Exploring the Time Scales of H-Atom Elimination from Photoexcited Indole

Iqbal, Azhar; Stavros, Vasillios G.

doi:10.1021/jp908195k

Cited by 34 publications

(44 citation statements)

References 24 publications

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“…Recent work by Stavros and co-workers employing femtosecond pump-probe spectroscopy also observed a bimodal H atom energy distribution following excitation at 200 nm. 31 These authors noted that the time constant for the appearance of the H atom photofragments was <200 fs in both elimination channels. They assigned the high kinetic energy component to direct dissociation via a 1 πσ* state following relaxation from the initially excited 1 ππ* state ( 1 B a / 1 B b ) but were unsure of the source of the low kinetic energy signal, as the timescale was significantly shorter than that expected for statistical unimolecular decay from the vibrationally excited ground state.…”

Section: Introductionmentioning

confidence: 99%

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Livingstone¹,

Schalk²,

Boguslavskiy³

et al. 2011

The Journal of Chemical Physics

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Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright 1 L a and 1 L b electronic states of 1 ππ* character and spectroscopically dark and dissociative 1 πσ* states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited 1 L a state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived 1 L b state or the 1 πσ* state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the 1 πσ* state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.

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Section: Introductionmentioning

confidence: 99%

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Livingstone¹,

Schalk²,

Boguslavskiy³

et al. 2011

The Journal of Chemical Physics

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“…20,21 Species like pyrrole, [22][23][24] indole, [25][26][27][28][29] or phenol [30][31][32] have shown a dependence of their photophysical properties to the location of the dark πσ * state. The dynamics in this electronic state has a great influence in very relevant phenomena like photodissociation, [22][23][24][25][26][27][28][29][30][31][32] charge transfer reactions, 33,34 or even internal conversion (IC) in biomolecules as DNA bases 35,36 or amino acids. 37,38 In order to gain more insight on the electronic structure of aniline and the relaxation pathways that involve the πσ * state, herein we investigate the ultrafast dynamics after direct excitation in the energy region where this state lies.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast dynamics of aniline in the 294-234 nm excitation range: The role of the πσ* state

Montero

Conde

Ovejas

et al. 2011

The Journal of Chemical Physics

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The ultrafast relaxation of jet-cooled aniline was followed by time-resolved ionization, after excitation in the 294-234 interval. The studied range of energy covers the absorption of the two bright ππ∗ excitations, S(1) and S(3), and the almost dark S(2) (πσ∗) state. The employed probe wavelengths permit to identify different ultrafast time constants related with the coupling of the involved electronic surfaces. A τ(1) = 165 ± 30 fs lifetime is attributed to dynamics along the S(2) (πσ∗) repulsive surface. Other relaxation channels as the S(1)→S(0) and S(3)→S(1) internal conversion are also identified and characterized. The work provides a general view of the photophysics of aniline, particularly regarding the role of the πσ∗ state. This state appears as minor dissipation process due to the ineffective coupling with the bright S(1) and S(3) states, being the S(1)→S(0) internal conversion the main non-radiative process in the full studied energy range. Additionally, the influence of the off-resonance adiabatic excitation of higher energy electronic states, particularly S(3), is also observed and discussed.

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“…5 Whilst a number of experiments have been directed at searching for spectroscopic evidence of 1 πσ* states with some success on smaller molecules (e.g. phenol [6][7][8] and indole, [9][10][11] the chromophores of the amino acids tyrosine and tryptophan…”

Section: Introductionmentioning

confidence: 99%

Time-resolved velocity map imaging of methyl elimination from photoexcited anisole

Hadden

Williams

Roberts

et al. 2011

Phys. Chem. Chem. Phys.

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To date, H-atom elimination from heteroaromatic molecules following UV excitation has been extensively studied, with the focus on key biological molecules such as chromophores of DNA bases and amino acids. Extending these studies to look at elimination of other non-hydride photoproducts is essential in creating a more complete picture of the photochemistry of these biomolecules in the gas-phase. To this effect, CH 3 elimination in anisole has been studied using time resolved velocity map imaging (TR-VMI) for the first time, providing both time and energy information on the dynamics following photoexcitation at 200 nm. The extra dimension of energy afforded by these measurements has enabled us to address the role of πσ* states in the excited state dynamics of anisole as compared to the hydride counterpart (phenol), providing strong evidence to suggest that only CH 3 fragments eliminated with high kinetic energy are due to direct dissociation involving a 1 πσ* state. These measurements also suggest that indirect mechanisms such as statistical unimolecular decay could be contributing to the dynamics at much longer times.

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Exploring the Time Scales of H-Atom Elimination from Photoexcited Indole

Cited by 34 publications

References 24 publications

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Ultrafast dynamics of aniline in the 294-234 nm excitation range: The role of the πσ* state

Time-resolved velocity map imaging of methyl elimination from photoexcited anisole

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