672 research outputs found
First examples of pyran based colorants as sensitizing agents of p-Type Dye-Sensitized solar cells
Three different pyran based dyes were synthesized and tested for the first time as photosensitizers of NiO based p-type dye-sensitized solar cells (p-DSSC). The molecules feature a similar molecular structure and are based on a pyran core that is functionalized with electron acceptor groups of different strength and is symmetrically coupled to phenothiazine donor branches. Optical properties of the dyes are deeply influenced by the nature of the electron-acceptor group, so that the overall absorption of the three dyes covers the most of the visible spectrum. The properties of devices based on the NiO electrodes sensitized with the investigated dyes were evaluated under simulated solar radiation: the larger short circuit current density exceeded 1mA/cm2 and power conversion efficiency as high as 0.04% could be recorded. The performances of the fabricated p-DSSC have been compared to a reference cell sensitized with P1, a high level benchmark, which afforded a photoelectrochemical activity similar to the best example of our pyran sensitized devices (1.19 mA/cm2 and 0.049%)
Stabilization of an elusive tautomer by metal coordination
The solid-state isolation of the different tautomers of a chemical comÂpound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol(−1) greater than the most stable 2H form, we show that metal comÂplexation is a sucÂcessful and reliable way for stabilizing the elusive tautoÂmer. We have preÂpared two comÂplexes of the neutral ligand with CuBr(2) and ZnBr(2), namely, aquaÂbromidoÂbisÂ[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C(8)H(7)N(7))(2)(H(2)O)]Br·3H(2)O, and diÂbroÂmidoÂ[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triÂazole]zinc(II) monohydrate, [ZnBr(2)(C(8)H(7)N(7))(2)]·H(2)O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two comÂplexes reflect the different coordination preferences of Cu(II) and Zn(II). The copper(II) comÂplex is homotautomeric as it only conÂtains the elusive 3H-tautomer of the ligand. The comÂplex can be described as octaÂhedral with tetraÂgonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molÂecule and a bromide ion in elongated axial positions comÂplete the coordination environment. The zinc(II) comÂplex, on the other hand, is heterotautomeric and conÂtains two bromide ions and two monodentate ligand molÂecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetraÂhedral geometry. The observation of mixed-tautomer comÂplexes is unprecedented for neutral ligands. The analysis of the X-ray molÂecular structures of the two comÂplexes allows the deduction of possible rules for a rational design of mixed-tautomer comÂplexes
Volume Holographic Optical Elements as Solar Concentrators
In this chapter, we investigate the possibility to realize a holographic solar concentrator by using a new photopolymeric material as recording medium. Therefore, two different configurations of holographic lenses (lenses with spherical and cylindrical symmetry) are described in terms of both recording process and optical response characterization. Finally, we propose the possibility to use this new photopolymer to realize holographic solar concentrator for space applications
The Binet-Legendre Metric in Finsler Geometry
For every Finsler metric we associate a Riemannian metric (called
the Binet-Legendre metric). The transformation is -stable
and has good smoothness properties, in contrast to previous constructions. The
Riemannian metric also behaves nicely under conformal or bilipshitz
deformation of the Finsler metric . These properties makes it a powerful
tool in Finsler geometry and we illustrate that by solving a number of named
Finslerian geometric problems. We also generalize and give new and shorter
proofs of a number of known results. In particular we answer a question of M.
Matsumoto about local conformal mapping between two Minkowski spaces, we
describe all possible conformal self maps and all self similarities on a
Finsler manifold. We also classify all compact conformally flat Finsler
manifolds, solve a conjecture of S. Deng and Z. Hou on the Berwaldian character
of locally symmetric Finsler spaces, and extend the classic result of H.C. Wang
about the maximal dimension of the isometry groups of Finsler manifolds to
manifolds of all dimensions.
Most proofs in this paper go along the following scheme: using the
correspondence we reduce the Finslerian problem to a similar
problem for the Binet-Legendre metric, which is easier and is already solved in
most cases we consider. The solution of the Riemannian problem provides us with
the additional information that helps to solve the initial Finslerian problem.
Our methods apply even in the absence of the strong convexity assumption
usually assumed in Finsler geometry. The smoothness hypothesis can also be
replaced by that of partial smoothness, a notion we introduce in the paper. Our
results apply therefore to a vast class of Finsler metrics not usually
considered in the Finsler literature.Comment: 33 pages, 5 figures. This version is slightly reduced fron versions 1
and 2. The paper has been published in Geometry & Topolog
Perylene diimides functionalized with N-thiadiazole substituents: Synthesis and electronic properties in OFET devices
Two new perylene diimide derivatives N,N′-bis(5-tridecyl-1,3,4- thiadiazol-2-yl)perylene-3,4,9,10-tetracarboxylic 3,4:9,10-diimide (PDI-T1) and N,N′-bis[5-(1-hexyl)nonyl-1,3,4-thiadiazol-2-yl]perylene-3,4,9, 10-tetracarboxylic 3,4:9,10-diimide (PDI-T2), achieved by functionalizing the basic perylene molecular core at imide nitrogen with 1,3,4-thiadiazole rings, have been synthesized. Both these compounds make possible the fabrication of n-type organic thin-film transistors able to work in air, even when bare SiO2 surfaces are utilized as gate dielectric. As active channels of transistors in the bottom-contact bottom-gate configuration, PDI-T1 evaporated films exhibited a maximum mobility of 0.016 cm2/V s in vacuum. For evaporated PDI-T2 films, instead, mobility values were found to be more than one order of magnitude lower, because of their reduced degree of crystalline order. However, PDI-T2 films can be also deposited by solution techniques and field-effect transistors were fabricated by spin-coating, displaying mobility values ranging between 10-6 and 10-5 cm2/V s. Similar to what previously found for other perylene diimide derivatives, our experimental work also demonstrates that the electrical response of both PDI-T1 and PDI-T2 transistors under ambient conditions can be improved by increasing the level of hydrophobicity of the dielectric surface. © 2012 Elsevier B.V. All rights reserved
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