Intermolecular hydrogen abstraction from triplet excited state of decafluorobenzophenone: a Raman investigation

Anandhi, R.; Umapathy, Siva

doi:10.1002/(sici)1097-4555(200004)31:4<331::aid-jrs546>3.0.co;2-0

Cited by 14 publications

(18 citation statements)

References 45 publications

(27 reference statements)

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“…36 The peak position concurs with the reported value. 31 With increasing temperature, the band center shifts to a lower frequency and the bandwidth shows broadening. The S/N ratio at the elevated temperature is decreased.…”

Section: Time-resolved Resonance Raman Spectra Of Dfbpkmentioning

confidence: 99%

“…The peak position concurs with the reported value. 31 As shown in Figure 2b, with increasing temperature the band shifts to a lower frequency, while the band shape does not show significant temperature dependence. We estimated the peak position and the bandwidth of this mode by fitting the Raman band to a Gaussian function.…”

Section: Time-resolved Resonance Raman Spectra Of Dfbpkmentioning

confidence: 99%

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Raman Spectroscopic Study of the Solvation of Decafluorobenzophenone Ketyl Radical and Related Compounds in 2-Propanol at Ambient to Supercritical Temperatures

et al. 2008

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Time-resolved Raman spectroscopy has been applied to the hydrogen-abstraction reaction of decafluorobenzophenone (DFBP) from 2-propanol in temperatures ranging from room to supercritical temperature (520 K) at 31 MPa. The Raman bands of the intermediate ketyl radical (DFBPK) were identified. The Raman bands assigned to the C=C stretching mode (1639 cm-1) and the C-O stretching modes (1274 cm-1) shift to lower frequencies with increasing temperature. The corresponding Raman bands of stable molecules (reference molecules), benzhydrol, decafluorobenzhydrol, and benzophenone (BP), which all have similar molecular structures to those of DFBP or DFBPK, were also investigated at the same range of temperatures. Assignments of the Raman bands were performed with the help of density functional theoretical calculations and the isotopic exchange method. By comparing the Raman peak shifts of the radical with those of the reference molecules, the shift of the C=C stretching mode with increasing temperature (or decrease in the solvent density) is considered to be primarily due to the decrease in the repulsive interaction between the solute and the solvent. On the other hand, the shift of the C-O stretching mode of the radical reflects the decrease in the solvent Lewis acidity or its hydrogen-bonding donating ability, which is clearly illustrated by the shifts of the C=O stretching mode of BP and the C-O stretching mode of 2-propanol. The frequency of the C-O stretching mode of DFBPK was relatively sensitive to the surrounding environment. It was observed that the bandwidth of the radical was generally large, and this observation supports the previous report by Terazima and Hamaguchi (Terazima, M.; Hamaguchi, H. J. Chem. Phys. 1995, 99, 7891). Additionally, the sensitivity and the deformability of the radical structure due to the change of the solvent temperature and density were revealed in our studies.

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Section: Time-resolved Resonance Raman Spectra Of Dfbpkmentioning

confidence: 99%

Section: Time-resolved Resonance Raman Spectra Of Dfbpkmentioning

confidence: 99%

Raman Spectroscopic Study of the Solvation of Decafluorobenzophenone Ketyl Radical and Related Compounds in 2-Propanol at Ambient to Supercritical Temperatures

et al. 2008

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“…In this work, conventional Raman and time‐resolved resonance Raman spectroscopy (TR 3 ) techniques were used to examine the ground and the triplet excited states structure, respectively. TR 3 spectroscopy is a powerful technique to elucidate the vibrational structure of the transient species . When the Raman excitation wavelength is in resonance with an allowed electronic transition of the molecule, the Raman peaks coupled to the chromophore become enhanced, accounting for the high sensitivity and selectivity of the technique .…”

Section: Introductionmentioning

confidence: 99%

Solvent effects on the structure of the triplet excited state of xanthone: a time-resolved resonance Raman study

