Showing papers on "HOMO/LUMO published in 2003"
TL;DR: In this article, the density functional theory was applied to representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, using density functional analysis.
Abstract: Representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, have been studied by using density functional theory. The calculations ...
1,061 citations
TL;DR: A single-electron transistor where the electronic levels of a single π-conjugated molecule in several distinct charged states control the transport properties is described, leading to a very significant reduction of the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.
Abstract: A combination of classical Coulomb charging, electronic level spacings, spin, and vibrational modes determines the single-electron transfer reactions through nanoscale systems connected to external electrodes by tunnelling barriers1. Coulomb charging effects have been shown to dominate such transport in semiconductor quantum dots2, metallic3 and semiconducting4 nanoparticles, carbon nanotubes5,6, and single molecules7,8,9. Recently, transport has been shown to be also influenced by spin—through the Kondo effect—for both nanotubes10 and single molecules8,9, as well as by vibrational fine structure7,11. Here we describe a single-electron transistor where the electronic levels of a single π-conjugated molecule in several distinct charged states control the transport properties. The molecular electronic levels extracted from the single-electron-transistor measurements are strongly perturbed compared to those of the molecule in solution, leading to a very significant reduction of the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. We suggest, and verify by simple model calculations, that this surprising effect could be caused by image charges generated in the source and drain electrodes resulting in a strong localization of the charges on the molecule.
799 citations
TL;DR: In this paper, the authors present a series of microscopic studies of electrical transport through individual molecules with metallic contacts, and analyze the device characteristics in terms of the charge and potential response of these atomic groups to the perturbation induced by the metal-molecule coupling and the applied bias voltage, which are modeled using a first-principles based self-consistent matrix Green's function (SCMGF) method.
Abstract: We present the first in a series of microscopic studies of electrical transport through individual molecules with metallic contacts. We view the molecules as ``heterostructures'' composed of chemically well-defined atomic groups, and analyze the device characteristics in terms of the charge and potential response of these atomic groups to the perturbation induced by the metal-molecule coupling and the applied bias voltage, which are modeled using a first-principles based self-consistent matrix Green's function (SCMGF) method. As the first example, we examine the devices formed by attaching two benzene-based molecular radicals---phenyl dithiol (PDT) and biphenyl dithiol (BPD)---symmetrically onto two semi-infinite gold electrodes through the end sulfur atoms. We find that both molecules acquire a fractional number of electrons with similar magnitude and spatial distribution upon contact with the electrodes. The charge transfer creates a potential barrier at the metal-molecule interface that modifies significantly the frontier molecular states depending on the corresponding electron density distribution. For both molecules, the metal Fermi level is found to lie closer to the highest-occupied-molecular-orbital (HOMO) than to the lowest-unoccupied-molecular-orbital (LUMO). Transmission in the HOMO-LUMO gap for both molecules is due to the metal-induced gap states arising from the hybridization of the metal surface states with the occupied molecular states. Applying a finite bias voltage leads to only minor net charge injection due to the symmetric device structure assumed in this work. But as current flows, the electrons within the molecular junction redistribute substantially, with resistivity dipoles developing in the vicinity of potential barriers. Only the delocalized $\ensuremath{\pi}$ electrons in the benzene ring can effectively screen the applied electric field. For the PDT molecule, the majority of the bias voltage drops at the metal-molecule interface. But for the BPD molecule, a significant amount of the voltage also drops in the molecule core. The field-induced modification of the molecular states (the static Stark effect) becomes significant as the bias voltage increases beyond the linear-transport region. A bias-induced reduction of the HOMO-LUMO gap is observed for both molecules at large bias. The Stark effect is found to be stronger for the BPD molecule than the PDT molecule despite the longer length of the former. For both molecules, the peaks in the conductance are due to electron transmission through the occupied rather than the unoccupied molecular states. The calculation is done at room temperature, and we find that the thermionic-emission contribution to the current-voltage characteristics of both molecules is negligible.
