Oriented External Electric Field Research Articles

Deoxygenation reactions of nitrous oxide assisted by oriented external electric field

AbstractDue largely to the high stability and the potential ozone‐depleting, the transformation of greenhouse gas nitrous oxide has gained much attentions. In present paper, a new insight into the deoxygenation of nitrous oxide with silane was reported by using oriented external electric field (OEEF) as a catalytic strategy. When the OEEF was employed, the reaction barrier of deoxygenation was marvelously decreased as it was oriented along the positive NO/OSi bond‐axis. Especially the field strength is 300 × 10−4 a.u., the differences are up to 22.4/18.3 kcal mol−1 as compared with that of nonfield. In addition, once the H atom in SiH4 was replaced by methyl, two reaction modes were obtained, in which the deoxygenation process was easier when the N2O captured the H atom attached to the Si atom, not attached to the C atom. Further, the solvent effects of deoxygenation reaction were also considered, but with a weak influence were obtained.

Optimal Oriented External Electric Fields to Trigger a Barrierless Oxaphosphetane Ring Opening Step of the Wittig Reaction.

The Wittig reaction is one of the most important processes in organic chemistry for the asymmetric synthesis of olefinic compounds. In view of the increasingly acknowledged potentiality of the electric fields in promoting reactions, here we will consider the effect of the oriented external electric field (OEEF) on the second step of Wittig reaction (i. e. the ring opening oxaphosphetane) in a model system for non-stabilized ylides. In particular, we have determined the optimal direction and strength of the electric field that should be applied to annihilate the reaction barrier of the ring opening through the polarizable molecular electric dipole (PMED) model that we have recently developed. We conclude that the application of the optimal external electric field for the oxaphosphetane ring opening favours a Bestmann-like mechanism.

Mechanistic Studies of Regiocontrolled Bisaddition of Fullerenes Driven by Oriented External Electric Fields.

The challenge of achieving regioselective multifunctionalization on highly symmetric C60 and C70 fullerenes persists as a significant hurdle. In this study, we present a novel approach involving the participation of an oriented external electric field (OEEF) to facilitate the regioselective formation of bisadducts in C60/C70 fullerenes. These products are obtained through consecutive Diels-Alder cycloaddition reactions. We constructed the field strength-barrier relationship and elucidated the OEEF-driven modulation mechanisms quantitatively. Leveraging the interplay between molecular dipoles and electric fields, the diverse reactions at distinct sites exhibit varying degrees of sensitivity to the applied electric fields, thereby leading to a pronounced regioselectivity in the bisaddition process. Our proposition suggests that the angle formed between the bonding direction (referred to as the reaction axis) and the external field can conveniently function as a predictive descriptor for the reactivity of different sites on the fullerene surface when subjected to electric fields.

Oriented External Electric Field Modulated Superhalogen Characteristic and Photoelectric Properties of Al4N2 Cluster: A Density Functional Theory Study

AbstractDesigning superatoms with special structural and photoelectric properties is vital for the applications in multiple fields including condensed matter physics, nanomaterials science etc. In this study, the effects of an oriented external electric field (OEEF) on the geometry, electronic properties, photoelectron spectrum (PES), and nonlinear optical (NLO) response of the main group metal‐doped cluster Al4N2 were investigated using density functional theory (DFT) calculations. The results demonstrate that the OEEF has the capability to increase the value of the electron affinity (EA) of Al4N2 continuously and dramatically, transforming it into a member of superhalogens while maintaining its geometrical stability. Such an enhancement of the EA value of Al4N2 is attributed to the downward shift of the electronic spectrum under the effect of the OEEF. Strikingly, the relationship between the EA value of Al4N2 and the OEEF strength can be fitted by a perfect polynomial formula, which indicates that the OEEF can realize the accurate and continuous regulation of the electronic properties of Al4N2. In addition, the simulated PES of the Al4N2− cluster was observed to be blue shifted following the enhancement of the OEEF intensities, and the NLO response of the cluster can also be remarkably altered by the OEEF.

OEEF-Driven Intramolecular Self-Redox of Superalkali Rb3BeB6Be'Rb'3: A High-Performance Candidate for NLO Molecular Switch.

