins functionalized with carboxy and pyridyl groups for application in DSSC. To obtain these compounds, nucleophilic substitution reactions were used in pentafluorophenyl groups present in the porphyrin structure. The photovoltaic performance of DSSC devices made with these derivatives was also evaluated.
Chapter 6 provides a summary overview of the main results obtained and some perspectives for future work to be developed. The last chapter contains all the experimental details related to the synthesis and structural characterization of the new compounds. The structures of all new compounds described in this thesis were confirmed using nuclear magnetic resonance (NMR), mass spectrometry and UV-vis spectrophotometry and this information is compiled in the experimental section.O trabalho descrito nesta tese teve como principal objetivo a síntese de novos tiazolotiazóis (TzTz) e de porfirinas e avaliar as potenciais aplicações destes compostos como corantes em células solares sensibilizadas por corante (DSSC) e como sensores de iões metálicos.
Este documento encontra-se dividido em sete capítulos. No primeiro, apresenta-se uma introdução descrevendo o estado da arte relativamente aos derivados de tiazolotiazóis. os métodos conhecidos para a síntese e funcionalização dos tiazolotiazóis, as suas caraterísticas gerais bem como as suas propriedades espetroscópicas. Neste capítulo são também apresentados alguns trabalhos relacionados com a aplicabilidade dos tiazolotiazóis em díodos orgânicos emissores de luz (OLED), como fotocatalisadores, sondas para imagens de células vivas, estruturas metalo-orgânicas luminescentes (LMOF) e como quimiossensores.
No segundo capítulo descreve-se a preparação do 2,5-bis(6-metilpiridin-2-il)tiazolo[5,4-d]tiazol e de abordagens sintéticas que conduziram à sua conversão noutros derivados de TzTz. Neste capítulo é também discutida a eficiência de alguns dos compostos sintetizados como sensores de iões metálicos recorrendo a titulações espetrofotométricas e espetrofluorimétricas. Nesses estudos verificou-se que as interações mais significativas ocorreram com os iões Zn²⁺ e Cu²⁺.
No terceiro capítulo é discutida a síntese de tiazolotiazóis não simétricos para utilização em células solares sensibilizadas por corante. Esses compostos, com caráter dador-aceitador, têm grupos carboxilo ou piridilo para permitirem a sua ancoragem à superfície do TiO₂. Os derivados com grupo carboxilo foram obtidos através da reação de condensação de ditiooxamida com 4-formilbenzoato de metilo e outros aldeídos adequados 4-(difenilamino)benzaldeído ou 4-[bis(4-bromofenil)amino]benzaldeído, seguida da hidrólise da função éster. A extensão destas metodologias ao piridina-4-carboxaldeído resultou na obtenção de derivados de TzTz com grupos piridilo. Ainda neste capítulo é avaliada a eficiência de dispositivos DSSC preparados com os TzTz sintetizados. As eficiências destes dispositivos variaram entre os 64% e 27% do valor atingido pela referência N719, sendo particularmente relevante os resultados obtidos com um TzTz com o grupo carboxilo (1,89%) e com um derivado contendo o grupo piridilo que apresentou a eficiência mais elevada (2,37%).
No capítulo 4 são discutidas as condições utilizadas para obter TzTz mono e dicatiónicos. Estes derivados foram obtidos por quaternização do substituinte piridilo com diferentes agentes alquilantes. As respetivas estruturas foram confirmadas recorrendo a técnicas espetroscópicas adequadas. No capítulo 5, é feito um pequeno enquadramento sobre as caraterísticas estruturais das porfirinas, a sua importância, reatividade e potenciais aplicações dando um foco especial a trabalhos relacionados com a sua aplicabilidade como corantes em DSSC. Neste capítulo são ainda descritas as abordagens sintéticas que permitiram preparar porfirinas funcionalizadas com grupos carboxilo e piridilo para aplicação em DSSC. Na obtenção destes compostos recorreu-se a reações de substituição nucleofílica em grupos pentafluorofenilo presentes na estrutura porfirínica. Foi ainda avaliado o desempenho fotovoltaico destes derivados em dispositivos DSSC.
No capítulo 6 dá-se uma visão sumária dos principais resultados obtidos e algumas perspetivas para futuros trabalhos a desenvolver. No último capítulo são indicados todos os detalhes experimentais relativos à síntese e à caracterização estrutural dos novos compostos. As estruturas de todos os novos derivados descritos nesta tese foram confirmadas recorrendo às técnicas de ressonância magnética nuclear, espetrometria de massa e espetrofotometria de UV-vis e esta informação encontra-se compilada na parte experimental.Programa Doutoral em Químic
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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