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[Display omitted] • Stability of Li 1.2 Ni 0.2 Mn 0.6 O 2 (0 0 3) cathode surface and its electronic properties during delithiation are explored. • Triggering factors for the oxygen dimerization at the cathode surface are identified. • Oxygen atoms linearly coordinated with two Li-ions are unstable during delithiation. • Oxygen oxidation proceeds via O2– to O− and finally, O 2 released at a higher degree of lithiation. Li-rich layered manganese oxide-based cathodes have drawn much attention for the next-generation lithium-ion batteries due to the large discharge capacities and low cost. However, the lattice oxygen release and subsequent surface densification during cycling inevitably lead to their instability, which incurs capacity failure at high voltage. Herein, we have systematically explored the oxygen oxidation mechanisms in Li 1.2 Ni 0.2 Mn 0.6 O 2 (0 0 3) surface by considering five possible different local oxygen coordination environments and investigate their oxidation process during the different degrees of delithiation. Based on the density functional theory calculations, we identify the triggering factors for the oxygen dimerization at the cathode surface. Our study reveals that the oxygen atoms linearly coordinated with two Li-ions (Li O Li geometries) are unstable and proceed oxidation via O2− to O− to O 2 2− to O 2 − and finally O 2 evolution occurred on the cathode surface at a higher degree of delithiation. Based on our theoretical results, we expect that the oxygen molecule release can be suppressed by modifying the surface's oxygen coordination environment. Such a comprehensive understanding is essential for developing the novel complex Li-rich layered manganese oxide cathodes. [ABSTRACT FROM AUTHOR]

• The C-O coupling is the RDS of CO oxidation via the L-H mechanism on O-IrO 2 (1 1 0). • The CO 2 desorption is the RDS of CO oxidation via the E-R mechanism on O-IrO 2 (1 1 0). • AIMD shows that CO 2 can desorb from O-IrO 2 (1 1 0) as the temperature higher than 400 K. • Microkinetic study shows a lower CO oxidation temperature via E-R mechanism than L-H. Though, oxygen-rich iridium oxide (O-IrO 2 (1 1 0)) surface exhibits excellent catalytic activity towards methane activation and oxygen evolution reactions, the CO oxidation mechanism on this surface remains elusive. Here, we used density functional theory calculations, ab initio molecular dynamics (AIMD), and microkinetic simulations to explore the CO oxidation reactions via Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R), and Mars-Van Krevelen (MvK) mechanisms on O-IrO 2 (1 1 0) surface. We find that the C-O coupling and CO 2 desorption are the rate-determining steps in L-H and E-R mechanisms, respectively. The CO oxidation via the MvK mechanism on the IrO 2 (1 1 0) surface is more difficult to proceed. Both AIMD and microkinetic simulation results demonstrate that CO 2 can desorb from the O-IrO 2 (1 1 0) surface at 400 K. The production temperature of CO 2 on the O-rich IrO 2 (1 1 0) surface via E-R mechanism is lower than that via the L-H mechanism. Therefore, we predict that the O-rich IrO 2 (1 1 0) surface can accelerate the CO oxidation reaction rate. [ABSTRACT FROM AUTHOR]

We report on the theoretical design of five new organic D−π−A sensitizers (JA1 ‒ JA5) featuring silole and selenophene space π‒linker, and an evaluation of their performance for application in dye-sensitized solar cells (DSSCs). Their structural, spectral and electronic properties were investigated using density functional theory (DFT) and time-dependent (TD)-DFT calculations. We found that incorporation of a silole as a π‒bridge substituent in the five-membered heterocyclic dye, in particular to JA2 and JA4 , remarkably improves the optical UV–Vis absorption spectra and achieves larger light-harvesting efficiency (LHE) relative to the conventional thiophene-based spacer (JA1), leading to a larger J sc response. Interaction of these two theoretically designed dyes JA2 and JA4 in combination with iodide electrolytes was calculated and the LHE is significantly larger than that of their isolated dyes, both contribute to improving the DSSC performance. Calculated results give insight into the optoelectronic properties of the rationally substituted π- spacer D−π−A sensitizers concerning their regeneration and applicability for DSSCs. Image 1 • Effects of chemical modification on the π‒linker has been designed and investigated. • Silole/selenophene-spaced groups are calculated to be superior for light-harvesting efficiency than the thiophene based dyes. • DFT/TD-DFT study reveals JA2 and JA4 show better DSSCs performance as sensitizers. • Explore the interaction of iodide with silane/selenene-spaced sensitizers which are better thermodynamically and kinetically. [ABSTRACT FROM AUTHOR]