To provide a novel intramolecular self-redox switch, a boron-based sandwich-like complex Rb3BeB6Be'Rb'3 is achieved by using theoretical computations. An applicable oriented external electric field (OEEF) can result in the occurrence of intramolecular self-redox (IMSR) with a long-range electron transfer from tetrahedral Be'Rb'3 to Rb3Be and subsequently [Rb3Be]3+[B6]6-[Be'Rb'3]3+ (D3d) changes to [Rb3Be]2+[B6]6-[Be'Rb'3]4+ (C3v), accompanying high-performance NLO switchable effect for both static and dynamic first hyperpolarizability (β0). [Rb3Be]3+[B6]6-[Be'Rb'3]3+ (off-form) owns zero of dipole moment (μ0) and β0, while [Rb3Be]2+[B6]6-[Be'Rb'3]4+ (on-form) exhibits a μ0 of 3.36 D and a β0e of 2.18 × 105 au. The different dynamic first hyperpolarizabilities between [Rb3Be]3+[B6]6-[Be'Rb'3]3+ and [Rb3Be]2+[B6]6-[Be'Rb'3]4+ are also significant. This indicates that Rb3BeB6Be'Rb'3 is a potential candidate for an IMSR NLO switch.

Oriented External Electric-Field Effects on the Activation of Aryl CO Bond in Anisole using Rh(PEP) (E=Al, B, Ga) Catalysts.

The present work reports a DFT-based mechanistic investigation of aryl C-O bond activation in anisole catalysed by a Rh-Al pincer-type complex at room temperature. The study is extended to analogues Rh-E complexes based on Group 13 elements (E=B/Ga). Our results show a preference for the heterolytic cleavage pathway over oxidative addition in the C-O bond activation. The calculated barriers range from 16 to 36 kcal/mol, following the order: E=Al<E=Ga<E=B. A strong correlation between the activation barriers and the local electric field (LEF) at the Rh metal centre for the studied Rh-E complexes was observed. Additionally, the ability of Oriented External Electric Field (OEEF) to lower the reaction barrier by applying the OEEF along the direction of electron reorganization, that is, "the reaction axis", was examined. Our results demonstrate the significant effect of applied OEEF on the aryl C-O bond activation in Rh-E systems. Furthermore, the effect of OEEF on the C-O bond activation using modified Rh-E (E=B, Al, or Ga) complexes, in which electronic structure modifications enable a more efficient barrier control by the OEEF, was showcased. Notably, applying a moderate field strength reduces the high reaction barrier for the Rh-B system by approximately 13 kcal/mol.

Does the Spin State and Oriented External Electric Field Boost the Efficiency of Fe(II) Pincer Catalyst toward CO2Hydrogenation Reaction?

In this study, we have explored the catalytic reactivities of four PNP-pincer supported Fe(II) complexes, namely, [(iPrPNMeP)FeH2(CO)] (1), [(iPrPNMeP)FeH(CO)(BH4)] (2), [(iPrPNHP)FeH2(CO)] (3), and [(iPrPNMeP)FeH(BH4)] (4) (iPrPNMeP = MeN{CH2CH2(PiPr2)}2 and iPrPNHP = HN{CH2CH2(PiPr2)}2) toward reductive CO2 hydrogenation for formate production. Our density functional theory and ab initio complete active space self-consistent field study have identified three fundamental steps in this catalytic transformation: (i) anchoring of the CO2 molecule in the vicinity of the metal using noncovalent interactions, (ii) catalyst regeneration via H2 cleavage, and (iii) formate rebound step leading to catalytic poisoning. The variations in the catalytic efficiency observed among these catalysts were attributed to either easing of steps (i) and (ii) or the hampering step (iii). This can be achieved in various chemical/non-chemical ways, for instance, (a) incorporation of strong-field ligands such as CO facilitating single-state reactivity and eliminating two-state reactivity that generally enhances the rate and (b) inclusion of Lewis acids such as LiOTf and strong bases found to either avoid catalytic poisoning or ease the H-H cleavages, to enhance the rate of reaction (c) evading mixing of excited open-shell singlet states to the ground closed-shell singlet state that hampers the catalytic regeneration. We have probed the role of oriented external electric fields (OEEFs) in the entire mechanistic profile for the best and worst catalyst, and our study suggests that imposing OEEFs opposite to the reaction axis (z-axis) fastens the catalytic regeneration step and, at the same time, hampers catalytic poisoning. The application of OEEFs is found to regulate the energetics of various spin states and can hamper two-state reactivity, therefore increasing the efficiency. Thus, this study provides insights into the CO2 hydrogenation mechanism where the role of bases/Lewis acid, ligand design, spin states, and electric field in a particular direction has been established and is, therefore, likely to pave the way forward for a new generation of catalysts.

