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A molecular switch having large contrast on the second-order nonlinear optical (NLO) properties has been studied based on tetrathiafulvalene (TTF)-π-polynitrofluorene (PTF) molecule. It can afford to switch second-order NLO response across 10 stable states by an effective combination of its photoisomerisation and redox properties. According to density functional theory (DFT) finite field calculations (BHandHLYP/CAM-B3LYP/LC-BLYP/6-31g(d)), the redox-active TTF, TCNQ (7,7′,8,8′-tetracyano-p-quinodimethane) units, and a photoisomerised chromophore (thiophene derivative of perfluorocyclopentene) act as the tuning centre to switch second-order NLO responses. Meanwhile, time-dependent DFT method has been employed to calculate excited-state nature for getting more insights of the second-order NLO responses. [ABSTRACT FROM PUBLISHER]

The electronic structure and bonding feature of a series of mono-ruthenium-substituted Keggin-type polyoxometalates (POMs) have been investigated by using density functional theory (DFT) calculation, natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). A comparison of the electronic properties of two known dimethyl sulfoxide (DMSO)-supported mono-ruthenium-substituted Keggin-type POMs shows that both complexes have the analogous frontier-molecular orbital feature. One of them possesses a relatively small HOMO–LUMO gap because of the high HOMO energy level. This difference comes from a high composition of POM ligand with antibonding feature in HOMO. In addition, three typical Keggin-type POM complexes [{PW11O39}RuII/III(L)]n−(L = H2O, C5H5N, NH3) have also been explored according to our computational studies. The NBO analysis shows that the RuII/III–L bond comes from donor–acceptor interactions between the end ligand and the ruthenium (II/III) centre. The EDA shows that the POM complex [{PW11O39}RuII(C5H5N)]5−has much stronger RuII–L bond than ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−. And the enhancement of the RuII–L bonding interaction in [{PW11O39}RuII(C5H5N)]5−is mainly due to the large orbital interaction energy ΔEorb. The ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−and the aqua-ruthenium derivative [{PW11O39}RuII(H2O)]5−have an analogous magnitude of the total bond energy. This result supports a non-aqueous environment for synthesis of an ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−. [ABSTRACT FROM AUTHOR]

The bonding features and electronic structures of a series of transition metal carbon dioxide complexes have been studied by density functional theory (DFT) calculations combined with natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). NBO analysis shows that the interaction between the metal center and the carbon atom of the carbon dioxide ligand (M–C) is stronger than the other interaction between the metal center and the carbon dioxide ligand. Natural hybrid orbital (NHO) analysis gives the detailed bonding features of the M–C bond for each complex. The NBO charge distribution on the carbon dioxide unit in all studied complexes is negative, which indicates charge transfer from the metal center to the carbon dioxide ligand for all studied complexes. The hyperconjugation effect of the metal center and the two C–O bonds of the carbon dioxide ligand has been estimated using the NBO second-order perturbation stabilization energy. It was found that the NBO second-order stabilization energy of C–O → nM* is sensitive to the coordinated sphere and the metal center. Frontier molecular orbital (FMO) analysis shows that complexes1and4may be good nucleophilic reagents for activation of the carbon dioxide molecule. However, the EDAs show that the M–CO2bond interaction energy of complex4is about two times as large as that of complex1. The high M–CO2bond interaction energy of complex4may limit its practical application. [ABSTRACT FROM PUBLISHER]

