Time-dependent density functional theory study on electronic and spectroscopic properties for Ph<Subscript>2</Subscript>Bq and its complexes

The molecular structures of the ground state and the first singlet excited state for diphenylboron analogs of Alq₃ [Ph₂Bq where q is 8-hydroxyquinoline (QH)] and its three derivatives were optimized with the Density Functional Theory and ab initio “configuration interaction with single excitations” method, respectively. The frontier molecular orbital characteristics of Ph₂Bq were analyzed systematically in order to study the electronic transition mechanism. Electronic and spectroscopic properties of complexes have been investigated with Time-Dependent Density Functional Theory, which indicates that the emissions of Ph₂Bq and its derivatives originate from the electronic π → π* transitions within the QH ligands. That means that one might tune the emission wavelengths and improve charge transfer properties through the effect of substituent on the 8-hydroxyquinoline ligand. Similar calculations were carried out for isolated QH and its three derivatives for comparison. We found that the highest occupied molecular orbital and the lowest unoccupied molecular orbital of Ph₂Bq are similar to those of QH and their spectroscopic properties change similarly when they are substituted by the same group, which suggests that one can search possibility of a red or blue emission from Ph₂Bq derivatives by analyzing QH and its derivatives.     

Substituent and solvent effects on geometric and electronic structure of C<Subscript>5</Subscript>H<Subscript>5</Subscript>Ir(PH<Subscript>3</Subscript>)<Subscript>3</Subscript> iridabenzene: A theoretical insight

Using MPW1PW91 quantum chemical calculations, we report structures, frontier orbital analysis, natural bond analysis, and aromaticity of the C₅H₅Ir(PH₃)₃ iridabenzene and XC₅H₄Ir(PH₃)₃ para-substituted iridabenzenes. The substituent effects were estimated from the donor–acceptor interaction energies of the natural bond orbitals of substituent and iridabenzene frame. Nucleus-independent chemical shift (NICS) has been evaluated to understand the aromaticity. Time dependent density functional theory (TD-DFT) is used to calculate the energy, oscillatory strength and wavelength absorption maxima (λ_max) of electronic transitions and their nature. Changes in hyperpolarizability of molecules are studied. Influence of solvent on the structure, frontier orbital energies, λ_max, and hyperpolarizability of C₅H₅Ir(PH₃)₃ iridabenzene has been studied.     

A Systemic DFT Study on Several 5<Emphasis Type="Italic">d</Emphasis>-Electron Element Dimers: Hf<Subscript>2</Subscript>, Ta<Subscript>2</Subscript>, Re<Subscript>2</Subscript>, W<Subscript>2</Subscript>, and Hg<Subscript>2</Subscript>

Eleven kinds of density functionals in conjunction with three different basis sets are employed to investigate the homonuclear 5d-electron dimers: Hf₂, Ta₂, Re₂, W₂ and Hg₂. The computed bond lengths, vibrational frequencies and dissociation energies of these molecules are used to compare with available experimental data to find the appropriate combination of functional and basis set. The different functionals and basis sets favor different ground electronic state for Hf₂ and Re₂ molecules, indicating that these two dimers are sensitive to the functionals used. The molecular properties of Hg₂ dimer depend strongly on both functionals and basis sets used. It is found that the BP86 and PBEPBE functionals are generally successful in describing the 5d-electron dimers. For the ground states of these dimers, the bonding patterns are determined by natural bond orbital (NBO) analysis. Natural electron configurations show that the 6s and 5d orbitals in the bonding atoms hybrid with each other for the studied dimers except for Hg₂.     

Electronic energy structure of As<Subscript>2</Subscript>S<Subscript>3</Subscript>, AsSI,AgAsS<Subscript>2</Subscript>, and TiS<Subscript>2</Subscript> semiconductors

Quantum-mechanical calculations with the FEFF8 code were used to study the electronic energy structure of 200-atomic clusters of As₂S₃, AsSI, AgAsS₂, and TiS₂ semiconductor compounds. The calculated local partial densities of electronic states are compared with the sulfur K and L X-ray emission spectra and sulfur K absorption spectra for fine powders of these compounds. Good agreement between theory and experiment has been obtained.     