Despite significant progress in low-temperature methane (CH 4 ) activation, commercial viability, specifically obtaining high yields of C 1 /C 2 products, remains a challenge. High desorption energy (>2 eV) and overoxidation of the target products are key limitations in CH 4 utilization. Herein, we employ first-principles density functional theory (DFT) and microkinetics simulations to investigate the CH 4 activation and the feasibility of its conversion to ethylene (C 2 H 4 ) on the RuO 2 (1 1 0) surface. The CH activation and CH 4 dehydrogenation processes are thoroughly investigated, with a particular focus on the diffusion of surface intermediates. The results show that the RuO 2 (1 1 0) surface exhibits high reactivity in CH 4 activation (E a  = 0.60 eV), with CH 3 and CH 2 are the predominant species, and CH 2 being the most mobile intermediate on the surface. Consequently, self-coupling of CH 2 * species via CC coupling occurs more readily, yielding C 2 H 4 , a potential raw material for the chemical industry. More importantly, we demonstrate that the produced C 2 H 4 can easily desorb under mild conditions due to its low desorption energy of 0.97 eV. Microkinetic simulations based on the DFT energetics indicate that CH 4 activation can occur at temperatures below 200 K, and C 2 H 4 can be desorbed at room temperature. Further, the selectivity analysis predicts that C 2 H 4 is the major product at low temperatures (300-450 K) with 100 % selectivity, then competes with formaldehyde at intermediate temperatures in the CH 4 conversion over RuO 2 (1 1 0) surface. The present findings suggest that the RuO 2 (1 1 0) surface is a potential catalyst for facilitating ethylene production under mild conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

A limiting factor for solid polymer electrolyte (SPE)-based Li-batteries is the functionality of the electrolyte decomposition layer that is spontaneously formed at the Li metal anode. A deeper understanding of this layer will facilitate its improvement. This study investigates three SPEs - polyethylene oxide:lithium tetrafluoroborate (PEO:LiBF 4 ), polyethylene oxide:lithium bis(oxalate)borate (PEO:LiBOB), and polyethylene oxide:lithium difluoro(oxalato)borate (PEO:LiDFOB) - using a combination of electrochemical impedance spectroscopy (EIS), galvanostatic cycling, in situ Li deposition photoelectron spectroscopy (PES), and ab initio molecular dynamics (AIMD) simulations. Through this combination, the cell performance of PEO:LiDFOB can be connected to the initial SPE decomposition at the anode interface. It is found that PEO:LiDFOB had the highest capacity retention, which is correlated to having the least decomposition at the interface. This indicates that the lower SPE decomposition at the interface still creates a more effective decomposition layer, which is capable of preventing further electrolyte decomposition. Moreover, the PES results indicate formation of polyethylene in the SEI in cells based on PEO electrolytes. This is supported by AIMD that shows a polyethylene formation pathway through free-radical polymerization of ethylene., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Sialic acid (SA) is a naturally occurring monosaccharide found in glycoproteins and glycolipids. Changes in the expression of SA are associated with several diseases; thus, the detection of SA is of great significance for biological research, cancer diagnosis, and treatment. Boronic acid analogs have emerged as a promising tool for detecting sugars such as SA due to its reversible covalent bonding ability. In this study, 11 bis-boronic acid compounds and 2 mono-boronic acid compounds were synthesized via a highly efficient Ugi-4CR strategy. The synthesized compounds were subjected to affinity fluorescence binding experiments to evaluate their binding capability to SA. Compound A1 was shown to have a promising binding constant of 2602 ± 100 M -1 at pH = 6.0. Density Functional Theory (DFT) calculations examining the binding modes between A1 and SA indicated that the position of the boronic acid functional group was strongly correlated with its interaction with SA's α-hydroxy acid unit. The DFT calculations were consistent with the observations from the fluorescence experiments, demonstrating that the number and relative positions of the boronic acid functional groups are critical factors in enhancing the binding affinity to SA. DFT calculations of both S and R configuration of A1 indicated that the effect of the S / R configuration of A1 on its binding with β-sialic acid was insignificant as the Ugi-4CR generated racemic products. A fluorine atom was incorporated into the R 2 substituent of A1 as an electron-withdrawing group to produce A5, which possessed a significantly higher capability to bind to SA ( K eq = 7015 ± 5 M -1 at pH = 6.0). Finally, A1 and A5 were shown to possess exceptional binding selectivity toward β-sialic acid under pH of 6.0 and 6.5 while preferring to bind with glucose, fructose, and galactose under pH of 7.0 and 7.5.

