Search results for "DENSITY"
showing 10 items of 4402 documents
Light-induced transmission nonlinearities in gallium selenide
1999
The intensity of a He–Ne laser (633 nm, 5 mW) transmitted by different GaSe samples is observed to change in correlation with a Nd-yttrium–aluminum–garnet laser pulse (532 nm, 7.8 ns, 3 mJ) which excites them. Such time response has been attributed to a nonlinear optical effect, i.e., a decrease in the refractive index due to the exciton screening by the photogenerated carriers. A calculation of the absorption coefficient and refractive index at different carrier concentrations has led to a reconstruction of transmittance transients which fully agree with the experimental data at different incident intensities and temperatures. Chantal.Ferrer@uv.es ; Jaqueline.Bouvier@uv.es ; Miguel.Andres@…
[Pt2Cu34(PET)22Cl4]2–: An Atomically Precise, 10-Electron PtCu Bimetal Nanocluster with a Direct Pt–Pt Bond
2021
Heteroatom-doped metal nanoclusters (NCs) are highly desirable to gain fundamental insights into the effect of doping on the electronic structure and catalytic properties. Unfortunately, their controlled synthesis is highly challenging when the metal atomic sizes are largely different (e.g., Cu and Pt). Here, we design a metal-exchange strategy that enables simultaneous doping and resizing of NCs. Specifically, [Pt2Cu34(PET)22Cl4]2- NC, the first example of a Pt-doped Cu NC, is synthesized by utilizing the unique reactivity of [Cu32(PET)24Cl2H8]2- NC with Pt4+ ions. The single-crystal X-ray structure reveals that two directly bonded Pt atoms occupy the two centers of an unusually interpenet…
Electronic structure of p-type ultraviolet-transparent conducting CuScO2 films
2008
Abstract We investigate the electronic structure of CuScO 2 thin films grown on sapphire and mica substrates by pulsed laser deposition. X-ray diffraction and microanalysis confirm that the films have the expected delafossite crystal structure and stoichiometric proportions. The electronic structure is investigated by means of X-ray and ultraviolet photoelectron spectroscopy. Electronic states in the range 0–1350 eV are identified, making reference to theoretical density-of-states calculations up to 80 eV. Photoelectron spectra near the Fermi energy confirm the p-character of the films. Optical absorption spectroscopy shows that the films are transparent up to 3.7 eV and exhibit an intense …
[Ir(C^N)2(N^N)]+ emitters containing a naphthalene unit within a linker between the two cyclometallating ligands
2016
The synthesis of four cyclometallated [Ir(C^N) 2 (N^N)][PF 6 ] compounds in which N^N is a substituted 2,2’- -bipyridine (bpy) ligand and the naphthyl-centred ligand 2,7-bis(2-(2-(4-(pyridin-2-yl)phenoxy)ethoxy) ethoxy)naphthalene provides the two cyclometallating C^N units is reported. The iridium( III ) complexes have been characterized by 1 H and 13 C NMR spectroscopies, mass spectrometry and elemental analysis, and their electrochemical and photophysical properties are described. Comparisons are made with a model [Ir(ppy) 2 (N^N)][PF 6 ] compound (Hppy = 2-phenylpyridine). The complexes containing the naphthyl-unit exhibit similar absorption spectra and excitation at 280 nm leads to an …
Microscopic origin of the charge transfer in single crystals based on thiophene derivatives: A combined NEXAFS and density functional theory approach
2016
We have investigated the charge transfer mechanism in single crystals of DTBDT-TCNQ and DTBDT-F4TCNQ (where DTBDT is dithieno[2,3-d;2',3'-d'] benzo[1,2-b;4,5-b']dithiophene) using a combination of near-edge X-ray absorption spectroscopy (NEXAFS) and density functional theory calculations (DFT) including final state effects beyond the sudden state approximation. In particular, we find that a description that considers the partial screening of the electron-hole Coulomb correlation on a static level as well as the rearrangement of electronic density shows excellent agreement with experiment and allows to uncover the details of the charge transfer mechanism in DTBDT-TCNQ and DTBDT-F4 TCNQ, as w…
