A theoretical investigation about sensing mechanism of fluoride anion for (E)‐2‐(2‐(dimethylamino)ethyl)‐6‐(4‐hydroxystyryl)‐1H‐benzo[de]‐isoquinoline‐1,3 (2H)‐dione

In the present work, we theoretical study the sensing mechanism of a new fluoride chemosensor (E)‐2‐(2‐(dimethylamino)ethyl)‐6‐(4‐hydroxystyryl)‐1H‐benzo[de]‐isoquinoline‐1,3(2H)‐dione (the abbreviation is NIM ). Based on density functional theory and time‐dependent density functional theory methods, the fluoride anion response mechanism has been confirmed via constructing potential energy curve. The exothermal deprotonation process along with the intermolecular hydrogen bond O–H···F reveals the uniqueness of detecting F^?. After capturing hydrogen proton forming NIM‐A anion configuration, a new absorption peak around 655 nm appears in dimethyl sulfoxide solvent. In addition, the emission of NIM can be quenched when adding F^? has been also confirmed. Due to the twisted intramolecular charge transfer character NIM‐A‐S ₁ form, we further verify the experimental phenomenon. The theoretical electronic spectra (vertical excitation energies and fluorescence peak) reproduced previous experimental results (ACS Appl. Mater. Interfaces 2014, 6, 7996), which not only reveals the rationality of our theoretical level used in this work but also confirms the correctness of geometrical attribution. In view of the excitation process, the strong intramolecular charge transfer process of S₀ → S₁ transition explain the redshift of absorption peak for NIM with the addition of fluoride anion. This work presents a straightforward sensing mechanism (deprotonation process) of fluoride anion for the novel NIM chemosensor.     

Theoretical analysis of fluorine-passivated germanium surface for high-k/Ge gate stack by molecular orbital method

Energy state and coordination of fluorine (F)-passivated Ge surface have been theoretically analyzed by semi-empirical molecular orbital method in comparison with hydrogen-passivated Ge surface to predict usefulness of F for passivation element and surface stabilization. Heat of formation for the reaction of F atoms and Ge layer system decreased simultaneously without energy barrier. Resultantly, F-Ge bonds were formed on Ge layer system and Ge surface dangling bonds were passivated by F dissimilar to the reaction of H atoms and Ge layer system. Furthermore, it was confirmed experimentally that the electrical properties of HfO₂/Ge gate stack were improved by F₂-ambient treatment of Ge substrate prior to HfO₂ deposition. It is concluded that F-passivation of Ge surface is useful in making stable and low-defective Ge substrate for high-k dielectric layer deposition.     

Electronic band structure and Fermi surface for new layered superconductor LaO0.5F0.5BiS2 in comparison with parent phase LaOBiS2 from first principles

By means of ab initio calculations, we have probed the peculiarities of the electronic band structure and Fermi surface for the recently discovered layered superconductor LaO_0.5F_0.5BiS₂ in comparison with the parent phase LaOBiS₂. The electronic factors promoting the transition of LaOBiS₂ upon fluorine doping to superconducting state: inter-layer charge transfer, the evolution of the Fermi surface, and the dependence of the near-Fermi densities of states on x for LaO_{1 ? x} F _x BiS₂ are evaluated and discussed in comparison with the available experiments.     

Band engineering of silicon for light emission: First-principles approach to the effect of co-doping with nitrogen and fluorine

A Si-based light emitter has long been the final key component for electronic and photonic integrated circuits on Si, because Si has an indirect band gap. Atomistic and electronic structures and energy gains of formation of possible nitrogen (N) and fluorine (F) complexes in Si have been researched from first-principles, in order to engineer the band structure of Si for light emission. The calculated results show that the substitutional nitrogen N_S and bond center fluorine F_BC pair complex has large stabilization energy, and that the pair-complex-doped Si has direct band gap, which is reduced with respect to that of Si. These results lead to the possibilities of doping-based engineering of Si optical properties with introduction of deep-level impurity and charge compensation.     

