C-Br Bond Dissociation Mechanisms of 2-Bromothiophene and 3-Bromothiophene at 267 nm

张锋,; 曹振洲,; 覃晓,; 刘玉柱,; 王艳梅,; Bing, Zhang Jing

doi:10.1016/s1872-1508(08)60055-8

Cited by 13 publications

(8 citation statements)

References 27 publications

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“…The first involves 2-iodo-and 2-bromothiophene, the photolyses of which have been probed via VMI measurements of the ground and spin-orbit excited halogen atom fragments. 134,135 The velocity distributions determined from images measured at longer UV wavelengths (e.g. 260270 nm in the case of 2-bromothiophene)…”

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confidence: 99%

Molecular Photofragmentation Dynamics in the Gas and Condensed Phases

Ashfold

Murdock

Oliver

2017

Annu. Rev. Phys. Chem.

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This is the submitted manuscript. The final published version (version of record) is available online via Annual Review of Physical Chemistry at http://www.annualreviews.org/doi/10.1146/annurev-physchem-052516-050756 . Please refer to any applicable terms of use of the publisher University of Bristol -Explore Bristol Research General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms 1 Molecular Photofragmentation Dynamics in the Gas and Condensed PhasesMichael N.R. Ashfold, Daniel Murdock and Thomas A.A. Oliver School of Chemistry, University of Bristol, Bristol, U.K., BS8 1TS AbstractExciting a molecule with a UV photon often leads to bond fission, but the final outcome of the bond cleavage is typically both molecule and phase dependent. The photodissociation of an isolated gasphase molecule can be viewed as closed system: energy and momentum are conserved, and the fragmentation is irreversible. The same is not true in a solution-phase photodissociation process.Solvent interactions may dissipate some of the photoexcitation energy prior to bond fission, and will dissipate any excess energy partitioned into the dissociation products. Products that have no analogue in the corresponding gas-phase study may arise by, for example, geminate recombination. Here we illustrate the extents to which dynamical insights from gas-phase studies can inform our understanding of the corresponding solution-phase photochemistry and how, in the specific case of photoinduced ring-opening reactions, solution-phase studies can in some cases reveal dynamical insights more clearly than the corresponding gas-phase study.Keywords photochemistry, photodissociation, photoinduced ring opening, non-adiabatic dynamics, conical intersections. 2 HISTORICAL CONTEXTCiamician is recognised as a pioneer of (organic) photochemistry and an early advocate for fuel production by means of artificial photo'synthesis'. 1 His studies were performed in solution and usually driven by sunlight, at a time when the concept of the photon was yet to be fully accepted.Identifying the ultimate reaction products was in itself a major achievement, and any ideas regarding reaction mechanism were rudimentary. Even the concatenation of ideas like ground and excited electronic states, radiative and non-radiative transitions, spin multiplicity, etc, into what would later be termed a Jablonski diagram 2 still lay far in the future.A potentially more fruitful path at that time for those curious about the mechanisms of photochemical reactions was to focus on very simple molecular systems -diatomic and 'diatomic-like' molecules. generally polychromatic) light sources were now available, and the development of grating spectrometers enabled the recording of electronic absorption spectra for many small gas-phase molecules. Vibrational and even rotational fine structure was resolved and interpreted in many such ...

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Molecular Photofragmentation Dynamics in the Gas and Condensed Phases

Ashfold

Murdock

Oliver

2017

Annu. Rev. Phys. Chem.

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“…Considering the reaction enthalpy of the above reactions, the appearance energy for the formation of the HCS + cation is calculated to be 295.9 kcal/mol for reaction 30 The second most abundant ion peak appears at m/z 39 corresponding to the C 3 H 3 + product ion in the mass spectra of 2-chlorothiophene.…”

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confidence: 99%

“…Photoelectron studies on 2‐bromothiophene and 2‐chlorothiophene suggest that the lone pair electrons on Br and Cl atoms, which is perpendicular to the molecular plane, is delocalized over much of the ring, and significantly involved in bonding and mixing with π electrons of the ring. Wang and co‐workers studied the dynamics of Br atom formation in the photodissociation of bromothiophenes at 267 nm, using an ion velocity imaging technique . The presence of another chromophore, namely the C−X bond, can alter the photochemistry.…”

