The .DELTA.H for thermal trans/cis-stilbene isomerization:  do S0 and T1 potential energy curves cross?

Saltiel, Jack; Ganapathy, Srinivasan; Werking, Constance.

doi:10.1021/j100295a022

Cited by 92 publications

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“…The calculated results reproduce quantitatively the enthalpy of cis to trans isomerization, þ4.6 kcal/mol, measured in benzene solution at 298 K. 108 The quantitative agreement is in stark contrast with the very small energy difference (0.2 kcal/mol) computed by the state-specific CASPT2 method. 44 3.2.…”

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confidence: 54%

Photoisomerization of Stilbene: A Spin-Flip Density Functional Theory Approach

2011

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The photoisomerization process of 1,2-diphenylethylene (stilbene) is investigated using the spin-flip density functional theory (SFDFT), which has recently been shown to be a promising approach for locating conical intersection (CI) points (Minezawa, N.; Gordon, M. S. J. Phys. Chem. A2009, 113, 12749). The SFDFT method gives valuable insight into twisted stilbene to which the linear response time-dependent DFT approach cannot be applied. In contrast to the previous SFDFT study of ethylene, a distinct twisted minimum is found for stilbene. The optimized structure has a sizable pyramidalization angle and strong ionic character, indicating that a purely twisted geometry is not a true minimum. In addition, the SFDFT approach can successfully locate two CI points: the twisted-pyramidalized CI that is similar to the ethylene counterpart and another CI that possibly lies on the cyclization pathway of cis-stilbene. The mechanisms of the cis-trans isomerization reaction are discussed on the basis of the two-dimensional potential energy surface along the twisting and pyramidalization angles. Disciplines Chemistry CommentsReprinted (adapted) with permission from

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confidence: 54%

Photoisomerization of Stilbene: A Spin-Flip Density Functional Theory Approach

2011

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“…10 A value of 4.59 kcal/mol was inferred from fluorescence excitation studies in ultra cold molecular beams and argon clusters, 11 and exactly the same value was obtained based on the temperature dependence of the cis-trans equilibrium in benzene, toluene, and p-xylene. 12 The latter study also provided an estimate for the barrier for the cis-trans conversion (relative to the cis conformer) on the ground state S 0 surface of 48 6 2 kcal/mol. 12 A structural isomer of C 14 H 12 related to cis-stilbene is 4a,4b-dihydrophenanthrene (DHP) (3), which can be obtained from it by the action of light or heat.…”

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confidence: 98%

“…12 The latter study also provided an estimate for the barrier for the cis-trans conversion (relative to the cis conformer) on the ground state S 0 surface of 48 6 2 kcal/mol. 12 A structural isomer of C 14 H 12 related to cis-stilbene is 4a,4b-dihydrophenanthrene (DHP) (3), which can be obtained from it by the action of light or heat. Its formation is a competing pathway to cis-trans isomerization on the photoexcited S 1 state PES with a reported activation energy of 1-2 kcal/mol.…”

Section: Introductionmentioning

confidence: 98%

Isomerization of stilbene using enforced geometry optimization

Baker

Woliński

2010

J Comput Chem

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Using our recently proposed quantum chemical model to simulate the effect of external forces acting on a molecule (Wolinski and Baker, Mol Phys 2009, 107, 2403), which we subsequently termed enforced geometry optimization (EGO), we investigate structural isomerism in C(14) H(12) , starting from cis-stilbene. By applying an external force to pairs of carbon atoms, one from each "half" of the molecule, we have generated 10 different structural isomers. Each was characterized as a minimum by vibrational analysis. Not only can EGO generate potentially new, metastable isomers it can also provide good initial guesses for transition states connecting the starting and final structures, thus giving an estimate of the stability of the new isomers to rearrangement back to the starting material. In addition to the new isomers, we provide a full set of vibrational fundamentals for cis- and trans-stilbene and 4a,4b-dihydrophenanthrene. The agreement with experimental assignments is excellent, with mean average deviations for the stilbenes of 5.0 cm(-1) or less.

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“…7 kcal mol -I, in addition to the exoergicity of reaction which is 4.6 kcal/mol. 19 In the gas phase this energy would be transferred into vibrational and rotational energy of the trans product. In the solution phase the surrounding molecules exchange energy with the activated solute during the course of the configurational changes that occur: This is the external friction.…”

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confidence: 99%