Density Functional Theory Study on the First Hyperpolarizabilities of Mono-and Bimetal Ir(Ⅰ)/Rh(Ⅰ)2,2'-Bidipyrrins Complexes

Metal complexes with excellent nonlinear optical（NLO） properties have attracted considerable attention. The geometry structure, electronic spectra and NLO properties of 2,2？-bidipyrrins（L） and mono-and bimetal Ir（I）/Rh（I）–L complexes have been investigated by density functional theory method. Our calculations revealed that L with planar configuration shows the largest first hyperpolarizability value, which is 2.2 to 5.5 times larger than that of others. It is attributed to the single direction of intramolecular charge transfer. When metal ions were embedded in ligands, the first hyperpolarizability values of mono-and bimetal Ir/Rh（I）–L complexes were smaller than that of L, and that of bimetal Ir/Rh（I）–L complexes were smaller than the corresponding monometallic Ir/Rh（I）–L. This is caused by the intramolecular charge transfer from multiple directions as well as the amount of charge transfer. On the other hand, on increasing the number of metal ions, the charge transfer in the opposite direction cancels each other more obviously. Our work would provide some theoretical reference for the second-order NLO responses of mono-and bimetal complexes.

Exploration of Earth-Abundant Transition Metals(Fe,Co,Ni)Doped on W_(18)O_(49)System as Electrocatalysts for Urea Productiont

The conversion of inert N_(2)and CO_(2)into urea by electrocatalytic technology not only reduces the cost of urea synthesis in future,but also alleviatesthe environmental pollution problem caused by carbon emission in traditional industrial production.However,facing downside factors such as strong competitive reactions and unclear reaction mechanism,the design of high-performance urea catalysts is imminent.This study demonstrates that W_(18)O_(49)system doped heteronuclear metals(TM=Fe,Co,Ni)can effectively solve the problem of competitive adsorption between N_(2)and CO_(2)and realize the co-adsorption of N_(2)and CO_(2)at diverse sites.Their theoretical limiting voltages for urea production on TM-W_(18)O_(49)(TM=Fe,Co,Ni)systems are-0.46 V,-0.42 V and-0.52 V,respectively.The results are all lower than that of the contrastive voltage in pristine W_(18)O_(49)system(-0.91 V),further indicating the rationality and necessity of single-atom doped strategy for the co-reduction of two molecules.Specially,Co-W_(18)O_(49)can theoretically inhibit the side reactions of NRR,CO_(2)RR,and HER,which deserve future experimental exploration in future.The study suggests that doping heteronuclear metal into transition metal oxides is a feasible scheme to solve competitive adsorption and improve catalytic performance.

Theoretical Studies on Reaction Mechanisms of HNCS with NH(X^3Σ)

The reaction mechanisms of HNCS with NH（X^3∑ ） were theoretically investigated. The minimum energy paths （MEP） of the reaction were calculated by using the density functional theory（DFT） at the B3LYP/6-311 ＋ ＋ G^＊＊ level. The equilibrium structural parameters, the harmonic vibrational frequencies, the total energies, and the zeropoint energies（ZPE） of all the species were calculated. The single-point energies along the MEP were further refined at the QCISD（T）/6-311 ＋ ＋ G^＊ ＊ level. It was found that the mechanisms of the HNCS ＋ NH（X^3∑） reaction involve two channels producing the HNC ＋ HNS and the N2H2 ＋ CS products. Channel 1 plays a dominant role and the HNC ＋ HNS are the main preduets. The reaction is exothermie.

Effects of Size and Surface Modification of Multi-walled Carbon Nanotubes on Mechanical Properties of Polyurethane-based Nanocomposites

Polyurethanes/multi-walled carbon nanotube （PU/CNT） composites were prepared with a help of ultrasonically dispersing CNT in the traditional procedure of synthesizing polyurethane. In this case, the various loading levels, sizes and surface-modified groups were considered to regulate the mechanical performances of the PU/CNT nanocomposites. Moreover, the structure and mechanical properties of all the PU/CNT nanocomposites were investigated by attenuated total reflection-Fourier transform infrared spectroscopy, dynamic mechanical analysis, scanning electron microscope, transmission electron microscope, and tensile testing. The experimental results showed that a moderate loading-level of 0.1wt% and a diameter of 10-15 nm for CNT could produce the maximum tensile strength and elongation while it was worth noting that the surface carboxylation of CNT could further enhance the tensile strength and elongation of the PU/CNT nanocomposites.