Impacts of fluorine on GaN high electron mobility transistors: Theoretical study

We investigate the role of fluorine (F) in GaN‐based high electron mobility transistors (HEMTs) with first principle calculations. Formation energy calculations of F in GaN and AlN reveal that energetically favored interstitial F (F_i) and substitutional F at N sites (F_N) could play important roles in the performance of HEMTs. F_i is responsible for positive threshold voltage (V_th) shift by forming F^– anion and depleting 2DEG carriers. The degradation of device performance at high temperature is ascribed to the defect energy state near conduction band edge of F_N. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sulphur dioxide insertion into tin―carbon bonds: solvent effects and the nature of the transition state

Data describing the insertion of sulphur dioxide into the carbon―tin bond of a range of substituted phenyltrimethyltin compounds in methanol and benzene solvents have been reconsidered. The reaction in methanol is cleanly second order, but the reaction in benzene has both a second‐order and third‐order component, the latter ascribable to an initial equilibrium formation of a SO₂ complex with the phenyl ring followed by the insertion of a second SO₂ molecule into the carbon–tin bond. Molecular orbital calculations have identified the transition states (TS) and the favoured reaction pathways for the second‐order and third‐order reaction pathways in benzene. The effects of solvents on TS and enthalpies of reaction have also been examined. New insights into the types of TS involved in electrophilic substitution reactions are revealed. Copyright © 2013 John Wiley & Sons, Ltd.     

Role of chemical pressure in enhancing the transition temperature (T<Subscript>c</Subscript>) and upper critical field (H<Subscript>c2</Subscript>) in the Y-doped Ce-oxyfluoride superconductor

Structural and superconducting properties of yttrium substituted Ce_1-xY_x(O/F)FeAs superconductors have been investigated for the first time. All the compounds crystallize in the tetragonal ZrCuSiAs structure type. There is a decrease in both the a and c lattice parameters on increasing yttrium substitution (with fixed F content) along with a substantial enhancement of the superconducting transition temperature (T_c) and upper critical field (H_c2) indicating the influence of chemical pressure. Interestingly the maximum T_c (~48 K) was observed for an intermediate composition (Ce_0.5Y_0.5O_0.9F_0.1FeAs) which is higher than either of the parent Y or Ce-compounds, (YO_0.9F_0.1FeAs (~10 K) and Ce(O/F)FeAs (~42 K)). The transition temperature was also found to be nearly independent of the electron -doping introduced by fluoride substitution (0.1 to 0.2 moles per formula unit) indicating the significance of the charge reservoir layer (Ce-O). The yttrium substituted (fluoride free) compositions of the type, Ce_1-xY_xOFeAs were found to be semimetallic like the parent compound CeOFeAs with the shift in the anomaly temperature towards low temperature on substitution of yttrium ions. Hall coefficient and thermopower measurements show an increase in charge carriers (electrons) through Y-doping in fluorine doped CeOFeAs.     

Infrared Spectra of Charge Transfer Complexes between I-C[tbnd]N and Pyridine Derivatives. I. - Complexation Constant and v I-C Stretching Vibration

The formation of a charge transfer complex brings about perturbations in the vibrational spectrum of both electron donor and electron acceptor molecules. Changes in band frequency which occur when pyridine bases^(1–2), organo phosphoryl compounds⁽³⁾ or sulfoxides⁽⁴⁾ form complexes with I-C[dbnd]N, have been studied. The infrared spectrum of I-C[dbnd]N, the σ acceptor, appears to be perturbed by complex formation: decrease of the frequency and increase of the intensity of the v_I-C stretching vibration^{(4, 6, 7)} and in some cases, decrease of the integrated intensity of the v_C[dbnd]N stretching vibration⁽⁶⁾. However, very little information exists about the stability constants of bases complexed with I-C[dbnd]N owing to the difficulty to observe the C-T band lying in the vacuum ultraviolet^{(4, 8})     

Charge‐transfer contributions in surface‐enhanced Raman scattering from Ag,Ag2S and Ag2Se substrates