Venkatraman

Umapathy

2016

J. Raman Spectrosc.

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Solvent effects, especially intermolecular hydrogen bonding, play a central role in the photophysics and photochemistry of aromatic ketones. To gain insight into the solute–solvent interactions and their implications for structure and reactivity, we studied xanthone (XT) in two different solvents of similar dipolarity: acetonitrile (ACN; aprotic) and methanol (MeOH; protic), using time‐resolved resonance Raman (TR3) spectroscopy in conjunction with time‐dependent density functional theory calculations. Raman excitation profiles of XT in ACN followed the triplet‐triplet absorption band with a shoulder at the blue end, but for MeOH, they followed the triplet‐triplet absorption band quite closely; therefore, we propose that the resonance enhancement of Raman peaks are from two states in ACN and from a single state in the MeOH solvent. Furthermore, a resonance Raman peak at 614 cm−1 (a2 symmetry) that appeared in ACN but not in the MeOH solvent has been identified as a vibronic active mode that could be involved in coupling the two lowest 13ππ* (13A1) and 13nπ* (13A2) excited states. This was further confirmed by depolarization ratio measurements of some of the representative TR3 peaks in ACN, which showed a depolarized intensity for the 614 cm−1 peak while the other peaks were polarized. Interestingly, we also observed blue shifting of some of the vibrational frequencies of XT in the 13ππ* state compared with the ground state with increasing solvent polarity. This anomalous blue shift casts doubt on the general use of the resonance canonical structure to explain the structure of the excited states. In summary, we propose that the different hydrogen bonding mechanisms exhibited by the two lowest triplet states of XT separate them further in energy and that this can contribute to its low reactivity towards H atom abstraction in protic solvents. Copyright © 2016 John Wiley & Sons, Ltd.

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“…On the other hand, electron‐withdrawing groups generally increase the photoreduction ability of substituted BP triplet states. The decafluoro‐BP derivative was found to be 10–40 times more reactive than the parent BP molecule, and the hydrogen abstraction rate of the triplet 4‐trifluoromethylacetophenone molecule is six times faster than the parent acetophenone molecule…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, electronwithdrawing groups generally increase the photoreduction ability of substituted BP triplet states. The decafluoro-BP derivative was found to be 10-40 times more reactive than the parent BP molecule, [19,20] and the hydrogen abstraction rate of the triplet 4-trifluoromethylacetophenone molecule is six times faster than the parent acetophenone molecule. [21] Some studies reported for the photochemistry and photophysics of BP determined that the energy gap of the lowest excited singlet state (S 1, np*) and the second triplet state (T 2, pp*) is fairly small and the spin-orbit coupling between these two states is allowed.…”

Section: Introductionmentioning

confidence: 99%

Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

Xue

Cheng

et al. 2011

J Raman Spectroscopy

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A nanosecond time‐resolved resonance Raman (ns‐TR3) spectroscopic investigation of the photoreduction reactions and ability of several chloro‐substituted benzophenone (Cl‐BP) triplets is described. The TR3 results show that the 3‐chlorobenzophenone (3‐Cl‐BP), 4‐chlorobenzophenone (4‐Cl‐BP) and 4,4′‐dichlorobenzophenone (4,4′‐dichloro‐BP) triplets exhibit similar hydrogen abstraction ability with the parent BP triplet. In 2‐propanol, the 3‐Cl‐, 4‐Cl‐ and 4,4′‐dichloro‐diphenylketyl (DPK) radicals were observed and they appear to react with dimethylketyl radicals at the para‐position to form a light absorption transient species. These transient species were characterized with TR3 spectra, and identified with the help of results from density functional theory calculations. In an acetontitrile/water (MeCN:H2O) 1:1 mixed solvent, these DPK radicals were also observed but with slower formation rates. However, the 2‐Cl‐DPK radical was observed to form with a lower yield and a significantly slower formation rate than the other chloro‐substituted benzophenones examined here in 2‐propanol under the same experimental conditions. These results reveal that the 2‐chloro substituent reduces the hydrogen abstraction ability of the substituted BP triplet, which was not as expected based on the assumption that the electron‐withdrawing group could increase its photoreduction ability. This unusual ortho effect of the chlorine substitution is briefly discussed. Copyright © 2011 John Wiley & Sons, Ltd.

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Intermolecular hydrogen abstraction from triplet excited state of decafluorobenzophenone: a Raman investigation

Cited by 14 publications

References 45 publications

Raman Spectroscopic Study of the Solvation of Decafluorobenzophenone Ketyl Radical and Related Compounds in 2-Propanol at Ambient to Supercritical Temperatures

Raman Spectroscopic Study of the Solvation of Decafluorobenzophenone Ketyl Radical and Related Compounds in 2-Propanol at Ambient to Supercritical Temperatures

Solvent effects on the structure of the triplet excited state of xanthone: a time-resolved resonance Raman study

Influence of the chloro substituent position on the triplet reactivity of benzophenone derivatives: a time‐resolved resonance Raman and density functional theory study

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