Ultrafast Polyene Dynamics in Solution:  The Conformational Relaxation and Thermalization of Highly Excited <i>cis</i>-1,3,5-Hexatriene as a Function of Initial Conformation and Solvent

Anderson, Neil O.; Pullen, Stuart H.; Walker, Larry A.; Shiang, Joseph J.; Sension, Roseanne J.

doi:10.1021/jp983181o

Cited by 39 publications

(79 citation statements)

References 60 publications

(186 reference statements)

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“…These studies have found that the conical intersection-mediated ring-opening step in isomerization is completed in less than 200 fs [22], after which the molecule undergoes conformational changes on a range of timescales (see inset in Fig. 1) [26,27]. We observe a clear signature of the isomerization in the fragmentation signal.…”

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confidence: 59%

“…An increase in the production of H + in HT compared to CHD had also been observed in x-ray fragmentation experiments on the stable CHD and HT isomers (a mixture of tZt and tEt forms in case of HT), performed at the Advanced Light Source synchrotron (to be published separately [32], also see The relative change in the ion-KER from before to after UV excitation should in principle provide information about the evolution of the geometry and the kinetic energy of the nuclei during the isomerization. In the x-ray experiment the kinetic energy and the ion count increase on a timescale considerably longer than electronic excitation, but consistent with subsequent conformational changes that the excited molecule undergoes after the ring opening [26,27] and possible other reactions of the hot product and educt in the ground state [28]. At present, it is difficult to separate different contributions to the observed signal.…”

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confidence: 73%

“…In CHD we observe that the kinetic energy and the H + ion-production per molecule are higher in the photoexcited molecule. The evolution of the ion-fragmentation patterns in CHD happens over a picosecond, considerably longer than the duration of the electronic excitation, but consistent with conformational changes and subsequent reactions that the hot ground-state molecule undergoes [26][27][28]. The method will greatly benefit from improvements in time resolution, through better optical laser-FEL synchronization, and higher statistics through greater availability of ultrafast xray pulses.…”

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confidence: 85%

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Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening

Petrović¹,

Siano²,

White³

et al. 2012

Phys. Rev. Lett.

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confidence: 85%

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Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening

Petrović¹,

Siano²,

White³

et al. 2012

Phys. Rev. Lett.

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“…In reactive systems, where bonds are broken and formed, the partitioning of energy may result in its localization in certain bonds associated with the reaction coordinate. Indeed, we observed incomplete energy partitioning even up to 400 ps in hot 1,3,5-hexatriene (HT), formed by the ultrafast ring opening of CHD (25)(26)(27)(28). Fig.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast diffraction and structural dynamics: The nature of complex molecules far from equilibrium

Ruan

Lobastov

Srinivasan

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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Studies of molecular structures at or near their equilibrium configurations have long provided information on their geometry in terms of bond distances and angles. Far-from-equilibrium structures are relatively unknown-especially for complex systems-and generally, neither their dynamics nor their average geometries can be extrapolated from equilibrium values. For such nonequilibrium structures, vibrational amplitudes and bond distances play a central role in phenomena such as energy redistribution and chemical reactivity. Ultrafast electron diffraction, which was developed to study transient molecular structures, provides a direct method for probing the nature of complex molecules far from equilibrium. Here we present our ultrafast electron diffraction observations of transient structures for two cyclic hydrocarbons. At high internal energies of Ϸ4 eV, these molecules display markedly different behavior. For 1,3,5-cycloheptatriene, excitation results in the formation of hot ground-state structures with bond distances similar to those of the initial structure, but with nearly three times the average vibrational amplitude. Energy is redistributed within 5 ps, but with a negative temperature characterizing the nonequilibrium population. In contrast, the ring-opening reaction of 1,3-cyclohexadiene is shown to result in hot structures with a COC bond distance of over 1.7 Å, which is 0.2 Å away from any expected equilibrium value. Even up to 400 ps, energy remains trapped in large-amplitude motions comprised of torsion and asymmetric stretching. These studies promise a new direction for studying structural dynamics in nonequilibrium complex systems.T he premise of ultrafast electron diffraction (UED) is similar to ultrafast spectroscopies (for recent work from this laboratory, see refs. 1-5): a femtosecond laser pulse excites the molecules, and a second pulse, in this case a picosecond burst of electrons, probes the resulting structural evolution with the zero-of-time precisely determined in situ. With UED, the changing nuclear coordinates are directly recorded in time-dependent diffraction patterns. By timing the electron pulses to arrive before the light pulses, ground-state diffraction images are obtained at negative times. Time-resolved diffraction snapshots of the transient molecular structures are then recorded at positive times by varying the time delay between light and electron pulses. In the present work, we prepare vibrationally hot structures by radiationless transfer after the initial photon absorption and͞or as a result of a chemical reaction. Scheme 1 depicts the two reactions that are the subject of this contribution. Concepts of Equilibrium vs. Nonequilibrium Structures.Differences between diffraction patterns of structures at equilibrium and those far from equilibrium can be understood by first considering the case of a single bond (Fig. 1). The diffraction of structures far from equilibrium manifests itself as (i) increased damping of the oscillating molecular scattering signal; and (ii) apparent sh...

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“…In solution, this energy is dissipated to the bath, cooling the internal temperature from an estimated 2200 K to the ambient temperature of the surroundings. 12 Interest in this reaction is driven by its role as a model system for modern mechanistic photochemistry. [9][10][11] The CHD ringopening is a prototypical pericyclic reaction and has contributed to the development and corroboration of the Woodward-Hoffman rules, 13 which predict the stereochemical outcome for pericyclic reactions by correlating the first excited state of the reactant with the first excited state of the product and the ground state of the reactant with a doubly excited state of the product, and vice versa.…”

Section: Introductionmentioning

confidence: 99%

Effects of probe energy and competing pathways on time-resolved photoelectron spectroscopy: the ring-opening of 1,3-cyclohexadiene

Tudorovskaya

Minns

Kirrander

2018

Phys. Chem. Chem. Phys.

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The ring-opening dynamics of 1,3-cyclohexadiene (CHD) following UV excitation is studied using a model based on quantum molecular dynamics simulations with the ab initio multiconfigurational Ehrenfest (AI-MCE) method coupled to the Dyson orbital approach for photoionisation cross sections.Time-dependent photoelectron spectra are calculated for probe photon energies in the range 2-15 eV. The calculations demonstrate the value of universal high-energy probes, capable of tracking the dynamics in full, but also the utility of more selective lower-energy probes with a more restricted ionisation range. The predicted signal, especially with the universal probes, becomes highly convoluted due to the contributions from multiple reaction paths, rendering interpretation challenging unless complementary measurements and theoretical comparisons are available.

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Ultrafast Polyene Dynamics in Solution: The Conformational Relaxation and Thermalization of Highly Excited cis-1,3,5-Hexatriene as a Function of Initial Conformation and Solvent

Cited by 39 publications

References 60 publications

Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening

Transient X-Ray Fragmentation: Probing a Prototypical Photoinduced Ring Opening

Ultrafast diffraction and structural dynamics: The nature of complex molecules far from equilibrium

Effects of probe energy and competing pathways on time-resolved photoelectron spectroscopy: the ring-opening of 1,3-cyclohexadiene

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