The degree of charge‐transfer in Ag–4‐mercaptopyridine (Mpy) and Ag₂S–4‐Mpy systems is investigated by use of surface‐enhanced Raman spectroscopy (SERS). Ag₂S and Ag₂Se nanoparticles are prepared on the basis of the former formation of Ag nanoparticles to make the SERS analytical objects comparable. We utilize the intensity of the non‐totally symmetric modes (either b₁ or b₂) as compared with the totally symmetric a₁ modes to measure the degree of charge‐transfer. We find ~25% of charge‐transfer contribution for Ag–4‐Mpy, whereas 81 ~ 93% for Ag₂S–4‐Mpy. It means that the charge‐transfer resonance contribution dominates the overall enhancement in SERS of Ag₂S–4‐Mpy. Energy level diagram is applied to discuss the likely charge‐transfer transition between Ag, Ag₂S, Ag₂Se and 4‐Mpy. This article may point out the link among the three main resonance sources and could enable some insights into the electronic pathways available to the metal‐molecule and semiconductor‐molecule systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural distortion,charge modulation and local anisotropies in magnetite below the Verwey transition using resonant X‐ray scattering

The pattern of charge modulations and local anisotropies below the Verwey transition has been determined and quantified in high‐quality Fe₃O₄ single crystals and thin films grown on MgO by using resonant X‐ray scattering at the Fe K‐edge. The energy, polarization and azimuthal angle dependencies of an extensive set of reflections with potential sensitivity to charge or local anisotropy orderings have been analyzed to explore their origins. A charge disproportion on octahedral B sites of 0.20 ± 0.05 e^? with [0 0 1] and cubic periodicities has been confirmed, while no significant charge disproportion has been obtained with [0 0 1/2] cubic periodicity. Additional charge modulations in the monoclinic a–b plane are also present. In addition, the occurrence of new forbidden (1, 1, 0) and (0, 0, 2n + 1/2) cubic reflections that arise from the anisotropy of the local structure around different tetrahedral and octahedral Fe atoms is shown. This complex pattern of weak charge modulations and local anisotropies is fully compatible with the low‐temperature crystal structure refined in the non‐polar C2/c space group and disproves any bimodal charge disproportion of the octahedral Fe atoms.     

Gas‐phase Acidities of 2‐Aryl‐2‐chloro‐1,1,1‐trifluoroethanes and Related Compounds. Experimental and Computational Studies

The gas‐phase acidities (GA) of 2‐aryl‐2‐chloro‐1,1,1‐trifluoroethanes ( 1a ), 2‐aryl‐2‐fluoro‐1,1,1‐trifluoroethanes ( 2a ), and related compounds, XC₆H₄CH(Z)R where Z = Cl ( 1 ) or F ( 2 ) and R = C₂F₅ ( b ), t‐C₄F₉ ( c ), C(CF₃)₂C₂F₅ ( d ), C(CF₃)₂Me ( e ), Me ( f ), H ( g ), were investigated experimentally and computationally. On the basis of an excellent linear correlation (R² > 0.99) of acidities of 1c , 1d , 1e , 1f and 2c , 2d , 2e , 2f where there is no fluorine atom at β‐position to the deprotonation site with the corrected number of fluorine atoms contained in the fluorinated alkyl group, the extent of β‐fluorine negative hyperconjugation of the CF₃ and C₂F₅ groups (ΔG^o_β‐F) was evaluated. The GA_el values given by subtraction ΔG^o_β‐F from the apparent GA value were considered to represent the electronic effect of the substituent X. The substituent effects on the GA_el values and GA values for 1c , 1d , 1e , 1f and 2c , 2d , 2e , 2f were successfully analyzed in terms of the Yukawa–Tsuno equation. The variation of resonance demand parameter r^? with the R group observed for various XC₆H₄CH(Z)R was linearly related to the GA (GA_el) value of the respective phenyl‐substituted fluorinated alkanes. On the other hand, the corresponding correlation for the ρ values provided three lines for ArCH(Cl)R, ArCH(F)R and ArCH₂R, respectively. These results supported our previous conclusion that the r^? and ρ values are governed by the thermodynamic stability of the parent ion (ring substituent = H). Other factors arising from an atom bonded to the acidic center also influence the ρ value. Copyright © 2016 John Wiley & Sons, Ltd.     

