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Inter-Excited State Phosphorescence in the Four-Component Relativistic Kohn–Sham Approximation: A Case Study on Lumiflavin
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
2015 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 119, no 49, 11911-11921 p.Article in journal (Refereed) Published
Abstract [en]

Electronic transitions from one excited state to another excited state of different spin symmetry play important roles in many biochemical reactions. Although recent years have seen much progress in the elucidation of nonradiative (intersystem crossing) relaxation mechanisms for such transitions, there is presently a scarcity of data available to assess whether also radiative (phosphorescence) mechanisms are relevant for these processes. Here, we demonstrate that the well-established ability of quantum chemical methods to describe intersystem crossing events between excited states, can be supplemented by the ability to also describe inter-excited state phosphorescence. Specifically, performing four-component relativistic time-dependent density functional theory calculations, we obtain rate constants for the radiative transitions from the absorbing 1(πHπL*) singlet state of lumiflavin to the 3(πHπL*), 3(nN2πL*) and 3(πH–1πL*) triplet states, and subsequently compare these results with rate constants calculated for the corresponding nonradiative transitions. Thereby, it is found that the radiative rate constants for these particular transitions are typically two to five orders of magnitude smaller than the nonradiative ones.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015. Vol. 119, no 49, 11911-11921 p.
Keyword [en]
Inter-excited state transition dipole moments, Radiative transitions, Nonradiative transitions, Response theory, Time-dependent density functional theory, Flavin chromophores
National Category
Chemical Sciences Physical Chemistry
URN: urn:nbn:se:liu:diva-122743DOI: 10.1021/acs.jpca.5b08908ISI: 000366339400016OAI: diva2:872563

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Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2016-01-11Bibliographically approved
In thesis
1. Computational Studies of Photobiological Keto-Enol Reactions and Chromophores
Open this publication in new window or tab >>Computational Studies of Photobiological Keto-Enol Reactions and Chromophores
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents computational chemistry studies of keto-enol reactions and chromophores of photobiological signicance.

The rst part of the thesis is concerned with two protein-bound chromophores that, depending on the chemical conditions, can exist in a number of dierent ketonic and enolic forms. The rst chromophore is astaxanthin, which occurs in the protein complex responsible for the deep-blue color of lobster carapace. By investigating how dierent forms of astaxanthin absorb UV-vis radiation of dierent wavelengths, a model is presented that explains the origin of the dramatic color change from deep-blue to red upon cooking of live lobsters.

The second chromophore is the oxyluciferin light emitter of fireflies, which is formed in the catalytic center of the enzyme firefly luciferase. To date, there is no consensus regarding which of the possible ketonic and enolic forms is the key contributor to the light emission. In the thesis, the intrinsic tendency of oxyluciferin to prefer one particular form over other possible forms is established through calculation of keto-enol and acid-base excited-state equilibrium constants in aqueous solution.

The second part of the thesis is concerned with two families of biological photoreceptors: the blue-light-absorbing LOV-domain proteins and the red-light-absorbing phytochromes. Based on the ambient light environment, these proteins regulate physiological and developmental processes by switching between inactive and active conformations. In both families, the conversion of the inactive into the active conformation is triggered by a chemical reaction of the respective chromophore.

The LOV-domain proteins bind a LOV-domain proteins bidn in flavin chromophore and regulate processes such as chloroplast relocation and phototropism in plants. An important step in the activation of these photoreceptors is a singlet-triplet transition between two electronically excited states of the flavin chromophore. In the thesis, this transition is used as a prototype example for illustrating, for the rst time, the ability of rst-principles methods to calculate rate constants of inter-excited state phosphorescence events.

Phytochromes, in turn, bind bilin chromophores and are active in the regulation of processes like seed germination and  flowering time in plants. Following two systematic studies identifying the best way to model the UV-vis absorption and fluorescence spectra of these photoreceptors, it is demonstrated that steric interactions between the chromophore and the apoprotein play a decisive role for how phytochromes are activated by light.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 76 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1713
National Category
Theoretical Chemistry
urn:nbn:se:liu:diva-122614 (URN)10.3384/diss.diva-122614 (DOI)978-⁠91-⁠7685-⁠922-⁠3 (print) (ISBN)
Public defence
2015-12-18, Nobel (BL32), B-huset, Campus Valla, Linköping, 13:15 (English)
Available from: 2015-11-19 Created: 2015-11-11 Last updated: 2015-11-26Bibliographically approved

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