On the low-lying singlet excited states of styrene: a theoretical contribution

Molina, Vicent; Merchán, Manuela; Roos, Björn O.; Malmqvist, Per‐Åke

doi:10.1039/a909174b

Cited by 54 publications

(82 citation statements)

References 49 publications

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“…Figure 1 displays these structures for thymine, the system under study in the present work. They correspond to two different excited state minima, one planar [11] and one partially twisted or "boat-like" found in more correlated computations or solvated environments [24,34,63,64], and an "ethene-like" CI [65,66] connecting the 1 (ππ*) and ground states. The CI is usually employed to rationalize the ultrafast decay of thymine [8] and the extremely low fluorescence quantum yields recorded experimentally [62], and was initially reported in the pioneering study of Perun et al [22].…”

Section: Introductionmentioning

confidence: 74%

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

et al. 2016

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Abstract:The present study provides new insights into the topography of the potential energy hypersurfaces (PEHs) of the thymine nucleobase in order to rationalize its main ultrafast photochemical decay paths by employing two methodologies based on the complete active space self-consistent field (CASSCF) and the complete active space second-order perturbation theory (CASPT2) methods: (i) CASSCF optimized structures and energies corrected with the CASPT2 method at the CASSCF geometries and (ii) CASPT2 optimized geometries and energies. A direct comparison between these strategies is drawn, yielding qualitatively similar results within a static framework. A number of analyses are performed to assess the accuracy of these different computational strategies under study based on a variety of numerical thresholds and optimization methods. Several basis sets and active spaces have also been calibrated to understand to what extent they can influence the resulting geometries and subsequent interpretation of the photochemical decay channels. The study shows small discrepancies between CASSCF and CASPT2 PEHs, displaying a shallow planar or twisted 1 (ππ*) minimum, respectively, and thus featuring a qualitatively similar scenario for supporting the ultrafast bi-exponential deactivation registered in thymine upon UV-light exposure. A deeper knowledge of the PEHs at different levels of theory provides useful insight into its correct characterization and subsequent interpretation of the experimental observations. The discrepancies displayed by the different methods studied here are then discussed and framed within their potential consequences in on-the-fly non-adiabatic molecular dynamics simulations, where qualitatively diverse outcomes are expected.

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Section: Introductionmentioning

confidence: 74%

Assessment of the Potential Energy Hypersurfaces in Thymine within Multiconfigurational Theory: CASSCF vs. CASPT2

et al. 2016

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“…A nonplanar conical intersection of S 1 /T 1 was found in the vicinity with R(1,6) ϭ2.4 Å. This conical intersection occurs at a geometry which is characterized with R (1,4)ϭ1.69 Å, R (3,6) ϭ1.77 Å and, D(4163)ϭ149°. This point is important to the photoinduced process because it serves as a bottleneck controlling the reaction direction.…”

Section: B Photoisomerization Mechanism In the Al 3 Omentioning

confidence: 89%

“…͑1͒ The photoinduced process occurs between the singlet Book structure (C 2v , 1 A 1 ) and the triplet Ring structure (C 2v , 3 B 2 ). Another energetically favorite Kite isomer (C 2v , 1 A 1 ) may coexist in the photoelectron spectroscopy experiment, but it is not involved in this photoinduced reaction.…”

Section: Discussionmentioning

confidence: 99%

“…1,2 Some of these processes are vital to the understanding of some topics in the life sciences and some are used for novel single molecule electronic devices. [3][4][5][6] In the past decade, great efforts have been made to study the mechanism of photoisomerization both experimentally and theoretically. [7][8][9] From a theoretical point of view, the central issue to understanding the photoisomerization mechanism lies in the exploration of the potential energy surfaces ͑PES͒ for both ground states and excited states.…”

Section: Introductionmentioning

confidence: 99%

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A computational study of photoisomerization in Al3O3− clusters

Cui

Morrison

Han

2002

The Journal of Chemical Physics

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Ab initio calculations are employed to understand the photoisomerization process in small Al 3 O 3 Ϫ clusters. This process is the first example of a photoinduced isomerization observed in an anion cluster gas-phase system. Potential energy surfaces for the ground state and the excited state ͑S 1 and T 1 ͒ are explored by means of B3LYP, MP2, CI-singles, and CASSCF methods. We demonstrate that the isomerization process occurs between the global minimum singlet state Book structure (C 2v , 1 A 1 ) and the triplet state Ring structure (C 2v , 3 B 2 ). The calculated vertical excitation energy is 3.62 eV at the CASSCF level of approximation, in good agreement with the experimental value ͑3.49 eV͒. A nonplanar conical intersection, which hosts the intersystem crossing between the S 1 and T 1 surfaces is identified at the region of around R(1,6)ϭ2.4 Å. Beyond the experimental results, we predict, that this isomerization is reversible upon absorption of a phonon with energy of 1.92 eV. Our results describe a unique system, whose structure depends on its spin multiplicity; it exists as the Book structure on singlet states and as the Ring structure on triplet states.

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“…In most cases the excitation energies are within Ϯ 0.2 eV of the experimental estimates (when comparison with experimental data is appropriate). Particularly connected to the present study are the investigations carried out on the trans-cis photoisomerization of retinal (18,19), stilbene (20,21), and styrene (22,23), as well as the determination of the electronic spectra of anions (24,25).…”

mentioning

confidence: 98%