Electronic structures of organic molecule encapsulated BN nanotubes under transverse electric field

The electronic structures of boron nitride nanotubes (BNNTs) doped by different organic molecules under a transverse electric field were investigated via first-principles calculations. The external field reduces the energy gap of BNNT, thus makes the molecular bands closer to the BNNT band edges and enhances the charge transfers between BNNT and molecules. The effects of the electric field direction on the band structure are negligible. The electric field shielding effect of BNNT to the inside organic molecules is discussed. Organic molecule doping strongly modifies the optical property of BNNT, and the absorption edge is redshifted under static transverse electric field.     

钴掺杂氮化硼纳米管吸附氯酚类污染物的理论研究

氯酚(CPs)类污染物是形成持久性有机污染物二噁英的先驱物, 具有较强的致畸、致癌和致突变性. 为探索去除或检测这类污染物的新型材料, 应用密度泛函理论研究了(8,0)单壁氮化硼纳米管(BNNT)和Co掺杂的(8,0)单壁氮化硼纳米管(Co-BNNT)对2-氯酚(2-CP)、2,4,6-三氯酚(TCP)、五氯酚(PCP)的吸附行为及作用机制. 结果表明, 与BNNT相比, Co-BNNT费米能级附近出现杂化态, 带隙明显减小. BNNT对2-CP、TCP和PCP呈现物理吸附, 而Co-BNNT对三种氯酚则是化学吸附, 纳米管与分子间发生了明显的电荷转移, 体系态密度在费米能级附近发生了明显变化. Co原子掺杂明显增强了BNNT的电子输运能力, 提高了纳米管对氯酚的吸附活性. Co-BNNT有望是去除或检测氯酚类污染物的潜在资源.     

Charge transfer in the TCNQ-sexithiophene complex

Molecular crystals from thiophene molecules can be doped with TCNQ-F4 molecules for use in all-organic optoelectronic and semiconductor devices. The charge transfer and the molecular orbital energy level formation in between these two organic molecules are investigated here by density functional theory calculations. The isolated molecules are calculated nonbonded and bonded together, forming a charge transfer complex (CTC). The relaxed structure of the complex shows essentially coplanar and centered molecules with the alpha-sexithiophene rings tilted alternatingly by 4.8 degrees. The bond formation of these molecules results in a charge transfer of approximately 0.4 e from the alpha-sexithiophene to the TCNQ-F4 molecule. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap width is reduced as compared to the isolated molecules due to the newly formed orbitals in the CTC. Upon adsorption on a Au(111) surface, electrons are transferred onto the molecule complex, thereby causing the molecular levels to align asymmetric with respect to the charge neutrality level. The theoretical results for the single molecule and CTC layer are compared to experimental photoemission and scanning tunneling spectroscopy results.     

铂掺杂氮化硼纳米管及CO在其表面的吸附行为的理论研究

采用基于密度泛函理论的PBEPBE方法对铂(Pt)掺杂的氮化硼(BN)纳米管进行了理论研究. 计算结果表明, Pt原子突出BN纳米管表面, Pt的d轨道暴露到外面, 使它更容易和外来分子发生相互作用, 提高了纳米管的反应活性. Pt取代掺杂缩小了纳米管的能隙, 从而提高BN纳米管的导电性. 一氧化碳(CO)在Pt掺杂BN纳米管上的吸附行为表明, 2个CO能化学吸附到纳米管表面, 更多的CO分子吸附是物理吸附.     