Abstract: Combination of porphyrin, tetrathiafulvalene (TTF), and trimetallic nitride template endohedral metallofullerenes (TNT-EMFs) chemistry is highly desired because this hybrid entity will possess the rich scientific heritage of porphyrin, TTF, and TNT-EMF. In the present paper, the electronic structure and second-order nonlinear optical (NLO) properties of a series of TNT-EMF derivatives have been calculated by density functional theory (DFT) and finite field (FF) method. Our DFT calculations well reproduce the geometrical structure of the known [5, 6]- and [6, 6]-benzyne monoadducts. Our DFT calculations show that the [5, 6]-benzyne monoadduct is the thermodynamic product because the calculated total energy including the electronic and zero-point corrected energies of [5, 6]-benzyne monoadduct is ∼4.9kcalmol−1 more stable than the [6, 6]-benzyne monoadduct. Two new molecular systems, porphyrin derivative (porphyrin+TNT-EMF) and TTF derivative (TTF+porphyrin+TNT-EMF) have been considered in this work. The optimized calculations show that introduction of porphyrin and TTF cannot significantly affects the geometry of the weak four-membered ring and Sc3N@Ih–C80. The electronic structure analysis shows that the TTF derivative possesses the smallest HOMO–LUMO gap (∼1.5eV) among all studied compounds in this work, and the one-electron-oxidized center will be the TTF unit. DFT–FF calculations show that the [6, 6]-benzyne monoadduct has a large static first hyperpolarizability relevant to the [5, 6]-benzyne monoadduct. Thus, the second-order optical nonlinearity may be an effective technique to determine the location of the functional groups on the cage surfaces of the TNT-EMF. A substantial enhancement in static first hyperpolarizability has been obtained in porphyrin and TTF derivatives according to our DFT–FF calculation. The calculated β values of porphyrin and TTF derivatives are ∼15 and ∼30 times as large as that of [5, 6]-monoadduct. The time-dependent (TD) DFT calculations confirm that the increasing trend of the static first hyperpolarizability. And the molecular orbital transition feature shows that the TTF unit does not display the electron donor character because of the non-planar arched structure. [Copyright &y& Elsevier]

In this article, the nonlinear optical (NLO) switching action of Ru(III/II) carboxylate complexes was investigated by density functional theory (DFT). Among the studied complexed, Ru(III)PhCOO− has the largest β value of 4972 × 10−30 esu. Through the proton transfer (PT) process, the COOH group of Ru(III)PhCOOH and Ru(III)COOH complexes can form the COO− group. Then, COO− group acts as a strong donor and Ru(III) acts as an acceptor, which may be the most favorably used in the development of metal complexes NLO material. The redox NLO switching and PT NLO switching of Ru(III)PhCOO−, Ru(III)PhCOOH, Ru(II)PhCOO−, and Ru(II)PhCOOH complexes have been studied. The β value of Ru(III)PhCOO− complex is ∼36 and ∼48 times larger than those of reduced Ru(II)PhCOO− and Ru(II)PhCOOH, respectively. Note that the β value of deprotonated Ru(III)PhCOO− is ∼215 times larger than that of Ru(III)PhCOOH. The molecular electrostatic potential analysis also confirms that Ru(III)PhCOOH may have poor performance in the second-order NLO response. In addition, the TDDFT calculations show that the ligand to metal charge transfer transition lead to the largest β value of the Ru(III)PhCOO− complex. This investigation provides important insight into the remarkably large NLO properties and NLO switching of Ru(III/II) carboxylate complexes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem 000: 000-000, 2011 [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) was employed to calculate the bonding feature, electron spectrum, and redox properties of a dumbbell-shaped polyoxometalate (POM) cluster, [ [image omitted](PW11O39)2]8-. Our DFT calculations confirm that the quadruple bond interaction between two ReIII centers consists of σ, 2π, and δ orbital overlaps, and the strength of the bonding interactions is in the order σ-bond > π-bond>δ-bond. Time-dependent (TD) DFT calculations suggest that this cluster possesses one strong and four weak absorption bands between 0.7 and 2.5 eV. Excited state calculations show that the Re-Re bond length increases when one electron of the Re-Re bonding δ orbital is shifted to the Re-Re δ* antibonding orbital. Molecular orbital predictions and spin unrestricted calculations indicate that the two Re atoms form the reduced center. The Re-Re bond length increases in one- and two-electron reduction processes because the Re-Re δ* antibonding orbital becomes occupied. However, these changes in the Re-Re bond length in excitation and reduction processes are not substantial because of the weak δ bond. The substitution effect of the central tetrahedron heteroatom of the POM ligand affects the Re-Re bond length, with the Re-Re distance decreasing with the substitution of X from Al to S, Al (2.345 Å) > Si (2.310 Å) > P (2.282 Å) > S (2.257 Å). [ABSTRACT FROM AUTHOR]

