Wavepacket Splitting in the First 100 fs Determines the Products from the Bond Cleavage of Diphenylmethylchloride

Sailer, Christian F.; Krebs, Nils; Fingerhut, Benjamin P.; Vivie‐Riedle, Regina de; Riedle, Eberhard

doi:10.1051/epjconf/20134105042

Cited by 7 publications

(16 citation statements)

References 6 publications

(9 reference statements)

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“…The step in the rise of Ph 2 CH _ (blue line) at about 50% amplitude happens at 100 fs. In agreement with the observation for Ph 2 CH-Cl, where we observe such a step at 80 fs, 43 we assign this to the delayed generation of the radical. The excited state wavepacket propagates from the Franck-Condon region to a rst conical intersection that leads part of the wavepacket to the radical product.…”

Section: The Generation and Interconversion Of Benzhydryl Radicals Ansupporting

confidence: 91%

Electronic transient spectroscopy from the deep UV to the NIR: unambiguous disentanglement of complex processes

et al. 2013

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Complex multi-stage relaxation and reaction pathways after the optical excitation of molecules makes the disentanglement of the underlying mechanisms challenging. We present four examples that a new transient spectrometer with excitation fully tunable from the deep UV to the IR and 225 to 1700 nm probing allows for an analysis with greatly reduced ambiguity. The temporal resolution of about 50 fs allows us to resolve all relevant processes. For each example there is a new twist in the sequence of relaxation steps that had previously been overlooked. In malachite green it appears that the importance of the phenyl twisting has been overemphasized and rather a charge transfer state should be considered. In TINUVIN-P the predicted twisting as the driving motion for the ultrafast IC is confirmed and leads to a resolution of the earlier puzzle that the sub-5 ps regime shows kinetics deviating from a pure cooling process despite the sub-ps proton transfer cycle. For the bond cleavage of Ph 2 CH-Cl and Ph 2 CH-Br the degree of electron transfer within the radical pair can now be determined quantitatively and leads to a profound understanding of the long term cation yield. For the first time coherent wavepacket motion in the photoproducts is reported. Last but not least the measurement of the GSB recovery in the deep UV allows for the surprising result, that even after S 2 excitation of cyclopentenones the triplet states are reached with near unity probability within a few picoseconds.

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Section: The Generation and Interconversion Of Benzhydryl Radicals Ansupporting

confidence: 91%

Electronic transient spectroscopy from the deep UV to the NIR: unambiguous disentanglement of complex processes

et al. 2013

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“…At 67 fs, the radical yield starts to grow very rapidly as more and more parts of the wave packet couple through the three-state CoIn seam. This delay time is in very good agreement with the experimentally observed 76 fs 21 . The delay time of 143 fs for the ion pairs is only slightly longer than the measured one of 124 fs (Ref.…”

Section: Bond Cleavage Of Ph2ch–clsupporting

confidence: 90%

“…The initial bond cleavage is found to be mainly homolytic on the sub-hundred femtosecond time scale, while a small heterolytic fraction is slightly delayed 21 . In a previous theoretical study, a S 1 / S 0 CoIn was identified connecting the heterolytic and homolytic product channel, but two-dimensional QD simulations revealed that the wave packet does not reach the CoIn 22 .…”

Section: Bond Cleavage Of Ph2ch–clmentioning

confidence: 79%

“…In previous CASSCF calculations for the whole molecule, it was demonstrated that the π - and π *-orbitals of the phenyl rings can be separated 22 . Furthermore, CASSCF calculations including the π -orbitals of both phenyl rings in the active space have shown that only one phenyl ring can interact with the σ *-orbital of the C1-Cl bond 21 . Therefore, it is possible that the high-level system treated at the CASSCF level of theory contains only one phenyl ring.…”

Section: Bond Cleavage Of Ph2ch–clmentioning

confidence: 99%

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Molecular features in complex environment: Cooperative team players during excited state bond cleavage

Thallmair

Roos

Vivie‐Riedle

2016

Structural Dynamics

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Photoinduced bond cleavage is often employed for the generation of highly reactive carbocations in solution and to study their reactivity. Diphenylmethyl derivatives are prominent precursors in polar and moderately polar solvents like acetonitrile or dichloromethane. Depending on the leaving group, the photoinduced bond cleavage occurs on a femtosecond to picosecond time scale and typically leads to two distinguishable products, the desired diphenylmethyl cations (Ph2CH+) and as competing by-product the diphenylmethyl radicals (Ph2CH•). Conical intersections are the chief suspects for such ultrafast branching processes. We show for two typical examples, the neutral diphenylmethylchloride (Ph2CH–Cl) and the charged diphenylmethyltriphenylphosphonium ions (Ph2CH−PPh3+) that the role of the conical intersections depends not only on the molecular features but also on the interplay with the environment. It turns out to differ significantly for both precursors. Our analysis is based on quantum chemical and quantum dynamical calculations. For comparison, we use ultrafast transient absorption measurements. In case of Ph2CH–Cl, we can directly connect the observed signals to two early three-state and two-state conical intersections, both close to the Franck-Condon region. In case of the Ph2CH−PPh3+, dynamic solvent effects are needed to activate a two-state conical intersection at larger distances along the reaction coordinate.

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“…The two lowest excited singlet states in the model system correspond to local π−π* transitions. Compared with other well-studied benzhydryl derivatives, 3,8,[10][11][12][13]19,22,24 the phosphonium leaving group offers a second chromophore and enhances the complexity of the excitation mechanism. Our calculations show that the excitation on the PH 2 Ph + moiety leads to the S 1 state, and the excitation on the PhCH 2 moiety leads to the S 2 state.…”

Section: Discussionmentioning

confidence: 99%

Ground and Excited State Surfaces for the Photochemical Bond Cleavage in Phenylmethylphenylphosphonium Ions

2013

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Photolytic bond cleavage is a well-established method to generate carbocations for organic synthesis. Changes in the leaving group have a large influence on the chemical yield. The underlying potential energy surfaces governing the initial process are mostly unknown. We provide potential energy surfaces of ground and excited states on the CASSCF/CASPT2 level of theory for the charged precursor phenylmethylphenylphosphonium ion. We present the electronic and structural changes accompanying the excitation process and the subsequent bond cleavage. Inter-ring charge-transfer processes play a crucial role in the Franck-Condon region. Beyond the Franck-Condon region, competing reaction pathways emerge connected through conical intersections. The phenylmethylphenylphosphonium ion is used as a model system for the commonly used diphenylmethyltriphenylphosphonium ion. The appropriateness of the model is tested by CC2 calculations of the excitation spectrum.

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Wavepacket Splitting in the First 100 fs Determines the Products from the Bond Cleavage of Diphenylmethylchloride

Abstract: Abstract. An elementary chemical reaction proceeds through two distinct conical intersections. Benzhydryl radicals are formed with a delay of 80 fs, cations after 125 fs. The optical signal increases more slowly due to planarization and solvation.

Cited by 7 publications

References 6 publications

Electronic transient spectroscopy from the deep UV to the NIR: unambiguous disentanglement of complex processes

Electronic transient spectroscopy from the deep UV to the NIR: unambiguous disentanglement of complex processes

Molecular features in complex environment: Cooperative team players during excited state bond cleavage

Ground and Excited State Surfaces for the Photochemical Bond Cleavage in Phenylmethylphenylphosphonium Ions

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