Fluorine mobility in an aluminum-doped CeF<Subscript>3</Subscript> crystal: NMR and conductivity studies

Electrical conductivity and NMR measurements were carried out for an aluminum-doped CeF₃ crystal to study the influence of substitutional impurities on the superionic fluorine mobility. Activation enthalpy was found to remain constant from low temperatures to about 325 K and to increase as compared to that of a pure CeF₃ crystal. Above about 325 K, a trend towards gradual conductivity saturation was observed. This change was ascribed to a superionic phase transition not accompanied by structural transformations. NMR also revealed some alterations in the local fluorine dynamics as compared to that reported for a pure CeF₃ crystal. According to NMR measurements, the superionic phase transition near 325 K results in acceleration of the exchange between rigid or slow fluorine in the F₁, F₂, and F₃ sublattices, while highly mobile F₁ fluorine ions move independently at least until 400 K.     

Mechanisms of inelastic scattering of low-energy protons by C6H6, C60, C6F12, and C60F48 molecules

The mechanisms of inelastic scattering of low-energy protons with a kinetic energy of 2–7 eV by C₆H₆, C₆F₁₂, C₆₀, and C₆₀F₄₈ molecules are studied using the methods of quantum chemistry and nonempirical molecular dynamics. It is shown that, for the C₆H₆ + proton and C₆₀ + proton systems, starting from a distance of 6 Å from the carbon skeleton, the electronic charge transfer from the aromatic molecule to H⁺ occurs with a probability close to unity and transforms the H⁺ ion into a hydrogen atom and the neutral C₆H₆ and C₆₀ molecules into cation radicals. The mechanism of interaction of low-energy protons with C₆F₁₂ and C₆₀F₄₈ molecules has a substantially different character and can be considered qualitatively as the interaction between a neutral molecule and a point charge. The Coulomb perturbation of the system arising from the interaction of the noncompensated proton charge with the Mulliken charges of fluorine atoms results in an inversion of the energies of the electronic states localized, on the one hand, on the positively charged hydrogen ion and, on the other hand, on the C₆F₁₂ and C₆₀F₄₈ molecules. As a result, the neutral molecule + proton state becomes the ground state. In turn, this inversion makes the electronic charge transfer energetically unfavorable. Quantum-chemical and molecular-dynamics calculations on different levels of theory showed that, for fluorine derivatives of some aromatic structures (C₆F₁₂, C₆₀F₄₈), the barriers to proton penetration through carbon hexagons are two to four times lower than for the corresponding parent systems (C₆H₆, C₆₀). This effect is explained by the absence of active π-electrons in the case of fluorinated molecules.     

Efficiencies of third bodies in the reaction H + O2 + M = HO2 + M

Vibrational transition probabilities have been calculated by the Schwartz, Slawsky and Herzfeld method [3] for the deactivation of HO₂* in collision with H₂, O₂ and CO₂. The relative efficiencies of H₂, O₂ and CO₂ are compared with their third-body efficiencies found experimentally and it is concluded that the transfer of large vibrational quanta from HO₂* is unlikely to play an important part in determining the position of the second explosion limit of the H₂/O₂ reaction. This conclusion is at variance with the explanation put forward by Walsh [1] of the ‘anomalous’ third-body efficiencies of H₂O and CO₂ in this reaction.     