The uneven settlement is one of the important factors which lead to the damage of the buried pipeline. The means first-order second-moment method and Monte-Carlo method in ANSYS are used to calculate the reliability of the buried pipeline considering the random variables, i. e. displacement of ground settlement, material parameters and internal pressure. Reliability coefficients and failure probabilities considering or without considering the internal pressure are obtained. The results obtained by reliability analysis show that the variability of settlement displacement has important impact on the reliability of the buried pipeline subjected to the settlement. Compared with the results which do not consider internal pressure, the failure probability which considers internal pressure is larger and the reliability coefficient is smaller. It is also found that the variability of pipe diameter and thickness has important impact on the reliability of the buried pipeline. [ABSTRACT FROM AUTHOR]

The water supply network is often damaged to some extent in earthquake, so the hydraulic analysis of the water supply network with leakage is performed and then its seismic performance is evaluated based on the failure state simulation of the pipelines. The relationship of nodal flow and nodal pressure is adopted during the hydraulic analysis of the network combined with Chinese leakage model,and the nodal flows and its pressure are obtained by solving a set of nonlinear equations. Since nodal flows are considered to vary with nodal pressures in this model based on traditional hydraulic calculation method of the network, negative pressures are avoided during the hydraulic calculations. The functional analysis approach is applied to an example of water supply network after an earthquake. [ABSTRACT FROM AUTHOR]

The density functional and ab initio theory were used to investigate the second-order nonlinear optical (NLO) properties of Schiff base ligands, open-shell Fe(III), and closed-shell Ni(II) complexes. The effect of the metal center in complexes is thus manifold: it templates the formation of acentric structures, imparts high thermal stability to the chelate ring, and display higher second-order NLO response than their ligands. The second-order NLO response of metal complexes are intensively sensitive to the exchange donor/acceptor because the differences of the extent of charge separation and the intraligand charge transfer processes. Thus, substituted metal complexes could realize “switches on” the second-order NLO response by exchange donor/acceptor. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Extensively researches have been carried out on seismic analysis of space structures subjected to multi-dimensional multi-support excitations. However, the research on dynamic reliability of stochastic response is just little. Extreme value distribution (EVD) of dynamic response of stochastic space structures is so necessary to dynamic reliability. Nevertheless, there is no effective approach to obtain EVD as yet. Hence the recently formulated probability density evolution method (PDEM) is adopted to obtain the EVD and subsequently evaluate dynamic reliability of space structure subjected to multi-dimensional multi-support excitations. PDEM can effectively gain the EVD and calculate the dynamic reliability of stochastic structures. To demonstrate the accuracy and efficiency of the PDEM in space structures, a single-layer spherical reticulated dome is extensively researched and the EVD and dynamic reliability is observed and analyzed, respectively. In the present paper five apparent wave velocities and four displacement thresholds in vertical direction are taken into consideration. Compared with the results evaluated by conventional simulation method, the PDEM is of accuracy, efficiency and versatility in space structures. [ABSTRACT FROM AUTHOR]

According to the wavelet singularity theory and numerical simulation studies of beam structure, two methods of wavelet damage diagnosis are employed to analyze the damage diagnosis of beam structure based on Gausl wavelet. Firstly, the first derivative of the mode shape (rotation) is studied and gotten. Then, the continuous wavelet transform(CWT) by a Gausl wavelet is employed to deeply analyze the rotation of beam structure, the damage position and the relation between damage extent and Lipschitz exponent, and some significant results are gotten. Finally, by comparing the above-mentioned method and the methods through CWT by Gaus2 applied to the mode shape, it is found that the above-mentioned method is much better than Gaus2 method. So, the above-mentioned method can be employed to study practical beam structure damage diagnosis, which suggests the new ideas and methods for the advanced development of the wavelet theory. [ABSTRACT FROM AUTHOR]