[Cu32(PET)24H8Cl2](PPh4)2: A Copper Hydride Nanocluster with a Bisquare Antiprismatic Core
2020
Atomically precise coinage metal (Au, Ag, and Cu) nanoclusters (NCs) have been the subject of immense interest for their intriguing structural, photophysical, and catalytic properties. However, the synthesis of Cu NCs is highly challenging because of low reduction potential and high reactivity of copper, demonstrating the need for new synthetic methods using appropriate ligand combinations. By designing a diamine-assisted synthetic strategy, here we report the synthesis and total structure characterization of a box-like dianionic Cu NC [Cu32(PET)24H8Cl2](PPh4)2 coprotected by 2-phenylethanethiolate (PET), hydride, and chloride ligands. Its crystal structure comprises a rare bisquare antipri…
Interactions of amino acids with aluminum octacarboxyphthalocyanine hydroxide. Experimental and DFT studies
2017
The influence of albumin and amino acids (l-serine, glycine, l-histidine, l-tryptophan, l-cysteine) on the properties of aluminum octacarboxyphthalocyanine hydroxide (Al(OH)PcOC) was investigated in a phosphate buffer (pH 8.0). Particular attention was paid to the spectroscopic properties and photostability of Al(OH)PcOC. The effect of albumin or amino acids on the photodegradation of Al(OH)PcOC was examined in water using red light: 685 nm and daylight irradiation. Analysis of kinetic curves indicated that interaction with those molecules increases the photostability of Al(OH)PcOC. The molecular structure of Al(OH)PcOC complexes (in vacuum and in water) with axially or equatorially coordin…
Reversible isomerization of metal nanoclusters induced by intermolecular interaction
2021
Most inorganic nanoparticles are directly surface-terminated (and -stabilized) by protecting ligands, which could greatly affect the atomic packing and physical/chemical properties of their inorganic cores. Here, we show that the intermolecular interactions between the adsorbed molecules and surface ligands can also affect the core structure of inorganic nanoparticles. Through the coupling/decoupling of cationic surfactants (cetyltrimethylammonium cations, CTA+) and anionic surface ligands (para-mercaptobenzoic acid, p-MBA) in the aqueous phase, we have achieved a reversible transformation between two isomers of [Au25(p-MBA)18]− nanoclusters. The interconversion process between the two isom…
Protonation of the Biliverdin IXα Chromophore in the Red and Far-Red Photoactive States of a Bacteriophytochrome
2019
The tetrapyrrole chromophore biliverdin IXα (BV) in the bacteriophytochrome from Deinococcus radiodurans (DrBphP) is usually assumed to be fully protonated, but this assumption has not been systematically validated by experiments or extensive computations. Here, we use force field molecular dynamics simulations and quantum mechanics/molecular mechanics calculations with density functional theory and XMCQDPT2 methods to investigate the effect of the five most probable protonation forms of BV on structural stability, binding pocket interactions, and absorption spectra in the two photochromic states of DrBphP. While agreement with X-ray structural data and measured UV/vis spectra suggest that …
Ag11(SG)7 : A New Cluster Identified by Mass Spectrometry and Optical Spectroscopy
2014
We report a one-step and high yield synthesis of a red-luminescent silver cluster with the molecular formula, Ag11(SG)7 (SG: glutathionate) via reduction of silver ions by sodium borohydride in the presence of the tripeptide, glutathione (GSH). The as-prepared cluster shows prominent absorption features at 485 and 625 nm in its UV-vis absorption spectrum. Aging of the as-prepared cluster solution led to the disappearance of the 625 nm peak, followed by broadening of the 485 nm peak to give three maxima at ?487, 437, and 393 nm in its absorption spectrum. These peaks remain unchanged even after polyacrylamide gel electrophoresis (PAGE), where a single band was observed confirming high purity…