364 citations
TL;DR: In this paper, p-type doping of hole-transport organic molecular material N,N′-diphenyl-N,N, N′-bis(1-naphthyl)-1,1′-biphensyl-4,4-diamine (α-NPD) with tetrafluorotetracyanoquinodimethane (F4-TCNQ) using direct and inverse photoemission spectroscopy, contact potential difference measurements, and in situ currentvoltage (I-V) measurements
Abstract: We investigate p-type doping of the hole-transport organic molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) with tetrafluorotetracyanoquinodimethane (F4-TCNQ) using direct and inverse photoemission spectroscopy, contact potential difference measurements, and in situ current–voltage (I–V) measurements. The close match between the ionization energy of α-NPD and the electron affinity of F4-TCNQ leads to an efficient charge transfer between highest occupied molecular orbital of the host and lowest occupied molecular orbital of the dopant. The Fermi level moves down towards the valence states by 0.62 eV in the 0.5% doped film with respect to the undoped film, and a narrow space charge layer (∼60 A) forms at the interface with Au. Hole injection in the doped devices increases by several orders of magnitude due to tunneling through the depletion region. The large relaxation energy of the ionized α-NPD molecule limits the movement of the Fermi level and, ultimately, the hol...
296 citations
TL;DR: In this article, the difference between oxide and hydrogen passivation of small Si nanocrystals is explored by all-electron, hybrid functional DFT calculations with unrestricted geometry optimization, and the experimental observation that hydrogen-passivated Si nan-ocrystals luminesce in the blue whereas oxide-passivant Si-nan-ocrystal luminesces in the yellow-red.
Abstract: The difference between oxide and hydrogen passivation of small Si nanocrystals is explored by all-electron, hybrid functional DFT calculations with unrestricted geometry optimization. Oxide passivation lowers the band gap by about 2.4 eV for Si35 cores and by about 1.5 eV for Si66 cores. The oxide-passivated nanocrystals have optically forbidden, indirect-gap-type transitions whereas the hydrogen-passivated nanocrystals have optically allowed, direct-gap-type transitions. The HOMO and LUMO are delocalized in both species. This result explains the experimental observation that hydrogen-passivated Si nanocrystals luminesce in the blue whereas oxide-passivated Si nanocrystals luminesce in the yellow-red.
279 citations
TL;DR: The synthesis, properties, and electroluminescent device applications of a series of five new diphenylanthrazoline molecules 1a-1e are reported, demonstrating that they are promising n-type semiconductors for organic electronics.
Abstract: The synthesis, properties, and electroluminescent device applications of a series of five new diphenylanthrazoline molecules 1a−1e are reported. Compounds 1b, 1c, and 1d crystallized in the monoclinic system with the space groups P21/c, C2/c, and P21/c, respectively, revealing highly planar molecules. Diphenylanthrazolines 1a−1e have a formal reduction potential in the range −1.39 to −1.58 V (versus SCE) and estimated electron affinities (LUMO levels) of 2.90−3.10 eV. Compounds 1a−1e emit blue light with fluorescence quantum yields of 58−76% in dilute solution, whereas they emit yellow-green light as thin films. The diphenylanthrazoline molecules as the emissive layers in light-emitting diodes gave yellow light with a maximum brightness of 133 cd/m2 and an external quantum efficiency of up to 0.07% in ambient air. Bilayer light-emitting diodes using compounds 1a−1e as the electron-transport layer and poly(2-methoxy-5-(2‘-ethyl-hexyloxy)-1,4-phenylene vinylene) as the emissive layer had a maximum external ...
273 citations
TL;DR: In this article, the authors observed red shifts of emission peaks of the absorptive adduct appear to depend on the energy level of the lowest unoccupied molecular orbital (LUMO) of the adsorbate, consistent with adsorption by a charge transfer interaction.
Abstract: Dye molecules (anthracene derivatives) are observed to strongly adsorb to single-walled carbon nanotubes (SWNTs). The adsorption coverage of anthracene molecules on SWNTs varied with the aromatic ring substituents. The observed red shifts of emission peaks of the absorptive adduct appear to depend on the energy level of the lowest unoccupied molecular orbital (LUMO) of the adsorbate, consistent with adsorption by a charge-transfer interaction, in which the SWNT is electron donor and anthracene is acceptor. The anthracene absorptive adducts can be displaced by adsorption of pyrene.
