Barrierless Single‐Electron‐Induced cis–trans Isomerization

Abstract

Lowering the activation energy of ac hemical reaction is an essential part in controlling chemical reactions. By attachingasingle electron, ab arrierless path for the cistrans isomerization of maleonitrile on the anionic surface is formed. The anionic activation can be applied in both reaction directions,y ielding the desired isomer.W ei dentify the microscopic mechanism that leads to the formation of the barrierless route for the electron-induced isomerization. The generalization to other chemical reactions is discussed. Theabilitytosurpasstheenergeticbarrierbetweenreactantsand products is at the very heart of controlling chemical reactions.V arious control strategies have been developed over the years that rely,f or example,o nt he use of light, mechanical force,o re lectric current. Regardless of the chosen external stimulation, the common strategy is either to move the reaction to ad ifferent potential energy surface, for example,p hotochemistry, [1] or to modify the potential energy surface of the reactants,f or example,m echanochemistry.[2] Ideally,t he target potential energy surface does not only energetically enable the reaction but provides ac lear directionality as well.Thei dea of activating ac hemical reaction by attaching as ingle electron has been around since the early days of electrochemistry.S till, the prominent role of the electron in many reactions has been restricted to inducing adissociative electron attachment (DEA) mechanism. Them ain use of DEA in promoting chemical reactions is through the creation of radicals that continue to react further.[3] Only in the past decade,e xperiments demonstrating more complicated reactions following electron capture have emerged, for example, multiple bond-breaking, [4] tautomerization, [5] and complex fragmentations.[6] Theu nderlying microscopic mechanism that leads to the electron-driven chemistry in the above examples is still unknown. There have also been af ew theoretical works predicting multiple bond-breaking rearrangements following electron attachment. [7] Herein we demonstrate how the attachment of as ingle electron can lead to ab arrierless cis-trans isomerization of maleonitrile (cis-1,2-dicyanoethylene,MN) and fumaronitrile (trans-1,2-dicyanoethylene,FN). Theexcess electron transfers the reactants to the anionic potential energy surface (PES) on which there is no longer an energetic barrier towards isomerization. By analyzing the microscopic mechanism responsible for this appealing topology,wegain new insights into the yet unexplored possibilities of electron-driven chemistry.The cis-trans isomerization reaction is one of the most studied reactions with regard to chemical control and chemical switching,f or example by light [8] or mechanical force.[9] Very recently it has been shown that the cis-trans isomerization rate can be tuned by the presence of an earby anion. [10] Thei somerization of FN to MN was previously studied using photoinduced electron transfer. [11] In these experiments the FN À anion is formed in its ground state ...

Intramolecular Torque Study of a Molecular Rotation Stimulated by Electron Injection and Extraction

“…The introduction of the charge in the isomerization significantly reduces the energy barrier, which is consistent with an earlier report. 12 To further validate the reliability of the calculated results by the CAM-B3LYP functional, we additionally calculated PES profiles using two other well-known DFT functionals, M062X and ωB97XD, with the same basis set 6-31+G(d,p). As shown in Figures 3b and S1, the PES profiles from these three DFT functionals are in good agreement with each other, with acceptable data differences (see Table S1).…”

“…Through the use of high-level ab initio methods, Cederbaum's group demonstrated that the barrierless cis−trans isomerization can be realized by attaching a single electron to the dicyanoethylene molecule. 12 Analysis of the electronic structure indicated that both electron affinity (formation of anionic radicals) in the π* orbitals of neutral olefins and electron ionization (generation of cationic radicals) in the π orbitals can significantly weaken the CC double bond of the neutral molecule and make the cis−trans isomerization occur more easily. In the past decade, electron injection or removal has been performed in many tip-induced isomerization experiments using a scanning tunneling microscope (STM) which can transfer electrons between the tip and the substrate.…”

Interatomic and Intermolecular Coulombic Decay

“…Electronic resonances are ubiquitous in physical chemistry and always appear whenever free electrons are present. Apart from ICD, electronic resonances are also central to processes such as autoionization, 71 the Auger effect, 72 and electron-activated chemical reactions, 73 , 74 all of which involve free electrons. In ICD, the final states of an electronically decayed chemical system, comprising the electron-detached system and the free electron, lie in the electronic continuum above the ionization potential of the initial system and are thus described by continuum eigenfunctions of the electronic Hamiltonian.…”

Understanding the Role of Aromaticity and Conformational Changes in Bond Dissociation Processes of Photo-Protecting Groups

“…The role of low-energy electrons (LEE) attached to molecules has been implicated in various branches of chemistry which helps in initiating chemical transformations such as repair processes in damaged DNA and in prebiotic synthesis. − Recently, Cederbaum et al have demonstrated theoretically that a LEE from an outside source can be absorbed by a molecule, and as a result bond dissociation occurs . This process is followed by the release of an electron to form the product, i.e., the electron is playing an unusual role, it appears as a catalyst. − …”