35 research outputs found
Synthesis of new bis[1-(thiophenyl)propynones] as potential organic dyes for colorless luminescent solar concentrators (LSCs)
No full textNew luminophores having different aryl nuclei and propynones moieties have been obtained via Sonogashira reactions. Their optical properties were evaluated and indicated that carbonyl groups are responsible for significant bathochromic effects and high Stokes shifts. The insertion of -OMe groups on the central benzene unit gives to the fluorophore high optical efficiency (7.7%) when homogeneously dispersed in a poly(cyclohexyl methacrylate) (PCMA) film and connected to a PV cell
Semantics of the Natural Environment in a Selection of Poetry by the Syrian Poet Kholoud Charaf
No full textBakalaura darba “Dabas vides semantika sīriešu dzejnieces Hulūdas Šarafas dzejas izlasē” mērķis ir atlasīt dabas attēlu veidus un analizēt to jēdzienisko nozīmi dzejas tekstā. Bakalaura darbs sastāv no trīs nodaļām: Pirmajā nodaļā tiek īsi apskatīts teorētiskais un praktiskais materiāls par semiotiku kopumā, dzejas teksta semiotisku interpretēšanu un vārda simbolikas nozīmi poētiskā tekstā. Otrajā nodaļā tiek apskatīta dzejnieces radošā biogrāfija, kā arī aplūkotas būtiskākās atšķirības starp arābu tradicionālās dzejas formām un Hulūdas Šarafas daiļradi. Trešajā nodaļā tiek veikta liriskā analīze. Darba rezultātā tika izdarīts secinājums, ka dzejnieces izlasē vārds kā simbols un tā jēdzieniskā nozīme tekstā pastiprina dabas vides unikalitāti. Darba izstrādē tika izmantotas grāmatas, publikācijas un zinātniskā literatūra. Darbs sastāv no 43 lappusēm, tajā ietverts 1 pielikums. Darba izstrādē izmantots 41 literatūras avots.The aim of the bachelor's thesis “Semantics of the Natural Environment in a Selection of Poetry by the Syrian Poet Kholoud Charaf” the aim is to select the types of natural images and analyze their conceptual meaning in the poetic text. The bachelor's thesis consists of three sections: The first chapter briefly discusses the theoretical and practical material on semiotics in general, the semiotic interpretation of the poetic text and the logical tendency of the word symbolism in the text. The second chapter examines the poet's creative biography, as well as the most important differences between the forms of traditional Arabic poetry and the work of Kholoud Charaf. In the third chapter, the author has performed a lyrical analysis. As a result of the work, it was concluded that in the poet's selection the word as a symbol and its conceptual meaning in the text reinforce the uniqueness of the natural environment. The work is based on books, publications, scientific literature. The work consists of 43 pages, it includes 1 appendix and 41 literature sources
Luminescent solar concentrators coupled with Perovskite solar cells
No full textLo scopo di questa tesi è quello di investigare le performance di dispositivi accoppiati costituiti da un concentratore solare luminescente (LSC) e una cella solare. La prima parte del progetto si concentra sulla caratterizzazione di LSC da fluorofori innovativi. Questi ultimi sono stati dispersi in due diverse matrici polimeriche, il convenzionale poli(metil metacrilato) e il poli(cicloesil metacrilato) come possibile alternativa. Gli LSC sono stati costruiti nella configurazione a film sottile e le loro performance sono state valutate tramite caratterizzazione spettroscopica (spettri UV-Vis e di fluorescenza, resa quantica) e misure di efficienza ottica. Nella seconda parte, ingegneria composizionale e tecniche di deposizione innovative sono state usate per costruire celle solari in perovksite ad ampia area, da accoppiare a LSC preparati con il fluoroforo dello stato dell’arte, il Lumogen Red.
