Conserving Coherence and Storing Energy during Internal Conversion: Photoinduced Dynamics of cis- and trans-Azobenzene Radical Cations

Handle URI:
http://hdl.handle.net/10754/625962
Title:
Conserving Coherence and Storing Energy during Internal Conversion: Photoinduced Dynamics of cis- and trans-Azobenzene Radical Cations
Authors:
Munkerup, Kristin ( 0000-0001-7097-8133 ) ; Romanov, Dmitri A.; Bohinski, Timothy; Stephansen, Anne B.; Levis, Robert J.; Sølling, Theis Ivan
Abstract:
Light harvesting via energy storage in azobenzene has been a key topic for decades, and the process of energy distribution over the molecular degrees of freedom following photoexcitation remains to be understood. Dynamics of a photoexcited system can exhibit high degrees of non-ergodicity when it is driven by just a few degrees of freedom. Typically, an internal conversion leads to the loss of such localization of dynamics, as the intramolecular energy becomes statistically redistributed over all molecular degrees of freedom. Here, we present a unique case where the excitation energy remains localized even subsequent to internal conversion. Strong-field ionization is used to prepare cis- and trans-azobenzene radical cations on the D1 surface with little excess energy, at the equilibrium neutral geometry. These D1 ions are preferably formed because in this case D1 and D0 switch place in the presence of the strong laser field. The post-ionization dynamics is dictated by the potential energy landscape. The D1 surface is steep downhill along the cis/trans isomerization coordinate and towards a common minimum shared by the two isomers in the region of D1/D0 conical intersection. Coherent cis/trans torsional motion along this coordinate is manifested in the ion transients by a cosine modulation. In this scenario, D0 becomes populated with molecules that are energized mainly along the cis-trans isomerization coordinate, with the kinetic energy above the cis-trans inter-conversion barrier. These activated azobenzene molecules easily cycle back and forth along the D0 surface, and give rise to several periods of modulated signal before coherence is lost. This persistent localization of the internal energy during internal conversion is provided by the steep downhill potential energy surface, small initial internal energy content, and a strong hole-lone pair interaction that drives the molecule along the cis-trans isomerization coordinate to facilitate the transition between the involved electronic states.
KAUST Department:
KAUST Catalysis Center (KCC); Physical Sciences and Engineering (PSE) Division
Citation:
Munkerup K, Romanov DA, Bohinski T, Stephansen AB, Levis RJ, et al. (2017) Conserving Coherence and Storing Energy during Internal Conversion: Photoinduced Dynamics of cis- and trans-Azobenzene Radical Cations. The Journal of Physical Chemistry A. Available: http://dx.doi.org/10.1021/acs.jpca.7b09185.
Publisher:
American Chemical Society (ACS)
Journal:
The Journal of Physical Chemistry A
Issue Date:
24-Oct-2017
DOI:
10.1021/acs.jpca.7b09185
Type:
Article
ISSN:
1089-5639; 1520-5215
Sponsors:
We gratefully acknowledge the generous support of the Villum foundation.
Additional Links:
http://pubs.acs.org/doi/pdf/10.1021/acs.jpca.7b09185
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; KAUST Catalysis Center (KCC)

Full metadata record

DC FieldValue Language
dc.contributor.authorMunkerup, Kristinen
dc.contributor.authorRomanov, Dmitri A.en
dc.contributor.authorBohinski, Timothyen
dc.contributor.authorStephansen, Anne B.en
dc.contributor.authorLevis, Robert J.en
dc.contributor.authorSølling, Theis Ivanen
dc.date.accessioned2017-10-30T07:55:29Z-
dc.date.available2017-10-30T07:55:29Z-
dc.date.issued2017-10-24en
dc.identifier.citationMunkerup K, Romanov DA, Bohinski T, Stephansen AB, Levis RJ, et al. (2017) Conserving Coherence and Storing Energy during Internal Conversion: Photoinduced Dynamics of cis- and trans-Azobenzene Radical Cations. The Journal of Physical Chemistry A. Available: http://dx.doi.org/10.1021/acs.jpca.7b09185.en
dc.identifier.issn1089-5639en
dc.identifier.issn1520-5215en
dc.identifier.doi10.1021/acs.jpca.7b09185en
dc.identifier.urihttp://hdl.handle.net/10754/625962-
dc.description.abstractLight harvesting via energy storage in azobenzene has been a key topic for decades, and the process of energy distribution over the molecular degrees of freedom following photoexcitation remains to be understood. Dynamics of a photoexcited system can exhibit high degrees of non-ergodicity when it is driven by just a few degrees of freedom. Typically, an internal conversion leads to the loss of such localization of dynamics, as the intramolecular energy becomes statistically redistributed over all molecular degrees of freedom. Here, we present a unique case where the excitation energy remains localized even subsequent to internal conversion. Strong-field ionization is used to prepare cis- and trans-azobenzene radical cations on the D1 surface with little excess energy, at the equilibrium neutral geometry. These D1 ions are preferably formed because in this case D1 and D0 switch place in the presence of the strong laser field. The post-ionization dynamics is dictated by the potential energy landscape. The D1 surface is steep downhill along the cis/trans isomerization coordinate and towards a common minimum shared by the two isomers in the region of D1/D0 conical intersection. Coherent cis/trans torsional motion along this coordinate is manifested in the ion transients by a cosine modulation. In this scenario, D0 becomes populated with molecules that are energized mainly along the cis-trans isomerization coordinate, with the kinetic energy above the cis-trans inter-conversion barrier. These activated azobenzene molecules easily cycle back and forth along the D0 surface, and give rise to several periods of modulated signal before coherence is lost. This persistent localization of the internal energy during internal conversion is provided by the steep downhill potential energy surface, small initial internal energy content, and a strong hole-lone pair interaction that drives the molecule along the cis-trans isomerization coordinate to facilitate the transition between the involved electronic states.en
dc.description.sponsorshipWe gratefully acknowledge the generous support of the Villum foundation.en
dc.publisherAmerican Chemical Society (ACS)en
dc.relation.urlhttp://pubs.acs.org/doi/pdf/10.1021/acs.jpca.7b09185en
dc.rightsThis document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry A, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/pdf/10.1021/acs.jpca.7b09185.en
dc.titleConserving Coherence and Storing Energy during Internal Conversion: Photoinduced Dynamics of cis- and trans-Azobenzene Radical Cationsen
dc.typeArticleen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.identifier.journalThe Journal of Physical Chemistry Aen
dc.eprint.versionPost-printen
dc.contributor.institutionDepartment of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmarken
dc.contributor.institutionDeparment of Physics, Temple University, Philadelphia, Pennsylvania 19122, United Statesen
dc.contributor.institutionCenter for Advanced Photonics Research, Temple University, Philadelphia, Pennsylvania 19122, United Statesen
dc.contributor.institutionDepartment of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United Statesen
dc.contributor.institutionFritz-Haber-Institut der Max-Planck-Society, Faradayweg 4-6, 14195 Berlin, Germanyen
kaust.authorMunkerup, Kristinen
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