Theoretical Study on Structural Stability and Nonlinear Optical Properties of Non-conjugated Carbon and Nitrogen Diradical Molecules

The geometrical structures and stability of non-conjugated C5H10 and C3H8N2 singlet and triplet diradical molecules have been investigated at the UCCSD/6-311g^＊＊ level. The effects of molecular structure, radical position, amount of Hartree Hork （HF） exchange and spin multiplicity on the nonlinear optical （NLO） coefficients have been also investigated. The reliable UCCSD results show that the triplets of all diradical molecules are more stable compared to their singlet analogues. In addition, the αs and βtot values of C5H10 and C3H8N2 triplet diradical mo-lecules have been investigated by the UBHandHLYP, UB3LYP, UBLYP, UHF and UCCSD methods. The investigation shows that the variations in αs and βtot values are closely connected to the amount of HF exchange. The increasing amount of HF exchange results in monotonic decreases in αs and βtot values, while the αs and βtot values of singlet diradical molecules and the γs of C5H10 and C3H8N2 singlet and triplet diradical molecules have been studied by the UBHandHLYP method. The results illustrate that the NLO coefficients for our studied non-conjugated carbon and nitrogen diradical species can be tuned by molecular structure, radical position and spin multiplicity, which are very significant for designing NLO materials.

Preparation and Characterization of Dichlorocarbene Modified Multiple-walled Carbon Nanotubes

Multiple-walled carbon nanotubes were functionalized by cycloaddition of dichlorocarbene.The chemical modification was performed by using chloroform and sodium hydroxide.Various phase transfer catalysts were used to increase the efficiency of the reaction.Benzyltriethylammonium chloride used as phase transfer catalyst could highly enhance the effect of functionalization.Elemental analysis was used to evaluate the degree of functionalization.Characterization was performed using scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.Fourier transform infrared spectroscopy（FTIR）and energy-dispersive X-ray spectroscopy（EDS）were used to confirm the resulting material.

Crystal Structure and Electronic Structure of a Luminescent Compound 2-(2-Pyridyl) Benzimidazole

The crystal structure of 2-(2-pyridyl) benzimidazole was determined by single- crystal X-ray diffraction at 193(2) K. It crystallizes in orthorhombic system, space group Pbca with unit cell constants a = 10.6204(7), b = 10.1407(4), c = 18.6327(8) , Z = 8, V = 2006.7(2) 3, Dc = 1.292 g/cm3, F(000) = 816 and m(MoK) = 0.081 mm-1. The structure was refined to R = 0.0317 and wR = 0.0454 for 795 observed reflections with I > 2s(I). In the solid state, it has an emission maximum at 369 nm, while in solution (DMSO), the maximum excitation is at 372 nm. Quantum chemistry calculation was performed by the method of density functional theory. Theoretical results show that atom N is the reactive site when coordinating with a metal, and the electronic structure of the title compound presents excellent carrier transport properties.

Synthesis of Hydroxypropyl-β-cyclodextrin Bonded Silica-gel and its Application to Resolution

In order to set up a simple and effective method for resolution of optical isomers, hydroxypropyl-β-cyclodextrin was bonded to silica-gel, which can be used for preparation of thin-layer chromatography plates. Resolution of clenbuterol and propranolol were investigated on these thin-layer chromatography plates using different combinations of solvent systems at ambient temperature. The best simultaneous resolution was achieved in solvent system of acetonitrilen-butanol （50：50, v/v）. Rst values of resolution of clenbuterol hydrochloride and propranolol hydrochloride are 3.6 and 4.3, respectively. The spots of different enantiomers are separated clearly. The results showed that hydroxypropyl-β-cyclodextrin bonded silica-gel could be successful in resolution of chiral adrenergic drugs. The study offers a direct, rapid and reliable method for separation of this kind of optically active compounds.