The main goal of this thesis is to investigate the performance of coupled devices made of a luminescent solar concentrator (LSC) and a solar cell. The first part of the project focuses on the characterization of LSCs from innovative fluorophores. These latter ones were dispersed in two different polymeric matrices, the conventional poly(methyl methacrylate) and poly(cyclohexyl methacrylate) as a possible alternative. LSCs were built with the thin film configuration and their performances were evaluated via spectroscopic characterization (UV-Vis and fluorescence spectra, quantum yield) and optical efficiency measurements. In the second part, compositional engineering and innovative deposition techniques were used to build large area perovskite solar cells and couple them with LSCs made with the state-of-the-art fluorophore, Lumogen Red
Photoinduced and Proton-Coupled Electron Transfer Mechanisms of Photoredox Catalysis
No full textIn photoredox catalysis, light is absorbed by a photocatalyst to form its excited state, which can then undergo electron transfer processes with organic substrates in the reaction mixture. This typically yields the formation of organic radicals, which can then react further to form new compounds of interest. The use of photoredox catalysis in organic synthesis has grown fast in the past fifteen years, and new synthetic methodologies are continuously proposed. At the same time, the mechanistic investigation of these new reactions has lagged behind. Understanding the reaction mechanism is crucial for further advances in the field of photoredox catalysis, as it can provide useful insights on how to design new protocols in the most efficient way. In this thesis, mechanisms of photoinduced electron transfer and proton-coupled electron transfer (PCET) in systems of relevance for photoredox catalysis are investigated, through spectroscopic measurements (steady-state absorption and emission, femtosecond and nanosecond transient absorption and stopped-flow techniques). In Paper I, the mechanism of halophosphines activation via an Ir-based photocatalyst is explored. Here, back electron transfer is found to be dominant over the productive reaction with the phosphine substrates, which can only react at later timescales. Papers II and III focus on the photoredox activation of O-H bonds with an organic photocatalyst (9-mesityl-10-methylacridinium), in the context of β-scission reactions from alcohols. As the very first steps of the photoredox catalytic cycle are explored, support to the photophysical characterization of the photocatalyst is provided, which has shown complexity and has been controversial in the literature. Evidence for a PCET pathway in the formation of the O-centered radical is shown, which is found to be dominant over other competing pathways. In Paper IV, an NADH (nicotinamide adenine dinucleotide) analogue is used as model system to explore the PCET activation of C-H bonds. In particular, the possibility of accessing the concerted transfer of the electron and the proton (CEPT) to two different acceptors is investigated, and the factors influencing the observed dominance of a stepwise over concerted mechanism are discussed. The results also suggest the symmetric dependence of the rate constant for the concerted mechanism on the driving forces for electron and proton transfer, as opposed to recent reports on C-H bond activation via CEPT
Photoinduced and Proton-Coupled Electron Transfer Mechanisms of Photoredox Catalysis
No full textIn photoredox catalysis, light is absorbed by a photocatalyst to form its excited state, which can then undergo electron transfer processes with organic substrates in the reaction mixture. This typically yields the formation of organic radicals, which can then react further to form new compounds of interest. The use of photoredox catalysis in organic synthesis has grown fast in the past fifteen years, and new synthetic methodologies are continuously proposed. At the same time, the mechanistic investigation of these new reactions has lagged behind. Understanding the reaction mechanism is crucial for further advances in the field of photoredox catalysis, as it can provide useful insights on how to design new protocols in the most efficient way. In this thesis, mechanisms of photoinduced electron transfer and proton-coupled electron transfer (PCET) in systems of relevance for photoredox catalysis are investigated, through spectroscopic measurements (steady-state absorption and emission, femtosecond and nanosecond transient absorption and stopped-flow techniques). In Paper I, the mechanism of halophosphines activation via an Ir-based photocatalyst is explored. Here, back electron transfer is found to be dominant over the productive reaction with the phosphine substrates, which can only react at later timescales. Papers II and III focus on the photoredox activation of O-H bonds with an organic photocatalyst (9-mesityl-10-methylacridinium), in the context of β-scission reactions from alcohols. As the very first steps of the photoredox catalytic cycle are explored, support to the photophysical characterization of the photocatalyst is provided, which has shown complexity and has been controversial in the literature. Evidence for a PCET pathway in the formation of the O-centered radical is shown, which is found to be dominant over other competing pathways. In Paper IV, an NADH (nicotinamide adenine dinucleotide) analogue is used as model system to explore the PCET activation of C-H bonds. In particular, the possibility of accessing the concerted transfer of the electron and the proton (CEPT) to two different acceptors is investigated, and the factors influencing the observed dominance of a stepwise over concerted mechanism are discussed. The results also suggest the symmetric dependence of the rate constant for the concerted mechanism on the driving forces for electron and proton transfer, as opposed to recent reports on C-H bond activation via CEPT