Cleavage of non-polar C(sp2)‒C(sp2) bonds in cycloparaphenylenes via electric field-catalyzed electrophilic aromatic substitution

Electrophilic aromatic substitution (EAS) is one of the most fundamental reactions in organic chemistry. Using an oriented external electric field (OEEF) instead of traditional reagents to tune the EAS reactivity can offer an environmentally friendly method to synthesize aromatic compounds and hold the promise of broadening its scope. Despite these advantages, OEEF catalysis of EAS is difficult to realize, due to the challenge of microscopically orienting OEEF along the direction of electron reorganizations. In this work, we demonstrate OEEF-catalyzed EAS reactions in a series of cycloparaphenylenes (CPPs) using the scanning tunneling microscope break junction (STM-BJ) technique. Crucially, the unique radial π-conjugation of CPPs enables a desired alignment for the OEEF to catalyze the EAS with Au STM tip (or substrate) acting as an electrophile. Under mild conditions, the OEEF-catalyzed EAS reactions can cleave the inherently inert C(sp2)-C(sp2) bond, leading to high-yield (~97%) formation of linear oligophenylenes terminated with covalent Au-C bonds. These results not only demonstrate the feasibility of OEEF catalysis of EAS, but also offer a way of exploring new mechanistic principles of classic organic reactions aided by OEEF.

Effects and Influence of External Electric Fields on the Equilibrium Properties of Tautomeric Molecules

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an oriented external electric field (OEEF) on excited-state intramolecular proton transfer (ESIPT) from the studies available to date. The possibilities provided by OEEF for regulating several processes and studying physicochemical processes in tautomers have turned this direction into an attractive area of research due to its numerous applications.

External Electric Field Induces a Mechanistic Crossover in the Reactivity of 1,3-Dienes with Sulfur Dioxide: Sulfolene Versus Sultine

1,3-Dienes (1) react with SO2 to produce sulfolenes (2) and sultines (3). Previous experiments and computational studies have shown that hetero-Diels-Alder (HDA) reaction producing the sultine is kinetically favorable compared to the chelotropic (CE) reaction producing the sulfolene. In this article, DFT calculations for a series of substituted 1,3-dienes show that under the influence of a moderate oriented external electric field (OEEF) of 2.0-4.0 V nm-1 along the reaction axis, the chelotropic reaction becomes the kinetically favorable reaction. In the absence of the OEEF, the destabilizing distortion involved in bringing the 1,3-diene and SO2 to the CE transition-state (TS) exceeds than for the HDA TS. However, under the influence of the OEEF, the strongly stabilizing electrostatic interactions in the CE TS effectively overcome the structural distortion energy. The enhanced dipole moment of the CE TS vis-à-vis the HDA TS under the OEEF accounts for the stabilization of the former.

Influence of an Oriented External Electric Field on the Mechanism of Double Proton Transfer between Pyrazole and Guanidine: from an Asynchronous Plateau Transition State to a Synchronous or Stepwise Mechanism.

The double proton transfer (DPT) reaction between pyrazole and guanidine, a concerted reaction but strongly asynchronous and presenting a "plateau transition region", has been theoretically reinvestigated in the presence of an external uniform electric field. First, we computed the reaction path by DFT and proposed a very detailed description of the constitutive electronic events, based on the ELF topology and the bond evolution theory. Then, we studied the effect of an oriented external electric field (OEEF) on the reaction mechanism, for an OEEF oriented along the proton transfer axis. We observe that in one direction, the DPT reaction can be transformed into a stepwise reaction, going through a stabilized single proton transferred intermediate. Contrarily, the two proton transfers occur simultaneously when the electric field is applied in the opposite direction. In the latter case, the order in which the two protons are transferred in the same elementary step can even be reversed if the OEEF is intense enough. Finally, it has been shown that the evolution of the double proton transfer reaction in the presence of an electric field could be quantitatively anticipated by analyzing the ELF value at the bifurcation point between V(A, H) proton donor and V(B) proton acceptor of the double hydrogen bonded complex in the entrance channel.

Dual External Field-Engineered Hyperhalogen.

