Picosecond Kinetic Study of the Photoinduced Homolysis and Heterolysis of Diphenylmethyl Bromide. 2. Role of Polarization Caging in Contact Ion Pair Recombination

Dreyer, J.; Lipson, Matthew; Peters, Kevin S.

doi:10.1021/jp961200t

Cited by 12 publications

(17 citation statements)

References 8 publications

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“…A similar broad distribution was reported for photo-detached electrons from I - [29]. The underlying assumption of all previous interpretations on the reaction dynamics of photo-excited benzhydryl halides was that homolysis would exclusively lead to geminate radical pairs (GRPs) [6][7][8][9][10]. We see no good arguments for this assumption.…”

Section: Conversion Of Radical Pairs To Ion Pairs By Electron Transfersupporting

confidence: 47%

“…In an earlier investigation with 20 ps resolution this important early contribution was overlooked and a reaction model was developed [7,8] that the new data cannot support. This shows the C. F. SAILER AND E. RIEDLE importance to use sufficient temporal resolution and a broad detection range to actually catch all intermediate species and reaction steps.…”

Section: Conversion Of Radical Pairs To Ion Pairs By Electron Transfermentioning

confidence: 99%

“…At first sight, the early reaction steps leading to the chemically relevant fragment populations might not seem very important, as the large majority of bimolecular reactions proceed at best in the diffusional limit. Yet, the early events have been investigated in great detail by Peters and co-workers [6][7][8][9][10]. Their aim was not only the elucidation of the bond cleavage and the subsequent reaction steps, but the hope to obtain information on the rates and barriers for the reverse processes leading to bond formation [10].…”

Section: Introductionmentioning

confidence: 99%

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Photogeneration and reactions of benzhydryl cations and radicals: A complex sequence of mechanisms from femtoseconds to microseconds

Sailer

Riedle

2013

Pure and Applied Chemistry

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Benzhydryl radicals and cations are reactive intermediates central to the understanding of organic reactivity. They can be generated from benzhydryl halides by UV irradiation. We performed transient absorption (TA) measurements over the range from femtoseconds to microseconds to unravel the complete reaction scheme. The 290-720-nm probe range allows the unambiguous monitoring of all fragments. The appearance of the radical is delayed to the optical excitation, the onset of the cation signal is found even later. Ab initio calculations show that this non-rate behavior in the 100 fs range is due to wavepacket motion from the Franck-Condon region to two distinct conical intersections. The rise of the optical signal with a quasi-exponential time of 300 fs is assigned to the planarization and solvation of the photoproducts. The bond cleavage predominantly generates radical pairs. A subsequent electron transfer (ET) transforms radical pairs into ion pairs. Due to the broad interradical distance distribution and the distance dependence, the ET is strongly non-exponential. Part of the ion pairs recombine geminately. The ET and the recombination are terminated by the depletion of close pairs and diffusional separation. The remaining free radicals and cations undergo further reactions in the nanosecond to microsecond regime.Benzhydryl cation and radical photogeneration 1489 Fig. 1 (a) Transient spectrum at a pump-probe delay of 40 ps and (b) false color representation of the 2D TA data matrix of tol(Ph)CHCl in CH 3 CN after 270 nm UV excitation. The delay time axis is linear between -1 and 1 ps and logarithmic beyond 1 ps. (c) Scheme of the ultrafast bond cleavage.

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Section: Conversion Of Radical Pairs To Ion Pairs By Electron Transfersupporting

confidence: 47%

Section: Conversion Of Radical Pairs To Ion Pairs By Electron Transfermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photogeneration and reactions of benzhydryl cations and radicals: A complex sequence of mechanisms from femtoseconds to microseconds

Sailer

Riedle

2013

Pure and Applied Chemistry

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“…Despite the clear importance of this topic, the study of ion-pair structure, dynamics, and thermodynamics, both experimentally 4,5 and theoretically, has been mainly limited to the bulk electrolyte solution. In particular, over the last two decades significant progress has been made by applying statistical mechanical [6][7][8] and computer simulation [9][10][11][12][13][14][15][16][17][18][19][20][21][22] techniques to better understand the factors that influence the stability and dynamics of ion pairs in bulk liquids.…”

Section: Introductionmentioning

confidence: 99%

Ion pairing and dissociation at liquid/liquid interfaces: Molecular dynamics and continuum models

Schweighofer

Benjamin

2000

The Journal of Chemical Physics

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“…46 We have to assume an initial radical and cation pair distance distribution that extends far beyond the contact distance considered explicitly in earlier work. 41,42,47,48 The various processes are treated as distance dependent. The time dependent populations can then be deduced by integration over the full radial distribution for each delay time.…”

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confidence: 99%

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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Picosecond Kinetic Study of the Photoinduced Homolysis and Heterolysis of Diphenylmethyl Bromide. 2. Role of Polarization Caging in Contact Ion Pair Recombination

Cited by 12 publications

References 8 publications

Photogeneration and reactions of benzhydryl cations and radicals: A complex sequence of mechanisms from femtoseconds to microseconds

Photogeneration and reactions of benzhydryl cations and radicals: A complex sequence of mechanisms from femtoseconds to microseconds

Ion pairing and dissociation at liquid/liquid interfaces: Molecular dynamics and continuum models

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

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