246 citations
TL;DR: The origin of the vanishing rectification for the investigated molecule is identified, and on the basis of this, parameters which are important for successful chemical engineering of DsigmaA rectifiers are suggested.
Abstract: We present state-of-the-art first principles calculations for the IV characteristics of a donor-insulator-acceptor (DsigmaA) type molecular diode anchored with thiolate bonds to two gold electrodes. We find very poor diode characteristics of the device, and the origin of this is analyzed in terms of the bias-dependent electronic structure. At zero bias, the highest occupied molecular orbital (HOMO) is confined to the D part, and the lowest unoccupied molecular orbital (LUMO) is confined to the A part, while at 3.8 V the two states align, and this gives rise to an increasing current. The latter is a potential mechanism for rectification and may in some cases lead to favorable diode characteristics. We identify the origin of the vanishing rectification for the investigated molecule, and on the basis of this we suggest parameters which are important for successful chemical engineering of DsigmaA rectifiers.
230 citations
TL;DR: In this paper, it is argued that this error is related to the ''gap'' problem of present density functionals and might be cured by functionals that increase the HOMO-LUMO separation.
Abstract: Semilocal density functionals predict that the stable adsorption site of carbon monoxide (CO) on Pt(111) is the hollow fcc site, in disagreement with experimental studies which indicate that CO adsorbs on the top site at low coverage. This site preference depends on a subtle balance between the interaction of the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) with the metal substrate. Local and semilocal functionals seem to overestimate the interaction of the LUMO with the metal substrate, in turn favoring the wrong site. It is argued that this error is related to the ``gap'' problem of present density functionals and might be cured by functionals that increase the HOMO-LUMO separation.
223 citations
TL;DR: Scanning tunneling spectroscopy is used to spatially map the energy-resolved local density of states of individual C60 molecules on the Ag(100) surface, revealing new details of the spatially inhomogeneous C60 local electronic structure.
Abstract: We have used scanning tunneling spectroscopy to spatially map the energy-resolved local density of states of individual C60 molecules on the Ag(100) surface. Spectral maps were obtained for molecular states derived from the C60 HOMO, LUMO, and LUMO+1 orbitals, revealing new details of the spatially inhomogeneous C60 local electronic structure. Spatial inhomogeneities are explained using ab initio pseudopotential density functional calculations. These calculations emphasize the need for explicitly including the C60-Ag interaction and STM tip trajectory to understand the observed C60 local electronic structure.
191 citations
TL;DR: In this article, the authors investigated the effect on molecular transport due to the different structural aspects of metal-molecule interfaces, and found that the dependence of the conductance on the metal molecule interface structure is determined by the competition between the modified metal molescule coupling and the corresponding modified energy level lineup at the molecular junction.
Abstract: We investigate the effect on molecular transport due to the different structural aspects of metal-molecule interfaces. The example system chosen is the prototypical molecular device formed by sandwiching the phenyl dithiolate molecule (PDT) between two gold electrodes with different metal-molecule distances, atomic structure at the metallic surface, molecular adsorption geometry, and with an additional hydrogen end atom. We find the dependence of the conductance on the metal-molecule interface structure is determined by the competition between the modified metal-molecule coupling and the corresponding modified energy level lineup at the molecular junction. Due to the close proximity of the highest occupied molecular orbital (HOMO) of the isolated PDT molecule to the gold Fermi level, this leads to the counterintuitive increase of conductance with increasing top-metal\char21{}molecule distance that decreases only after the energy level line up saturates to that of the molecule chemisorbed on the substrate. We find that the effect on molecular transport from adding an apex atom onto the surface of a semi-infinite electrode is similar to that from increasing the metal-molecule distance. The similarity is reflected in both the charge and potential response of the molecular junction and consequently also in the nonlinear transport characteristics. Changing the molecular adsorption geometry from a threefold to a top configuration leads to slightly favorable energy level lineup for the molecular junction at equilibrium and consequently larger conductance, but the overall transport characteristics remain qualitatively the same. The presence of an additional hydrogen end atom at the top-metal\char21{}molecule contact substantially affects the electronic processes in the molecular junction due to the different nature of the molecular orbitals involved and the asymmetric device structure, which leads to reduced conductance and current. The results of the detailed microscopic calculation can all be understood qualitatively from the equilibrium energy level lineup and the knowledge of the voltage drop across the molecular junction at finite bias voltages.
