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Axial stereogenicity for designing inherently chiral organic semiconductors.
Full text linkThe topic of my research is focused on the discovery and development of new inherently chiral molecules that, due to their peculiar properties, can be used both as semiconductive material and, when the molecules are deposited as an enantiopure film, as surfaces able to enantiorecognize chiral probes.
In the last years, the interest for the organic semiconductors has increased and especially multi-thiophene molecules have attracted considerable attention. Such multi-thiophene materials are obtained by chemical or electrochemical oxidation of a monomer and they are insulator in neutral state but become conductor after p- or n-type doping.
Chirality is generally introduced in the polyconjugated semiconductors by attaching chiral pendants to the electroactive backbone but these materials give relevant chirality manifestations only under particular experimental conditions [1]. The idea on which is based this research project is to design a class of compounds that could strictly correlate the conductive polythiophenes backbone to the chirality properties. This requirement is satisfied by the exploitation of the inherent chirality that is based on the concept that the scaffold constituting the stereogenic element responsible for chirality is also the functional group responsible for properties.
The peculiarities of the inherently chiral system are that the chirality results from a tailored torsion produced along the conducting oligothiophene backbone, the stereogenic core responsible for chirality is an atropoisomeric bi-thiophene or bi-pyrrole, and the same conjugated system responsible for the electro-optical properties is also responsible for molecular chirality.
The first member of this new class, nicknamed BT2T4 (because it consists in a bithianaphthene scaffold leading four thiophenes), showed outstanding properties such as a very high racemization barrier, great chiroptical properties and, deposited as an enantiopure polymeric film on an electrode, it showed amazing enantiorecognition ability [2].
Furthermore, BT2T4 was chemical oxidized by FeCl3 and the mixture of the oligomers was analyzed through HR MALDI spectrometry giving a very surprising result since all the oligomers, namely dimers, trimers and superior oligomers, were found to be cyclic and not open and linear [3].
Prompted by these outstanding results, during the first year of the PhD research we modified the structure of BT2T4 in order to obtain new inherently chiral compounds following two different strategies. The first one is based on the bithiophene tail elongation in order to achieve, after the oxidation, cyclic compounds with bigger cavity. The second strategy, on the other hand, aims to achieve a compound where the bithiophene tails are blocked in a rigid coplanar structure: the rigidity of the system indeed should provide material endowed with better optoelectronic properties.
All these compounds were prepared according to the same general procedure starting from the 2,2’-dibromo-3,3’- bithianaphatene that was functionalized with different “pendants” through a Stille reaction.
As shown in figure 2 the selected “pendants” were the ter-thiophene (BT2T6), the 3',4'-dibutyl-2,2':5',2''-terthiophene (BT2T6 Bu), the dithienopyrrole-N-octyl (BT2DTP2), the dithienopyrrole-N-methyl-phenyl (BT2DTP2 Ph) and the 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BT2BTD2).
In particular, the introduction of a benzothiadiazole system has a double role: to extend the pendant lenth and, at the same time, to lead to a compound exhibiting optical properties slightly different from the other monomers (i.e. high quantum yields and λ absorption red-shifted).
After one year, we reached many promising results: we could confirm that the modification introduced on the BT2 scaffold leads to monomers able to oligomerize through chemical and electrochemical oxidation producing cyclic oligomers with different dimension and shape. We analyzed both monomers and oligomers by different techniques. Futhermore, some of them were separated into enantiomers and their chiroptical properties were investigated.
As expected, the compound nicknamed BT2BTD2 has remarkable properties, especially from an optical point of view but unfortunately, we could not exploit it due to its low solubility. For this reason, we planned to modify the structure of the monomer in order to improve the solubility by introducing four EDOT units in place of the four thiophenes.