Theoretical study of elementary reactions of dissociative addition of an H<Subscript>2</Subscript> molecule to doped aluminide clusters MAl<Subscript>12</Subscript> (M = Cr,Mo, and W)

The potential energy surfaces of elementary reactions of dissociative addition of one and two H₂ molecules to Cr-, Mo-, or W-doped aluminide clusters MAl12 in the states of different multiplicity have been calculated by the density functional theory method. The results are compared with the previous calculations of analogous reactions involving the singlet and triplet TiAl₁₂ cluster. The effect of the dopant nature and electronic state multiplicity on the energies and activation barriers of hydrogenation reactions is considered.     

Spectroscopic investigation of structure and mechanism of proton conductivity CsHSO<Subscript>4</Subscript> and composites CsHSO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

IR and RS spectra, structural, thermodynamical and transport properties of CsHSO₄ and CsHSO₄/SiO₂ composites have been investigated. It is shown that CsHSO₄ is stabilized in composites in phase II (monoclinic modification), which turns into amorphous state with increasing silicon dioxide content. A formation of disordered highly conducting states of CsHSO₄ in composites at the temperatures noticeably lower than superionic phase transition was stated. Bond length equalization in sulfate-ions, weakening of hydrogen bond system, and as a result easier proton transfer in composites in comparison with pure salt take place in these conducting states. Mechanism for formation of composites and their proton conductivity is proposed.     

Giant correlation effects in the photoelectron spectrum of Ni(C<Subscript>3</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>: clues from accurate calculation of ionization cross-sections

Several general issues relating to the strong correlation effects present in the ionic states and the interpretation of molecular photoelectron spectra are discussed in the context of the Ni(C₃H₅)₂ molecule, and the problematic assignment of its spectrum is considered. Accurate calculations of photoionization cross-sections relative to all the valence ionizations are computed and compared with the available experimental evidence. It is shown that most ambiguities are resolved by a careful analysis of cross-section profiles and branching ratios, which reveal a wealth of details on the complex electronic structure of this molecule.     

Internal rotation potential functions of the acryloyl chloride molecule in the ground (<Emphasis Type="Italic">S</Emphasis><Subscript>0</Subscript>) and excited (<Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>) electronic states

The internal rotation potential function of the acryloyl chloride molecule in the S ₀ and S ₁ electronic states was reproduced using systems of torsional vibration levels obtained for its trans and cis isomers by analyzing the vibrational structure of the UV spectrum of the molecule. The kinematic factor F in the S ₀ ground state was calculated including geometric parameter relaxation as a function of internal rotation angle. The torsional potential parameters in the S ₀ state obtained in this work were substantially different from those determined from the infrared Fourier-transform spectrum ignoring the resonance perturbation of the level with v = 3. The form of the internal rotation potential function and the higher stability of the trans isomer (the main isomer) were substantiated by high-level quantum-mechanical calculations.     

Density functional theory (DFT) study of O<Subscript>3</Subscript> molecules adsorbed on nitrogen-doped TiO<Subscript>2</Subscript>/MoS<Subscript>2</Subscript> nanocomposites: applications to gas sensor devices

Density functional theory calculations were carried out to investigate the adsorption behaviors of O₃ molecules on the undoped and N-doped TiO₂/MoS₂ nanocomposites. With the inclusion of vdW interactions, which correctly account the long-range dispersion energy, the adsorption energies and final geometries of O₃ molecules on the nanocomposite surfaces were improved. For O₃ molecules on the considered nanocomposites, the binding sites were located on the fivefold coordinated titanium atoms of the TiO₂ anatase. The structural properties of the adsorption systems were examined in view of the bond lengths and bond angles. The variation of electronic structures was also discussed in view of the density of states, molecular orbitals and distribution of spin densities. The results suggest that the adsorption of the O₃ molecule on the N-doped TiO₂/MoS₂ nanocomposite is more favorable in energy than that on the pristine one, indicating that the N-doped nanocomposite has higher sensing capability than the pristine one. This implies that the N-doped TiO₂/MoS₂ nanocomposite would be an ideal O₃ gas sensor. However, our calculations thus provide a theoretical basis for the potential applications of TiO₂/MoS₂ nanocomposites as efficient O₃ sensors, leading to very interesting results in the context of air quality measurement.     

Can five-membered Te<Subscript>2</Subscript>N<Subscript>2</Subscript>S rings be considered aromatic?