Rechargeable zinc aqueous batteries are key alternatives for replacing toxic, flammable, and expensive lithium-ion batteries in grid energy storage systems. However, these systems possess critical weaknesses, including the short electrochemical stability window of water and intrinsic fast zinc dendrite growth. Hydrogel electrolytes provide a possible solution, especially cross-linked zwitterionic polymers that possess strong water retention ability and high ionic conductivity. Herein, an in situ prepared fiberglass-incorporated dual-ion zwitterionic hydrogel electrolyte with an ionic conductivity of 24.32 mS cm -1 , electrochemical stability window up to 2.56 V, and high thermal stability is presented. By incorporating this hydrogel electrolyte of zinc and lithium triflate salts, a zinc//LiMn 0.6 Fe 0.4 PO 4 pouch cell delivers a reversible capacity of 130 mAh g -1 in the range of 1.0-2.2 V at 0.1C, and the test at 2C provides an initial capacity of 82.4 mAh g -1 with 71.8% capacity retention after 1000 cycles with a coulombic efficiency of 97%. Additionally, the pouch cell is fire resistant and remains safe after cutting and piercing., (© 2023 Wiley-VCH GmbH.)

Sulfide-based solid-state lithium-ion batteries (SSLIB) have attracted a lot of interest globally in the past few years for their high safety and high energy density over the traditional lithium-ion batteries. However, sulfide electrolytes (SEs) are moisture-sensitive which pose significant challenges in the material preparation and cell manufacturing. To the best of our knowledge, there is no tool available to probe the types and the strength of the basic sites in sulfide electrolytes, which is crucial for understanding the moisture stability of sulfide electrolytes. Herein, we propose a new spectral probe with the Lewis base indicator BBr 3 to probe the strength of Lewis basic sites on various sulfide electrolytes by 11 B solid-state NMR spectroscopy ( 11 B-NMR). The active sulfur sites and the corresponding strength of the sulfide electrolytes are successfully evaluated by the proposed Lewis base probe. The probed strength of the active sulfur sites of a sulfide electrolyte is consistent with the results of DFT (density functional theory) calculation and correlated with the H 2 S generation rate when the electrolyte was exposed in moisture atmosphere. This work paves a new way to investigate the basicity and moisture stability of the sulfide electrolytes., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Methane is the major component of natural gas, and it significantly contributes to global warming. In this study, we investigated methane activation on the α-Fe 2 O 3 (110) surface and M/α-Fe 2 O 3 (110) surfaces (M = Ag, Ir, Cu, or Co) using the density-functional theory (DFT) + U method. Our study shows that the Ir/α-Fe 2 O 3 (110) surface is a more effective catalyst for C-H bond activation than other catalyst surfaces. We have applied electron density difference (EDD), density of states (DOS), and Bader charge calculations to confirm the cooperative CH⋯O and agostic interactions between CH 4 and the Ir/α-Fe 2 O 3 (110) surface. To further modify the reactivity of the Ir/α-Fe 2 O 3 (110) surface towards methane activation, we conducted a study of the effect of oxygen vacancy (O V ) on C-H activation and CH 4 dehydrogenation. In the comparison of pristine α-Fe 2 O 3 (110), Ir/α-Fe 2 O 3 (110), and Ir/α-Fe 2 O 3 (110)-O V surfaces, the Ir/α-Fe 2 O 3 (110)-O V surface is the best in terms of CH 4 adsorption energy and C-H bond elongation, whereas the Ir/α-Fe 2 O 3 (110) surface catalyst has the lowest C-H bond activation barrier for the CH 4 molecule. The calculations indicate that the Ir/α-Fe 2 O 3 (110)-O V surface could be a candidate catalyst for CH 4 dehydrogenation reactions., Competing Interests: The authors declare that there is no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Fenton's reagent provides a method to produce active hydroxyl radicals (˙OH) for chemical oxidation by mixing iron oxide and hydrogen peroxide, which divides into homogeneous and heterogeneous Fenton's reagent. Heterogeneous Fenton's reagent is fabricated from H 2 O 2 and various iron oxide solid materials, such as α-FeOOH, α-Fe 2 O 3 , and Fe 3 O 4 . Fe 3 O 4 possesses the Fe 2+ /Fe 3+ mixed valence oxidational state and has been reported to have good catalytic activity. However, the reaction mechanism of H 2 O 2 decomposition on Fe 3 O 4 surfaces is still unclear. In this work, we performed DFT calculations to investigate the H 2 O 2 decomposition mechanisms over the Fe 3 O 4 (311) surface. There are two iron environments for H 2 O 2 adsorption and decomposition on the Fe 3 O 4 (311) surface, a Fe 2+ /Fe 3+ environment and a Fe 3+ /Fe 3+ environment. We found that the H 2 O 2 can adsorb on the Fe 2+ /Fe 3+ environment by molecular adsorption but by dissociative adsorption on the Fe 3+ /Fe 3+ environment. Our results show that both adsorption structures can produce two OH groups on the Fe 3 O 4 (311) surface thermodynamically. In addition, based on the electronic property analysis, H 2 O 2 on the Fe 2+ /Fe 3+ environment follows the Haber-Weiss mechanism to form one OH anion and one OH radical. On the other hand, H 2 O 2 on the Fe 3+ /Fe 3+ environment follows the radical mechanism to form two OH radicals. In particular, the OH radical formed on Fe 2+ /Fe 3+ has energy levels on both sides of the Fermi energy level. It can be expected that this OH radical has good redox activity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