Luminescent solar concentrators with outstanding optical properties by employment of D–A–D quinoxaline fluorophores
No full textLuminescent solar concentrators (LSCs) are devices designed to efficiently collect both direct and diffuse solar radiation and concentrate it on photovoltaic cells to foster their use in building-integrated photovoltaics (BIPV). The optimization of LSC performances involves the adjustment of both the fluorophore and the guest polymer matrix. On this account, we investigated a series of high quantum yield, donor-acceptor-donor (D-A-D) photostable fluorophores (DQ1-5), presenting a central quinoxalinic acceptor core, not previously employed in LSCs, and triarylamines or phenothiazine as donor groups. The molecules were also decorated with alkyl chains on the central core and/or the donor groups, to explore their compatibility with the poly(methyl methacrylate) (PMMA) and poly(cyclohexyl methacrylate) (PCMA) matrices utilized in this study. The PMMA and PCMA films (25 μm thick), containing 0.2-2.2 wt% of DQ1-5, absorbed in the 370-550 nm range and presented emission maxima at 550-600 nm, with fluorescence quantum yields higher than 40% even at the highest doping contents. Notably, the DQ1/PMMA thin-films showed enhanced phase compatibility and excellent quantum yields, i.e., >95%. Accordingly, they were designed to obtain 25 cm2 area LSCs with remarkable internal (ηint) and external (ηext) photon efficiencies of 42.9% and 6.2%, respectively, higher than those observed from state-of-the-art devices based on the Lumogen Red 305 (LR305) as the reference fluorophore. Overall, these were the best results ever achieved in our laboratory for thin-film LSCs built with organic fluorescent emitters. © The Royal Society of Chemistry
Rethinking the Infra- Culture space: bridging, providing, enhancing
No full textMashhad has been geopolitically an important city in the region and a trade and connection hub to Central and East Asian countries. It is also the second-largest Muslim pilgrimage city after Mecca. It is a global city for which religion shaped the identity and influenced the spatial configuration of the city.Religion, politics and economics are the main forces which run the city and have not only affected the growth and development of the whole city but are involved in the shift toward a large-scale infrastructure, which has become a dominant idea of city planning during the last few centuries. Overlapping the flows and its agencies reveals that district six is the logistic hub and the entrance to the city, it encounters both scales regional and local, therefore it is the site of intervention. Mapping the different flows, spaces and everyday life reveals that the big infrastructure is informed, and has strong connectivity with its surrounding region however it creates discontinuous relationships on the local scale, the local scale is neglected. moreover, its main spaces are economic driving, and the marginal settlement, are result of this spaces.People are vulnerable society, they have access only to groundwater due to technical problems associated with expansion of the system in marginal areas, groundwater is highly contaminated. The project aims to bridge not only physically but also socially culturally and environmentally. It is located within the infrastructure node (Ghadir square) transferring its space into Hybrid spaces which have multifunctional use, inhabiting the infrastructure space and transforming its spaces into places. Its atmosphere encounters both natural and urban, regional and local. The main emphasis is on the water, driving from the research, the project is an assemblage of different function water filtration system, metro, market, educational centre, parking and communal spaces, each function with its own individual character has its border and territorial scale but all are connected to the central park and water tank. Creating neighbourhood identities based on their distinctive interrelationship with water. Architecture, Urbanism and Building Sciences | Borders and Territorie
Erratum to: Search for direct pair production of scalar top quarks in the single- and dilepton channels in proton-proton collisions at √s = 8 TeV
No full textIn the original paper, the wrong plot was used in figure 4. The corrected figure is given below. (Figure presented.). © 2016, The Author(s)
Erratum to: Search for third-generation scalar leptoquarks in the tτ channel in proton-proton collisions at √s = 8 TeV
No full textIn the original paper, the wrong plot was used in figure 6. The correct figure is given below. (figure presented.). © 2016, The Author(s)
Mechanistic Insights and Synthetic Explorations of the Photoredox-Catalyzed Activation of Halophosphines
No full textThe light-driven activation of halophosphines R2PX (R = alkyl- or aryl, X = Cl, Br) by an IrIII-based photocatalyst is described. It is shown that initially formed secondary phosphines R2PH react readily with the remaining R2PX in a parent–child reaction to form diphosphines R2P–PR2. Aryl-containing diphosphines can be further reduced to secondary phosphines RAr2PH under identical photoredox conditions. Dihalophosphines RPX2 are also activated by the photoredox protocol, giving rise to unusual 3-, 4-, and 5-membered cyclophosphines. Transient absorption studies show that the excited state of the Ir photocatalyst is reductively quenched by the DIPEA (N,N-di-iso-propylethylamine) electron donor. Electron transfer to R2PX is however unexpectedly slow and cannot compete with recombination with the oxidized donor DIPEA•+. As DIPEA is not a perfectly reversible donor, a small proportion of the total IrII population escapes recombination, providing the reductant for the observed transformations
