Properties Of Electronic States Research Articles

Synthesis, structural characterization and spectroscopic properties of cobalt complexes with the 2,6-bis(8′-quinolinyl)pyridine ligand

Coordination of the 2,6-bis(8′-quinolinyl)pyridine (bqp) ligand to a cobalt (Co) core and its influence to electron spin and configuration on the structures and properties of the resulting complexes has been investigated. The homoleptic complexes Co(mer-bqp-κ3N,N′,N″)]2+ (1) and [Co(mer-bqp-κ3N,N′,N″)]3+ (2) were prepared and characterized. X-ray structure determinations of complexes 1 and 2 revealed twisted, near-octahedral arrangements relative to the cobalt center. The magnetic data for 1 is typical of those for distorted octahedral (i.e., D4h symmetry) high-spin d7 species despite the near-ideal octahedral coordination of the bqp ligand around the Co(II) core. Electronic spectra for 1 and 2 have been investigated and assigned. Both complexes exhibit intense π–π∗bqp ligand centered transitions in the UV region and low intensity mixed charge transfer transitions in the visible region. Neither complex strongly absorbs in visible spectral region. The electrochemistry of these compounds has been studied and compared to that of similar cobalt terpyridine compounds. A metal-centered Co2+/3+ redox wave and ligand-based reduction processes were observed for 1 and 2 in acetonitrile. The metal-centered redox potentials were reversible with potentials more positive than comparable cobalt-terpyridine complexes. Density functional theory (DFT) calculations of the electronic and ground state properties are in good agreement with the experimental data.

Synthesis of surface plasmon resonance (SPR) triggered Ag/TiO2 photocatalyst for degradation of endocrine disturbing compounds

Surface deposition of silver nanoparticles (Ag NPs) onto the 100% anatase titania (Ag/TiO2) for evolution of surface plasmon resonance (SPR) was achieved sustainably with the assistance of solar energy. The preparation resulted in Ag/TiO2 photocatalyst with varied Ag depositions (0.5wt%, 1.0wt%, 3.0wt% and 5.0wt%). All obtained photocatalysts were characterized for the evolution of SPR via crystalline phase analysis, morphology, lattice fringes, surface area and pore size characteristics, chemical composition with chemical and electronic state, Raman scattering, optical and photoluminescence properties. The deposition of synthesized Ag NPs exhibited high uniformity and homogeneity and laid pathway for effective utilization of the visible region of electromagnetic spectrum through SPR. The depositions also lead for suppressing recombination rates of electron–hole. The photocatalytic evaluation was carried out by adopting two different class of endocrine disturbing compound (EDC) i.e., amoxicillin (pharmaceutical) and 2,4-dichlorophenol (pesticide) excited with artificial visible light source. Ag/TiO2 with Ag>0.5wt% exhibited significant degradation efficiency for both amoxicillin and 2,4-dichlorophenol. Thus synthesized Ag/TiO2 revealed the implication of plasmonics on TiO2 for the enhanced visible light photocatalytic activity.

Ab initio MRCI+Q Investigations of Spectroscopic Properties of Several Low-lying Electronic States of S2+Cation

The complete active space self-consist field method followed by the internally contracted multireference configuration interaction method has been used to compute the potential energy curves of <TEX>$X^2\prod_g$</TEX>, <TEX>$a^4\prod_u$</TEX>, <TEX>$A^2\prod_u$</TEX>, <TEX>$b^4\sum_{g}^{-}$</TEX>, and <TEX>$B^2\sum_{g}^{-}$</TEX> states of <TEX>$S{_2}^+$</TEX> cation with large correlation-consistent basis sets. Utilizing the potential energy curves computed with different basis sets, the spectroscopic parameters of these states were evaluated. Finally, the transition dipole moment and the Franck-Condon factors of the transition from <TEX>$A^2\prod_u$</TEX> to <TEX>$X^2\prod_g$</TEX> were evaluated. The radiative lifetime of <TEX>$A^2\prod_u$</TEX> is calculated to be 887 ns, which is in good agreement with experimental value of <TEX>$805{\pm}10$</TEX> ns.