An extended Kalman filter (EKF) which is optimized by the improved particle swarm optimization (IPSO) algorithm is proposed to estimate the state-of-charge (SOC) of battery. A new state space equation applied to EKF algorithm is constituted to reduce the influence of non-linear characteristics of parameters, and the optimal estimation of SOC is obtained based on the real-time identification of battery model parameters. IPSO algorithm is applied to optimize the system state error covariance matrix and measurement noise covariance matrix to improve the estimation accuracy of SOC by solving the problems in achieving the optimal solutions of these covariance matrixes. The results show that the IPSO-EKF algorithm can estimate the model parameters and SOC of battery accurately, and correct the state variable initial error. [ABSTRACT FROM AUTHOR]

• The mechanism of CO oxidation by O 2 was studied over two POM-supported SACs (Rh 1 /PTA and Rh 1 /PMA). • The oxidation process involves consecutive oxidation of three CO molecules via a Rh-assisted MvK mechanism. • The second CO molecule was oxidized by the corner O atom of the POM support rather than adsorbed O 2 molecule. • Oxidation state of the Rh center changes among III, II, and I, which promotes electron transfer and the whole reaction. The low and insufficient anchored site on support structure is the bottleneck problem for development of single-atom catalysts (SACs). Owing to the discrete anionic structure, the surface structure of unimolecular polyoxometalates (POMs) in solid is more like the fragments of metal oxide and possesses the unique separate structure, which can be viewed as the separate small "island" and effectively prevent agglomeration of single metal atoms. In the present paper, the mechanism of CO oxidation by O 2 was systematically studied over two POM-supported SACs, Rh 1 /PTA and Rh 1 /PMA (PTA = [PW 12 O 40 ]3− and PMA = [PMo 12 O 40 ]3−) by means of density functional theory (DFT) calculations. The results indicated that this process involves consecutive oxidation of three CO molecules over Rh 1 /PTA and Rh 1 /PMA SACs via a Rh-assisted Mar-van Krevelen (MvK) mechanism. The first CO molecule was oxidized by a bridged O atom of POM support to form CO 2 molecule and an oxygen vacancy. The surface oxygen vacancy was refilled by O 2 molecule, and the second CO molecule was oxidized by a corner O atom of the POM support to form CO 2 molecule and a new oxygen vacancy. Finally, the forming surface oxygen vacancy was replenished by the O 2 molecule to form the key Mo-O-O-Mo unit, which can easily oxidize the third CO to form the CO 2 molecule. Compared with the reported MvK mechanism, the significant difference arises from oxidation of the second CO molecule, in which the second CO molecule was oxidized by the corner O atom of the POM support rather than adsorbed O 2 molecule. This is mainly due to a low reactivity for the adsorbed O 2 molecule, which comes from a bonding interaction between the adsorbed O 2 molecule and the single Rh atom. The atomic charge analysis show that the single Rh atom stabilized on the POM supports promotes the whole catalytic cycle via the change of oxidation state among III, II, and I. All these results show that the presence of single Rh atom on the unimolecular PTA and PMA supports is a key factor for determination of new reaction pathway and high reactivity. We hope our computation results can provide new physical insights to design SACs for CO oxidation by using unimolecular POM cluster. The reaction mechanism of CO oxidation by O 2 was systematically studied over two polyoxometalate-supported single-atom catalysts by means of density functional theory calculations. [Display omitted] [ABSTRACT FROM AUTHOR]