Unfortunately, due to the low solubility of the benzothiadiazole-bis-EDOT (BTDE) it was not possible to obtain the target monomer through the classical synthetic scheme which requires a Pd (0) catalyzed Stille reaction. However, since the bare BTDE appeared an interesting monomer, we investigated its chemical and electrochemical copolymerization in the presence of 3,3’-bithianaphtene. These experiments were carried out in the group of prof. S. Ludwigs of the University of Stuttgart, where I spent my abroad period, exploiting the expertise of the group in the polymer synthesis and electrochemical analysis.
Since both chemical and electrochemical oxidation did not give the expected results, we moved our attention to the possibility to achieve a donor-acceptor (D-A) copolymer by copolymerization of the benzothiadiazole-bis-EDOT with the branched terthiophene, nicknamed T3, deeply investigated in that group [4,5]. D-A polymers have recently attracted particular interest since they exhibit a reduced band-gap, due to their in-chain donor-acceptor interaction and for this reason they are used as light-harvesting system in solar cells. Furthermore, besides a long time focused on electrochemical analysis, during the period spent in Germany I synthetized two new compounds.
In order to investigate the role of ramification, we prepared a product with the same number of thiophenes as BT2T6 but with a branched structure by functionalizing the atropisomeric scaffold with two T3 units.
On the other hand, we synthetized a compound functionalized with four EDOT units, nicknamed BT2E4 which should have provided a material with interesting properties, being EDOT electron-richer than thiophene and ubiquitous in the electroactive materials.
During my third year, we focused our attention on a new class of inherently chiral monomer based on the scaffold of the 2,2’-biindole. The design of the new class has two main motivations:
the 2,2’-biindolic core is more electron rich than that of 3,3’-bithianaphtene and the first two oxidations result at an oxidative potential particularly low. This could allowed to discriminate analytes in a different potential window.
the nitrogen atom can be functionalized, tuning solubility and processability of the final material.
Especially interesting is the monomer derived from the introduction of a chiral pendant, namely the (R)- or (S)-phenylethyl group, that leads to the formation of two diastereoisomers, theoretically separable through a classical method, avoiding the chiral HPLC.
Indeed, the major disadvantage presented by the compounds investigated until now is the fact that their separation into antipodes must be performed through HPLC on a chiral stationary phase. Developing a method that could allow to avoid this tedious step would be an appealing target. In figure 5 are reported two other monomers synthetized according to this strategy: the first is characterized by the presence of two carboxylic groups that could allowed a classical resolution through the formation of diastereoisomeric salts with a chiral base. The second, on the other hand, was obtained as an enantiopure compound through an enantioselective synthesis starting from an enantiopure precursor obtained, in turn, by resolution with camphosulfonic acid.
In addition, due to the remarkable properties showed by BT2BTD2, we decided to introduce the benzothiadiazole system on the 2,2’-biindole scaffolds obtaining the first example of a biindole with a pendant different from the bithiophene. The presence of the nitrogen atoms allows the functionalization with two hexylic chains that strongly increase the solubility of the monomer, overcoming the problem found for BT2BTD2.
In conclusion, after three years research on inherently chiral electroactive materials new compounds, based on 3,3’-bithianaphtene and 2,2’-biindole core, were synthetized and fully characterized.
The new frontier of this kind of inherently chiral monomers results to be the achievement of enantiopure compounds without the use of chiral HPLC and some preliminary interesting results have been obtained.
[1] Janssen et al.; J. Molecular Structure, 2000, 521, 285;
[2] Sannicolò, F.; Benincori, T. et al.; Angew. Chem., Int Ed., 2014, 53, 2623;
[3] Sannicolò, F.; Benincori, T. et al.; Chemistry: an European Journal, 2014, 20, 15261;
[4] Link, S.; Ludwigs, S. et al.; Langmuir, 2013, 29, 15463;
[5] Goll, M.; Ludwigs, S. et al.; Beilstein J. Org. Chem, 2015, 11, 335;
[6] Abbiati, G.; Arcadi, A. el al.; Tetrahedron, 2006, 62, 3033
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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