Structure of Na2O·MO·SiO2·CaF2 (M=Mg,Ca) oxyfluoride glasses

(9−x)CaO·xMgO·15Na₂O·60SiO₂·16CaF₂(x=0, 2, 4, 6, and 9) oxyfluoride glasses were prepared. Utilizing the Raman scattering technique together with ²⁹Si and ¹⁹F MAS NMR, the effect of alkaline metal oxides on the Q species of glass was characterized. Raman results show that as magnesia is added at the expense of calcium oxide, the disproportional reaction Q³→Q⁴+Q² (Qⁿ is a SiO₄ tetrahedron with n bridging oxygens) prompted due to the high ionic field strength of magnesia, magnesium oxide entered into the silicate network as tetrahedral MgO₄, and removed other modifying ions for charge compensation. This reaction was confirmed by ²⁹Si MAS NMR. ¹⁹F MAS NMR results show that fluorine exists in the form of mixed calcium sodium fluoride species in all glasses and no Si–F bonds were formed. As CaO is gradually replaced by MgO (x=6, 9), a proportion of the magnesium ions combines with fluorine to form the MgF⁺ species. Meanwhile, some part of Na⁺ ions complex F⁻ in the form of F–Na(6).     

A natural bond orbital analysis of aryl‐substituted polyfluorinated carbanions: negative hyperconjugation

Aryl‐substituted polyfluorinated carbanions, ArCHR_f^? where R_f = CF₃ ( 1 ), C₂F₅ ( 2 ), i‐C₃F₇ ( 3 ), and t‐C₄F₉ ( 4 ), were analyzed by means of the natural bond orbital (NBO) theory at the B3LYP/6‐311+G(d,p) computational level. A lone pair NBO at the formal anionic center carbon (Cα) was not found in the Lewis structure. Instead, significant donor/acceptor NBO interactions between π(Cα‐C1) and σ*(Cβ‐F) or σ*(Cβ‐Cγ) were observed for 1 , 2 , 3a (strong electron‐withdrawing substituent, from p‐CF₃ to p‐NO₂), and 4 . Their second‐order donor/acceptor perturbation interaction energy, E(2), values decreased with the increase of the stability of carbanions. A larger E(2) value corresponds to longer Cβ‐F and Cβ‐Cγ bonds and a shorter Cα‐Cβ bond, indicating that the E(2) values can be associated with the negative hyperconjugation of the Cβ‐F and Cβ‐Cγ bonds. In accordance with this, the E(2) values for π(Cα‐C1) → σ*(Cβ‐F) were linearly correlated with the ΔG^o_β‐F values (an empirical measure of β‐fluorine negative hyperconjugation obtained from an increased acidity). In 3b (weak electron‐withdrawing substituents, from H to m‐NO₂) very large E(2) values for LP(Fβ) → π*(Cα‐Cβ) were obtained. This was attributed to the Cβ‐F bond cleavage and the Cα‐Cβ double bond formation in the Lewis structure that is caused by the extremely strong negative hyperconjugation of the Cβ‐F bond.     

Structures,stabilities and electronic properties of manganese oxyfluoride (MnOxFy) species (x + y = 1–4; x,y = 0–4)

In this work, a density functional survey on manganese oxyfluoride (MnO_xF_y) species for x + y = 1–4 is performed, in which an Mn atom interacts simultaneously with O as well as F atoms. The stabilities of all these species are established against dissociation to manganese oxides as well as fluorides and their relative stabilities are also discussed. It is revealed that the most favourable oxidation state of Mn is +4 in its oxyfluorides, same as in fluorides. For the first time, the superhalogen properties of MnOF₃, MnO₃F and MnO₂F₂ species are introduced on the basis of their high electron affinities as compared to halogens. The interaction of MnO₂F₂ superhalogen with an alkali metal (K) is considered via F atoms as well as O atoms which is similar to that in KF and leads to the formation of stable KMnO₂F₂ complex. Thus, this study is expected to motivate theorist to design a new series of superhalogen species using transition metals with mixed F and O ligands, as well as experimentalists to synthesise such novel complex compounds.     