Structure and Mechanical Properties of Waterborne Polyurethane-based Composites Filled with Self-assembled Supramolecular Nanoplatelets

New composites of waterborne polyurethane （WPU） as a matrix were prepared by incorporating rigid supramolecular nanoplatelets （SNs） as filler, which were self-assembled by the selective inclusion of β-cyclodextrin （β-CD） onto poly（propylene oxide） （PPO） segment in the poly（ethylene oxide）- block-PPO-block-poly（ethylene oxide） （PEO-b-PPO-b-PEO）. It is worth noting that, when the loading level of SN is lower than 3wt%, the SNs with moderate PEO length result in the simultaneous increase in strength, elongation and Young＇s modulus in contrast with neat WPU. If there is no stretching free PEO chain, both strength and elongation decrease in spite of an increase in Young＇s modulus. However, too long PEO chains result in the decrease of mechanical performances while the relatively higher loading-level of SNs also inhibits the enhancement of strength and elongation.

Theoretical Studies on Structures and Properties of Endohedral Fullerenes Complexes: XH_n@C_(32)(X=F, O, N, C; n=1―4)

Theoretical studies on structures and properties of endohedral fullerene complexes formed by encapsulating small molecules of HF, H20, NH3, and CH4 in a C32 fullerene cage, were carried out by ab initio method. Current calculations reveal that these processes to encase them in fullerene are energetically unfavorable because of the small cavity size of C32. The red shift in the F-H stretching frequency indicates the potential existence of hydrogen bonding between the HF molecule and the carbon cage.

Photo-isomerization of Aromatic α-Hydroxy Hydrazone

Photo-isomerization of aromatic α-hydroxy hydrazone was reported. We investigated the structures of salicylaldehyde phenylhydrozone（SP） in the ground state using density functional theory（DFT） with the B3LYP functional and the 6-311＋G（d） basis set. All nine possible isomers of SP in the ground state consist of seven phenol forms and two ketone forms. Intrisic reaction coordinate（IRC） analysis discloses the existence of a cycle driven by the two proton transfer processes in the ground and excited states of SP, which suggests that no ketonic form could exist in the ground state. Further theoretical studies of the potential energy surfaces support a trans-cis conversion followed by a relaxation to the stable form of SP in the excited states.

The structural, electronic, and optical properties of organic–inorganic mixed halide perovskites CH_3NH_3Pb(I_(1-y)X_y)_3(X = Cl, Br)

Methylammmonium lead iodide perovskites（CH3NH3PbI3） have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH3NH3Pb（I（1-y）Xy）3（X = Cl, Br; y = 0, 0.33, 0.67）. Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl-/Br-at I-. Electronic structure calculations indicate that the valance band maximum（VBM） is mainly governed by the halide p orbitals and Pb 6 s orbitals, Pb 6 p orbitals contribute the conduction band minimum（CBM） and doping does not change the direct semiconductor material. The organic cation [CH3NH3]~＋does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y = 0（0.793 eV） to y = 0.33（0.953 eV） then to y = 0.67（1.126 eV）. The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.

Effects of Electron Donor and Different Solvents on Polarizability and Second Hyperpolarizability of Diradical Complex Involving X(X=B,Al,Ga)

The polarizability（α） and second hyperpolarizability（γ） were systemically investigated for singlet diradical complex involving X（X=B,Al,Ga） atom.The results show that both the α and γ can be effectively tuned by varying the distance R（between compound A and a water molecule） and acceptor atom X.The lone pair of electrons from the O atom of the water molecule entered into the vacant p orbital of atom X,which increased the diradical character and led to the increase of the α and γ values.Furthermore,the polarizable continuum model（PCM） was used to test the effects of H2O and CCl4 solvents on the α and γ values.Both the α and γ values of the studied diradical complex 1a（1b,1c） in H2O and CCl4 were uniformly enhanced.And the solvent effects of H2O on either α or γ were larger than those of CCl4.

