Amount Of Charge Transfer Research Articles

A Comparative Computational Study of the Adsorption of TCNQ and F4-TCNQ on the Coinage Metal Surfaces.

The adsorption of tetracyanoquinodimethane and of the closely related derivative tetrafluorotetracyanoquinodimethane on the (111) surfaces of the coinage metals, namely, copper, silver, and (unreconstructed) gold, has been studied by dispersion-corrected ab initio density functional theory calculations. In order to separate the molecule–substrate interaction from the effects of molecule–molecule interaction, only the isolated molecules are considered. The results show that, in this case, the strength of the interaction of both molecules with the surfaces decreases in the expected order Cu > Ag > Au. The total amount of charge transfer, however, behaves in a different way, being larger for Ag and smaller for Cu and Au. This trend can be explained by a combination of the differences in the work functions of the three metals and the amount of backdonation between the molecule and the metal.

Gas Sensing of Monolayer GeSe: A First-Principles Study

The adsorption of various gas molecules (H2, H2O, CO, NH3, NO and NO[Formula: see text] on monolayer GeSe were investigated by first-principles calculations. The most stable configurations, the adsorption energies, and the amounts of charge transfer were determined. Owing to the appropriate adsorption energies and the non-negligible charge transfers, monolayer GeSe could be a promising candidate as a sensor for NH3, CO, NO and NO2. According to the band structures of the H2O, CO, NH3, NO and NO2 adsorbed systems, the reductions of the bandgaps are caused by the orbital hybridizations between the gas molecules and the underlying GeSe. The partial densities of states reveal the degrees of these orbital hybridizations. The mechanisms of charge transfer are discussed in the light of both traditional and orbital mixing charge transfer theories. The charge transfer of the paramagnetic molecules NO and NO2 could be governed by both charge transfer mechanisms, while for the other gas molecules H2, H2O, CO and NH3, it was most likely determined by the mixing of the HOMO or LUMO with the GeSe orbitals.

Control of the metal-to-insulator transition by substrate orientation in nickelates

We proved that the critical thickness for metal-to-insulator transition (MIT) of LaNiO3 could be controlled by substrate orientation. By means of density functional theory calculations, films grown on SrTiO3 substrates with (001), (110) and (111) orientations have different amount of charge transfer across the interface. Different charge transfer induces different interfacial conductivity behavior and at the same time modifies the carrier density of adjacent LaNiO3 films. The manipulation of MIT by substrate orientation can be achieved through interfacial charge transfer induced interfacial conductive layer with the modified conductivity of LNO layer.

Thioxanthen-Based Blue Thermally Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes

Novel thermally activated delayed fluorescence (TADF) materials with 9,9-dimethyl-9H-thioxanthene 10,10-dioxide (SB) as an electron acceptor and andspiro[acridine-9,9'-fluorene] (D1) and spiro[acridine-9,9'-xanthene] (D2) as electron donors (2D1-SB and 2D2-SB) and their characteristics were compared with those of a reference material using 9,9-dimethylacridin (DMAC) as an electron donor (2DMAC-SB) for blue organic light-emitting diodes (OLEDs). We obtain the energies of the first singlet (S1) and first triplet (T1) excited states of TADF materials by performing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the ground state using the dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. We show that 2D2-SB would be a suitable blue OLED emitter because it has sufficiently small value (0.064 eV) of energy difference (ΔEST) between the S1 and T1 states, which is favorable for a reverse inter system crossing process from the T1 to S1 states and an emission wavelength of 439.5 nm with sufficiently large oscillator strength (F) value.

Molecular Design of Triazole Based Thermally Activated Delayed Fluorescence Hosts for Blue Electrophosphorescence.