Hyperhalogens, a superatom featuring the highest known electron affinity (EA), have promising applications in the synthesis of superoxidizers. Contributions regarding the identified numbers and corresponding design strategies of hyperhalogens, however, are scarce. Herein, a novel and noninvasive dual external field (DEF) strategy, including the ligand field and oriented external electric field (OEEF), is proposed to construct hyperhalogens. The DEF strategy was shown to possess the power to increase Au8's EA, forming the hyperhalogen. Strikingly, the ligation process can increase the cluster's stability, while OEEF can realize the precise and continuous regulation of the cluster's EA. Moreover, besides the model Au8 system, an experimentally synthesized Ag17 nanocluster was also investigated, further demonstrating the reliability of the proposed strategy. Considering the crucial role of ligands in the liquid synthesis of clusters and the convenient source of OEEF, such a DEF strategy may greatly increase the synthesis and applications of hyperhalogens in the condensed phase.

On the Precise and Continuous Regulation of the Superatomic and Spectroscopic Behaviors of the Quasi-Cubic W4C4 Cluster by the Oriented External Electric Field

Designing and realizing novel superatoms with controllable and tunable electronic properties is vital for their potential applications in cluster-assembly nanomaterials. Here, we investigated the effect of the oriented external electric field (OEEF) on the geometric and electronic structures as well as the spectroscopic properties of the quasi-cubic W4C4 cluster by utilizing the density functional theory (DFT) calculations. Compared with traditional models, the OEEF was observed to hold the special capability in continuously and precisely modulating the electronic properties of W4C4, that is, remarkably increasing its electron affinity (EA) (1.58 eV) to 5.61 eV under the 0.040 au OEEF (larger than any halogen atoms in the periodic table), which possesses the superhalogen behavior. Furthermore, the downward movement of the lowest unoccupied molecular orbital level of the cluster accompanied by the enhancement of the OEEF intensity was demonstrated to be the origin of the EA increment. Additionally, the photoelectron spectra (PES) of W4C4- were also simulated under different OEEF intensities, where the PES peaks move to a higher energy area following the enhancement of the OEEF strength, exhibiting the blue-shift behavior. These findings observed here open a new avenue in conveniently and precisely adjusting the electronic properties of clusters, which will be beneficial for the rational design of superatoms or superatom-assembled nanomaterials under the external field.

Modulating the catalytic activity of metal-organic frameworks for CO oxidation with N2O through an oriented external electric field

One of the most promising ways to solve various environmental issues caused by toxic gasses is to effectively reduce them to less hazardous gasses. Here, we investigate the effect of an oriented external electric field (OEEF) on the oxidation of CO with N2O over the metal-organic framework Fe3(btc)2 (btc=1,3,5-benzentricarboxylate) by deriving the relevant reaction profiles with density functional theory calculations. We apply the OEEF to Fe3(btc)2 in the range of -0.010 to +0.010 a.u. The reaction is assumed to proceed in two steps: the breaking of the NO bond of N2O and CO bond formation. The applied OEEF is found to mainly affect the transition states and intermediates along the reaction path. A strong correlation between the activation barriers for NO bond breaking, the rate-determining step of the reaction, and the magnitude of the OEEF is observed. The activation energies are reduced from 16.0 to 10.5 and 4.0 kcal/mol by applying positive OEEFs of +0.005 and +0.010 a.u., respectively. In contrast, by applying negative OEEFs of -0.005 and -0.010 a.u., the barriers increase to 20.1 and 23.1 kcal/mol, respectively. Based on charge transfer analysis, the applied positive OEEF enhances the charge transfer from the catalytic site to antibonding molecular orbitals of N2O, thus facilitating NO bond breaking. The results show that an OEEF can customize the catalytic performance of CO oxidation with N2O over MOF catalysts.

Computational Insights into the Role of External and Local Electric Fields in Macrocyclic Chemical and Biological Systems.

The investigation of the role of the electric field in systems of widespread interest employing computational techniques is an emerging area of research. The outcome of applying an oriented external electric field (OEEF) on the geometric and electronic properties of the chemically unique π-conjugated cyclic carbon ring compounds has been explored with density functional theory (DFT). Distinct changes in the structural and electronic features of such ring compounds are observed upon the application of OEEFs. Importantly, the calculations indicate that a mixed aliphatic-aromatic conjugated ring converts from a singlet to a triplet after the application of an OEEF, suggesting potential applications in optoelectronics for such molecules, without the need for photochemically induced change in the spin state. Furthermore, the influence of built-in local electric fields (LEFs) present in naturally occurring macrocyclic systems such as valinomycin has also been explored. Static and ab initio molecular dynamics (AIMD) calculations indicate that LEFs are the primary driving factor in determining the energetically favoured position of counter anions such as chloride (Cl- ) in the potassium (K+ ) and sodium (Na+ ) coordinated valinomycin macrocycle structures: they exist inside the cage in the case of K+ sequestration by valinomycin and outside for Na+ . This divergence has been proposed to be the determining factor for the selectivity of the valinomycin macrocycle for binding a K+ cation over Na+ .