Study of Structural and Electronic Behavior of BeH2 as Hydrogen Storage Compound: An Ab Initio Approach

The quantum mechanical calculations based on density functional theory (DFT) have been performed to study ground state structural and electronic properties of BeH2 and along with doping of two (BeH2 + 2H) and four (BeH2 + 4H) hydrogen atoms. The generalized gradient approximation (GGA) has been employed for the exchange correlation energy. The most stable space group of BeH2 is Ibam. Its optimized equilibrium unit cell volume, bulk modulus and its first-order pressure derivative, and electronic properties have been obtained. Our predicted unit cell parameters for BeH2 a=9.2463 Å, b=4.2352 Å, and c=7.8464 Å are in very good agreement with the earlier reported experimental and theoretical results. The electronic band structure of BeH2 shows its behavior as an insulator. The stability of BeH2 along with doped hydrogen atoms increases, while the energy band gap decreases with the increase in number of doped hydrogen atoms. On these bases, we predict that BeH2 is a promising material for hydrogen storage.

Structure, Electronic States, and Anion-Binding Properties of Cyclo[4]naphthobipyrroles

Three octaalkyl-substituted cyclo[4]naphthobipyrroles, studied in solution in the form of their sulfates, reveal absorption and magnetic circular dichroism (MCD) spectra very similar to those of the parent cyclo[8]pyrrole. A unique feature of these systems is a strong absorption in the near IR region. The analysis of MCD patterns based on a perimeter model reveals a hard-chromophore character of cyclo[4]naphthobipyrroles, i.e., ΔHOMO ≪ ΔLUMO. Comparison of Raman spectra obtained for crystalline samples and solutions, combined with the analysis of absorption and MCD spectra based on quantum chemical calculations reveals that cyclo[4]naphthobipyrroles exist in solutions as undissociated sulfates of the doubly protonated forms.

Molybdenum–molybdenum quadruple bonds supported by 9,10-anthraquinone carboxylate ligands. Molecular, electronic, ground state and unusual photoexcited state properties

The preparation of trans-Mo2(TiPB)2(O2C-2-AnQ)2, I, and Mo2(DAniF)3(O2C-2-AnQ), II, where, O2C-2-AnQ = 9,10-anthraquinone-2-carboxylate, TiPB = 2,4,6-triisopropylbenzoate and DAniF = N,N′-di-(p-anisyl)formamidinate are described together with electronic structure calculations employing density functional theory on model compounds. Compounds I and II have been further characterized by 1H NMR spectroscopy, MALDI-TOF mass spectrometry, electrochemical studies, UV-vis-NIR and steady state emission spectroscopy, time-resolved (fs and ns) transient absorption and infrared spectroscopy. Compound II has been structurally characterized by a single crystal X-ray crystallography study. Both compounds show metal-to-ligand charge transfer transitions, 1MLCT, corresponding to Mo2 δ to L π* (L = O2C-2-AnQ) and have S1 states with relatively long lifetimes (τI ∼ 8 ps; τII ∼ 2 ps). Femtosecond time-resolved IR studies, fs-TRIR indicate that for I, despite its relatively small HOMO–LUMO gap, and II the negative charge in the S1 state resides on one anthraquinone carboxylate ligand. For II, fs-TRIR spectroscopy detects the Mo23δδ* state with τ ∼ 100 ns despite the presence of a lower energy 3MLCT state. This, together with earlier findings indicates a significant kinetic barrier to the interconversion of MLCT and Mo2 δδ* states.

Influence of CeO2 addition on the physicochemical and catalytic properties of Pd/TiO2 catalysts in CO oxidation

The influence of CeO2 addition on the formation of the microstructure, electronic state, and catalytic properties of Pd/TiO2 supported catalysts in CO oxidation were investigated. It was shown that, when Pd is supported on titanium dioxide modified with cerium dioxide, annealing at 500°C results in the formation of Pd/(CeO2-TiO2) catalysts with a nanocrystalline structure composed of incoherently intergrown fine anatase crystals and interblock boundaries in which palladium and cerium are stabilized. The higher catalytic activity of Pd/(CeO2-TiO2) catalysts compared to Pd/TiO2 catalysts is explained by the smaller size of Pd particles and the higher proportion of palladium in the Pdδ+ state.

