Search results for "Localized"
showing 10 items of 297 documents
Coherent Electronic Coupling versus Localization in Individual Molecular Dimers
2004
International audience; The electronic excitation transfer and coherent electronic coupling strength were investigated in molecular dimers by spectrally resolved confocal fluorescence spectroscopy. The direct probe of electronic coupling strength distribution was possible due to static disorder in polymer host by single molecule measurements. The dimers with delocalized excitation were also found in comparison to emission originated from localized states. The delocalized and localized state transitions were observed for dimers which were attributed to structural fluctuations of guest-host system.
Positron Annihilation in Alkali Halides at Low Temperatures
1986
We report on low-temperature positron studies for pure, single crystals of the alkali halides KCl, NaCl and NaF. Strong temperature dependences are observed in the lifetime and angular correlation measurements in the temperature range 10–300 K. Delocalized para-positronium is observed at low temperatures in the three crystals. The broadening, with rising temperature, of the narrow peak in the angular correlation curve can be accounted for by the self-trapping model of positronium. The results are discussed in the light of this model, in terms of positronium localization at imperfections and in terms of positron interactions with imperfections created in the spur of the positron. The increas…
Surface plasmon near-field imaging of very thin microstructured polymer layers.
2004
We report on the near-field imaging of microstructured polymer layers deposited on an homogeneous metal thin film on which a surface plasmon mode is excited. The microstructures in the polymer layers are designed by electron beam lithography, and the near-field imaging is performed with a photon scanning tunneling microscope (PSTM). We show that, despite their very small height, the microstructures can be conveniently imaged with a PSTM thanks to the field enhancement at the surface of the metal thin film supporting the surface plasmon. The influence of the illumination conditions on the contrast of the PSTM images is discussed. In particular, we show that both the field enhancement and the…
Electrochemical study of dinuclear ruthenium(II)—arene compounds: Electrogeneration of Ru(II)—Ru(I) species
1987
Abstract The preparation and characterization of Ru(II)—arene compounds [{RuCl2(p-cym)}2(μ-L-L)] where p-cym = p-MeC6H4CHMe2; and L-L = diphenylphosphinomethane (I), 1,1′-bisdiphenylphosphinoferrocene (II), pyrazine (III) and 4,4′-bipyridine (IV), are described. Electrochemical data for these compounds obtained by cyclic voltammetry and coulometry are reported. The electrochemical reduction of compounds I or II yields ruthenium(O) species. However, compounds III or IV containing ligands with delocalized Π orbitals undergo one-electron reduction. The ESR signal detected during the electrolysis of compounds III or IV is consistent with one delocalized electron through the whole dinuclear unit.
Dinuclear copper(II) complexes as testing ground for molecular magnetism theory
2019
Abstract A leitmotiv in the field of molecular magnetism is the study of the electron exchange (EE) magnetic interactions among distant metal centers through the corresponding bridging ligands in polynuclear coordination compounds. The present review provides a historical perspective on the use of dinuclear copper(II) complexes with either simple inorganic or extended organic bridging ligands as experimental and theoretical models for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the EE interaction across σ- and π-type orbital pathways. Particular focus is placed on the work by Professor Miguel Julve, outstanding researche…
Substituent and temperature controlled tautomerism: Multinuclear magnetic resonance, X-ray, and theoretical studies on 2-phenacylquinolines
2000
Proton-transfer equilibria in chloroform solution of twelve 2-phenacylquinolines were studied by 1H, 13C and 15N NMR spectroscopies. The (Z)-enaminone form stabilized by an intramolecular hydrogen bond was found to prevail in all cases. Electron-donating substituents in the phenacyl part of the molecule lead to an increase of the ketimine form (to 33% for p-NMe2). Variable temperature 1H NMR measurements show that higher temperatures have the same effect. The negative logarithm values of the equilibrium constant, pKT, were found to be linearly dependent on Hammett σ substituent constants. The pKTvs. temperature correlation also has a linear character. In general, strong electron-withdrawing…
Photoinduced switching of electrical properties in thin films of polar indandione type organic molecules
2006
The optically induced switching of organic materials with large dipole moments consisting of acceptor and donor groups bridged by a delocalized π-electron system is important for investigations of optoelectronic effects. To the contrary of azobenzene molecule, photoinduced change of dipole moment of indandione molecule does not need free volume in thin films. To modify the dipole moment and also to optimise properties of film formation, a number of novel indandione derivatives is investigated. Reversible switching of the surface potential of polymer films with incorporated or chemically attached indandione molecules is observed at irradiation in photoinduced intramolecular electron transfer…
Relation between resonance energy and substituent resonance effect inP-phenols
2005
Molecular geometries of phenol and its 17 p-substituted derivatives were optimized at the B3LYP/6–311 + G** level of theory. Three homodesmotic and three isodesmotic reaction schemes were used to estimate aromatic stabilization energies (ASE) and the substituent effect stabilization energy (SESE). Other descriptors of π-electron delocalization (HOMA and NICS, NICS(1) and NICS(1)zz) were also estimated. The SESE and ASE values correlated well with one another as well as with substituent constants. Much worse correlations with substituent constants were found for other aromaticity indices. The NICS(1)zz values are the most negative for unsubstituted phenol, indicating its highest aromaticity;…
Temperature, fluid content and rheology of localized ductile shear zones in subsolidus cooling plutons
2020
Temperature and fluid content are critical parameters that control rock rheology and strain localization in the continental crust. Here, we determine by thermodynamic modelling the urn:x-wiley:02634929:media:jmg12553:jmg12553-math-0004 of localized ductile shearing during cooling of three different granitoid plutons: the Rieserferner and the Adamello plutons in the Italian Alps, and the Lake Edison pluton in the Sierra Nevada—USA. Shear zones exploited precursor joints, associated veins and alteration zones. urn:x-wiley:02634929:media:jmg12553:jmg12553-math-0005 and P−T phase diagram sections were computed with Perple_X in the system MnO−Na2O−CaO −K2O−FeO−MgO−Al2O3−SiO2−H2O−Fe2O3. The phase…
Crystal structure of N′′-benzyl-N′′-[3-(benzyldimethylazaniumyl)propyl]-N,N,N′,N′-tetramethylguanidinium bis(tetraphenylborate)
2015
In the crystal structure of the title salt, C24H38N42+·2C24H20B−, the C—N bond lengths in the central CN3unit of the guanidinium ion are 1.3364 (13), 1.3407 (13) and 1.3539 (13) Å, indicating partial double-bond character. The central C atom is bonded to the three N atoms in a nearly ideal trigonal–planar geometry and the positive charge is delocalized in the CN3plane. The bonds between the N atoms and the terminal methyl groups of the guanidinium moiety and the four C—N bonds to the central N atom of the (benzyldimethylazaniumyl)propyl group have single-bond character. In the crystal, C—H...π interactions between the guanidinium H atoms and the phenyl C atoms of the tetraphenylborate ions …