To develop a high-performance methane storage material, an understanding of the mechanism and electronic interactions between methane and the material is essential. In this study, we performed detailed theoretical analyses to investigate the methane storage capacity of Ni-MOF-74 using a large-scale periodic DFT code CONQUEST. In a single pore of the unit cell, we considered three possible sites, iSBU, L, and P sites, where iSBU is the inorganic secondary building unit with a metal center, and L is the linker consisting of the organic building unit, while the P site is the vacuum site in the center of the pore. It shows that the methane molecule adsorption possesses the largest methane molecule adsorption energy on the iSBU site. Our calculations indicate that both C-HO and weak agostic interactions exist between the methane molecule and the iSBU site. The adsorption energy of one methane molecule on the iSBU site is in good agreement with previous experimental and theoretical studies. The calculation of the stepwise methane molecule adsorption shows that the first six methane molecules can first occupy the iSBU sites via C-HO and weak agostic interactions. The second six methane molecules are adsorbed on the remaining L sites, where the C-Hπ interaction becomes important, leading to the synergistic effect together with the C-HO interaction to enhance the adsorption energy of the methane molecule. Finally, it can adsorb up to sixteen CH4 molecules in a single pore of a unit cell at Ni-MOF-74. Moreover, we conducted DOS and EDD analyses, which clearly show that the interactions play a vital role in the adsorption of a methane molecule on Ni-MOF-74, especially the C-HO interaction.

The Si(100) surface carbonization mechanisms by acetylene are explored using density functional theory calculations combined with microkinetic simulations. The most stable acetylene adsorption geometries and their subsequent decomposition mechanisms to form a carbon dimer on the Si surface are investigated. Microkinetics simulations are further used to examine the optimal reaction conditions for obtaining a single-crystalline silicon carbide (SiC). We find that the carbon dimer (C 2 *) as an end-bridge structure can be formed at 560 K, and the maximum of C 2 * can be obtained near 640 K. The acetylene adsorbed via the di-σ configuration starts to dehydrogenate when the heating rate is too fast and will form two possible carbon dimers (di-C 2 * and C 2 *), which will lead to a polycrystalline SiC buffer layer. We predict that 750 K and 10 -6 bar will be the optimum temperature and pressure for obtaining a single-crystalline SiC buffer layer, respectively.

The iodide/triiodide interaction with the dye on a semiconductor surface plays a significant role in understanding the dye-sensitized solar cells (DSSCs) mechanism and improving its efficiency. In the present study, density functional theory (DFT) calculations were used to determine the interaction between the complexed iodide redox couple with dye/TiO2 for the relevance of DSSCs. Three new metal-free organic dyes noted as D1Y, D2Y and D3Y, featured with D-π-A configuration were designed by varying functional groups on the donor moiety. We analyzed the structural and electronic properties of these dyes when standing alone and being adsorbed on the oxide surface with the iodide electrolyte. Of the designed dyes, the incorporation of a strong donor unit in D1Y and D2Y sensitizers in conjunction with iodide electrolytes on the TiO2 surface provides better adsorption and electronic properties in comparison to those from the dye alone on the TiO2 surface. Analysis of density of states (DOS) indicates that the introduction of a strong electron-donating group into the organic dye, mainly D1Y and D2Y with an iodide electrolyte on the surface remarkably upshifts the Fermi energy, thereby improving the efficiency of the DSSCs by an increase of the open-circuit voltage (Voc). The present finding constitutes the basis for achieving a deeper understanding of the intrinsic interaction taking place at the electrolyte/dye/TiO2 interface and provides us with directions for the design of efficient dyes and redox electrolytes for improving DSSCs.