TL;DR: In this article, Nd3+-doped TiO2 nanoparticles were synthesized by chemical vapor deposition in order to tailor the band gap of the nanoparticles, which was measured by ultraviolet-visible light absorption experiments.
Abstract: Undoped and Nd3+-doped TiO2 nanoparticles were synthesized by chemical vapor deposition in order to tailor the band gap of TiO2. The doping reduced the band gap. The band gap was measured by ultraviolet-visible light absorption experiments and by near-edge x-ray absorption fine structure. The maximum band gap reduction was 0.55 eV for 1.5 at. % Nd-doped TiO2 nanoparticles. Density functional theory calculations using the generalized gradient approximation with the linearized augmented plane wave method were used to interpret the band gap narrowing. The band gap narrowing was primarily attributed to the substitutional Nd3+ ions which introduced electron states into the band gap of TiO2 to form the new lowest unoccupied molecular orbital.
TL;DR: In this article, the electronic properties of differently fluorinated copper phthalocyanines (CuPC, CuPCF4, and CuPCf16) were compared using x-ray and ultraviolet spectroscopy.
Abstract: We compare the electronic structure of differently fluorinated copper phthalocyanines (CuPC, CuPCF4, and CuPCF16) using x-ray photoemission spectroscopy and valence-band ultraviolet photoemission spectroscopy. Whereas the ionization potential (IP) is increased by more than 1 eV as a function of the degree of fluorination, further electronic properties such as the optical gap or the composition of the highest occupied molecular orbital and lowest unoccupied molecular orbital remain nearly unchanged. This fact renders these compounds an ideal tool for the investigation of the influence of the IP on the interface properties. At the interface to gold, besides interface dipoles we observe both downward and upward band bending. These phenomena depend clearly on the IP of the phthalocyanines.
TL;DR: In this article, a large anisotropy of the hole and electron effective masses within the molecular planes is found and the band dispersion of the HOMO and the LUMO is analyzed with the help of a tight-binding (TB) fit.
TL;DR: The energy partitioning analysis of Cl(3)B[bond]NH(3).
Abstract: Geometries and bond dissociation energies of the complexes Cl3B−NH3 and F3B−NH3 have been calculated using DFT (PW91) and ab initio methods at the MP2 and CCSD(T) levels using large basis sets. The calculations give a larger bond dissociation energy for Cl3B−NH3 than for F3B−NH3. Calculations of the deformation energy of the bonded fragments reveal that the distortion of BCl3 and BF3 from the equilibrium geometry to the pyramidal form in the complexes requires nearly the same energy. The higher Lewis acid strength of BCl3 in X3B−NH3 compared with BF3 is an intrinsic property of the molecule. The energy partitioning analysis of Cl3B−NH3 and F3B−NH3 shows that the stronger bond in the former complex comes from enhanced covalent interactions between the Lewis acid and the Lewis base which can be explained with the energetically lower lying LUMO of BCl3.
TL;DR: The band structures of the silver halides AgX, X = F, Cl, and Br are very similar as discussed by the authors, but their photochemical and chemical properties are very different, and they are, to a large extent, controlled by surface properties (states) and by the secondary processes of the halides.
Abstract: The band structures of the silver halides AgX, X = F, Cl, and Br, which all form face centred cubic crystals are very similar. Especially the nature of the HOMO/LUMO region is similar. They differ somewhat in the band gap, in the dispersion of some bands and in the splitting between the 4d (Ag) and the np (X) levels and the ionicity which both are most pronounced in AgF. But their photochemical and chemical properties are very different. They are, to a large extent, controlled by surface properties (states) and by the secondary processes of the halides.