In this case, various characterization technologies have been employed to probe dissociation mechanism of cellulose in N , N -dimethylacetamide/lithium chloride (DMAc/LiCl) system. These results indicate that coordination of DMAc ligands to the Li+–Cl− ion pair results in the formation of a series of Li x (DMAc) y Cl z (x = 1, 2; y = 1, 2, 3, 4; z = 1, 2) complexes. Analysis of interaction between DMAc ligand and Li center indicate that Li bond plays a major role for the formation of these Li x (DMAc) y Cl z complexes. And the saturation and directionality of Li bond in these Li x (DMAc) y Cl z complexes are found to be a tetrahedral structure. The hydrogen bonds between two cellulose chains could be broken at the nonreduced end of cellulose molecule via combined effects of basicity of Cl− ion and steric hindrance of [Li (DMAc) 4 ]+ unit. The unique feature of Li bond in Li x (DMAc) y Cl z complexes is a key factor in determination of the dissociation mechanism. [ABSTRACT FROM AUTHOR]

The feasibility of electro-oxidation between ethylene and active oxygen intermediate (*O) utilizing the water electrolysis on single active site is investigated. [Display omitted] • Firstly, a screening criterion: the ΔG of *O + C 2 H 4 → *+ C 2 H 4 O is proposed for the potential electrocatalyst towards ethylene electro-epoxidation. • Secondly, the feasibility to utilize *O to react with ethylene is its applied potential lower than that for following step in electrolytic water. • After screening, CuN 3 @graphene exhibits excellent catalytic potential for ethylene electro-epoxidation in this study. Ethylene oxide (EO) is an important petrochemical product, widely used in printing and dyeing, automotive, medicine, and other fields. Direct epoxidation of ethylene by electrocatalysis is a simple and sustainable route to produce EO, which can avoid the disadvantage of traditional industrial production, such as high temperature and CO 2 emissions. An efficient electrocatalyst could generate active oxygen intermediate during the electrolytic water process, which escape from the tremendous activation barrier of breaking molecular oxygen. In addition, ethylene and active oxygen are both required to be adsorbed or produce interaction on the same active site, which is more effective to directly transfer oxygen. Motivated by this strategy, we used first-principle to screen the possibility of 27 single transition metal atoms in MN 3 moiety as active site starting from the Gibbs free energy change (ΔG) of *O + C 2 H 4 → *+ C 2 H 4 O. Dispersed Cu, Ni, Co can absorb both active oxygen and ethylene, and exhibits the excellent catalytic performance through stability, selectivity, thermodynamics and kinetics evaluation. Electronic structure analysis indicates that the catalytic activity roots from the high electron transfer from the absorbed ethylene to the empty M–O anti-bonding, which weaken the M–O bonding and promote the oxygen transfer. Notably, for CuN 3 @graphene, the applied potential to produce active oxygen intermediate is 1.53 V vs RHE, and the kinetic energy barrier for subsequent oxygen transfer to form EO is 1.00 eV. This study verified the feasibility of single atomic electrocatalysts for EO production and offers valuable clues to design/discover active center to explore experimentally. [ABSTRACT FROM AUTHOR]

• The hydrogen activation, spillover and desorption in single-atom alloys have been systematically studied. • CuPd, CuMn, CuPt single-atom alloys possess excellent catalytic activity superior to pure metal Cu. • The rare electronic structure of CuMn single-atom alloy shows that Mn is even like a free atom. Towards the computational design of single-atom alloys (SAAs) catalysts, we systematically studied the hydrogen activation, spillover and desorption by density functional theory (DFT) and first-principles calculations. Herein, we designed a model with 27 individual isolated metals in Cu(111) slab and described the scaling relationships and meticulous electronic structures. The results show that CuPd, CuMn, CuPt SAAs possess appropriate H atom binding ability and lower H 2 dissociation barrier superior to pure metal Cu. There have been many reports about the design of hydrogenation catalysts before, but most of them are about CuPd and CuPt SAAs. Here we found that CuMn SAAs exhibits excellent catalytic performance, even comparable to CuPd and CuPt SAAs. Based on exhaustive electronic structure analysis, we discovered a rare electronic structure on CuMn SAAs, where Mn has no obvious electronic interaction with the host metal Cu, even like a free atom. The incredible phenomenon promotes CuMn SAAs to possess extraordinary hydrogenation catalytic activity. This paper seeks to provide deep insights into chemistry, catalysis, and interfaces for people to design new catalysts. [ABSTRACT FROM AUTHOR]

