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181.
Garcia-Bosch I Ribas X Costas M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(7):2113-2122
Reactions of the unsymmetric dicopper(II) peroxide complex [Cu(II)(2)(μ-η(1):η(1)-O(2))(m-XYL(N3N4))](2+) (1?O(2), where m-XYL is a heptadentate N-based ligand), with phenolates and phenols are described. Complex 1?O(2) reacts with p-X-PhONa (X = MeO, Cl, H, or Me) at -90?°C performing tyrosinase-like ortho-hydroxylation of the aromatic ring to afford the corresponding catechol products. Mechanistic studies demonstrate that reactions occur through initial reversible formation of metastable association complexes [Cu(II)(2)(μ-η(1):η(1)-O(2))(p-X-PhO)(m-XYL(N3N4))](+) (1?O(2)?X-PhO) that then undergo ortho-hydroxylation of the aromatic ring by the peroxide moiety. Complex 1?O(2) also reacts with 4-X-substituted phenols p-X-PhOH (X = MeO, Me, F, H, or Cl) and with 2,4-di-tert-butylphenol at -90?°C causing rapid decay of 1?O(2) and affording biphenol coupling products, which is indicative that reactions occur through formation of phenoxyl radicals that then undergo radical C-C coupling. Spectroscopic UV/Vis monitoring and kinetic analysis show that reactions take place through reversible formation of ground-state association complexes [Cu(II)(2)(μ-η(1):η(1)-O(2))(X-PhOH)(m-XYL(N3N4))](2+) (1?O(2)?X-PhOH) that then evolve through an irreversible rate-determining step. Mechanistic studies indicate that 1?O(2) reacts with phenols through initial phenol binding to the Cu(2)O(2) core, followed by a proton-coupled electron transfer (PCET) at the rate-determining step. Results disclosed in this work provide experimental evidence that the unsymmetric 1?O(2) complex can mediate electrophilic arene hydroxylation and PCET reactions commonly associated with electrophilic Cu(2)O(2) cores, and strongly suggest that the ability to form substrate?Cu(2)O(2) association complexes may provide paths to overcome the inherent reactivity of the O(2)-binding mode. This work provides experimental evidence that the presence of a H(+) completely determines the fate of the association complex [Cu(II)(2)(μ-η(1):η(1)-O(2))(X-PhO(H))(m-XYL(N3N4))](n+) between a PCET and an arene hydroxylation reaction, and may provide clues to help understand enzymatic reactions at dicopper sites. 相似文献
182.
Philippe Tassin Thomas Koschny Costas M. Soukoulis 《Physica B: Condensed Matter》2012,407(20):4062-4065
An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media. 相似文献
183.
Daeho Lee Heng Pan Seung Hwan Ko Hee K. Park Eunpa Kim Costas P. Grigoropoulos 《Applied Physics A: Materials Science & Processing》2012,107(1):161-171
A solution-processable, high-concentration transparent ZnO nanoparticle (NP) solution was successfully synthesized in a new
process. A highly transparent ZnO thin film was fabricated by spin coating without vacuum deposition. Subsequent ultra-short-pulsed
laser annealing at room temperature was performed to change the film properties without using a blanket high temperature heating
process. Although the as-deposited NP thin film was not electrically conductive, laser annealing imparted a large conductivity
increase and furthermore enabled selective annealing to write conductive patterns directly on the NP thin film without a photolithographic
process. Conductivity enhancement could be obtained by altering the laser annealing parameters. Parametric studies including
the sheet resistance and optical transmittance of the annealed ZnO NP thin film were conducted for various laser powers, scanning
speeds and background gas conditions. The lowest resistivity from laser-annealed ZnO thin film was about 4.75×10−2 Ω cm, exhibiting a factor of 105 higher conductivity than the previously reported furnace-annealed ZnO NP film and is even comparable to that of vacuum-deposited,
impurity-doped ZnO films within a factor of 10. The process developed in this work was applied to the fabrication of a thin
film transistor (TFT) device that showed enhanced performance compared with furnace-annealed devices. A ZnO TFT performance
test revealed that by just changing the laser parameters, the solution-deposited ZnO thin film can also perform as a semiconductor,
demonstrating that laser annealing offers tunability of ZnO thin film properties for both transparent conductors and semiconductors. 相似文献
184.
185.