Nitrogen monoxide storage and sensing applications of transition metal–doped boron nitride nanotubes: a DFT investigation

The structural properties, electronic properties, and adsorption abilities for nitrogen monoxide (NO) molecule adsorption on pristine and transition metal (TM = V, Cr, Mn, Nb, Mo, Tc, Ta, W, and Re) doping on B or N site of armchair (5,5) single-walled boron nitride nanotube (BNNT) were investigated using the density functional theory method. The binding energies of TM-doped BNNTs reveal that the Mo atom doping exhibits the strongest binding ability with BNNT. In addition, the NO molecule weakly interacts with the pristine BNNT, whereas it has a strong adsorption ability on TM-doped BNNTs. The increase in the adsorption ability of NO molecule onto the TM-doped BNNTs is due to the geometrical deformation on TM doping site and the charge transfer between TM-doped BNNTs and NO molecule. Moreover, a significant decrease in energy gap of the BNNT after TM doping is expected to be an available strategy for improving its electrical conductivity. These observations suggest that NO adsorption and sensing ability of BNNT could be greatly improved by introducing appropriate TM dopant. Therefore, TM-doped BNNTs may be a useful guidance to be storage and sensing materials for the detection of NO molecule.

     

Theoretical Study of Adsorption Behavior of Vemurafenib Drug over BNNT(5,5-9) as a Factor of Drug Delivery: a DFT Study

In this research, a density functional theory(DFT) calculation was performed for investigation adsorption behavior of the anticancer drug Vemurafenib on BNNT(5,5-9) by using the M06-2X/6-31 G* level of theory in the solvent water. The electronic spectra of the Vemurafenib drug, BNNT(5,5-9) and complex BNNT(5,5-9)/Vemurafenib in solvent water were calculated by Time Dependent Density Functional Theory(TD-DFT) for the study of adsorption effect. The non-bonded interaction effects of the Vemurafenib drug with BNNT(5,5-9) on the electronic properties, natural charges and chemical shift tensors have been also detected. The results display the change in title parameters after process adsorption. According to the natural bond orbital(NBO) results, the molecule Vemurafenib and BNNT(5,5-9) play as both electron donor and acceptor at the complex BNNT(5,5-9)/Vemurafenib. On the other hand, the charge transfer occurs between the bonding, antibonding or nonbonding orbitals in two molecules drug and BNNT. As a consequence, BNNT(5,5-9) can be considered as a drug delivery system for the transportation of Vemurafenib as anticancer drug within the biological systems.     

Adsorption studies of dimethyl and methyl-ethyl ester molecules on silicene nanoring: Application of DFT study

The electronic and adsorption properties of dimethyl and methyl-ethyl ester molecules on a silicene nanoring (SiNR) are studied using first-principles calculations. The adsorption properties of dimethyl and methyl-ethyl ester molecules on the surface of a silicene nanoring is investigated in terms of density of states spectrum, adsorption energy, average energy gap variation, Mulliken charge and Bader charge transfer. The structural stability of the SiNR is ensured using formation energy. The variation in the electron density and energy gap is noticed upon adsorption of dimethyl and methyl-ethyl ester molecules in the SiNR base material compared with its isolated counterpart. The highlights of the present work are silicene nanoring is used as a base material for ester molecule adsorption. The adsorption behavior of ester molecules is studied using energy band structure. The DOS spectrum confirms the transfer of electrons between the SiNR and ester molecules. The findings suggest that a SiNR can be used as a base material for the detection of dimethyl and methyl-ethyl ester molecules.     

Exciton-mediated hydrosilylation on photoluminescent nanocrystalline silicon

A novel white light-promoted reaction using photoluminescent nanocrystalline silicon enables the hydrosilylation of alkenes and alkynes, providing stabilization of the porous silicon without significant loss of the photoemissive qualities of the material. Photopatterning and lithographic fabrication of isolated porous silicon structures are made possible. Experiments and observations are presented which indicate that the light promoted hydrosilylation reaction is unique to photoluminescent silicon, and does not function on nonemissive material. Hydrosilylation using a reactive center generated from a surface-localized exciton is proposed based upon experimental evidence, explaining the photoluminescence requirement. Indirect excitons formed by light absorption mediate the formation of localized electrophilic surface states which are attacked by incoming alkene or alkyne nucleophiles. Supra-band gap charge carriers have sufficient energy to react with nucleophilic alkenes and alkynes, thereupon causing Si-C bond formation, an irreversible event. The light-promoted hydrosilylation reaction is quenched by reagents that quench the light emission from porous silicon, via both charge transfer and energy transfer pathways.     