An understanding of the interaction of water with perovskite is crucial in improving the structural stability of the perovskite. Hence, in this study, the structural and electronic properties of the γ-CsPbI 3 (220) perovskite surface upon the adsorption of water molecules have been investigated based on density functional theory calculations. Also, we perform first-principles ab initio molecular dynamics simulations (AIMD) to explore the structural stability of the γ-CsPbI 3 (220) perovskite surface in the presence of water molecules, and the results are compared with the conventional cubic CH 3 NH 3 PbI 3 (100) perovskite surface. The water molecules show stronger interactions with the (220) surface of γ-CsPbI 3 than the (100) surface of CH 3 NH 3 PbI 3 . However, AIMD results demonstrate that the former is much more stable, and no trace of surface degradation was observed upon the adsorption of water molecules.

Improving the stability of lithium-rich cathode materials is important in refining the overall performance of lithium-ion batteries. Here, we have proposed doping of different metal atoms such as K + , Ca 2+ , Cd 2+ , and Al 3+ in different sites of Li 1.2 Ni 0.2 Mn 0.6 O 2 , and we have investigated their structural and electronic properties using first-principles calculations. We found that the Ni ions in the pristine Li 1.2 Ni 0.2 Mn 0.6 O 2 structure maintained the +3 oxidation state for a longer time and resulted in the structural deformation during the long cycling process. Whereas, the Ni ions in the Cd-, K-, and Ca-doped Li 1.2 Ni 0.2 Mn 0.6 O 2 structure are in the +3 oxidation state for a very short time, compared to the pristine system. Our density functional theory (DFT) results show that the doping of the Cd ion in the Ni site of Li 1.2 Ni 0.2 Mn 0.6 O 2 is the most suitable one, because it inhibits structural change, decreases the formation energy, and suppresses the Jahn-Teller distortion, compared with the pristine system and other dopant atoms. This theoretical study gives new insight about doping strategy and will help in improving the electrochemical performance of Li-rich cathode materials.

We propose a linkage approach by merging ambipolar electrochromic (EC) materials in both π-acceptor-π (π-A-π) and donor-acceptor-donor (D-A-D) configurations and investigated their electrochemical and spectroelectrochemical properties using density functional theory calculations. Here, we considered anthracene, toluene, and pyrene as π-conjugated molecules, triphenylamine (TPA) as a donor, and viologen as an acceptor moiety for π-A-π and D-A-D configurations. We have also explored the substitutional effects in the donor moiety on the overall electrochromism during both oxidation and reduction processes. Here, we mainly focused on the relationship between the structure, substitution of functional groups, electronic and spectral properties, as well as redox potential of the designed monomers. Our calculations indicate that the designed monomers have attractive absorption properties and show clear color switching upon the redox process. We find that the substitution of stronger electron-donating and π-spacer groups create new absorption peaks in the oxidation states. These designed viologen derivatives will be potential candidates, which can be used in both oxidation and reduction processes for upcoming EC devices.

Temperature-programmed desorption (TPD) is one of the most straightforward surface science experiments for the determination of the thermodynamic and kinetic parameters of a reaction. In our previous study (J. Phys. Chem. C, 2013, 117, 6136-6142), we proposed a model combining DFT methods with microkinetics to investigate the TPD spectra of NH3 and H2O on the RuO2(110) surface. Although our model predicted both the physisorption and chemisorption peaks of both adsorbates in agreement with the experimental TPD spectra, it failed to explain the region between the physisorption and chemisorption areas and underestimated the intensity of the adsorbate in these areas. Hence, to improve our model, in this study, we considered the diffusion of adsorbates from the sub-monolayer to the second layer. Accordingly, we simulated the TPD spectra of both NH3 and H2O on the RuO2(110) surface using condensation approximation. Our results indicate that the diffusion barriers of the adsorbates at high coverage are smaller than their direct desorption energies. Hence, the diffusion of the adsorbates to the second layer from the sub-monolayer at higher coverage is kinetically favorable, which then desorb directly even at low temperatures. Furthermore, the simulated TPD spectra clearly depict the previous experimental results of both adsorbates after considering the diffusion.

