Sudden polarization in zwitterionic excited states of organic intermediates in photochemical reactions. On a possible mechanism for bicyclo[3.1.0]hex-2-ene formation

Bonačić‐Koutecký, Vlasta

doi:10.1021/ja00470a008

Cited by 55 publications

(10 citation statements)

References 7 publications

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“…For

θ ≃ 90^{\circ}

, and vanish and is too small, i. e. much smaller than the energy difference between

A^{-} B^{+}

and

A^{+} B^{-}

, to prevent the charge separation in the excited states. In agreement with previous calculations, in the

S_{1}

state the negative charge prefers the s,trans subsystem ( B ), while in

S_{2}

the negative charge suddenly flows into the s,cis fragment ( A ) of the molecule (see Figure ). This sudden charge separation is confirmed by the Mulliken population analysis of the adiabatic wavefunctions (see Figure S1).…”

Section: Applicationssupporting

confidence: 92%

“…Moreover, since 1970s polyenes and substituted polyenes have attracted much attention for their tendency to undergo, upon excitation, a strong charge separation in a region around the 90°‐twisted geometry. This effect was called “sudden polarization” and has been considered the crucial event in important mechanisms like the vision, highly stereospecific photocyclizations and the photochemistry of provitamin D …”

Section: Applicationsmentioning

confidence: 99%

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Diabatization by Localization in the Framework of Configuration Interaction Based on Floating Occupation Molecular Orbitals (FOMO−CI)

2019

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This work is dedicated to Jean-Paul Malrieu on the occasion of his 80 th birthday.We present a diabatization method of general applicability, based on the localization of molecular orbitals on user specified groups of atoms. The method yields orthogonal molecular orbitals similar to the canonical ones for the isolated atom groups, that are the basis to build reference spin-adapted configurations representing localized or charge transfer excitations. An orthogonal transformation from the adiabatic to the quasi-diabatic basis is defined by requiring maximum overlap with the diabatic references. We present the diabatization algorithm as implemented in the framework of semiempirical configuration interaction based on floating occupation molecular orbitals (FOMOÀ CI), but the same transformation can also be applied to ab initio wavefunctions, obtained for instance with state-average CASSCF. The diabatic representation so obtained and the associated hamiltonian matrix are particularly suited to assess quantitatively the interactions that account for charge and energy transfer transitions, and to analyze the results of nonadiabatic dynamics simulations involving such phenomena.

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“…For

θ ≃ 90^{\circ}

, and vanish and is too small, i. e. much smaller than the energy difference between

A^{-} B^{+}

and

A^{+} B^{-}

, to prevent the charge separation in the excited states. In agreement with previous calculations, in the

S_{1}

state the negative charge prefers the s,trans subsystem ( B ), while in

S_{2}

Section: Applicationssupporting

confidence: 92%

Section: Applicationsmentioning

confidence: 99%

Diabatization by Localization in the Framework of Configuration Interaction Based on Floating Occupation Molecular Orbitals (FOMO−CI)

2019

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“…The charge transfer nature of T is a quite general phenomenon that arises in the cis−trans isomerizations of bonds with a partial double-bond character, as long as the two halves have different abilities for attracting electrons, and is related to the effect of sudden polarization. This analysis has been applied by Michl and Bonacic-Koutecky to a great variety of reactions. , The fact that the T geometry does not have a biradicaloid character was also confirmed by performing CI calculations at that geometry, without observing any significant change in the computed energy.…”

Section: Resultsmentioning

confidence: 78%

AM1 Study of the Ground and Excited State Potential Energy Surfaces of Symmetric Carbocyanines

et al. 1997

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Ground (S0) and first excited singlet state (S1) potential energy surfaces were calculated for a series of six symmetric carbocyanines as a function of the twisting angle (θ), around a carbon−carbon bond of the polymethine chain. The surfaces were computed using AM1 semiempirical quantum mechanical calculations. Rotations around different bonds were considered in order to determine the relevant rotation for isomerization, that is, the rotation with the lowest activation energy for the isolated molecule (E 0). For that rotation, the computed values of E 0 are in good agreement with values extrapolated from experiments in solutions of n-primary alcohols. The same holds for the computed transition energies between both surfaces for the thermodynamically stable N isomer (θ = 0°) and the P photoisomer (θ = 180°). The effects of chain length and pattern substitution of the indoline moiety on E 0 were also analyzed for both surfaces. The shape of the potential surfaces referred as the Rullière's model holds in all cases for at least one rotational coordinate. The electrical dipole moment with respect to the center of electrical charges was calculated as a function of θ. The calculations show that the dipole moment remains almost constant except in the vicinity of θ = 90°, where a sudden increase with a sharp peak was obtained in both surfaces. This gives a simple explanation for the well-known experimental observation that the activation energy on the excited state surface is independent of solvent polarity, as the angle of the transition state is smaller than 90°. On the other hand, the transition state is at θ = 90° on the ground state, and a polarity influence is predicted. An improvement in the description of the experimental isomerization rate constants in S0 is obtained for the two smallest carbocyanines considered when polarity contributions are included.

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“…This effect is known for excited-state isomerizations. Even in hydrocarbon reactants, such as ( E )-stilbene, the S 1 twisted configuration II (the minimum on S 1 curve, Figure ) is strongly polarized in a narrow range of twisting angle Ô near 90°; this effect has been called “sudden polarization”. − Although its early estimates seem to be exaggerated, quantum-chemical studies of model systems − and experiment support significant charge separation in excited configuration II. No such estimates are available for TS configurations of photoreactions (point I in Figure ) but some polarization at this TS point for ( E )-stilbene and 1,4-diphenylbutadiene (DPB) is confirmed implicitly by a significiant lowering of activation barriers in polar alcohols as compared to hydrocarbon solvents (see Table ). ,,− Solvent effects on the potential barrier have been also assumed for ( E )-stilbene in hydrocarbon solvents, − ,− where polar effect is not expected.…”

Section: E Static Effects In Isomerization Reactionsmentioning

confidence: 99%

Activation and Reaction Volumes in Solution. 3

et al. 1998

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Sudden polarization in zwitterionic excited states of organic intermediates in photochemical reactions. On a possible mechanism for bicyclo[3.1.0]hex-2-ene formation

Cited by 55 publications

References 7 publications

Diabatization by Localization in the Framework of Configuration Interaction Based on Floating Occupation Molecular Orbitals (FOMO−CI)

Diabatization by Localization in the Framework of Configuration Interaction Based on Floating Occupation Molecular Orbitals (FOMO−CI)

AM1 Study of the Ground and Excited State Potential Energy Surfaces of Symmetric Carbocyanines

Activation and Reaction Volumes in Solution. 3

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