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Spectral character of intermediate state in solid-state photoarrangement of alpha-santonin
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-3915-300X
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. (Swedish E-Science Research Center (SeRC))
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-9123-8174
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2012 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 405, 40-45 p.Article in journal (Refereed) Published
Abstract [en]

The vibronically resolved spectra of an intermediate and a product involved in the photoreaction of alpha-santonin have been explored by the density functional theory and the post-SCF methodologies, and a detailed comparison of theory with experiment was conducted to obtain reliable assignments to the observed spectra. The predicted emission energies of photosantonic acid and a topochemical product are found to match with the experimental values reasonably. The further calculations manifest that the absorption spectrum of photosantonic acid exhibits vibrationally resolved features, while the absorption band of topochemical product without vibrational resolution is opposite to the experimental observation. These new computational findings lead to a revised assignment to the observed bands and provide a basis for experimentalists to draw a convinced reaction mechanism for the alpha-santonin photorearrangement.

Place, publisher, year, edition, pages
2012. Vol. 405, 40-45 p.
Keyword [en]
Vibronically resolved spectra, Simulation, alpha-Santonin, Spectral assignment
National Category
Theoretical Chemistry
URN: urn:nbn:se:kth:diva-52822DOI: 10.1016/j.chemphys.2012.06.004ISI: 000308720500007ScopusID: 2-s2.0-84866059119OAI: diva2:467789
Swedish e‐Science Research Center

QC 20121008. Updated from manuscript to article in journal.

Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2012-10-08Bibliographically approved
In thesis
1. Theoretical Studies on Magnetic and Photochemical Properties of Organic Molecules
Open this publication in new window or tab >>Theoretical Studies on Magnetic and Photochemical Properties of Organic Molecules
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is concerned with the theoretical studies on magnetic and photochemical properties of organic molecules. The ab initio and first principles theories were employed to investigate the vibrational effects on the isotropic hyperfine coupling constant (HFCC) known as the critical parameter in electron paramagnetic resonance spectrum, the theoretical simulations of the vibronically resolved molecular spectra, the photo-induced reaction mechanism of α-santonin and the spin-forbidden reaction of triplet-state dioxygen with cofactor-free enzyme. The theoretical predictions shed light on the interpretation of experimental observations, the understanding of reaction mechanism, and importantly the guideline and perspective in respect of the popularized applications.

We focused on the vibrational corrections to the isotropic HFCCs of hydrogen and carbon atoms in organic radicals. The calculations indicate that the vibrational contributions induce or enhance the effect of spin polarization. A set of rules were stated to guide experimentalist and theoretician in identification of the contributions from the molecular vibrations to HFCCs. And the coupling of spin density with vibrational modes in the backbone is significant and provides the insight into the spin density transfer mechanism in organic π radicals.

The spectral characters of the intermediates in solid-state photoarrangement of α-santonin were investigated in order to well understand the underlying experimental spectra. The molecular spectra simulated with Franck-Condon principle show that the positions of the absorption and emission bands of photosantonic acid well match with the experimental observations and the absorption spectrum has a vibrationally resolved character.

α-Santonin is the first found organic molecule that has the photoreaction activities. The photorearrangement mechanism is theoretically predicted that the low-lying excited state 1(nπ*) undergoing an intersystem crossing process decays to 3(ππ*) state in the Franck-Condon region. A pathway which is favored in the solid-state reaction requires less space and dynamic advantage on the excited-state potential energy surface (PES). And the other pathway is predominant in the weak polar solvent due to the thermodynamical and dynamical preferences. Lumisantonin is a critical intermediate derived from α-santonin photoreaction. The 3(ππ*) state plays a key role in lumisantonin photolysis. The photolytic pathway is in advantage of dynamics and thermodynamics on the triplet-state PES. In contrast, the other reaction pathway is facile for pyrolysis ascribed to a stable intermediate formed on the ground-state PES.

 The mechanism of the oxidation reaction involving cofactor-free enzyme and triplet-state dioxygen were studied. The theoretical calculations show that the charge-transfer mechanism is not a sole way to make a spin-forbidden oxidation allowed. It is more likely to take place in the reactant consisting of a non-conjugated substrate. The other mechanism involving the surface hopping between the triplet- and singlet-state PESs via a minimum energy crossing point (MECP) without a significant charge migration. The electronic state of MECP exhibits a mixed characteristic of the singlet and triplet states. The enhanced conjugation of the substrate slows down the spin-flip rate, and this step can in fact control the rate of the reaction that a dioxygen attaches to a substrate.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xvi, 62 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2012:2
National Category
Theoretical Chemistry
urn:nbn:se:kth:diva-52818 (URN)978-91-7501-227-8 (ISBN)
Public defence
2012-01-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
QC 20111220Available from: 2011-12-20 Created: 2011-12-19 Last updated: 2012-01-20Bibliographically approved

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