We designed novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence by combining electron donor acridine derivatives and the electron acceptor 3,4,5-triphenyl-1,2,4-triazole (TPT) unit into a single molecule based on density functional theory (DFT). We obtain the energies of the first singlet (S1) and first triplet (T1) excited states of TADF materials by performing DFT and time-dependent DFT (TD-DFT) calculations on the ground state using dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results showed that these molecules are promising TADF host materials because they have a low barrier to hole and electron injection, a balanced charge transport for both holes and electrons, and a small energy difference (ΔEST) between the S1 and T1 states.

DFT+U study of sulfur hexafluoride decomposition components adsorbed on ceria (110) surface

The detection of sulfur hexafluoride (SF6) decomposition components is significant for monitoring the conditions of SF6-gas-insulated equipment. In present study, the adsorption of SF6 and its decomposition components (H2S, SO2, SOF2, and SO2F2) on ceria (110) was investigated by performing calculations based on density functional theory (DFT). Adsorption energy, adsorption configuration, charge transfer, density of states, potential energy and work function for molecular adsorption were adopted to evaluate the performance of ceria (110) on sensing SF6 decomposition components. Among all the gas molecules, H2S, SO2 and SOF2 were chemically adsorbed on ceria surface with the adsorption energy following the order: SOF2 > SO2 > H2S, while SO2F2 and SF6 were physically adsorbed on the substrate. Besides, the amount of charge transfer and work function modification of H2S, SO2 and SOF2 molecule’s adsorption were larger than those of SO2F2 and SF6. These calculation results demonstrated ceria (110) showed prominent sensitivity to H2S, SO2 and SOF2 while less activity to SF6, which means sensor based on ceria is promising for detecting H2S, SO2 and SOF2 in SF6 gas background, and thus has the potential to online monitor the working condition of SF6-gas-insulated equipment.

Highly Charge Transport Thermally Activated Delayed Fluorescence Host Materials Based on Phenyl-Biscarbazolyl Derivatives.

We designed novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence by combining the electron donor 1,3-Bis(N-carbazolyl)benzene (mCP) unit and the electron acceptor diphenylphosphine oxide-4-(triphenylsilyl) phenyl (TSPO1) unit in a single molecule based on density functional theory. We obtained the energies of the first singlet (S1) and the first triplet (T1) excited states of the TADF materials by performing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to the ground state using dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. Using DFT and TD-DFT calculations, the large separation between the HOMO and LUMO caused a small difference in energy (ΔEST) between the S1 and T1 states. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results showed that these molecules are promising TADF host materials because they have a low barrier to hole and electron injection, balanced charge transport for both holes and electrons, and small ΔEST.

Density functional theory study of NOx adsorption on alkaline earth metal oxide and transition metal surfaces

Since the emissions of nitrogen oxides (NOx) from automobiles cause air pollution, NOx storage-reduction (NSR) catalyst has been used to convert the NOx into harmless components such as N2 through the reduction of NOx. In this study, to provide fundamental understanding of key elementary steps of NSR, we established an extensive database for the adsorption properties of NO and NO2 on a wide range of metal and metal oxide surfaces. Our results show that the amount of charge transfer between NOx and surface is closely related to the molecular adsorption strength of NOx, and it changes the molecular stability of NOx on the surfaces by enlarging the inner bond length of N-O. Understanding the adsorption energy of the molecules or atoms that would participate in the reaction can be important to predict the ability of NOx storage and conversion in NSR. This study provides a useful insight for designing metals or metal oxides for NSR catalyst.

Donor-acceptor complex of 1-benzoylpiperazine with p-chloranil: Synthesis, spectroscopic, thermodynamic and computational DFT gas phase/PCM analysis