Initial growth at the F16CoPc/Ag(111) interface

An extended, combined (STM/STS)–(UPS/XPS) study was carried out towards a comprehensive understanding of the mechanism responsible for the F₁₆CoPc/Ag(111) interface formation. The evolution of the morphology and the electronic properties at the organic/metal interface is investigated for the early-stage growth of the ultrathin molecular film. Template-guided molecular structures are formed via a strong molecule–substrate interaction which leads to the formation of a new adsorption-induced interface state close to the Fermi energy (E_F). With increasing the thickness the molecular coupling to the metal surface states becomes less important while the more dominant molecule–molecule interaction governs the second layer formation. The quenching of the interface state upon increasing the molecular thickness, together with the changes observed in the Co 2p and F 1s core levels, is explained based on a charge transfer at the interface and a corresponding charge redistribution within the molecular ligand. A detailed “picture” of the energy level alignment close to E_F is achieved by correlating the high resolution UPS and highly localized STS data.     

Nucleophilic substitution reactions promoted by oligoethylene glycols: a mechanistic study of ion‐pair SN2 processes facilitated by Lewis base

We present a mechanistic study for nucleophilic substitution (S_N2) reactions facilitated by multifunctional n‐oligoethylene glycols (n‐oligoEGs) using alkali metal salts MX (M⁺ = Cs⁺, K⁺, X^– = F^–, Br^–, I^–, CN^–) as nucleophilic agents. Density functional theory method is employed to elucidate the underlying mechanism of the S_N2 reaction. We found that the nucleophiles react as ion pairs, whose metal cation is ‘coordinated’ by the oxygen atoms in oligoEGs acting as Lewis base to reduce the unfavorable electrostatic effects of M⁺ on X^–. The two terminal hydroxyl (?OH) function as ‘anchors’ to collect the nucleophile and the substrate in an ideal configuration for the reaction. Calculated barriers of the reactions are in excellent agreement with all experimentally observed trends of S_N2 yields obtained by using various metal cations, nucleophiles and oligoEGs. The reaction barriers are calculated to decrease from triEG to pentaEG, in agreement with the experimentally observed order of efficiency (triEG < tetraEG < pentaEG). The observed relative efficiency of the metal cations Cs⁺ versus K⁺ is also nicely demonstrated (larger [better] barrier [efficiency] for Cs⁺ than for K⁺). We also examine the effects of the nucleophiles (F^–, Br^–, I^–, CN^–), finding that the magnitudes of reaction barriers are F^– > CN^– > Br^– > I^–, elucidating the observation that the yield was lowest for F^–. It is suggested that the role of oxygen atoms in the promoters is equivalent to that of –OH group in bulky alcohols (tert‐butyl or amyl‐alcohol) for S_N2 fluorination reactions previously studied in our lab. Copyright © 2012 John Wiley & Sons, Ltd.     

Resonance Raman spectroscopy studies on photoinduced AgTCNQF4 charge transfer and its electrical switching behavior

The photoinduced charge transfer (CT) phenomenon of a metal–organic complex, Ag ion‐coordinated tetrafluorotetracyano‐p‐quinodimethane (AgTCNQF₄), produced by a solution reaction of immersing an Ag deposited film into TCNQF₄ acetonitrile solution, was studied by the resonance Raman spectroscopy. The produced AgTCNQF₄ formed abundant crystalline microrods over the slide. The analysis of Raman results shows that the photoinduced CT in the AgTCNQF₄ microrods possesses a light energy threshold that the excitation wavelengths should be shorter than 514 nm. And the complete degree of CT reaction from TCNQF₄⁻ to TCNQF₄²⁻ accelerates with the irradiation energy increasing. A divalent metal–organic complex (Ag₂TCNQF₄) is produced as a result of the photoinduced electron transition of AgTCNQF₄. The conductive‐atomic force microscope characterization of the AgTCNQF₄ microrods proves that this metal–organic complex possesses the reversible electrical bistable switching property. This study is of significance in deeper understanding the electrical and optical properties of such kinds of metal–organic CT complexes and promoting the promising application potential based on the light and electric dual control devices. Copyright © 2015 John Wiley & Sons, Ltd.