TL;DR: In this article, density functional theory (DFT) calculations are performed to determine the accurate first static hyperpolarizability ( β ) of nitrogen bound low valent (M 0 ) group six metal carbonyls representing the class of chromophores displaying weak coupling between donor and acceptor.
Abstract: Density Functional Theory (DFT) calculations are performed to determine the accurate first static hyperpolarizability ( β ) of nitrogen bound low valent (M 0 ) group six metal carbonyls representing the class of chromophores displaying weak coupling between donor and acceptor. The nonlinear optical (NLO) response of this class of second-order NLO metal complexes is dominated by metal-to-ligand charge transfer excitations involving low lying, filled metal-carbonyl based orbitals and empty π ∗ orbitals of nitrogen bound ligand. We report novel organometallic systems with high β values. The full geometry optimizations of chromium and tungsten carbonyls were performed using DFT method at B3LYP/LanL2DZ level of theory using gaussian 98W. The calculations of the first hyperpolarizability ( β ) of these complexes were performed at the same level of theory. The calculated values of β were compared with available data in the literature. To understand the variation of β in these complexes, we examined the molecular HOMO and molecular LUMO generated via gaussian 98W. The present study concludes that these organometallic systems may contribute to the development of NLO materials.
TL;DR: The electron transmission and dissociative electron attachment (DEA) spectra of chloroalkyl ethene and ethyne derivatives are reported in this paper, where the virtual orbital energies for the optimised geometries of the neutral states of these molecules and other related π-systems are evaluated.
Abstract: The electron transmission (ET) and dissociative electron attachment (DEA) spectra of chloroalkyl ethene and ethyne derivatives are reported. B3LYP/6-31G* calculations are employed to evaluate the virtual orbital energies for the optimised geometries of the neutral states of these molecules and other related π-systems. The calculated π* MO energies correlate linearly with the energies of electron attachment to the π* LUMO measured in the ET spectra with a correlation coefficient of 0.993. The vertical attachment energies supplied by B3LYP/6-311+G** calculations, where the basis set includes diffuse functions, are often in significant disagreement with experiment, describing the singly occupied MO of the lowest-lying anion state as a diffuse σ* MO rather than a valence π* MO. The relative Cl− anion currents measured in the DEA spectra of the present molecular systems are compared to those previously found in benzene analogues. The Cl− yield reflects the efficiency of intramolecular electron transfer from the π-system (where the extra electron is first trapped) to the remote chlorine atom. Replacement of a carbon atom with a silicon atom in the intermediate saturated alkyl chain causes a notable increase of the Cl− current, ascribed to the lower energy of the empty σ*Si–C MOs and consequent greater ability to promote through-bond coupling between the π* and σ*C–Cl MOs. Comparison between the corresponding benzene, ethene and ethyne derivatives reveals that the Cl− current is also significantly influenced by the nature of the π-functional group, in agreement with the inverse dependence on energy of the lifetime of the temporary π* anion state.
TL;DR: In this paper, a novel heterobimetallic alkynyl-bridged complex, [Re(bpy)(CO)3(C⋮CC6H4C)µFe(C5Me5)(dppe)][PF6], was synthesized and its X-ray crystal structures determined.
Abstract: A novel heterobimetallic alkynyl-bridged complex, [Re(bpy)(CO)3(C⋮CC6H4C⋮C)Fe(C5Me5)(dppe)], 1, and its oxidized species, [Re(bpy)(CO)3(C⋮CC6H4C⋮C)Fe(C5Me5)(dppe)][PF6], 2, have been synthesized and their X-ray crystal structures determined. A related vinylidene complex, [Re(bpy)(CO)3(C⋮CC6H4(H)CC)Fe(C5Me5)(dppe)][PF6], 3, has also been synthesized and characterized. The cyclic voltammogram of 1 shows a quasireversible reduction couple at −1.49 V (vs SCE), a fully reversible oxidation at −0.19 V, and a quasireversible oxidation at +0.88 V. In accord with the electrochemical results, density-functional theory calculations on the hydrogen-substituted model complex Re(bpy)(CO)3(C⋮CC6H4C⋮C)Fe(C5H5)(dHpe) (Cp = C5H5, dHpe = H2P(CH2)2PH2) (1-H) show that the LUMO is mainly bipyridine ligand π* in character while the HOMO is largely iron(II) d orbital in character. The electronic absorption spectrum of 1 shows low-energy absorption at 390 nm with a 420 nm shoulder in CH2Cl2, while that of 2 exhibits less intense...