• In the present paper, we highlight the role of oxophilic Al atom in the Cu(111) surface for the CO 2 adsorption and in the subsequent reduction reactions. • Our periodic density functional theory (DFT) calculations show that introduction of the oxophilic Al atom into the Cu(111) surface effectively improves the CO 2 adsorption ability via formation of a Alδ+- (Cu6)δ- configuration on the Al/Cu(111) surface. • The adsorbed CO2 was easily reduced to CO via a unique dissociated adsorption process induced by the oxophilic Al center. Our energy calculations show that introduction of the Al atom into the Cu(111) surface is both thermodynamically and kinetically favorable for CO dimerization when compared with the pristine Cu(111) surface. And the Al center acts as an electron-transfer medium for the coupling of two CO molecules over Al/Cu(111) surface. Inspired by the work of Sargent et al. (Nature , 2020, 581 , 178–183), the oxophilic Al atom was introduced into the Cu(111) surface to design a Al/Cu(111) bimetallic catalysts for implementing electrochemical CO 2 reduction reaction based on the first-principles calculations. The results indicate that introduction of the oxophilic Al atom into the Cu(111) surface effectively improves the CO 2 adsorption ability via formation of a Alδ+- (Cu 6)δ− configuration on the Al/Cu(111) surface. And the adsorbed CO 2 was easily reduced to CO via a unique dissociated adsorption process induced by the oxophilic Al center. Our energy calculations show that introduction of the Al atom into the Cu(111) surface is both thermodynamically and kinetically favorable for CO dimerization when compared with the pristine Cu(111) surface. And the Al center acts as an electron-transfer medium for the coupling of two CO molecules over Al/Cu(111) surface. Finally, our mechanism investigation shows that the presence of oxophilic Al atom in the Cu(111) surface effectively improves the selectivity of ethanol product via the formation of the Al-O bond along the hydrogenation path. [Display omitted] [ABSTRACT FROM AUTHOR]

This study proposes a probabilistic performance evaluation framework for sea-crossing cable-stayed bridges (SCBs) subjected to wind and wave excitations with the incorporation of wind speed and direction, bridge orientation, wind-wave correlation and parameter uncertainties. Both the bridge serviceability and safety are taken into account in the performance assessment. The fragility analysis of the SCB under wind and wave loads is conducted using the wind-wave correlation model constructed based on field data. The actual damage probability of a local SCB is computed by combining the fragilities of bridge under different wind incidence angles with the copula-based joint probability distribution (JPD) of wind speed and direction, which is developed using the wind field data recorded in Lianyungang city of China from 1971 to 2020. The results show that under the defined wind incidence angle of 0°, the exemplar SCB suffers the highest fragility. Moreover, with the data-based occurrence probability model of wind and wave hazards, the damage probabilities under all possible wind speeds and directions are computed; then the optimal and most unfavorable orientations of the SCB are obtained. This investigation provides a comprehensive and practical method for the performance evaluation and design optimization of SCBs under wind and wave loads with long-term recorded hazard data at the local site. • Probabilistic occurrence model of wind and wave is developed with recorded hazard data. • Fragilities of a SCB under various wind and wave incidence angles are studied. • Actual damage probability is assessed considering hazard occurrence probability and bridge fragility. • Effects of bridge orientation on the performance of a SCB are evaluated. [ABSTRACT FROM AUTHOR]

