Internal conversion versus intersystem crossing: What drives the gas phase dynamics of cyclic α,β-enones?

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DOIResolve DOI: http://doi.org/10.1021/jp4124937
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TypeArticle
Journal titleJournal of Physical Chemistry A
ISSN1089-5639
Volume118
Issue12
Pages22792287; # of pages: 9
SubjectAlkylation; Photoelectron spectroscopy; Quantum chemistry; Quantum yield; Ab initio computations; Conical intersection; Inter-system crossings; Internal conversions; Non-radiative relaxation; Singlet and triplet state; Singlet ground state; Time-resolved photoelectron spectroscopy; Quantum theory
AbstractWe investigate the competition between intersystem crossing (ISC) and internal conversion (IC) as nonradiative relaxation pathways in cyclic α,β-unsaturated enones following excitation to their lowest lying 1ππ* state, by means of time-resolved photoelectron spectroscopy and ab initio computation. Upon excitation, the 1ππ* state of 2-cyclopentenone decays to the lowest lying 1nπ* state within 120 ± 20 fs. Within 1.2 ± 0.2 ps, the molecule subsequently decays to the triplet manifold and the singlet ground state, with quantum yields of 0.35 and 0.65, respectively. The corresponding dynamics in modified derivatives, obtained by selective methylation, show a decrease in both IC and ISC rates, with the quantum yields of ISC varying between 0.35 and 0.08. The rapid rates of ISC are explained by a large spin orbit coupling of 45-60 cm-1 over an extended region of near degeneracy between the singlet and triplet state. Furthermore, the rate of IC is depressed by the existence of a well-defined minimum on the 1nπ* potential energy surface. The nonadiabatic pathways evinced by the present results highlight the fact that these molecular systems conceptually represent "intermediate cases" between ultrafast dynamics mediated by vibrational motions at conical intersections versus those by statistical decay mechanisms.
Publication date
PublisherACS Publications
LanguageEnglish
AffiliationNRC Steacie Institute for Molecular Sciences; Security and Disruptive Technologies; National Research Council Canada
Peer reviewedYes
NPARC number21272921
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Record identifier36f80283-c080-4d5b-b6d4-7f3021ca6cf9
Record created2014-12-03
Record modified2016-05-09
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