Structural, Spectroscopic and Vibrational Properties for Low-Lying Electronic States of LiCl

A multireference configuration interaction (MRCI) study has been carried out on the LiCl molecule. The potential energy has been calculated over a wide range of internuclear separation for the 21 low-lying electronic states of the LiCl molecule dissociating into Li (2S, 2P, 3S)+Cl (2P). The (4)1Σ+, (3)1Π, 1–33Σ+, 1–33Π, 1,3Δ, 1,3Σ−, (5)1Σ+, (4)3Σ+, (4)1Π, (4)3Π excited states are studied for the first time in theory. Molecular spectroscopic constants (Re,De, ωe, ωeχe, Be and αe) have been derived for the 9 bound states (X1Σ+, (3)1Σ+, (2)3Σ+, 1,3Δ, 1,3Σ−, (4)1Π, (4)3Π) with a regular shape, and the spectroscopic constants of ground states X1Σ+ are in good agreement with available experimental and theoretical values. The relative differences between experimental values and our values for Re, De,ωe, ωeχe, Be and αe are 1.02%, 0.60%, 1.72%, 9.46%, 2.0%, and 0.75%, respectively. Moreover, vibrational levels of 9 bound states, which have not been investigated experimentally, are computed.

Excited State Charge Redistribution and Dynamics in the Donor-π-Acceptor Flavin Derivative ABFL

Chromophores containing a donor-π-acceptor (D-π-A) motif have been shown to exhibit many interesting photophysical properties. The lowest electronic transition of a flavin derivative containing this motif, azobenzylflavin (ABFL), has previously been shown to be highly sensitive to solvent environment and hydrogen bonding ligands. To better understand this sensitivity, we have investigated the excited state charge redistribution and dynamics of ABFL in a low-dielectric, non-hydrogen bonding solvent by steady-state Stark and femtosecond optical transient absorption spectroscopies. The Stark measurements reveal the difference dipole moment, Δμ01, between the ground and first excited states to be 22.3 ± 0.9 D. The direction of Δμ01 in the molecular frame was assigned with the aid of TD-DFT and finite field calculations, verifying the hypothesis that electron density moves from the diethylaniline donor to the flavin acceptor in the excited state. The magnitude of the difference dipole moment was used to estimate the hyperpolarizability of ABFL, β0 = 720 × 10(-30) esu. Subsequent excited state decay via charge recombination was shown to take place in a few picoseconds. The data was best fit to a kinetic model composed of a sub-picosecond internal conversion step from S2→S1, followed by a 5 ps decay to the ground state. A competing process involving formation of an additional long-lived state from S1 was also observed. Cyclic voltammetry shows one oxidation and two reduction waves and is completely reversible. This analysis lays the groundwork for developing new flavin dyads with the desired excited electronic state properties for applications such as nonlinear optical devices, molecular electronics applications, or dye-sensitized solar cells.

Multireference configuration interaction study on spectroscopic properties of low-lying electronic states of As2 molecule

The potential energy curves (PECs) of four electronic states (X1Σg+, e3Δu, a3Σu−, and d3Πg) of an As2 molecule are investigated employing the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in conjunction with the correlation-consistent aug-cc-pV5Z basis set. The effect on PECs by the relativistic correction is taken into account. The way to consider the relativistic correction is to employ the second-order Douglas-Kroll Hamiltonian approximation. The correction is made at the level of a cc-pV5Z basis set. The PECs of the electronic states involved are extrapolated to the complete basis set limit. With the PECs, the spectroscopic parameters (Te, Re, ωe, ωexe, ωeye, αe, βe, γe, and Be) of these electronic states are determined and compared in detail with those reported in the literature. Excellent agreement is found between the present results and the experimental data. The first 40 vibrational states are studied for each electronic state when the rotational quantum number J equals zero. In addition, the vibrational levels, inertial rotation and centrifugal distortion constants of d3Πg electronic state are reported which are in excellent agreement with the available measurements. Comparison with the experimental data shows that the present results are both reliable and accurate.

