Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole

The excited state relaxation pathways of isoxazole and oxazole upon excitation with UV-light were investigated by nonadiabatic ab initio dynamics simulations and time-resolved photoelectron spectroscopy. Excitation of the bright ππ*-state of isoxazole predominantly leads to ring-opening dynamics. Both the initially excited ππ*-state and the dissociative πσ*-state offer a combined barrier-free reaction pathway, such that ring-opening, defined as a distance of more than 2 Å between two neighboring atoms, occurs within 45 fs. For oxazole, in contrast, the excited state dynamics is about twice as slow (85 fs) and the quantum yield for ring-opening is lower. This is caused by a small barrier between the ππ*-state and the πσ*-state along the reaction path, which suppresses direct ring-opening. Theoretical findings are consistent with the measured time-resolved photoelectron spectra, confirming the timescales and the quantum yields for the ring-opening channel. The results indicate that a combination of time-resolved photoelectron spectroscopy and excited state dynamics simulations can explain the dominant reaction pathways for this class of molecules. As a general rule, we suggest that the antibonding σ*-orbital located between the oxygen atom and a neighboring atom of a five-membered heterocyclic system provides a driving force for ring-opening reactions, which is modified by the presence and position of additional nitrogen atoms.

Ehrmaier, Johannes (author)
Schalk, OliverStockholms universitet,Fysikum,University of Copenhagen, Denmark(Swepub:su)oscha (author)
Richings, Gareth W. (author)
Hansson, TonyStockholms universitet,Fysikum(Swepub:su)thansson (author)
Worth, Graham (author)
Thomas, Richard D.Stockholms universitet,Fysikum(Swepub:su)rdt (author)
Stockholms universitetFysikum (creator_code:org_t)

In:Journal of Physical Chemistry A: American Chemical Society (ACS)124:20, s. 3984-39921089-56391520-5215

By the author/editor: Geng, Ting; Ehrmaier, Johann ...; Schalk, Oliver; Richings, Gareth ...; Hansson, Tony; Worth, Graham; show more...; Thomas, Richard ...; show less...

About the subject

NATURAL SCIENCES: NATURAL SCIENCES; and Physical Science ...; and Atom and Molecul ...

NATURAL SCIENCES: NATURAL SCIENCES; and Chemical Science ...; and Physical Chemist ...

Kungliga biblioteket hanterar dina personuppgifter i enlighet med EU:s dataskyddsförordning (2018), GDPR. Läs mer om hur det funkar här.
Så här hanterar KB dina uppgifter vid användning av denna tjänst.