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Theoretical Study of the Chemiluminescence Mechanism of Dewar Dioxetane
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. (Theoretical Chemistry programme)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Light emission from the heating of Dewar benzene was first reported by McCapra (McCapra, PureAppl. Chem. 1970, 24, 611–629). Since most of the chemiluminescence reactions occur through anO-O cleavage, light observed through the thermal decomposition of Dewar benzene was suggested to becaused by the chemiluminescence mechanism of a dioxetane-based intermediate produced after oxidation.However, no prove of this proposal has been suggested so far and the details of the mechanism are thusunknown. In this paper, thermally activated decomposition mechanism of Dewar dioxetane has been studiedby the multiconfigurational CASPT2//CASSCF approach, and accurate reaction path descriptions havebeen provided for a two-step biradical mechanism consisting of O1-O’1and C2-C’2ruptures based onminimum energy path and intrinsic reaction coordinate computations. A radiationless decay path has beendetermined for the molecule along the excited triplet state, while in the excited singlet state the systemevolves toward an equilibrium structure that might be responsible of the light emission. This findingsprovide clues for rationalizing the observed light emission and point to higher efficiency of fluorescencethan triplet emission. Furthermore, the study allows to understand the effect of conjugated double bondsadjacent to the dioxetane moiety in the chemiluminescence mechanism of dioxetane.

National Category
Theoretical Chemistry
URN: urn:nbn:se:uu:diva-232217OAI: oai:DiVA.org:uu-232217DiVA: diva2:747019
Chemiluminescence, Multiconfigurational Methods, Dewar Dioxetane
Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2014-10-22
In thesis
1. Theoretical Studies of Ground and Excited State Reactivity
Open this publication in new window or tab >>Theoretical Studies of Ground and Excited State Reactivity
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To exemplify how theoretical chemistry can be applied to understand ground and excited state reactivity, four different chemical reactions have been modeled. The ground state chemical reactions are the simplest models in chemistry. To begin, a route to break down halomethanes through reactions with ground state cyano radical has been selected. Efficient explorations of the potential energy surfaces for these reactions have been carried out using the artificial force induced reaction algorithm. The large number of feasible pathways for reactions of this type, up to eleven, shows that these seemingly simple reactions can be quite complex. This exploration is followed by accurate quantum dynamics with reduced dimensionality for the reaction between Cland PH2Cl. The dynamics indicate that increasing the dimensionality of the model to at least two dimensions is a crucial step for an accurate calculation of the rate constant. After considering multiple pathways on a single potential energy surface, various feasible pathways on multiple surfaces have been investigated. As a prototype of these reactions, the thermal decomposition of a four-membered ring peroxide compound, called 1,2-dioxetane, which is the simplest model of chemi- and bioluminescence, has been studied. A detailed description of this model at the molecular level can give rise to a unified understanding of more complex chemiluminescence mechanisms. The results provide further details on the mechanisms and allow to rationalize the high ratio of triplet to singlet dissociation products. Finally, a thermal decomposition of another dioxetane-like compound, called Dewar dioxetane, has been investigated. This study allows to understand the effect of conjugated double bonds adjacent to the dioxetane moiety in the chemiluminescence mechanism of dioxetane. Our studies illustrate that no matter how complex a system is, theoretical chemistry can give a level of insight into chemical processes that cannot be obtained from other methods.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 86 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1179
Chemical Reactivity, Computational Chemistry, Dynamics, Ground and Excited States, Chemiluminescence, Atmospheric Chemistry
National Category
Theoretical Chemistry
urn:nbn:se:uu:diva-232219 (URN)978-91-554-9036-2 (ISBN)
Public defence
2014-10-30, Häggsalen, Ångström laboratory, Uppsala, 13:00 (English)
Available from: 2014-10-09 Created: 2014-09-15 Last updated: 2015-01-23Bibliographically approved

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Farahani, Pooria
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