Electrode Properties of P2–Na2/3MnyCo1–yO2 as Cathode Materials for Sodium-Ion Batteries

The development of high-performance Na-ion intercalation electrodes has been required recently because Na-ion batteries hold much promise for inexpensive and efficient energy storage, which can be deployed in a power grid. For both optimization and better understanding of the electrode materials, it is indispensable to clarify the relationship between the electronic state and electrochemical properties systematically. In this work, we studied the electrochemical properties of P2–Na2/3MnyCo1–yO2 in detail. A series of the P2 phases was successfully synthesized by the conventional solid-state reaction. The solid solution P2 compounds showed that the redox potential of Co4+/Co3+ and Mn4+/Mn3+ shifts systematically by the transition-metal substitution. The charge–discharge cycle tests revealed that with increasing y the initial specific capacity increases while the cycle stability degrades. The origin for the cycle degradation was analyzed by the electrochemical impedance spectroscopy, which evidenced that th...

Effect of Packing on Formation of Deep Carrier Traps in Amorphous Conjugated Polymers.

We theoretically investigate the role of conformational disorder and intermolecular interactions on the localization properties of electronic states, leading to the formation of carrier traps in amorphous aggregates of conjugated polymers. Samples of amorphous conformations of poly(p-phenylene vinylene) (PPV), poly2-methoxy-5-(2-ethyl-hexyloxy)PPV (MEH-PPV), and [poly-(9,9'-dioctyluorene)] (PFO) oligomers are simulated by classical molecular dynamics, while their electronic structure is calculated using first-principles density functional theory. Localization and delocalization properties of molecular orbitals are studied based on the participation ratio analysis, an approach commonly used in inorganic semiconductors. Our simulations confirm that the alkyl side chains insignificantly affect the conformational disorder in amorphous polymers while having a dramatic effect on the intermolecular disorder and packing. The nature of the disorder and its impact on charge-carrier localization in amorphous polymers with alkyl side chains differ drastically from those of disordered polymers without side chains, such as PPVs. Thus, long-range intermolecular interactions and sparse packing are responsible for the formation of multiple, deep, highly localized trap states in amorphous MEH-PPVs and PFOs, while close packing in combination with conformational disorder leads to the trap states distributed mostly near the bandgap edges in PPV aggregates.

Nonequilibrium Dynamical Mean-Field Theory: An Auxiliary Quantum Master Equation Approach

We introduce a versatile method to compute electronic steady-state properties of strongly correlated extended quantum systems out of equilibrium. The approach is based on dynamical mean-field theory (DMFT), in which the original system is mapped onto an auxiliary nonequilibrium impurity problem imbedded in a Markovian environment. The steady-state Green's function of the auxiliary system is solved by full diagonalization of the corresponding Lindblad equation. The approach can be regarded as the nontrivial extension of the exact-diagonalization-based DMFT to the nonequilibrium case. As a first application, we consider an interacting Hubbard layer attached to two metallic leads and present results for the steady-state current and the nonequilibrium density of states.

Optical Spectrum Analysis of CuInSe&lt;sub&gt;2&lt;/sub&gt; Materials Applied in Solar Cell

Since CuInSe2 (commonly called as CIS) materials has become one of most important photovoltaic materials, they are investigated with optical spectroscopies in this paper. The crystal structure, surface microstructure morphology and composition of the samples are analyzed in XRD and SEM with EDX, and the surface electronic state and optical properties of the samples are characterized in X-ray photoelectron spectroscopy (XPS) and Ultraviolet-visible Spectrum instruments. The results show that CIS phase is very uniform, some impurity phases appear in the samples， the atomic distributing percentages of the surfaces of bulk samples are very consistent in the composition ratio forming the crystal phases of the samples, and the atomic electrons are more active than ones in the relevant elements. Furthermore, the thin film of the sample has high solar energy absorptivity, and is suitable for to be manufactured as solar cell.

Electrical Properties and Interface States of Rare-Earth Metal Ytterbium Schottky Contacts to p-Type InP

The electronic parameters and interface state properties of Yb/p-InP Schottky diode have been investigated by current­voltage (I­V), capacitance­voltage­frequency (C­V­f) and conductance­voltage­frequency (G­V­f) measurements at room temperature. The barrier height and ideality factor of the Yb/p-InP Schottky diode are found to be 0.68eV (I­V)/0.79eV (C­V) and 1.24, respectively. As well, the values of barrier heights, ideality factors and series resistance are estimated by Cheung and Norde methods are compared. Under forward bias conditions, ohmic and space charge limited conduction (SCLC) mechanisms are identified at low and higher voltages, respectively. The C­V characteristics of the Yb/p-InP Schottky diode are also measured at different frequencies at room temperature. Further, the C­f and G­f measurements of the