A new charge transfer (CT) complex is formed between the n- and π-donor 1-Benzoylpiperazine (1-BNZP) with π- acceptor p-chloranil (CHL). The CT-interaction is characterized in the defined polar solvent (acetonitile: ACN) at different temperatures. The 1:1 composition of the CT complex is proved. Benesi-Hildebrand method is used to find the stability constant (KCT) and molar extinction coefficient (ε). The more stability of CT complex is suggested from observed results. The thermodynamic parameters (ΔH° and ΔS°) were calculated by using Van't Hoff plot. From these values, CT complex formation process is found to be endothermic and spontaneous. FT-IR study gives information about stretching frequencies of mono substituted product of CT complex. TGA-DTA study is used for thermal stability of product. Morphology study is used to estimate the size and structure of the product. EDX spectrum is used for elemental analysis in the stoichiometric ratio. Theoretical investigation of the CT complex using DFT and TD-DFT also supports the experimental work. The C=O bond length of CHL increases on complexation with 1-BNZP along with significant amount of charge transfer from donor to acceptor. The HOMO-LUMO computation for protonated form of complex suggests a mono substituted product is formed via inner sigma (σ) complex.

Binding of model polycyclic aromatic hydrocarbons and carbamate-pesticides to DNA, BSA, micelles and liposomes

The binding to biosubstrates and micellar systems of pollutants as the polycyclic aromatic hydrocarbon (PAH) derivatives 1-aminopyrene (1-PyNH2) and 1-hydroxymethylpyrene (1-PyMeOH) and the carbamate-pesticides 1-naphthyl-N-methylcarbamate (carbaryl, CA) and methyl benzimidazol-2-ylcarbamate (carbendazim, CBZ) was analysed through an integrated strategy combining spectroscopy and quantum chemistry. As biosubstrates, natural DNA and bovine serum albumin (BSA) were taken into account for a thermodynamic analysis of the binding features through spectrophotometric and spectrofluorometric techniques. In all cases, a strong DNA interaction is present and intercalation is supposed as the major binding mode. For the PAH derivatives, DNA binding is found to be favoured under high salt conditions and BSA static quenching and binding with 1:1 stoichiometry occurs. The molecular structure and optical properties of 1-PyNH2, CA and CBZ together with their intercalated adducts in DNA were studied also by means of quantum chemical approach. The (TD)DFT calculations on intercalated dye/DNA adducts quantitatively reproduce the experimentally observed spectroscopic changes, thus confirming the intercalation hypothesis. The theoretical approach also provides information on the adducts' geometries and on the amount of charge transfer with DNA. Moreover, ultrafiltration tests in the presence of anionic (SDS), cationic (DTAC) and neutral (Triton X) micellar aggregates and liposomes provided insights into lipophilicity and cellular membrane affinity. PAH derivatives show high retention coefficient in all cases, whereas in the case of carbamate-pesticides micellar retention might be significantly reduced and is very limited in the case of liposomes.

A first-principles simulation of the metal borohydride ammonia borane complex (LiBH4)2(NH3BH3) and the decomposition reaction pathway for hydrogen storage

In this work, we predict a range of favorable functional properties of (LiBH4)2NH3BH3, a relatively new member of the boron-containing metal borohydride ammonia borane family, by means of ab initio calculations, as well as its parent compounds, LiBH4 and NH3BH3, for comparisons. Both the mechanical and dynamical stabilities of this new compound have been demonstrated theoretically for the first time. Results from elastic modulus calculations show that the mechanical properties of (LiBH4)2NH3BH3 are remarkably improved compared with its parent compounds. Secondly, Electronic structure results show that it remains to an insulator with large band gap typical of the boron-containing hydrogenous family, but the band gap can be tuned by the compositions of NH3BH3 and LiBH4. Charge analysis demonstrates that charge transfers in individual layers of LiBH4 and NH3BH3 are similar to LiBH4 and NH3BH3, respectively. A measurable amount of charge transfers from the LiBH4 layers to the NH3BH3 layers result in enhanced activation properties for hydrogenation and dehydrogenation in (LiBH4)2NH3BH3. Thirdly, Free energies of six possible dehydrogenation reactions have been calculated from 0 K to 700 K, and the results show that combination of NH3BH3 and LiBH4 can reduce the dehydrogenation energies compared with the parent compounds, a result consistent with recent experiments. Meanwhile, the N–B bond strengths increase and thereby borazine and diborane formation are reduced upon dehydrogenation.