Section: Introductionmentioning

confidence: 99%

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Ground‐state dissociation pathways for the molecular cation of 2‐chlorothiophene: A time‐of‐flight mass spectrometry and computational study

Upadhyaya

2019

Rapid Comm Mass Spectrometry

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Rationale Halogenated thiophenes are an important class of compounds mostly used in the synthesis of various materials, showing unusual electronic and optical properties. The Thiophene Ring Fragmentation (TRF) process is widely used in synthetic chemistry. In this study, the fragmentation pattern of the molecular cation of halogenated thiophene, namely, 2‐chlorothiophene, was monitored to establish its dissociation mechanism. Methods The molecular cation of 2‐chlorothiophene was prepared using multiphoton excitation using a laser at 235 nm. Various product ions upon fragmentation of the molecular ion were mass analyzed using time‐of‐flight mass spectrometry. Laser power dependence studies were also conducted for various product ions to arrive at the dissociation mechanism. Theoretical calculations were carried out to estimate the reaction enthalpies for various reactions and compared with the experimental data available in the literature. Results The most abundant product ion was observed as the HCS+ radical cation followed by the C3H3+ ion and the H2CCCCS+ radical cation. Other product ions such as SCCl+, ClHCCS+ radical cations were also observed to a lesser extent in the fragmentation pattern of the parent molecular ion. Various dissociation channels were identified and supported with ab initio calculation. It has been inferred that the TRF process is usually initiated by the H/Cl atom transfer process. The appearance energies of the various fragment ions were also estimated theoretically and compared with literature values. Conclusions In conclusion, the fragmentation pattern of the molecular cation of 2‐chlorothiophene was studied and the formation mechanisms of various product ions have been assigned. The appearance energies of the various fragment ions were also calculated. Finally, it is inferred that a TRF process is initiated by the H/Cl atom migration and subsequent ring opening either by C–C or C–S bond cleavage leading to the various isomers and their subsequent fragmentation. The ionization energies were accurately predicted for various species using ab initio calculation.

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“…Associated with resonance-enhanced multiphoton ionization (REMPI), TR-PEI is a Vol.28 powerful experimental means for probing radiationless transitions in polyatomic molecules. [2][3][4][5][6][7][8][9][10] Nitrogen-containing aromatic compounds have received a great deal of attention as benchmark systems for the investigation of electronic dephasing processes. [11][12][13][14][15][16] In particular, pyrazine is the best-studied molecule of an intermediate coupling cases.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Internal Conversion Dynamics of 2-Chloropyridine by Femtosecond Time-Resolved Photoelectron Imaging

Ahmed-Yousif¹,

Xue-Jun²,

Qin³

et al. 2012

Acta Physico-Chimica Sinica

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Ultrafast internal conversion dynamics of 2-chloropyridine were studied by femtosecond time-resolved photoelectron imaging spectroscopy coupled with time-resolved mass spectroscopy. The ultrafast internal conversion from the second excited state (S2) to the first excited state (S1) via an adjacent conical intersection within (162±5) fs was clearly observed from the time-dependence of the photoelectron spectra. The subsequent deactivations involved the coupling of S2/S0 (the ground state) and S1/S0 conical intersections, which occurred on a timescale of about (5.5±0.3) ps, and led to the internal conversion to the ground state from the S2 and S1 states.

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C-Br Bond Dissociation Mechanisms of 2-Bromothiophene and 3-Bromothiophene at 267 nm

Cited by 13 publications

References 27 publications

Molecular Photofragmentation Dynamics in the Gas and Condensed Phases

Molecular Photofragmentation Dynamics in the Gas and Condensed Phases

Ground‐state dissociation pathways for the molecular cation of 2‐chlorothiophene: A time‐of‐flight mass spectrometry and computational study

Ultrafast Internal Conversion Dynamics of 2-Chloropyridine by Femtosecond Time-Resolved Photoelectron Imaging

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