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Coupling Matrix Element (coupling + matrix_element)
Selected AbstractsMulticomponent Supramolecular Devices: Synthesis, Optical, and Electronic Properties of Bridged Bis-dirhodium and -diruthenium Complexes,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2006Anne Petitjean Abstract Four ruthenium- and rhodium-based metal,metal-bonded multicomponent systems have been synthesized, and their absorption, redox, spectroelectrochemical and structural properties have been studied. The absorption spectra of the four bis-dimetallic compounds M2LM2, where L is a bridging ligand and M is rhodium or ruthenium, exhibit very strong bands in the UV, visible and, for the diruthenium species, near-IR region. The low-energy absorption bands are assigned to charge-transfer transitions involving a metal,metal bonding orbital as the donor and an orbital centered on the bis-tetradentate aromatic ligands as the acceptor (metal,metal to ligand charge transfer, M2LCT). Each compound exhibits reversible bridging-ligand-centered reductions at mild potentials and several reversible oxidation processes. The oxidation signals of the two equivalent dimetallic centers of each bis-dimetallic compound are split, with the splitting , a measure of the electronic coupling , depending on both the metal and bridging ligand. The mixed-valence species of the dirhodium species was investigated, and the electronic coupling matrix element calculated from the experimental intervalence band parameters for one of them (86 cm,1) indicates a significant inter-component electronic interaction which compares well with good electron conducting anionic bridges such as cyanides. Although none of these compounds is luminescent, the M2LCT excited state of one of the bis-dirhodium complexes is relatively long-lived (about 6 ,s) in degassed acetonitrile at room temperature. The results presented here are promising for the development of linear poly-dimetallic complexes built on longer naphthyridine-based strands, with significant long-range electronic coupling and molecular-wire-like behavior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The relationship between adsorption energies of methyl on metals and the metallic electronic properties: A first-principles DFT studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2005Gui-Chang Wang Abstract A theoretical study of CH3 adsorbed on the (111) surface of some transition and noble metal surfaces M (M = Cu, Ni, Rh, Pt, Pd, Ag, Au) and on the Fe(100) is presented. We find that the hollow site is preferred more than the top one for Fe, Ni, Rh, and Cu, but it is the other way for Pt, Pd, Au, and Ag. In addition, a good linear relationship was observed between the chemisorption energy and d-band center for Group VIII metals or the square of the coupling matrix element for Group IB metals at the hollow site. Interestingly, with a detailed comparison of the adsorption energies at the top and hollow sites, we find that the adsorption energies among each group are very similar on the top site, which supports the theoretical model of Hammer and Nørskov that the coupling between the HOMO of adsorbate and sp states of the metal is dominant and almost equal, and that the second coupling to the d-band contributes less but reflects the change of the adsorption energy. It confirms that the coupling to the d band comprises two opposite factors, that is, the d-band center was attractive and the square of the coupling matrix element was repulsive, such that the contributions from the two factors can counteract each other at the top site. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 871,878, 2005 [source] Kinetic, Thermodynamic, and Mechanistic Patterns for Free (Unbound) Cytochrome c at Au/SAM Junctions: Impact of Electronic Coupling, Hydrostatic Pressure, and Stabilizing/Denaturing AdditivesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2006Dimitri E. Khoshtariya Prof. Dr. Abstract Combined kinetic (electrochemical) and thermodynamic (calorimetric) investigations were performed for an unbound (intact native-like) cytochrome c (CytC) freely diffusing to and from gold electrodes modified by hydroxyl-terminated self-assembled monolayer films (SAMs), under a unique broad range of experimental conditions. Our approach included: 1) fine-tuning of the charge-transfer (CT) distance by using the extended set of Au-deposited hydroxyl-terminated alkanethiol SAMs [-S-(CH2)n -OH] of variable thickness (n=2, 3, 4, 6, 11); 2) application of a high-pressure (up to 150,MPa) kinetic strategy toward the representative Au/SAM/CytC assemblies (n=3, 4, 6); 3) complementary electrochemical and microcalorimetric studies on the impact of some stabilizing and denaturing additives. We report for the first time a mechanistic changeover detected for "free" CytC by three independent kinetic methods, manifested through 1) the abrupt change in the dependence of the shape of the electron exchange standard rate constant (ko) versus the SAM thickness (resulting in a variation of estimated actual CT range within ca. 15 to 25 Å including ca. 11 Å of an "effective" heme-to-,-hydroxyl distance). The corresponding values of the electronic coupling matrix element vary within the range from ca. 3 to 0.02 cm,1; 2) the change in activation volume from +6.7 (n=3), to ,0 (n=4), and ,5.5 (n=6) cm3,mol,1 (disclosing at n=3 a direct pressure effect on the protein's internal viscosity); 3) a "full" Kramers-type viscosity dependence for ko at n=2 and 3 (demonstrating control of an intraglobular friction through the external dynamic properties), and its gradual transformation to the viscosity independent (nonadiabatic) regime at n=6 and 11. Multilateral cross-testing of "free" CytC in a native-like, glucose-stabilized and urea-destabilized (molten-globule-like) states revealed novel intrinsic links between local/global structural and functional characteristics. Importantly, our results on the high-pressure and solution-viscosity effects, together with matching literature data, strongly support the concept of "dynamic slaving", which implies that fluctuations involving "small" solution components control the proteins' intrinsic dynamics and function in a highly cooperative manner as far as CT processes under adiabatic conditions are concerned. [source] Theoretical investigation of charge transfer excitation and charge recombination in acenaphthylene,tetracyanoethylene complexINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2003Hai-Bo Yi Abstract Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge-balanced electron donor,acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor,acceptor complex was obtained by the second-order Møller,Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor,acceptor complex in this work reveals that the S1 and S2 states of the electron donor,acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S0 , S1 and S0 , S2 transitions arise from ,,,* excitations. The charge recombination in the ion pair complex will produce the charge-balanced ground state or excited triplet state. According to the generalized Mulliken,Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2-dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23,35, 2003 [source] | ||||||||||