Photoaddition of cis-cyclo-octene to hexafluorobenzene

Bryce‐Smith, D.; Gilbert, A.; Orger, B. H.

doi:10.1039/c2969000800b

Cited by 14 publications

(9 citation statements)

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“…4 The 4π electrocyclic ring-closing reaction is known for many highly fluorinated cyclic polyenes, many of which result from cycloadditions with HFB. [6][7][8][9] HFB itself undergoes the same ringclosing reaction, 10 photochemically isomerizing to hexafluoro-Dewar-benzene (Dewar-HFB) chemoselectively. The hexafluoro-benzvalene or -fulvene isomers are not observed, but are the major products of benzene photochemistry (Figure 1a).…”

Section: Figure 1 (A)mentioning

confidence: 99%

Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene

et al. 2021

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Hexafluorobenzene and many of its derivatives exhibit a chemoselective photochemical isomerization, resulting in highly-strained, Dewar-type bicyclohexenes. While the changes in absorption and emission associated with benzene hexafluorination have been attributed to the socalled "perfluoro effect," the resulting electronic structure and photochemical reactivity of hexafluorobenzene are still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4πelectrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ~100 nm Stokes shift in fluorescence-in stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway towards hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene. File list (2)download file view on ChemRxiv HFB_SI_JACS-final.docx (3.46 MiB) download file view on ChemRxiv HFB_JACS-final.pdf (1.38 MiB)

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Section: Figure 1 (A)mentioning

confidence: 99%

Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene

et al. 2021

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“…This was previously reported to improve the ordering of electronic states in conjugated systems when a CASPT2 correction is not performed. 31 CASSCF (6,7) predicts that the S2 state has doubly-excited (π*π*) character, which is corrected via XMS-CASPT2 to the level of S7. This intruder state is absent from the frontier excited states in CASSCF(6,6)'.…”

Section: Non-adiabatic Molecular Dynamicsmentioning

confidence: 99%

“…The electronic structure at each time step was computed at the SA-5-CAS(6,6)'/ANO-S-VDZP level. The (6,6)' active space used here eliminates the highest-energy π* orbital from the (6,7) space described above. This was previously reported to improve the ordering of electronic states in conjugated systems when a CASPT2 correction is not performed.…”

Section: Non-adiabatic Molecular Dynamicsmentioning

confidence: 99%

Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene

Cox¹,

Kellogg²,

Bain³

et al. 2021

Preprint

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Hexafluorobenzene and many of its derivatives exhibit a chemoselective photochemical isomerization, resulting in highly-strained, Dewar-type bicyclohexenes. While the changes in absorption and emission associated with benzene hexafluorination have been attributed to the socalled “perfluoro effect,” the resulting electronic structure and photochemical reactivity of hexafluorobenzene are still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4πelectrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ~100 nm Stokes shift in fluorescence– in stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway towards hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene.

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“…(1)) is attributed to the lack of sufficient donor-acceptor interactions between the potential 257 + 2~ partners (14,15). This situation resembles that found for the dienes 28 (16) and 30 (17), where only polar substituted 28 undergoes the ring closure process (+ 29, Scheme 8).…”

Section: Excited State Multiplicitiesmentioning

confidence: 99%