The role of oxygen in catalysis

Catalytic reactions with oxygen are divided into two groups: electrophilic oxidation proceeding through activation of oxygen, and nucleophilic oxidation in which insertion of nucleophilic oxygen species into previously activated organic molecule occurs. The role of different types of lattice oxygen in the nucleophilic oxygen addition as well as catalyst properties determining the electrophilic pathway are discussed.     

A comprehensive theoretical study on the hydrolysis of carbonyl sulfide in the neutral water

The detailed hydration mechanism of carbonyl sulfide (COS) in the presence of up to five water molecules has been investigated at the level of HF and MP2 with the basis set of 6-311++G(d, p). The nucleophilic addition of water molecule occurs in a concerted way across the C==S bond of COS rather than across the C==O bond. This preferential reaction mechanism could be rationalized in terms of Fukui functions for the both nucleophilic and electrophilic attacks. The activation barriers, DeltaH( not equal) (298), for the rate-determining steps of one up to five-water hydrolyses of COS across the C==S bond are 199.4, 144.4, 123.0, 115.5, and 107.9 kJ/mol in the gas phase, respectively. The most favorable hydrolysis path of COS involves a sort of eight-membered ring transition structure and other two water molecules near to the nonreactive oxygen atom but not involved in the proton transfer, suggesting that the hydrolysis of COS can be significantly mediated by the water molecule(s) and the cooperative effects of the water molecule(s) in the nonreactive region. The catalytic effect of water molecule(s) due to the alleviation of ring strain in the proton transfer process may result from the synergistic effects of rehybridization and charge reorganization from the precoordination complex to the rate-determining transition state structure induced by water molecule. The studies on the effect of temperature on the hydrolysis of COS show that the higher temperature is unfavorable for the hydrolysis of COS. PCM solvation models almost do not modify the calculated energy barriers in a significant way.     

Theoretical Prediction of Adsorption Properties of Carmustine Drug on Various Sites of the Outer Surface of the Single-Walled Boron Nitride Nanotube and Investigation of Urea Effect on Drug Delivery by DFT and MD

In this work, the adsorption behavior of Carmustine (BCNU) drug over the (6,0) zigzag single-wall boron nitride nanotube (SWBNNT) is studied by means of density functional theory calculations and molecular dynamics simulations (MD). The calculated adsorption energies proved that the adsorption of BCNU molecule on SWBNNT is a physisorption process. The natural bond orbital calculations demonstrated that existence of a charge transfer from the SWBNNT to the BCNU molecule. Moreover, quantum theory of atoms in molecules showed that the hydrogen bonds and electrostatic interactions are two major factors contributed to the overall stabilities of the complexes. Furthermore, interaction of BCNU with the surface of single wall BNNT at 310 K and 1 bar in the present of water and different concentration of Urea molecules has been studied by MD simulation. The MD results confirm that the highest number of hydrogen bond and the lowest value of Lennard-Jones (L-J) energy between nanotube and drug exist in the simulation system with concentration of 1 mol L^?1 Urea.     

The Nature of Electrophilic and Nucleophilic Oxygen Adsorbed on Silver

Results of a spectroscopic study of two forms of adsorbed atomic oxygen on a silver surface, which participate in ethylene epoxidation reaction, are presented. The possibility of the combined use of the methods of photoelectron spectroscopy and X-ray absorption for a detailed analysis of adsorbate electron structure on solid surfaces is demonstrated. It is found that a significant difference in the position of O 1s lines for nucleophilic (528.3 eV) and electrophilic (530.4 eV) oxygen is determined by the effects of the initial state, that is, by the difference in the charge state of oxygen anions. The use of the well-know correlation of the Auger line splitting with a Pauling charge at an oxygen atom showed a substantial difference (1 electron charge unit) in charge transfer from metal to the nucleophilic or electrophilic adsorbed oxygen atom. Based on the X-ray absorption data of the oxygen K-edge, it is found that there is a substantial overlap of the 4d- and 5sp orbitals of silver with oxygen 2p orbitals in the nucleophilic state in the formation of an Ag–O bond and there is only an overlap of 5sp orbitals of silver with oxygen 2p orbitals in the electrophilic state. Structural models of the adsorption site are presented for both states. The conclusion is drawn that the charge state of oxygen in oxide systems may depend substantially on its binding to metal atoms.     