Quantum Chemistry Studies on the Fe-Cu Interactions and ^(31)P NMR in Fe(CO)_3(Ph_2Ppy)_2(CuX_n) (X_n=Cl_2^(2-),Cl^-,Br^-)

In order to study the Fe-Cu interactions and their effects on 31p NMR, the structures of mononuclear complex Fe（CO）3fPhzPpy）a 1 and binuclear complexes Fe（CO）3（PhEPpy）z（CuXn） （2： Xn = Cl2^2-, 3： Xn = Cl-, 4： Xn = Br-） are calculated by density functional theory （DFT） PBE0 method. For complexes 1, 3 and 4, the 31p NMR chemical shifts calculated by PBE0-GIAO method are in good agreement with experimental results. The 31p chemical shift is 82.10 ppm in the designed complex 2. The Fe-Cu interactions （including Fe→Cu and Fe←Cu charge transfer） mainly exhibit the indirect interactions. Moreover, the Fe-Cu（I） interactions （mostly acting as σFe-p→4Scu and aFe-C→4Scu charge transfer） in complexes 3 and 4 are stronger than Fe-Cu（Ⅱ） interactions （mostly acting as σFe-p→4Scu and σFe-p←4Sc,） in complex 2. In complex 2, the stronger Fe←Cu interac- tions, acting as σFe-p←44SCu charge transfer, increase the electron density on P nucleus, which causes the upfield 31p chemical shift compared with mononuclear complex 1. For 3 and 4, although a little deshielding for P nucleus is derived from the delocalization of σFe-p→4Scu due to the Fe→Cu interactions, the stronger σFe-c→np charge-transfer finally increases the electron density on P nucleus. As a result, an upfield 31p chemical shift is observed compared with 1. The stability follows the order of 2〉3=4, indicating that Fe（CO）3（PhzPpy）2（CuCl2） is stable and could be synthesized experimentally. The N-Cu（Ⅱ） interaction plays an important role in the stability of 2. Because the delocalization of σFe-p→4SCu and σFe-c→πc-o weakens the a bonds of Fe-C and ~r bonds of CO, it is favorable for increasing the catalytic activity of binuclear complexes. Complexes 3 and 4 are expected to show higher catalytic activity compared to 2.

Luminescent Properties of Mercury-taining Diethynylfluorene Derivatives

Excited state structures and spectroscopic properties of mercury（ 11 ） complexes, Hg-TFT（1） and its electronwithdrawing substituents Hg-TFOT （ 2 ）, Hg-TFCNT （ 3 ）, where TFT = dietbynylfluorenyl, TFOT = diethynylfluorenone, and TFCNT = diethynyl-[9-（dicyanomethylene） fluorene], were studied using singlet excitation configuration interaction（CIS） and time-dependent density functional theory（TDDFT） methods. The results of the theoretical calculations indicate that the electron-withdrawing substitutions lead to a significant decrease in the energy gap between the ground state and the first excited states. In the case of Hg-TFCNT, the second singlet excited state （S2 ） may contribute to the luminescence because of its large S1-S2 separation.

Density Functional Theory Investigation on the Second-Order Nonlinear Optical Properties of Chlorobenzyl-o-Carborane Derivatives

The structures and second-order nonlinear optical （NLO） properties of a series of chlorobenzyl-o-carboranes derivatives （1 12） containing different push-pull groups have been studied by density functional theory （DFT） cal- culation. Our theoretical calculations show that the static first hyperpolarizability （fltot） values gradually increase with increasing the π-conjugation length and the strength of electron donor group. Especially, compound 12 exhibits the largest βtot （62.404 × 10^-30 esu） by introducing tetrathiafulvalene （TTF）, which is about 76 times larger than that of compound 1 containing aryl. This means that the appropriate structural modification can substantially increase the first hyperpolarizabilities of the studied compounds. For the sake of understanding the origin of these large NLO responses, the frontier molecular orbitals （FMOs）, electron density difference maps （EDDMs）, orbital energy and electronic transition energy of the studied compounds are analyzed. According to the two-state model, the lower transition energy plays an important role in increasing the first hyperpolarizability values. This study may evoke possible ways to design preferable NLO materials.