TL;DR: Spectroscopic, computational, redox, and photochemical behavior of a self-assembled donor-acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand was investigated in toluene and o-dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile.
Abstract: Spectroscopic, computational, redox, and photochemical behavior of a self-assembled donor-acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand (2-(4′-imidazolylphenyl)fulleropyrrolidine, C60Im) was investigated in noncoordinating solvents, toluene and o-dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile. The optical absorption and ab initio B3 LYP/3–21G(*) computational studies revealed self-assembled supramolecular 1:1 dyad formation between the ZnNc and C60Im entities. In the optimized structure, the HOMO was found to be entirely located on the ZnNc entity while the LUMO was found to be entirely on the fullerene entity. Cyclic voltammetry studies of the dyad exhibited a total of seven one-electron redox processes in o-dichlorobenzene, with 0.1 M tetrabutylammonium perchlorate. The excited-state electron-transfer processes were monitored by both optical-emission and transient-absorption techniques. Direct evidence for the radical-ion-pair (C60Im.−:ZnNc.+) formation was obtained from picosecond transient-absorption spectral studies, which indicated charge separation from the singlet-excited ZnNc to the C60Im moiety. The calculated rates of charge separation and charge recombination were 1.4×1010 s−1and 5.3×107 s−1in toluene and 8.9×109 s−1and 9.2×107 s−1in o-dichlorobenzene, respectively. In benzonitrile, intermolecular electron transfer from the excited triplet state of ZnNc to C60Im occurs and the second-order rate constant (kqtriplet) for this quenching process was 5.3×108 M−1 s−1.
TL;DR: In this paper, the results of the quantum calculations and corrosion rate measurements, respectively, were applied to elucidate the chestnut tannin inhibitory action on low-carbon steel corrosion in 2 M HCl.
Abstract: The frontier orbital theory and the inhibitor adsorption theory were applied to the results of the quantum calculations and corrosion rate measurements, respectively, in order to elucidate the chestnut tannin inhibitory action on low-carbon steel corrosion in 2 M HCl. Nine major constituents of chestnut tannin—vescalagin, castalagin, vescalin, castalin, gallic acid, ellagic acid, mono-, di- and trigalloylglucose—were modeled by molecular mechanics, molecular dynamics and semiempirical quantum NDDO method with PM3 parametrization. The geometrical structure, the energy of the highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO), the HOMO–LUMO energy gap, the distribution of the HOMO electron density and the magnitude and direction of the dipole moment were calculated for each molecule. Molecular reactivity that is related to its adsorbability by the HSAB principle, was studied by calculating the absolute electronegativity, absolute hardness and the electron donating ability. The quantum calculations results, coupled with those derived from the adsorption theory, gave a consistent picture of the investigated corrosion system.
TL;DR: Density functional theory molecular orbital calculations show that the LUMO of the bipyridine phosphonated ligands is at higher energy than the corresponding dicarboxylate complexes and that the thiocyanato ligands are not simple spectator ligands, but are also involved in transitions from PiRu-NCS to Pibpy that extend the absorbance of the dye in the low energy part of the absorption spectrum.