Density functional theory study of fullerenes adsorption on nitrogenated holey graphene sheet

The effect of C20 and C60 fullerenes adsorption on the electronic properties of nitrogenated holey graphene sheet was investigated using density functional theory. The optimal configurations, adsorption energies, charge transfer, electronic band structures, and density of states of nitrogenated graphene sheets with adsorbed fullerenes were obtained. The small adsorption energy, large adsorption distance, and small amount of charge transfer indicate physisorption of fullerenes on nitrogenated graphene sheets. It is found that C20 fullerenes behave as p-type dopant, while C60 fullerenes work similar to n-type one. Adsorption of fullerene decreases the energy band gap of the nitrogenated holey graphene sheets with semiconducting properties. The C60 fullerene decreases the energy band gap of nitrogenated holey graphene sheet more than the C20 fullerene. The effect of the number of adsorbed fullerenes on the energy band gap of the nitrogenated holey graphene sheets is not considerable. Our results suggest hybrid structures composed of fullerenes and nitrogenated holey graphene sheet with great potential for electronics applications.

Thermally activated delayed fluorescence host materials based on triphenylphosphine oxide derivatives

Novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence were developed by combining the electron donor acridine derivatives with the electron acceptor triphenylphosphine oxide unit in a single molecule based on density functional theory. We obtained the energies of the first excited singlet (S1) and triplet (T1) states of the TADF materials by performing procedures in accordance with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to the ground state using dependence on the charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. Using DFT and TD-DFT calculations, the significant separation between the HOMO and LUMO caused a small difference in energy (ΔEST) between the S1 and T1 states. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results also showed that these molecules are promising TADF host materials because they demonstrate a low barrier to hole and electron injection, balanced charge transport for both holes and electrons, and small ΔEST.

Electronic and optical properties of C-doped BN nanotubes by adsorption of typical decomposition products of C3F7CN gas

Abstract C3F7CN((CF3)2CFCN) is a potential environmentally friendly insulating gas to alternative SF6. Finding an effective way to monitor C3F7CN gas decomposition products is necessary to ensure the stable operation of power equipment. The adsorption behaviors of typical decomposition products (CF4 and CF3CN) on pristine boron nitride nanotubes(BNNT) and C-doped boron nitride nanotubes(C-BNNT) were investigated. The adsorption energy of CF4 and CF3CN on pristine BNNT is small, and the interaction distance between molecules is large, which indicates that pristine BNNT and gas molecules form physical adsorption through weak van der Waals forces. Then, we studied the adsorption behaviors between C-doped BNNT and gas molecules. The adsorption of CF4 on C-doped BNNT has a few effect on the band gap of CB-BNNT. For CF3CN molecules, the adsorption of F atoms on the C-doped BNNT is physical adsorption, while the N atom in the -CN group forms chemical adsorption at the CN and CB sites, with higher charge transfer amount. After adsorption -CN group, and the 2p orbital of N atom and the 2p orbital of doped C atom dominate at the Fermi level, which changes band gap of C-doped BNNT. Meanwhile, adsorption behaviors weaken the absorption capacity of C-BNNT for infrared light and reduce its reflectivity to ultraviolet light. Tube diameter has a significant effect on the adsorption of N atom of CF3CN on C-BNNTs, the band gap and optical properties changes with the diameter increases. These changes of electronic and optical properties indicated that C-doped BNNT can be used as a potential material for detecting CF3CN.

