Triplet recombination of radical ion pairs: CIDNP effects and DFT calculations on 1,2-dicyanoethylene

Roth, Heinz D.; Sauers, R.

doi:10.1039/c3pp50213a

Cited by 3 publications

(9 citation statements)

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“…It corresponds to the broad transition peaking around 4 eV (labeled 3 A due to reduced symmetry, as explained below). The broad and congested nature of the band reflects a significant change in equilibrium geometry upon the photodetachment to the triplet state, which is consistent with its previously calculated nonplanar structure . For this reason, we can estimate only the upper limit for the adiabatic binding energy of the 3 A state, EA( 3 A) ≤ 3.8 eV.…”

Section: Resultssupporting

confidence: 87%

“…The triplet state of fumaronitrile was observed to lie 59 ± 2 kcal/mol (2.56 ± 0.09 eV) above the ground-state singlet, using the Herkstroeter–Hammond laser flash photolysis method . The triplet energy surface has a minimum at a bisected geometry, with a depth ∼9 kcal/mol with respect to H–C–CN rotation, as determined from the M06-2X/6-311+G(2d,p) density-functional theory (DFT) calculations . The same calculations predicted that the radical anion surface has a minimum at a planar geometry and the barrier to geometric isomerization of 31.2 kcal/mol.…”

Section: Introductionmentioning

confidence: 86%

“…7 The triplet energy surface has a minimum at a bisected geometry, with a depth ∼9 kcal/mol with respect to H−C−CN rotation, as determined from the M06-2X/6-311+G(2d,p) density-functional theory (DFT) calculations. 8 The same calculations predicted that the radical anion surface has a minimum at a planar geometry and the barrier to geometric isomerization of 31.2 kcal/mol.…”

Section: Introductionmentioning

confidence: 90%

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Photochemistry of Fumaronitrile Radical Anion and Its Clusters

et al. 2014

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The photodetachment and photochemistry of the radical anion of fumaronitrile (trans-1,2-dicyanoethylene) and its clusters are investigated using photoelectron imaging and photofragment spectroscopy. We report the first direct spectroscopic determination of the adiabatic electron affinity (EA) of fumaronitrile (fn) in the gas phase, EA = 1.21 ± 0.02 eV. This is significantly smaller than one-half the EA of tetracyanoethylene (TCNE). The singlet-triplet splitting in fumaronitrile is determined to be ΔES-T ≤ 2.6 eV, consistent with the known properties. An autodetachment transition is observed at 392 and 355 nm and assigned to the (2)Bu anionic resonance in the vicinity of 3.3 eV. The results are in good agreement with the predictions of the CCSD(T) and EOM-XX-CCSD(dT) (XX = IP, EE) calculations. The H2O and Ar solvation energies of fn(-) are found to be similar to the corresponding values for the anion of TCNE. In contrast, a very large (0.94 eV) photodetachment band shift, relative to fn(-), is observed for (fn)2(-). In addition, while the photofragmentation of fn(-), fn(-)·Ar, and fn(-)(H2O)1,2 yielded only the CN(-) fragment ions, the dominant anionic photofragment of (fn)2(-) is the fn(-) monomer anion. The band shift, exceeding the combined effect of two water molecules, and the fragmentation pattern, inconsistent with an intact fn(-) chromophore, rule out an electrostatically solvated fn(-)·fn structure of (fn)2(-) and favor a covalently bound dimer anion. A C2 symmetry (fn)2(-) structure, involving a covalent bond between the two fn moieties, is proposed.

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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 90%

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Photochemistry of Fumaronitrile Radical Anion and Its Clusters

et al. 2014

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“…The isomerization of FN to MN was previously studied using photoinduced electron transfer 11. In these experiments the FN − anion is formed in its ground state where an energetic barrier for isomerization is still found, albeit a much smaller barrier 12. Nevertheless, the isomerization mechanism in these experiments has been shown to proceed through the triplet state of FN which is occupied through electron transfer back to the solvent.…”

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confidence: 93%

Barrierless Single‐Electron‐Induced cis–trans Isomerization

Klaiman

Cederbaum

2015

Angew Chem Int Ed

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Lowering the activation energy of a chemical reaction is an essential part in controlling chemical reactions. By attaching a single electron, a barrierless path for the cis-trans isomerization of maleonitrile on the anionic surface is formed. The anionic activation can be applied in both reaction directions, yielding the desired isomer. We identify 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.

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“…[11] In these experiments the FN À anion is formed in its ground state where an energetic barrier for isomerization is still found, albeit am uch smaller barrier. [12] Nevertheless,t he isomerization mechanism in these experiments has been shown to proceed through the triplet state of FN which is occupied through electron transfer back to the solvent. Thus in this photochemical isomerization, the ground state of FN À anion is only temporarily populated and the reaction proceeds on the PES of the triplet state of the neutral FN.Aswes hall see in the following,avery different situation occurs if the anionic metastable excited state is populated rather than its ground state.…”

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confidence: 91%

Barrierless Single‐Electron‐Induced cis–trans Isomerization

Klaiman

Cederbaum

2015

Angewandte Chemie

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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 ...

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Triplet recombination of radical ion pairs: CIDNP effects and DFT calculations on 1,2-dicyanoethylene

Cited by 3 publications

References 58 publications

Photochemistry of Fumaronitrile Radical Anion and Its Clusters

Photochemistry of Fumaronitrile Radical Anion and Its Clusters

Barrierless Single‐Electron‐Induced cis–trans Isomerization

Barrierless Single‐Electron‐Induced cis–trans Isomerization

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