Studies on the encapsulation of F- in single walled nanotubes of different chiralities using density functional theory calculations and Car-Parrinello molecular dynamics simulations

In this study, the encapsulation of F(-) in different nanotubes (NTs) has been investigated using electronic structure calculations and Car-Parrinello molecular dynamics simulations. The carbon atoms in the single walled carbon nanotube (CNT) are systematically doped with B and N atoms. The effect of the encapsulation of F(-) in the boron nitride nanotube (BNNT) has also been investigated. Electronic structure calculations show that the (7,0) chirality nanotube forms a more stable endohedral complex (with F(-)) than the other nanotubes. Evidence obtained from the band structure of CNT calculations reveals that the band gap of the CNT is marginally affected by the encapsulation. However, the same encapsulation significantly changes the band gap of the BNNT. The density of states (DOS) derived from the calculations shows significant changes near the Fermi level. The snapshots obtained from the CPMD simulation highlight the fluctuation of the anion inside the tube and there is more fluctuation in BNNT than in CNT.     

乙炔与氢化锂单体和二聚体加成反应中的HOMO-HOMO相互作用

用前线分子轨道分析乙炔与氢化锂单体和二聚体加成反应的过渡态.结果表明,在其反应过渡态形成过程中,反应物间的HOMO-LUMO和HOMO-HOMO相互作用均起重要作用.较强烈的HOMO-HOMO相互作用与过渡态附近反应由亲电性加成向亲核性加成转变相关,该反应特性的转变又与LiH中的氢原子在反应中的电荷转移相关.     

Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

Versatile Room‐Temperature‐Phosphorescent Materials Prepared from N‐Substituted Naphthalimides: Emission Enhancement and Chemical Conjugation

Purely organic materials with room‐temperature phosphorescence (RTP) are currently under intense investigation because of their potential applications in sensing, imaging, and displaying. Inspired by certain organometallic systems, where ligand‐localized phosphorescence (³π‐π*) is mediated by ligand‐to‐metal or metal‐to‐ligand charge transfer (CT) states, we now show that donor‐to‐acceptor CT states from the same organic molecule can also mediate π‐localized RTP. In the model system of N‐substituted naphthalimides (NNIs), the relatively large energy gap between the NNI‐localized ¹π‐π* and ³π‐π* states of the aromatic ring can be bridged by intramolecular CT states when the NNI is chemically modified with an electron donor. These NNI‐based RTP materials can be easily conjugated to both synthetic and natural macromolecules, which can be used for RTP microscopy.     

A Density Functional Theory Study on Electronic Structure and Second—order Nonlinear Optical Properties of Some Push—Pull Molecules

Time-dependent density-functional theory(TDDFT)has been applied to calculate the electronic structure and second-order nonlinear optical(NLO) properties of some organic molecules.The two-dimensional(2-D)charge transfer charateristics of calculated molecules were studied and compared with corresponding experimental results.All the theoretical results agree well with the measurement.For 2-D molecule with two-fold symmetry,the dominant charge transfer is off-diagonal,while for three-fold symmetry 2-D molecule,the dominant charge transfer is not only between branches and central group but also among branches.     

The Effects of Methylene Blue on the Optical Properties of Nanometer-sized CdS Organosol

The inverse micelle system of nanometer-sized CdS doped with Methylene Blue(MB) was synthesized and characterized by using absorption and fluorescence spectra. The results show that MB molecules were absorbed onto the surface of CdS nanoparticles and interacted with surfactants when its concentration was lower than 4×10^-6 mol/L. From the comparison of their spectra, MB molecules by adsorption have a strong quenched fluorescence emission of CdS nanoparticles with surface defect states. All responses and main mechanism are ascribed to the charge transfer between the CdS organosol and Methylene Blue molecules.