This theoretical study on dye-sensitized solar cells (DSSCs) includes design strategies for dye donor units to improve the efficiency of DSSCs, and further illuminates the organic dye regeneration mechanism. We have designed a series of new organic sensitizers based on a D-D-π-A architecture to exhibit easy electron transfer and to have remarkable light harvesting properties in the visible region by density functional theory (DFT) and time-dependent (TD)-DFT calculations. Furthermore, the interaction of the organic sensitizers with the conventional redox electrolyte using the triiodide/iodide couple (I3-/I-) is investigated. Our calculations indicate that incorporation of strong electron-donating groups remarkably improves the charge transfer characteristics, optoelectronic properties and rapid dye regeneration as compared to less electron donating substituents. In addition, our study demonstrates the possibility of second electron injection from the oxidized dye complex to the semiconductor surface, which further confirms our recently proposed dye regeneration mechanism.

The decomposition of methanol is currently attracting research attention due to the potential widespread applications of its end products. In this work, density functional theory (DFT) calculations have been performed to investigate the adsorption and decomposition of methanol on a Ru-Pt/boron doped graphene surface. We find that the most favorable reaction pathway is methanol (CH3OH) decomposition through O-H bond breaking to form methoxide (CH3O) as the initial step, followed by further dehydrogenation steps which generate formaldehyde (CH2O), formyl (CHO), and carbon monoxide (CO). The calculations illustrate that CH3OH and CO groups prefer to adsorb at the Ru-top sites, while CH2OH, CH3O, CH2O, CHO, and H2 groups favor the Ru-Pt bridge sites, indicating the preference of Ru atoms to adsorb the active intermediates or species having lone-pair electrons. Based on the results, it is found that the energy barrier for CH3OH decomposition through the initial O-H bond breaking is less than its desorption energy of 0.95 eV, showing that CH3OH prefers to undergo decomposition to CH3O rather than direct desorption. The study provides in-depth theoretical insights into the potentially enhanced catalytic activity of Ru-Pt/boron doped graphene surfaces for methanol decomposition reactions, thereby contributing to the understanding and designing of an efficient catalyst under optimum conditions.

Spin filtering materials are of great current interest in part due to their applications in molecular electronics. In this study, we carried out a theoretical investigation on the charge transport properties of transition metal (TM) dithiolene complexes with TM = Ni, Fe and Mn by using non-equilibrium Green's function/density functional theory (NEGF-DFT) methods. The characteristics of current-voltage and spin-resolved transmission spectra pointed out that Ni complexes are non-polarized, while Fe and Mn complexes exhibit high polarization and can be regarded as excellent candidates for spin-filtering materials with high spin-filtering efficiency. These differences were rationalized on the basis of electron delocalization over the molecular junction of the partial distribution of α- and β-spin molecular projected self-consistent Hamiltonian (MPSH) orbitals, and also the first eigenchannels of molecular junctions.

Determining an ideal adsorption configuration for a dye on the semiconductor surface is an important task in improving the overall efficiency of dye-sensitized solar cells. Here, we present a detailed investigation of different adsorption configurations of designed model dyes on TiO 2 anatase (101) surface using first principles methods. Particularly, we aimed to investigate the influence of cyano group in the anchoring part of dye on its adsorption stability and the overall photovoltaic properties such as open circuit voltage, electron injection ability to the surface. Our results indicate that the inclusion of cyano group increases the stability of adsorption only when it adsorbs via CN with the surface and it decreases the photovoltaic properties when it does not involve in binding. In addition, we also considered full dyes based on the results of model dyes and investigated the different strength of acceptor abilities on stability and electron injection ability. Among the various adsorption configurations considered here, the bidentate bridging mode (A3) is more appropriate one which has higher electron injection ability, larger V OC value and more importantly it has higher dye loading on the surface.