Abstract: The preparation and the properties of several ruthenium complexes of the general formula cis-RuL2X2 with L = 2,2‘-bipyridine-4,4‘-bisphosphonic acid, L‘ = 2,2‘-bipyridine-5,5‘-bisphosphonic acid, and X = Cl, CN, or NCS are reported. The synthesis of these complexes relies on the preparation of the key intermediates cis-Ru(bipyridinebis(diethyl ester phosphonate))Cl2. The ground-state second pKa values of the thiocyanato complexes were determined and are 6.0 and 6.1 for cis-RuL2(NCS)2 and for cis-RuL‘2(NCS)2, respectively. For these species, 13C NMR and IR demonstrate that the thiocyanato ligands are bound to Ru via the N atom. The new complexes exhibit a blue-shifted electronic absorption spectrum with respect to the analogous complexes containing carboxylic acid groups. Density functional theory molecular orbital calculations show that the LUMO of the bipyridine phosphonated ligands is at higher energy than the corresponding dicarboxylate complexes and that the thiocyanato ligands are not simple spectato...
TL;DR: A field-effect-transistor operation of dimetallofullerene La2@C80 with the icosahedral cage symmetry with n-type behavior indicates an occurrence of carrier conduction through encapsulated La ions, suggesting an intermolecular hopping mechanism.
Abstract: We first demonstrate a field-effect-transistor operation of dimetallofullerene La2@C80 with the icosahedral cage symmetry. The thin-film device showed an n-type behavior with a mobility of 1.1 × 10-4 cm2/V s at room temperature under high vacuum. Taking the nature of LUMO into account, the n-type behavior indicates an occurrence of carrier conduction through encapsulated La ions. The low mobility, suggesting an intermolecular hopping mechanism, is ascribed to the intrinsic and extrinsic reasons, which are discussed in the text.
TL;DR: A quantitative structure-activity relationship (QSAR) for structurally diverse phenols, nine alkylphenols with only oneAlkyl group, four hydroxyl biphenyls, bisphenol A and four natural and man-made estrogens was established by applying a quantum chemical modeling method.
TL;DR: In this article, a well-oriented perylene-3,4,9,10,tetracarboxylic acid-dianhydride multilayer was studied by angle-resolved ultraviolet photoemission spectroscopy using synchrotron radiation.
Abstract: The electronic structure of a well-oriented perylene-3,4,9,10-tetracarboxylic acid-dianhydride multilayer prepared on ${\mathrm{MoS}}_{2}$ single crystal surface were studied by angle-resolved ultraviolet photoemission spectroscopy using synchrotron radiation. From the photon energy dependence of normal emission spectra, we observed an intermolecular energy-band dispersion of about 0.2 eV for the highest occupied molecular orbital (HOMO) band of single $\ensuremath{\pi}$ character. The observed energy-band dispersion showed a cosine curve, which originates from the intermolecular $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ interaction. Analyses using the tight-binding model gave that the transfer integral of about 0.05 eV for the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ interaction, the effective mass of HOMO hole ${m}_{h}^{*}{=5.28m}_{0},$ and the hole mobility ${\ensuremath{\mu}}_{h}g3.8{\mathrm{cm}}^{2}/\mathrm{V}\mathrm{}\mathrm{s}.$ This is the first observation of the intermolecular energy-band dispersion of a conventional single-component organic semiconductor only with the weak intermolecular van der Waals interaction.
TL;DR: In this article, a model for the process of the growth of carbon nanotubes obtained by chemical vapour deposition in the presence of transition metal nanoparticles (Me-NPs) which act as a catalyst is presented.
Abstract: We present a model for the process of the growth of carbon nanotubes (CNTs) obtained by chemical vapour deposition in the presence of transition metal nanoparticles (Me-NPs) which act as a catalyst. We have deduced that the growth of a CNT occurs in the presence of two forces: (i) a viscous force, due to the surrounding hot gas, which opposes and slows down the growth of the CNT, and (ii) an extrusive force that causes the growth and that in the steady-state stage of the growth is completely balanced by the viscous force. We believe that it is the great decrease in free energy in the assembling reaction that occurs at the interface of the Me-NP catalyst that causes the extrusive force for the growth of a CNT. Moreover, the process of chemisorption of a C2 fragment, through the interaction of the C2?? ?system with the 3d metal orbitals, has been considered as well as the coordination action of the Fe, Ni and Co metal surfaces. The structural properties of the Fe, Co and Ni surfaces show that the (1, ? 1, 0) planes of Fe and the (1, 1, 1) planes of Co and Ni exhibit the symmetry and distances required to overlap with the lattice of a graphene sheet. This gives us information about the coordination mechanism responsible for assembling the CNTs. In fact, we show that it is possible to cleave an Me-NP in such a way as to match the correct symmetry and dimension of the armchair structure of a single-walled nanotube. The mechanism of C2 addition at the edge of the growing CNT has also been considered in relation to the highest occupied molecular orbital?lowest unoccupied molecular orbital (HOMO?LUMO) symmetry. We demonstrate that the action of d orbitals of the metal atoms forming the Me-NP makes possible the thermally forbidden reaction, which involves the C2?? system.