Crown ether can bind the alkali metal ions, and the binding is related to numerous factors. In present work, we investigated the effect of the species and number of heteroatom on the interaction energy and charge transfer between crown ether and alkali metal ions in the three complexes (12C4O-Li, 15C5O-Na and 18C6O-K) using density functional method. Our results show that the N- or S-substitution is more favorable to the enhancement of charge transfer between the alkali metal ions and crown ethers than P-substitution; furthermore, the interaction energy of N- or S-substitution is also higher than that of P-substitution. The 12C4O has strongest affinity for Li in the three complexes from the perspective of the variation of the species and the number of heteroatom. Thus, take 12C4O for example, it is concluded that the number of N-substitution has slight influence on the interaction energy; however, as the number of P- or S-substitutions increases, the interaction energy values decrease sharply. [ABSTRACT FROM AUTHOR]

The driving cycle of tracked vehicle is so complex, and the drive motor with wide speed range runs under nonlinear, uncertain and strong coupling load. How to control the motor speed to improve the stability of steering has become a research hot point. An electric differential control strategy is put forward. And the LADRC control algorithm is used in speed control of PMSM system, and LESO is used to estimate and compensate the unknown disturbance, thus rejecting the disturbance and improving the dynamic performance of system. The collaborative model of Matlab and RecurDyn softwares and test bench are built. The simulation and experimental results show that the speed control strategy with LADRC can be used to achieve rapid response without overshoot, strong disturbance rejection and good parameter a-daptability, which improve the vehicle stability. [ABSTRACT FROM AUTHOR]

Abstract: The second-order nonlinear optical (NLO) properties of a series of the polyoxometalate (POM)-spiropyran derivatives have been studied by using quantum chemical calculations. The photochemical reaction of spiropyran compounds will produce two different species, spiropyran and merocyanine. The merocyanine species has a large second-order NLO responses because of its good π-conjugated character. And thus a large contrast of the first hyperpolarizability has been obtained. According to quantum chemical calculation, this photo-triggered switchable effect derived from the spiropyran-merocyanine conversion has been enhanced because of introduction of the POM unit. Meanwhile, the substituted effect of the POM species also has been considered in this work. It can be found that introduction of the electron donor/acceptor group into the POM derivative does not significantly affect the magnitude of the first hyperpolarizability. [Copyright &y& Elsevier]

Abstract: We systematically investigate the linear optical properties and the static second-order nonlinear optical (NLO) properties on a series of two-dimensional (2D) D-π-A-π-D/A-π-D-π-A sandwich metallocarborane-containing molecules with density functional theory (DFT). It can be found that the substitution effect has an influence on the electronic absorption and NLO responses of the 2D molecules. For example, the value is sensitive to the substitution from amino (–NH2) to nitryl (–NO2); the angle between the two A–D branches significantly affects the dipole moment and value. In addition, time-dependent DFT calculations and the analysis of major molecular orbitals predict that the sandwich metallocarborane acts as an electron donor better than electron acceptor. Furthermore, the two strong synchronized charge transfer (CT) coming from the two branches and p–π (B2p–C≡C) conjugation contributes to the second-order polarizabilities in our studied systems. [Copyright &y& Elsevier]

Abstract: The Λ-shaped phenanthroline-hexamolybdate compounds that are based on the reversible Mo-centered redox process were investigated. The attachment of hexamolybdate terminals to phenanthroline by a π-conjugated phenylamine bridge generated the organic ligand-centered or Ni-centered HOMO and the transition metal Mo-centered LUMO. The population in HOMO and LUMO predicted the reversible MoVI/V redox process and the ligand-to-metal charge transfer (LMCT) to a polyanion acceptor, which consequently evoked a significant second-order nonlinear optical (NLO) response. Moreover, the electron transition of these compounds exhibited a large β zyy tensor along the y-axis, which confirms a promising two-dimensional (2D) character with sizable anisotropy values. Interestingly, the addition of electrons into the high-valence Mo atom in the hexamolybdate acceptor evoked dramatic enhancements in the NLO response for the reduction states in contrast to the response of the corresponding oxidation states. The reduction states in system I exhibited second-order NLO responses about 200 times larger than the oxidation states. In addition, the attachment of the Ni atom in compound IIa red enhanced the NLO response to nearly 1019 times greater than the response of the corresponding oxidation state compound IIa. The Ni atom as the electron donor plays an important role in the major electron transition for the reduction states in system II. Therefore, the NLO response of such compounds can be reversibly switched through the transition metal MoVI/V redox that is effectively coupled with the LMCT transition. Thus, the NLO activity can be controlled by a one-electron redox process, and the redox-active phenanthroline-hexamolybdate compounds are promising candidates for 2D redox-switching NLO materials in novel optoelectronic applications. [ABSTRACT FROM AUTHOR]

