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Photoisomerization mechanism of 4-methylpyridine explored by electronic structure calculations and nonadiabatic dynamics simulations
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
2011 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 4, 044307- p.Article in journal (Refereed) Published
Abstract [en]

In the present paper, different electronic structure methods have been used to determine stationary and intersection structures on the ground (S-0) and (1)pi pi* (S-2) states of 4-methylpyridine, which is followed by adiabatic and nonadiabatic dynamics simulations to explore the mechanistic photoisomerization of 4-methylpyridine. Photoisomerization starts from the S-2((1)pi pi*) state and overcomes a small barrier, leading to formation of the prefulvene isomer in the S-0 state via a S-2/S-0 conical intersection. The ultrafast S-2 -> S-0 nonradiative decay and low quantum yield for the photoisomerization reaction were well reproduced by the combined electronic structure calculation and dynamics simulation. The prefulvene isomer was assigned as a long-lived intermediate and suggested to isomerize to 4-methylpyridine directly in the previous study, which is not supported by the present calculation. The nonadiabatic dynamics simulation and electronic structure calculation reveal that the prefulvene isomer is a short-lived intermediate and isomerizes to benzvalene form very easily. The benzvalene form was predicted as the stable isomer in the present study and is probably the long-lived intermediate observed experimentally. A consecutive light and thermal isomerization cycle via Dewar isomer was determined and this cycle mechanism is different from that reported in the previous study. It should be pointed out that formation of Dewar isomer from the S-2((1)pi pi*) state is not in competition with the isomerization to the prefulvene form. The Dewar structure observed experimentally may originate from other excited states.

Place, publisher, year, edition, pages
2011. Vol. 134, no 4, 044307- p.
Keyword [en]
EXCITATION-ENERGY DEPENDENCE, VAPOR-PHASE PHOTOCHEMISTRY, THEORETICAL CHARACTERIZATION, RADIATIONLESS TRANSITIONS, CONICAL INTERSECTIONS, ULTRAFAST DIFFRACTION, FEMTOSECOND DYNAMICS, EXCITED-STATE, PYRIDINE, MOLECULES
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-31334DOI: 10.1063/1.3547207ISI: 000286897600050Scopus ID: 2-s2.0-79551581806OAI: oai:DiVA.org:kth-31334DiVA: diva2:404581
Note
QC 20110317Available from: 2011-03-17 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Mechanistic photodissociation of small molecules explored by electronic structure calculation and dynamics simulation
Open this publication in new window or tab >>Mechanistic photodissociation of small molecules explored by electronic structure calculation and dynamics simulation
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vi, 57 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2011:17
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-33585 (URN)978-91-7415-981-3 (ISBN)
Public defence
2011-06-13, FA32, AlbaNova, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110520Available from: 2011-05-20 Created: 2011-05-10 Last updated: 2011-05-20Bibliographically approved

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