TL;DR: [Ph-Ge9-SbPh2](2-) is the first ogranically functionalized deltahedral Zintl ion, i.e., a deltahedral ion with a direct carbon-cluster covalent bond, that can exists without the substituents as well.
Abstract: The type of the reactions of addition of exo-bonded groups to deltahedral Zintl ions such as Ge9n- has been established as addition of anionic nucleophiles. Various nucleophiles such as Ph2Bi-, Ph2Sb-, Ph- interact with the relatively low-lying LUMO of Ge92- and/or the half filled HOMO of Ge93- and bond to the clusters. The title anions, characterized in their (K-crypt) salts where crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]-hexacosane, and the previously characterized [Ph2Sb−Ge9−SbPh2]2- are made by a reaction of K4Ge9 with SbPh3 in ethylenediamine. [Ph−Ge9−SbPh2]2- is the first ogranically functionalized deltahedral Zintl ion, i.e., a deltahedral ion with a direct carbon-cluster covalent bond, that can exists without the substituents as well. The Ge9 clusters resemble tricapped trigonal prisms with one elongated edge (one of the three edges parallel to the pseudo 3-fold axis). The two substituents are always bonded to the vertexes of such an elongated edge. The same is true for the intercl...
TL;DR: The stereocontrolled synthesis of oligodeoxyribonucleoside phosphorothioates (PS-ODNs) using nucleoside 3'-O-oxazaphospholidine derivatives as monomer units is described, finding that the diastereoselectivity of the reaction depended on the structure of the enantiopure 1,2-amino alcohol, the reaction temperature, and the amine used as a scavenger of HCl.
Abstract: The stereocontrolled synthesis of oligodeoxyribonucleoside phosphorothioates (PS-ODNs) using nucleoside 3‘-O-oxazaphospholidine derivatives as monomer units is described. 2-Chloro-1,3,2-oxazaphospholidine derivatives were prepared from six kinds of enantiopure 1,2-amino alcohols and used for the phosphitylation reactions of 5‘-O-protected nucleosides. A detailed study of these reactions revealed that the diastereoselectivity of the reaction depended on the structure of the enantiopure 1,2-amino alcohol, the reaction temperature, and the amine used as a scavenger of HCl. In addition, ab initio molecular orbital calculations for the 2-chlorooxazaphospholidine derivatives were carried out to elucidate the mechanism of these diastereoselective phosphitylation reactions. The LUMO of the 2-chloro-5-phenyloxazaphospholidine derivatives on the phosphorus atom was found to be almost orthogonal to the P−Cl bond. This LUMO may be involved in the phosphitylation reactions with predominant retention of the P-configura...
TL;DR: In this article, the piperazine derivatives behave as corrosion inhibitor for steel in presence of KI in sulphuric acid of different normality in gas and aqueous phases using semi-empirical methods (i.e. MINDO/3, MNDO, PM3 and AM1).
Abstract: Computational calculations on some piperazine derivatives those behave as corrosion inhibitor for steel in presence of KI in sulphuric acid of different normality in gas and aqueous phases using semi-empirical methods (i.e. MINDO/3, MNDO, PM3 and AM1) were carried out to search possible correlation between corrosion rates and geometric structures, charges on nitrogen atoms, highest occupied molecular energy level ( E HOMO ), lowest unoccupied molecular energy level ( E LUMO ), the differences between highest occupied molecular orbital energies and lowest unoccupied molecular orbital energies ( E HOMO − E LUMO ) were carried out. The obtained correlations were satisfactory.