Effects of surface structure and halogen substitution on electronic charge transfer in adlayers of (BETS)2-GaCl4 on silver surfaces

Results of DFT calculations are presented that focus on changes to charge transfer, energetics, and geometry in adlayers of (BETS)2-GaCl4 (an organic superconductor Bechgaard salt, ʻOSC’) as modulated by changes in surface and degree of substitution to its halogens. Specifically, results are presented for the charge transfer to/in adlayers of λ-(BETS)2-GaCl4 on the Ag(111) and Ag(100) surfaces; and on both surfaces including further the effects of multiple successive F substitutions for Cl onto the Ga center. Results show two interesting important phenomena: first, that the amount of charge transfer is indeed highly surface sensitive (by about 0.5 net electron in this case), and second, that substitution of different amounts of F atoms on the Ga center also has profound effects on the charge transfer to the Ga atom in the GaCl(4−x)Fx center, albeit in nonlinear and counterintuitive ways which essentially conserve total net charge in the overall adlayer.The results of this work, in summary, provide insight which should help understand the degree to which surface-mediated modulation of assembled adlayers of nanoelectronic materials and their electronic structure can be varied and further supplements recent work on superhalogenated OSC charge transfer materials.

Facile synthesis of bismuth vanadate/bismuth oxide heterojunction for enhancing visible light-responsive photoelectrochemical performance

BiVO4 is a well-known photocatalyst for water oxidation due to small band gap and suitable band positions, but short diffusion length is necessary to solve for practical applications. This study adopts common alkaline etching process for fabricating BiVO4 and BiOx composite as photocatalyst for water oxidation for the first time. The BiVO4/BiOx heterojunction is fabricated on conducting glasses using hydrothermal synthesis and NaOH etching process for establishing heterojunction. Different NaOH concentrations are used for fabricating BiVO4/BiOx electrodes with different BiOx amounts. Due to adequate amount of BiOx for achieving effective charge transfer and suitable amount of continuous aggregations on the surface for reducing charge recombination at nanoparticle boundaries, the BiVO4/BiOx electrode prepared using 0.15 M NaOH for etching shows the highest photocurrent density of 0.48 mA/cm2 at 1.23 V versus reversible hydrogen electrode under air mass 1.5 global illumination. The BiVO4 electrode only shows the photocurrent density of 0.06 mA/cm2 measured at the same conditions. Long-term stability of the BiVO4/BiOx electrode is further improved by ten-fold after depositing NiOOH co-catalyst on the surface for reducing charge recombination. The result indicates the significance for the bismuth oxide amount in the BiVO4/BiOx composite on influencing the photoelectrochemical catalytic ability toward water oxidation.

Cyclic dimers of formamidine with its N-halogenated formamidine analogues: Structure, energetics, and proton-halonium transfer

Ab initio calculations were carried out to investigate cyclic dimers of formamidine with its N-halogenated analogues, HN = CHNHX (X = Cl, Br, or I). Geometry optimizations and frequency calculations were completed with the MP2 method and both the aug-cc-pVDZ and the aug-cc-pVTZ basis sets. BSSE-corrected interaction energies were calculated at the MP2, QCISD, and CCSD(T) methods. Electron density at relevant critical points, and charge transfers were examined through AIM and NBO analyses respectively. Both the electron density at each of the critical points and the amount of charge transfer correlate with the strength of the dimer interactions. The N-X stretching frequencies and the 15N NMR chemical shifts were also found to correlate with the dimer interaction strengths. Proton-halonium transfer for each of the dimers was also investigated. For any given X, the potential energy profile along the intrinsic reaction coordinate demonstrates that the proton-halonium transfer occurs in one step, without any intermediates. Similarly, the profile of the corresponding force constant (the second derivative of the potential energy) in the transition region indicates that the proton-halonium transfer is a synchronous process. In all cases, the energy barrier for proton-halonium transfer was found to decrease with increasing size of the halogen. Solvent effects were examined using the SMD model with two solvents of differing polarity: tetrahydrofuran and water. Although the proton-halonium transfer remains concerted and synchronous, the energy barrier to proton-halonium transfer increases in solution to the extent that the barrier becomes higher for X = I than it is for X = Br.