Pisignano D Mele E Persano L Athanassiou A Fotakis C Cingolani R 《The journal of physical chemistry. B》2006,110(10):4506-4509
This work presents evidence for line-narrowing from the UV photoexcited open form of the photochromic molecule, indolinospiropyran (1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro [2H-1-benzopyran-2,2'-(2H)-indole]) in the solid state. The line-narrowing is attributable to amplified spontaneous emission induced by optical gain and assisted by the waveguiding within the organic film. Optical gain throughout a band as large as 28 nm, with a maximum gain coefficient of 5.6 cm(-1), is observed in the merocyanine emission region (660-730 nm). These results open the way to the realization of hybrid devices based on the coupling between photochromic behavior and stimulated emission from conjugated molecules, such as lasing optical memories, and lasers gated by optical molecular switches. 相似文献
186.
Company A Güell M Popa D Benet-Buchholz J Parella T Fontrodona X Llobet A Solà M Ribas X Luis JM Costas M 《Inorganic chemistry》2006,45(24):9643-9645
A molecular bipaddled flipper based on a tetradentate chiral Cu complex has been designed. The paddling motion of this unprecedented molecular-scale machine can be controlled by reversible oxidation of the metal center. Kinetic and computational (density functional theory) analyses provide a detailed picture of the flipper motion at the molecular scale, rationalize the switching role of the metal-ion oxidation state, and pose the basis for the fine-tuning of the dynamic motion of this new class of molecular-scale devices. 相似文献
187.
Ferm M Watt J O'Hanlon S De Santis F Varotsos C 《Analytical and bioanalytical chemistry》2006,384(6):1320-1330
A new passive particle collector (inert surrogate surface) that collects particles from all directions has been developed.
It was used to measure particle deposition at 35 test sites as part of a project that examined corrosion of materials in order
that variation in particulate material could be used in development of dose–response functions in a modern multi-pollutant
environment. The project, MULTI-ASSESS, was funded by the EU to examine the effects of air pollution on cultural heritage.
Passive samplers were mounted rain-protected, and both in wind-protected and wind-exposed positions, to match the exposure
of the samples for corrosion studies. The particle mass and its chemical content (nitrate, ammonium, sulfate, calcium, sodium,
chloride, magnesium and potassium) were analysed. The loss of light reflectance on the surrogate surface was also measured.
Very little ammonium and potassium was found, and one or more anions are missing in the ion balance. There were many strong
correlations between the analysed species. The mass of analysed water-soluble ions was fairly constant at 24% of the total
mass. The particle mass deposited to the samplers in the wind-protected position was about 25% of the particles deposited
to an openly exposed sampler. The Cl−/Na+ ratios indicate a reaction between HNO3 and NaCl. The deposited nitrate flux corresponds to the missing chloride. The Ca2+ deposition equals the deposition and the anion deficiency. The deposition most likely originates from SO2 that has reacted with basic calcium-containing particles either before or after they were deposited. The particle depositions
at the urban sites were much higher than in nearby rural sites. The deposited mass correlated surprisingly well with the PM10 concentration, except at sites very close to traffic. 相似文献
188.
G.J. Tserevelakis G. Filippidis A.J. Krmpot M. Vlachos C. Fotakis N. Tavernarakis 《Micron (Oxford, England : 1993)》2010,41(5):444-447
In this study, third-harmonic generation (THG) imaging measurements were performed to characterize different developmental stages of the nematode Caenorhabditis elegans (C. elegans) embryos. Femtosecond laser pulses (1028 nm) were utilized for excitation. THG image contrast modality proved as a powerful diagnostic tool, providing valuable information and offering new insights into the complex developmental process of C. elegans embryogenesis. 相似文献
189.
C. Fotakis D. Zevgolis T. Efthimiopoulos E. Patsilinakou 《Chemical physics letters》1984,110(1):73-78
Multiphoton excitation of CS2 by means of a frequency-narrowed tunable KrF laser (248 nm) leads to ionisation and photofragment fluorescence from CS(A 1Π) and CS(d3Δ). Emission spectra can be obtained without any interference from the strong laser-induced flourescence from CS(X1Σ+) observed in previous work with broad-band KrF laser. Excitation and fragmentation mechanisms are discussed within the context of higher Rydberg states of CS2. 相似文献
190.
A. Klini A. Mourka V. Dinca C. Fotakis F. Claeyssens 《Applied Physics A: Materials Science & Processing》2007,87(1):17-22
We report a method for micropatterning (25–900 μm2 pixel size) of ZnO nanorods onto a silicon substrate via a low-temperature (overall under 100 °C) two-step process, involving
a laser-based direct-write technique (laser-induced forward transfer) and sequential chemical growth. The rods produced via
this route are aligned in the [0001] crystal direction. Photoluminescence shows, next to the band-gap emission, strong green-yellow
emission centred at ∼570 nm. Additionally, the rod arrays show excellent field-emission properties with a threshold field
for emission of 5 V/μm.
PACS 61.82.Rx; 81.10.Dn; 81.16.Mk 相似文献