We have investigated the effect of pressure on imidazolium C-H---O interactions in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMI(+)TFSA(-))/L64 and EMI(+)TFSA(-)/1,4-dioxane mixtures. The addition of Pluronic L64 to EMI(+)TFSA(-) leads to appreciable changes in band frequencies and shapes of the imidazolium C-H stretching bands. A possible explanation is the formation of C-H---O interactions between imidazolium C-H groups and oxygen atoms of polyethylene oxides (PEOs). In other words, L64 can be added to change the relative contribution of the isolated and associated components of EMI(+)TFSA(-). In contrast to L64, the oxygen atoms of 1,4-dioxane cannot perturb the local structures of imidazolium C-H groups of EMI(+)TFSA(-) and the association configuration is still favored in the presence of 1,4-dioxane. As the pressure is elevated, 1,4-dioxane molecules tend to associate with themselves and TFSA(-) interacts with EMI(+) to form associated configurations. Our results suggest the formation of association between EMI(+) cation and L64 and the complexes are stable up to the pressure of 2.5 GPa.

Using high-pressure infrared methods, we have investigated close interactions of charge-enhanced C-H-O type in ionic liquid∕dimethyl sulfoxide (DMSO) mixtures. The solvation and association of the 1-butyl-3-methylimidazolium tetrafluoroborate (BMI(+)BF(4)(-)) and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMM(+)BF(4)(-)) in DMSO-d(6) were examined by analysis of C-H spectral features. Based on our concentration-dependent results, the imidazolium C-H groups are more sensitive sites for C-H-O than the alkyl C-H groups and the dominant imidazolium C-H species in dilute ionic liquid∕DMSO-d(6) should be assigned to the isolated (or dissociated) structures. As the dilute mixtures were compressed by high pressures, the loss in intensity of the bands attributed to the isolated structures was observed. In other words, high pressure can be used to perturb the association-dissociation equilibrium in the polar region. This result is remarkably different from what is revealed for the imidazolium C-H in the BMM(+)BF(4)(-)∕D(2)O mixtures. DFT-calculations are in agreement with our experimental results indicating that C(4)-H-O and C(5)-H-O interactions seem to play non-negligible roles for BMM(+)BF(4)(-)∕DMSO mixtures.

There is a growing interest in developing low-band gap conjugated polymers via synthesis of copolymers containing alternating units of different pi-electron-donating/accepting capabilities. In this study, electronic and optical properties of conjugated copolymers containing fluorene and thiophene/cyclopentadithiophene derivatives are determined using density function theory and semiempirical ZINDO calculations. A remarkable linear correlation is found between the amount of charge transfer between the donor-acceptor pair, the band gap, the bandwidth, and the oscillator strength of S(0)-->S(1) electronic transition (ground state to first excited state) of the copolymers. Strong pi-electron withdrawing substituents, such as dicyanoethenyl and carbonyl groups, on the thiophene moiety effectively reduce the band gap of the copolymers. However, the reduction of band gap is frequently accompanied by a linear reduction in bandwidths and in the oscillator strength of S(0)-->S(1) transition. For very strong pi-electron withdrawing thiophene derivatives, the occurrence of maximum oscillator strength may even shift from S(0)-->S(1) to S(0)-->S(n>1) (ground state to a higher excited state), giving a blue shift in maxima absorption peak and a red shoulder in the UV-vis spectra as reported in recent experimental measurements. Therefore, the achievement of low band gap for conjugated polymers with alternating arrangement of pi-electron-donating/accepting moieties may be achieved at a cost of lowering electron mobility and optical efficiency and sometimes a blue-shift in the major optical (UV-vis) absorption.

This paper describes the initial reaction kinetics of Ge deposition after exposure of Si(100)-2 x 1 to GeH4 in a UHV-CVD system. The rate of Ge growth, especially at the wetting layer stage, was investigated using in situ X-ray photoelectron spectroscopy to measure the Ge signal at the onset of deposition. A kinetic analysis of the initial growth of the Ge wetting layer at temperatures ranging from 698 to 823 K revealed an activation energy of 30.7 kcal/mol. Density functional theory calculations suggested that opening of the Si dimer--with a closely matching energy barrier of 29.7 kcal/mol, following hydrogen atom migration--was the rate controlling step for the incorporation of a GeH2 unit into the lattice to complete the growth of the Ge wetting layer after dissociative adsorption of GeH4.