The adsorption of nitrogen oxides on noble metal-doped graphene: The first-principles study

The first-principles method based on density functional theory has been used to investigate the adsorption performance of NO/NO2 molecules on intrinsic, Ag-doped, Pt-doped and Au-doped graphene. Results show that graphene doped with Ag/Pt/Au has shorter final adsorption distance, larger adsorption energy and charge transfer amount with NO/NO2 molecules than intrinsic graphene, and the charge densities of doped graphene and NO/NO2 molecules overlap effectively. Therefore, doping graphene with noble metals can greatly enhance the adsorption between graphene and NO/NO2 molecules. Analysis also reveals that Au-doped graphene has the strongest adsorption effect on NO/NO2 molecules, followed by Ag-doped graphene, while Pt-doped graphene has the weakest role on the adsorption of NO/NO2 molecules. The work conducted in this research provides a theoretical guidance for the application of NO/NO2 gas sensors based on graphene.

How oxides affect the stretching modes of carbon monoxide adsorbed on Ni catalyst?

Testing the stretching frequency shift of adsorbed CO has been a popular tool to evaluate the chemical property change of catalysts. We demonstrated first-principles models to reveal the mechanism of oxides effect on the frequency shift of CO on the Ni catalysts. Our calculations show that higher coverage of CO molecules leads to blue frequency shift, and there is negligible frequency shift when co-adsorbed with Al2O3 species and red frequency shift when co-adsorbed with ZrO2 or CeO2 species, which are consistent with the experimental literatures. The frequency shift is conformed to be proportional to the charge transfer amount of the π back-donation from Ni to the π⁎ orbital of CO molecule. The frequency shift direction is not determined by whether the oxide species is an electron acceptor or donor when adsorbed on Ni surface, but by how the oxide species affects the electrons on t2g and eg orbitals of the Ni atom under the CO molecule. The redistribution between t2g and eg orbitals induces the decreasing or increasing back-donation when a CO molecule co-adsorbed with the CO molecules or CeO2 species.

Design and output performance of vibration energy harvesting triboelectric nanogenerator

With the advent of global warming and energy crisis, the search for renewable energy to reduce carbon emissions has become one of the most urgent challenges. Ithas become a research hotspot to collect or harvest various mechanical energy in nature and convert it into electric energy. Vibration is a common form of mechanical movement in our daily life. It is visible both on most working machines and in nature and is a type of potential energy. There are several methods that can convert such mechanical energy into electric energy. Triboelectric nanogenerator (TENG) based on the principle of contact electrification and electrostatic induction which first appeared in 2012 by Zhonglin Wang provides a feasible method of efficiently collecting the vibrational energy with different vibrating frequencies. In this paper, a contact-separation mode of TENG is designed and implemented. The voltage- quantity of charge- distance(V-Q-x)relation of TENG is calculated. During the experiment, the factors such as load resistance, vibration frequency, etc. which affect the output performance, are considered and analyzed. An electrically driven crank-connecting rod mechanism is employed to provide the vibration source with adjustable frequency in a range of 1-6 Hz. The result shows that the amount of charge transfer in each working cycle remains almost unchanged, while the voltage and current increase with frequency increasing. When the frequency is 5 Hz, the best power matching resistance of the TENG is about 33 MΩ and the maximum output power reaches 0.5 mW. For a further study, a COMSOL software is used to simulate the distribution rule and variation rule of the electric potential in the contact-separation process, then the theoretical charge density and the experimental charge density on the polymer surface are compared and analyzed in order to provide theoretical and practical support for the design of TENG with collected vibration energy and self-powered vibration sensor. The result shows that the electric potential is proportional to the distance between two friction layers. While as the distance between two friction layers increases, the electric potential and the charge density both show a tendency to concentrate in the middle of the friction layer. The huge difference between experimental result and the simulation predicts thatmuch work should be done continually to improve the output of the TENG. Finally, the obtained results conduce to understanding the contact electrification and electrostatic induction mechanism and also provide a new method of harvesting the vibration energy.