The structures and molecular properties of three cyclic tellurium species [Te₂N₂S]²⁺ (1 ²⁺ ), [Te₂N₂SCl]⁺ (1 ⁺ ), and Te₂N₂SCl₂ (1) were studied using Density Functional Theory (DFT) with the aim of analyzing and quantifying the degree of electron delocalization in the rings. The structural data for the AsF₆⁻ salt of the cation 1 ⁺ , as well as the experimental vibrational frequencies of 1 and 1 ⁺ , were compared to calculated structures and vibrational modes. While only the five-membered ring of 1 ²⁺ obeys the classic Hückel aromaticity criteria, reflected in the nature of the π orbitals and natural resonance structures, all the three species are magnetic aromatic according to nucleus-independent chemical shift (NICS). However, the out-of-plane component of the NICS tensor (NICS_zz) is able to provide a reliable characterization of the π aromatic character, by showing that successive binding of two chlorine atoms to the same tellurium atom disrupts the π electron delocalization, and that total NICS cannot always be trusted as an aromaticity indicator.     

Benzene Adsorption on C<Subscript>24</Subscript>, Si@C<Subscript>24</Subscript>, Si-Doped C<Subscript>24</Subscript>, and C<Subscript>20</Subscript> Fullerenes

The absorption feasibility of benzene molecule in the C₂₄, Si@C₂₄, Si-doped C₂₄, and C₂₀ fullerenes has been studied based on calculated electronic properties of these fullerenes using Density functional Theory (DFT). It is found that energy of benzene adsorption on C₂₄, Si@C₂₄, and Si-doped C₂₄ fullerenes were in range of –2.93 and –51.19 kJ/mol with little changes in their electronic structure. The results demonstrated that the C₂₄, Si@C₂₄, and Si-doped C₂₄ fullerenes cannot be employed as a chemical adsorbent or sensor for benzene. Silicon doping cannot significantly modify both the electronic properties and benzene adsorption energy of C₂₄ fullerene. On the other hand, C₂₀ fullerene exhibits a high sensitivity, so that the energy gap of the fullerene is changed almost 89.19% after the adsorption process. We concluded that the C₂₀ fullerene can be employed as a reliable material for benzene detection.     

Mass spectrometric determination of the electron affinity of C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>10</Subscript> and C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>12</Subscript> molecules

Knudsen cell mass spectrometry was used to study ion-molecular electron exchange reactions between some trifluoromethyl derivatives of C₆₀ fullerene. Electron affinity values were experimentally determined for C₆₀(CF₃)₁₀ and the S ₆ isomer of C₆₀(CF₃)₁₂ and compared with the results of calculations and the data in the literature.     

Adsorption of NO,NH<Subscript>3</Subscript> and H<Subscript>2</Subscript>O on V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalysts

The adsorption of small molecules NO, NH₃ and H₂O on V₂O₅/TiO₂ catalysts is studied with the semiempirical SCF MO method MSINDO as pre-stage for the selective catalytic reduction of NO. The mixed catalyst is represented by hydrogen-terminated cluster models. The local arrangement of the cluster atoms is in accordance with available experimental information. Partial relaxation of cluster atoms near the adsorption sites is taken into account. Calculated adsorption energies are compared with experimental literature data. Rapid convergence of computed properties with cluster size is observed. A possible reaction mechanism for the catalytic reduction of NO with NH₃ and O₂ is outlined.     

A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

Modeling the active centers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> and V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> supported catalysts. DFT theoretical analysis of optical properties

Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm^?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V₂O₅/SiO₂ and V₂O₅/TiO₂ catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂ were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified.     

Theoretical study on S<Subscript>1</Subscript>(<Superscript>1</Superscript>B<Subscript>3u</Subscript>) state electronic structure and absorption spectrum of pyrazine

Making use of a set of quantum chemistry methods, the harmonic potential surfaces of the ground state (S₀(¹ A _g)) and the first (S₁(¹ B _3u)) excited state of pyrazine are investigated, and the electronic structures of the two states are characterized. In the present study, the conventional quantum mechanical method, taking account of the Born-Oppenheimer adiabatic approximation, is adopted to simulate the absorption spectrum of S₁(¹ B _3u) state of pyrazine. The assignment of main vibronic transitions is made for S₁(¹ B _3u) state. It is found that the spectral profile is mainly described by the Franck-Condon progression of totally symmetric mode ν_6a. For the five totally symmetric modes, the present calculations show that the frequency differences between the ground and the S₁(¹ B _3u) state are small. Therefore the displaced harmonic oscillator approximation along with Franck-Condon transition is used to simulate S₁(¹ B _3u) absorption spectra. The distortion effect due to the so-called quadratic coupling is demonstrated to be unimportant for the absorption spectrum, except the coupling mode ν_10a. The calculated S₁(¹ B _3u) absorption spectrum is in reasonable agreement with the experimental spectra. Supported by Taiwan National Science Council (Grant Nos. NSC 96-2113-M-009-021 and NSC 96-2811-M-009-023)     