Theoretical investigations of the electronic states of NaXe: A comparative study

The electronic state properties of NaXe are investigated using ab initio methodologies and various pseudopotential approaches for comparison. The spectroscopic terms and dipole moments of the lowest electronic states up to the Na(3d) +Xe dissociation limit are determined. The difference between valence or smaller core pseudopotential on Xe is shown to be negligible and so is the difference between all-electron and valence pseudopotential completed by core-polarization treatments of Na. These calculations are used as references to test the performance of a treatment involving a zero electron pseudopotential description of xenon together with a one-electron pseudopotential description of Na. When compared with the reference calculations, the one-electron model leads to reasonable quantitative results. The potential energy curves and spectroscopic data of all Rydberg excited states of NaXe up the Na(5f)+Xe dissociation limit are determined using this method. Long distance wells and barriers in the range R = 15-40 bohrs are identified for some of the higher states with (2)Σ(+) symmetry.

Collective light emission of a finite-size atomic chain

The radiative properties of collective electronic states for a finite one-dimensional atomic chain are investigated. The influence of the chain size on the collective damping rates is examined through the dependence on both the chain length and the lattice constant. The symmetric state damping rate is shown to grow up linearly with the length for short chains, in relative to the atomic transition wavelength, and to saturate for long ones. For large lattice constants the saturation is achieved for small number of chain atoms, and vice versa for small ones. The results can be adopted for any chain of active materials, e.g., an array of quantum dots or organic molecules on a linear matrix.

Controlling the Electronic States and Physical Properties of MMX-Type Diplatinum-Iodide Chain Complexes via Binary Countercations

MMX-type quasi-one-dimensional iodide-bridged dinuclear Pt complexes (MMX chains) with binary countercations show a new alternating charge-polarization + charge-density-wave (ACP+CDW) electronic state and reversible switching of the electronic states and physical properties upon dehydration and rehydration process. By comparing several MMX chains with various binary countercations with previous chains, we found that the short backbone of the aliphatic diammonium ion was indispensable for realizing the ACP+CDW state because it induces a 2-fold periodicity along the chain axis via twisting of the ligands. Moreover, the reversibility of the changes in the structure and electrical conductivity upon dehydration and rehydration depend on the length of aliphatic diammonium ion. Short diammonium ions support a robust framework, which undergoes reversible structural changes. On the other hand, long and bent aliphatic diammonium ions weaken the framework, which causes partial degradation of the crystal and a decrease in the electrical conductivity when the structure changes. However, the decrease in the activation energy of the electrical conductivity after the dehydration process is independent of the robustness of the complex, indicating that the orbital overlap in MMX chains with binary countercations increases upon dehydration. Controllable electronic states and physical properties provide a platform for designing the multifunctional materials based on MMX chains.

Strained and Unstrained Macrocycles Composed of Carbazole and Butadiyne Units: Electronic State and Optical Properties

Cu(OAc)(2) catalyzes dehydrogenative condensation of 3,6-bis(2-ethynylphenyl)carbazole in the presence of O(2) to afford the cyclization product 1 and cyclodimer 2. Compound 1 contains bent carbazole and butadiyne groups, while 2 has a less strained structure with Z shape around the two parallel butadiyne groups. Optical properties of the compounds are discussed based on the electronic states estimated from electrochemical measurement and density functional theory calculation.

Delocalization to localization transition in one-dimensional systems with long-range correlated off-diagonal disorder

The combined effects of long-range correlations and disorder strength on critical properties of electronic states in one-dimensional systems with long-range correlated off-diagonal disorder are investigated for the whole energy band. Numerical studies on the localization length demonstrate the existence of disorder-induced delocalization-to-localization transition (DLT) and energy-induced DLT in such systems when the correlations of hopping terms are strong enough to generate extended states. Further calculations confirm that the critical disorder strength and critical energy related to these DLTs are Wc=2t0−|E| and ±Ec=±|2t0−W|, respectively. Based on these critical points, the detailed phase diagrams in different parameter spaces are obtained.