The photodissociation of jet-cooled alpha-fluorotoluene and 4-fluorotoluene at 193 and 248 nm was studied using vacuum ultraviolet (vuv) photoionization/multimass ion imaging techniques as well as electron impact ionization/photofragment translational spectroscopy. Four dissociation channels were observed for alpha-fluorotoluene at both 193 and 248 nm, including two major channels C6H5CH2F-->C6H5CH2 (or C7H7)+F and C6H5CH2F-->C6H5CH (or C7H6)+HF and two minor channels C6H5CH2F-->C6H5CHF+H and C6H5CH2F-->C6H5+CH2F. The vuv wavelength dependence of the C7H7 fragment photoionization spectra indicates that at least part of the F atom elimination channel results from the isomerization of alpha-fluorotoluene to a seven-membered ring prior to dissociation. Dissociation channels of 4-fluorotoluene at 193 nm include two major channels C6H4FCH3-->C6H4FCH2+H and C6H4FCH3-->C6H4F+CH3 and two minor channels C6H4FCH3-->C6H5CH2 (or C7H7)+F and C6H4FCH3-->C6H5CH (or C7H6)+HF. The dissociation rates for alpha-fluorotoluene at 193 and 248 nm are 3.3 x 10(7) and 5.6 x 10(5) s(-1), respectively. The dissociation rate for 4-fluorotoluene at 193 nm is 1.0 x 10(6) s(-1). An ab initio calculation demonstrates that the barrier height for isomerization from alpha-fluorotoluene to a seven-membered ring isomer is much lower than that from 4-fluorotoluene to a seven-membered ring isomer. The experimental observed differences of dissociation rates and relative branching ratios between alpha-fluorotoluene and 4-fluorotoluene may be explained by the differences in the six-membered ring to seven-membered ring isomerization barrier heights, F atom elimination threshold, and HF elimination threshold between alpha-fluorotoluene and 4-fluorotoluene.

The hydrogen bonding structures of room-temperature ionic liquids 1,3-dimethylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate have been studied by infrared spectroscopy. High-pressure infrared spectral profiles and theoretical calculations allow us to make a vibrational assignment of these compounds. The imidazolium C-H bands of 1,3-dimethylimidazolium methyl sulfate display anomalous non-monotonic pressure-induced frequency shifts. This discontinuity in frequency shift is related to enhanced C-H...O hydrogen bonding. This behavior is in contrast with the trend of blue shifts in frequency for the methyl C-H stretching mode at ca. 2960 cm(-1). Our results indicated that the imidazolium C-H groups are more favorable sites for hydrogen bonding than the methyl C-H groups in the pure 1,3-dimethylimidazolium methyl sulfate. Nevertheless, both methyl C-H and imidazolium C-H groups are favorable sites for C-H...O hydrogen bonding in a dilute 1,3-dimethylimidazolium methyl sulfate/D(2)O mixture. Hydrogen bond-like C-H...F interactions were observed between PF(6)(-) and H atoms on the alkyl side chains and imidazolium ring for 1-butyl-3-methylimidazolium hexafluorophosphate.

Close interactions of the charge-enhanced C-H...O type have been analyzed both experimentally and computationally in the protonated thiazole-water system. The formation of a weak hydrogen bond was directly evidenced by a low-frequency shift of the hydrogen-bonded aromatic C-H stretch in the protonated thiazole moiety. For pure thiazole, the pressure dependence of the C-H bands yielded blue frequency shifts. The peak frequency of the aromatic C-H stretch band of protonated thiazole in a dilute D2O solution possesses an unusual nonmonotonic pressure dependence, which indicates enhanced C-H...O hydrogen-bond formation at high pressure. We performed density functional theory calculations to predict the frequency shift of the C-H stretching vibrations. The reorganization of the hydrogen-bonded network may be one of the factors to induce the blue frequency shift to the red frequency shift.

Close interactions of the C(alpha)[bond]H- - -O type have been analyzed via X-ray crystallography and high-pressure infrared spectroscopy. The results demonstrate that the C(alpha)[bond]H- - -O interactions can offer an additional stability to the beta-sheet formation. X-ray structural data suggest that while 1-acetamido-3-(2-pyrimidinyl)-imidazolium bromide exhibits a bilayer stacking, the PF(6)(-) salt reveals a beta-sheetlike pattern. The appearance of the free-NH infrared absorption indicates that the conventional N[bond]H- - -O or N[bond]H- - -N hydrogen bonds do not fully dominate the packing for the PF(6)(-) salt. The high-pressure infrared study suggests that the C(alpha)[bond]H- - -O hydrogen bonds are the important determinants for the stability of the PF(6)(-) salt. This study also verifies that the imidazolium C[bond]H stretching frequency shifts to a longer wavelength upon the formation of the C[bond]H- - -O hydrogen bonds.