One-Pot Synthesized Polyurethane-Based Nanocomposites Filled by Original Rectorite with Enhanced Strength and Elongation

The unmodified rectorite（REC）,a kind of layered silicate,was incorporated into polyurethane （PU）as matrix by the process of one-pot synthesizing polyurethane in situ,and hence produced a series of nanocomposite materials with enhanced strength and elongation.It is worth noting that the nanocomposite containing 2 wt%REC had the maximum elongation（1 449%）and strength（32.66 MPa）as ca.2.7-and 1.4-fold over those of neat PU film,respectively.Meanwhile,the unexfoliated agglomerates and exfoliated nanoplatelets of REC co-existed in PU matrix.By virtue of strong interfacial interaction on the surface of REC lamella,the stress facilely transferred to the rigid RECs and hence contributed to the enhancement of strength in spite that the original structure and interaction in the PU matrix were partly cleaved.Moreover,the intertwisting of polymer chains in PU matrix with REC as well as the gliding among the REC lamellae might produce greater strain.Nevertheless,excess unexfoliated REC agglomerates under high loading level inhibited the enhancement of mechanical performances,which verified the key role of exfoliated REC nanoplatelet in improving mechanical performances.As a result,this work submitted a simple method to develop a polyurethane-based nanocomposite with high mechanical performances without any modification of layered silicates and the complicated treatment for exfoliation and dispersion.

Density Functional Study on the Mechanism of Collision Reaction among Protons, N_2 and Water Vapor

The mechanism of collision reaction among protons, N2 and water vapor was theoretically studied using Den-sity Functional Theory. The geometries of reactants, transition states, intermediates and products were optimized at the B3LYP/6-311+G** level by the BERNY gradient analysis method. Transition states and intermediates have been identified by vibrational frequency analysis. The relationship among reactants, intermediates, transition states and products was affirmed by IRC calculation. The variations of energy and geometry along the IRC-determined reaction paths were described. The possible reaction pathways were represented and the optimal one was decided from the viewpoint of energy.

Theoretical Studies on N_2H+O Reaction

The N2H＋O potential energy profile was studied at the CCSD（T）/6-311G＋＋（df,p）//MP2/6-311G（d,p） level. Reactions associated with four intermediates（cis-HNNO, trans-HNNO, NNHO, and NNOH） were investigated. The results indicate that N2H＋O reaction toward H＋N2O is more favored than that toward N2＋OH, consistent with previous experimental studies. The pathways for the two reactions are found to go through cis-HNNO, transition state, and finally to the products. The N2H＋O→NH＋NO reaction was studied in detail. Product NO in such a reaction is likely to occur via cis-HNNO, followed by trans-HNNO, and finally dissociates into NH＋NO. These results suggest that N2H＋O→NH＋NO is an important channel in NO production.

Radical Mechanism of IrⅢ/NiⅡ Metallaphotoredox-Catalyzed C(sp^(3))-H Functionalization Triggered by Proton-Coupled Electron Transfer:Theoretical Insight

Photoredox catalysis can be induced to activate organic substrates or to modulate the oxidation state of transition-metal catalysts via unique singleelectron transfer processes,so as to achieve challenging C(sp^(3))-H functionalization under mild conditions.However,the specific reaction mechanism and relevant electron transfer process still need to be clarified.Here,a highly regioselective Ir^(Ⅲ)/Ni^(Ⅱ)-metallaphotoredox-catalyzed hydroalkylation of asymmetrical internal alkyne with an etherα-hetero C(sp^(3))-H bond has been investigated by density functional theory(DFT)calculations.A novel radical mechanism was predicted to merge oxidative quenching(Ir^(Ⅲ)-*Ir^(Ⅲ)-Ir^(Ⅳ)-Ir^(Ⅲ))and nickel catalytic cycles(NiⅡ-NiⅢ-NiI-NiⅢ-NiⅡ)for this C(sp^(3))-H functionalization to construct C(sp^(3))-C(sp^(2))bonds.It consists of seven major steps:the single-electron transfer involved in the photoredox cycle for generating active Ni(Ⅰ)-chloride complexes,proton-coupled electron transfer process to provide α-carbon-centered tetrahydrofuran(THF)radicals,radical capture by Ni(Ⅱ),reductive elimination to obtain 2-chlorotetrahydrofuran,alkyne oxidative hydrometallation,innersphere electron transfer,and σ-bond metathesis to yield the desired alkyne hydroalkylation product.Importantly,both the thermodynamic performance for redox potentials and the kinetic exploration for energy barriers and electron-transfer rates have also been evaluated for the corresponding electron transfer processes.In addition,the steric effects play a major role in determining the regioselectivity of alkyne oxidative hydrometallation.