Structure of acetyl chloride molecule isotopomers CH<Subscript>3</Subscript>COCl and CD<Subscript>3</Subscript>COCl in the ground and lowest excited singlet and triplet electronic states: a quantum mechanical study

The structures of isotopomers of conformationally flexible acetyl chloride molecule, CH₃COCl and CD₃COCl, in the ground (S₀ and lowest excited singlet (S₁) and triplet (T₁) electronic states were calculated by the RHF, MP2, and CASSCF methods. The equilibrium geometric parameters and harmonic vibrational frequencies of the molecules in these electronic states were estimated. According to calculations, electronic excitation causes considerable conformational changes involving rotation of the CH₃ (CD₃) top and a substantial deviation of the CCOCl fragment from planarity. The results of calculations agree with experimental data. Two dimensional torsional inversion sections of the potential energy surface were calculated and analyzed. Vibrational problems for large amplitude vibrations (torsional vibration in the S₀ state and both torsional and inversion vibrations in the T₁ and S₁ states) were solved in one- and two-dimensional approximations.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 62–70, January, 2005.     

Electroactive Polymerization Behaviors of Fused-Pentagon Chlorofullerenes: <Superscript>#1809</Superscript>C<Subscript>60</Subscript>Cl<Subscript>8</Subscript> and <Superscript>#271</Superscript>C<Subscript>50</Subscript>Cl<Subscript>10</Subscript>

The fullerenes that violate isolated pentagon rule (IPR) have unusual electronic properties resulting from their fused-pentagon structures. Numerous non-IPR fullerenes have now been captured by chlorination, affording opportunity to go insight into the properties involved in non-IPR fullerenes in the forms of chlorofullerenes (CFs). Here cyclic voltammetry (CV) is employed to probe the electrochemical properties of non-IPR ^#1809C₆₀Cl₈ in comparison with those of ^#271C₅₀Cl₁₀. Differing from IPR-satisfying CFs such as C₆₀Cl₈ and C₆₀Cl₁₀ (referring to I _h-symmetric C₆₀), the two non-IPR CFs exhibit divergent electroactive polymerization characters. In addition, the electrocatalytic effect of ferrocene that is otherwise employed as internal reference has been shown in the CV process of CFs.     

Lithium AlPO<Subscript>4</Subscript> composite polymer battery with nanostructured LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode

The borate ester plasticized AlPO₄ composite solid polymer electrolytes (SPE) have been synthesized and studied as candidates for lithium polymer battery (LPB) application. The electrochemical and thermal properties of SPE were shown to be suitable for practical LPB. Nanostructured LiMn₂O₄ with spherical particles was synthesized via ultrasonic spray pyrolysis technique and has shown a superior performance to the one prepared via conventional methods as cathode for LPB. Furthermore, the AlPO₄ addition to the polymer electrolyte has improved the polymer battery performance. Based on the AC impedance spectroscopy data, the performance improvement was suggested as being due to the cathode/polymer electrolyte interface stabilization in the presence of AlPO₄. The Li/composite polymer electrolyte/nanostructured LiMn₂O₄ electrochemical cell showed stable cyclability during the various current density tests, and its performance was found to be quite acceptable for practical utilities at ambient temperature and showed remarkable improvements at 60 °C compared with the solid state reaction counterpart.     

Experimental Studies on Isonicotinato Cadmium(II) Complex [Cd(C<Subscript>6</Subscript>H<Subscript>4</Subscript>NO<Subscript>2</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>] and Density Functional Calculations

Isonicotinato cadmium(II) complex [Cd(C₆H₄NO₂)₂(H₂O)₄] has been synthesized by hydrothermal method and characterized by elemental analysis, electronic-spectra and thermogravimetric analysis. Density functional theory (DFT) method calculations of the structure, atomic charges distribution, electronic spectra, natural population analysis and the thermodynamic properties at different temperatures have been performed. The calculated results show the electronic transitions are mainly derived from the contribution of bands π → π^* and the decomposition of the title compound should first occur at the bond of Cd—O, then at the bond of Cd—N, which agrees very well with the experimental data.