The S2 → S1 Internal Conversion of Benzophenone and p-Iodobenzophenone

Shah, Bela; Rodgers, Michael A. J.; Neckers, Douglas C.

doi:10.1021/jp049615z

Cited by 45 publications

(62 citation statements)

References 29 publications

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“…9(b) renders a first exponential time constant of 1.0 ps and a second one of 6.3 ps. Due to the 310 nm excitation, there is a first ultrafast S 2 →S 1 relaxation [38], the intersystem crossing seems to be accelerated both by water as solvent and the S 2 excitation from the typical 10 ps [37,39].…”

Section: Improved Spectroscopic Resultsmentioning

confidence: 99%

Temporal and spectral correlations in bulk continua and improved use in transient spectroscopy

Bradler

Riedle

2014

J. Opt. Soc. Am. B

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Newly generated frequencies during bulk continuum generation with femtosecond pump pulses do not fluctuate statistically and show strong correlations in spectrum and time. When a femtosecond continuum is used as probe light for transient spectroscopic measurements, these correlations result in a seemingly low noise level but largescale pseudo-structures that obscure the interpretation. We investigate the correlations for continua generated in YAG and calcium fluoride plates and incorporate the results into the design of our pump-probe setup. The high degree of correlation to the next pulse is utilized through chopping of the pump and referencing between successive laser shots. To suppress the adverse effect of the high degree of correlation to other wavelengths, we extend the detection by multichannel referencing with a second camera. The combination of both referencing schemes renders a precise spectral calibration unnecessary and increases the sensitivity of our spectrometer by a factor of 5 down to 20 μOD. This is already very close to the shot noise limit. To demonstrate the improvements, we present and discuss measurements on two different molecular solutions.

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Section: Improved Spectroscopic Resultsmentioning

confidence: 99%

Temporal and spectral correlations in bulk continua and improved use in transient spectroscopy

Bradler

Riedle

2014

J. Opt. Soc. Am. B

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“…The short growth time is due to the ultrafast internal conversion (IC) of S n directly to S 1 (S 1 also has an absorption contribution at 505 nm) and the higher value results from the S 1 →T 1 transition. The S 1 →T 1 transition time of ≈6 ps is shorter than the ≈10 ps observed for BP38 and this indicates that the presence of nitrogen in the aromatic ring accelerates the ISC rate of the 2‐BPy molecule. Considering the remarkable differences in the polarity and hydrogen‐bonding ability of MeCN and water, the similarity of the spectra and dynamics of the two solvent systems suggests there is only a modest influence of these solvent properties on these processes.…”

Section: Resultsmentioning

confidence: 75%

“…Inspection of Figure 3 shows that the spectra acquired in neat MeCN (A) and in neutral aqueous solvent (B) are similar at short delay times as a broad absorption ( λ max =560 nm) was observed that can be assigned to the S 1 →S n transition 24. 38 The initial changes in the spectra have mainly been attributed to S 1 →T 1 intersystem crossing (ISC), which results in the well‐known absorption corresponding to the T 1 →T n transition with a maximum at 505 nm. The formation of the T 1 states was monitored at 505 nm and the results are displayed in Figure 4 together with exponential fittings of the experimental data points.…”

Section: Resultsmentioning

confidence: 98%

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Unravelling the Reaction Mechanism for the Fast Photocyclisation of 2‐Benzoylpyridine in Aqueous Solvent by Time‐Resolved Spectroscopy and Density Functional Theory Calculations

Xue

et al. 2010

Chemistry A European J

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A combined femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopic investigation of the photoreaction of 2-benzoylpyridine (2-BPy) in acetonitrile and neutral, basic and acidic aqueous solvents is reported. fs-TA results showed that the npi* triplet 2-BPy is the precursor of the photocyclisation reaction in neutral and basic aqueous solvents. The cis triplet biradical and the cis singlet zwitterionic species produced during the photocyclisation reaction were initially characterised by ns-TR(3) spectroscopy. In addition, a new species was uniquely observed in basic aqueous solvent after the decay of the cis singlet zwitterionic species and this new species was tentatively assigned to the photocyclised radical anion. The ground-state conformation of 2-BPy in acidic aqueous solvent is the pyridine nitrogen-protonated 2-BPy cation (2-BPy-NH(+)) rather than the neutral form of 2-BPy. After laser photolysis, the singlet excited state (S(1)) of 2-BPy-NH(+) is generated and evolves through excited-state proton transfer (ESPT) and efficient intersystem crossing (ISC) processes to the triplet exited state (T(1)) of the carbonyl oxygen-protonated 2-BPy cation (2-BPy-OH(+)) and then photocyclises with the lone pair of the nitrogen atom in the heterocyclic ring. Cyclisation reactions take place both in neutral/basic and acidic aqueous solvents, but the photocyclisation mechanisms in these different aqueous solvents are very different. This is likely due to the different conformation of the precursor and the influence of hydrogen-bonding of the solvent on the reactions.

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“…For example, the properties and reaction mechanisms of the ketyl radical and the radical from the solvent and their reaction to produce a light absorbing transient (LAT) have been reported . The intersystem crossing from S 1 to T 1 for BP and its derivatives has been observed directly by ultrafast TA with measured rates of ~10 11 s –1 , and a rapid water addition process to the protonated BP triplet was identified to result in the fast deactivation of the triplet BP in acidic aqueous solution . Moreover, nanosecond time‐resolved resonance Raman (ns‐TR 3 ) spectroscopy is an effective technique for further clearly characterizing the structural and electronic properties of transient species, and has been used to help identify the intermediates and photoproducts of BP and its derivatives .…”

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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The S₂ → S₁ Internal Conversion of Benzophenone and p-Iodobenzophenone

Cited by 45 publications

References 29 publications

Temporal and spectral correlations in bulk continua and improved use in transient spectroscopy

Temporal and spectral correlations in bulk continua and improved use in transient spectroscopy

Unravelling the Reaction Mechanism for the Fast Photocyclisation of 2‐Benzoylpyridine in Aqueous Solvent by Time‐Resolved Spectroscopy and Density Functional Theory Calculations

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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