How Oriented External Electric Fields Modulate Reactivity.

A judiciously oriented external electric field (OEEF) can catalyze a wide range of reactions and can even induce endo/exo stereoselectivity of cycloaddition reactions. The Diels–Alder reaction between cyclopentadiene and maleic anhydride is studied by using quantitative activation strain and Kohn–Sham molecular orbital theory to pinpoint the origin of these catalytic and stereoselective effects. Our quantitative model reveals that an OEEF along the reaction axis induces an enhanced electrostatic and orbital interaction between the reactants, which in turn lowers the reaction barrier. The stronger electrostatic interaction originates from an increased electron density difference between the reactants at the reactive center, and the enhanced orbital interaction arises from the promoted normal electron demand donor–acceptor interaction driven by the OEEF. An OEEF perpendicular to the plane of the reaction axis solely stabilizes the exo pathway of this reaction, whereas the endo pathway remains unaltered and efficiently steers the endo/exo stereoselectivity. The influence of the OEEF on the inverse electron demand Diels–Alder reaction is also investigated; unexpectedly, it inhibits the reaction, as the electric field now suppresses the critical inverse electron demand donor–acceptor interaction.

On the dual aromaticity and external field induced superhalogen modulation of the AuSc2 cluster: A computational study

The geometrical structures, aromatic character, and oriented external electric field (OEEF) regulated superhalogen formation of the neutral and charged AuSc2 clusters were explored by employing the density functional theory (DFT) calculations. The open-shell dual aromaticity involving the delocalization of d orbitals of transition metal atoms was evidenced in AuSc2−. Additionally, the OEEF was demonstrated to possess the power in precisely and continuously regulating the electron affinity (EA) of AuSc2, enabling the cluster to have the superhalogen characteristic. More interestingly, the transformation point between the non-superhalogen and superhalogen in AuSc2 under OEEF can also be located based on the fitted curve.

On the structures, electronic properties, and superhalogen regulation of the MnB6− cluster: A density functional theory investigation

By employing the density functional theory calculations, we report a theoretical study about the geometrical and electronic structures of MnB6−1/0. Their ground states are planar featuring open-shell configurations. Additionally, the oriented external electric field (OEEF) was found to possess the capability in altering the electron affinity (EA) of MnB6 to enable it to hold the superhalogen characteristics. Interestingly, the power of the OEEF was evidenced to be direction-dependent, in which the OEEF along -z direction can dramatically lift the EA to about 4.01 eV at 0.020 au, higher than those of any halogen atoms in the periodic table.

On the theoretical construction of Nb2N2-based superatoms by external field strategies

By using the density functional theory calculations, two external fields, ligand field and the oriented external electric field (OEEF), were introduced to examine their capability in regulating electronic properties of the polymeric Nb2N2 cluster. The ligation strategy was observed to be able to dramatically lower the AIPs of the ligated Nb2N2 clusters forming superalkalis, while the OEEF was confirmed to have power in continuously and precisely modulating the EAs of Nb2N2 at will leading to the formation of superhalogens. These external fields are considered as novel strategies in superatom design, which may broaden the fundamental science of the superatom framework.

A density functional theory calculation on the geometrical structures and electronic properties of Ag19 under the oriented external electric field

We report a comprehensive theoretical study on the effect of the oriented external electric field (OEEF) on the geometrical structures and electronic properties of Ag19. The OEEF was confirmed to have the power in dramatically increasing the EA of Ag19 precisely and continuously while maintaining its geometry and energetic stability. Moreover, the EA variation of Ag19 linearly correlates with its LUMO level, whose downward shift trend was proposed as the microscopic origin of the enhancement of EA. The present letter provides evidence on the modulation effect of OEEF on clusters, which may be beneficial for designing superatoms or superatom-assembly nanomaterials.