Cu catalyst modified by B single-atom obtained unprecedented catalytic property compared to the corresponding pure metal catalyst, which is due to the special active site for water dissociation that the embedded B single-atom creates two heterogeneous Cu atoms with different electronic structures. [Display omitted] • B-doped Cu catalyst exhibits excellent performance compared to pure Cu catalyst in WGSR. • Doping strategy creates heterogeneous Cu atoms with different electronic structures by doping B single-atom in pure Cu catalyst to promote WGSR. • Due to its charming electronic property, B atom can act as a charge transfer medium, freely switching between anionic and cationic states. It is crucial to explore the best active center for a catalyst in heterogeneous catalysis. Here we probe the performance of B single-atom doped Cu catalyst and the corresponding pure metal catalyst in water-gas shift reaction (WGSR) through density functional theory (DFT). The results show that Cu catalyst modified by B single-atom obtained unprecedented catalytic property compared to the corresponding pure metal catalyst, which is due to the special active site for water dissociation that the embedded B single-atom creates two heterogeneous Cu atoms with different electronic structures. Moreover, due to its charming electronic property, B atom can act as a charge transfer medium, freely switching between anionic and cationic states. More importantly, the synergy of heterogeneous Cu atoms reduces the activation energy barrier of the rate-limiting step (water dissociation) by 0.11 eV on B-doped Cu surface in WGSR. Electronic structure analysis emerges a downshifted d -band center of surface Cu atoms coordinated with B atom and an upshifted d -band center of those by Cu-Cu coordination originated from strain and ligand effects. The findings aim to provide deep insights for people to design new catalysts using earth-abundant elements in WGSR. [ABSTRACT FROM AUTHOR]

Based on PDCz (1), eight regioisomers (2 – 9) were designed by changing Br substituent position at the carbazole to investigate the structure and property relationship. The calculated results indicate that simply changing the Br substituent position results in significant spin-orbital coupling (SOC) variation. The (n = 1–5) values of 3 and 7 with Br substituent at 3, 6-position and 1, 3-position are close to those of 1. The other compounds (2 , 4 – 6 , 8 and 9) have significant increase in SOC between singlet and triplet excited states. On the whole, most compounds containing Br substituent has higher SOC than the one that is not substituted. Moreover, the SOC increase is related to the Br substituent positions on the carbazole group. • PDCz and eight regioisomers have been optimized using density functional method. • Change of different Br substituent position lead to a change in T 1 geometries. • The HOMO and LUMO energy levels are mainly influence by the Br substituent position. • Simply change of the Br substituent position results in significant SOC variation. Based on reported PDCz (1), eight isomers (2 – 9) were designed by changing Br substituent positions at the carbazole group to investigate the structure-property relationship by quantum chemistry calculations. The calculated results indicate that an appropriate Br substituent position at the carbazole group is essential for enhancing the spin–orbit coupling (SOC) strength. Among 2 – 9 , The (n = 1–5) values of 3 and 7 with Br substituent at 3, 6-position and 1, 3-position are close to those of 1. However, other compounds (2 , 4 – 6 , 8 and 9) have significant increase in SOC values between singlet and triplet excited states. Thus, simply changing the Br substituent position would result in significant SOC variation. The systematical investigation on Br substituent position at the carbazole group would provide valuable information for choosing better Br position in experimental synthesis. [ABSTRACT FROM AUTHOR]