Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene
Photoinduced electrocyclic ring opening reactions in conjugated cylcoalkenes are among the most elementary processes in organic chemistry. One prototypical ring opening reaction transforms cyclohexadiene into hexatriene. It is known that a sequence of sub-100 fs internal conversion transitions prece...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2013-01-01
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| Series: | New Journal of Physics |
| Online Access: | https://doi.org/10.1088/1367-2630/15/2/025007 |
| _version_ | 1827874440464039936 |
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| author | Brantley A West Brian P Molesky Nicholas P Montoni Andrew M Moran |
| author_facet | Brantley A West Brian P Molesky Nicholas P Montoni Andrew M Moran |
| author_sort | Brantley A West |
| collection | DOAJ |
| description | Photoinduced electrocyclic ring opening reactions in conjugated cylcoalkenes are among the most elementary processes in organic chemistry. One prototypical ring opening reaction transforms cyclohexadiene into hexatriene. It is known that a sequence of sub-100 fs internal conversion transitions precedes bond breaking in cyclohexadiene and some of its derivatives. However, these excited state dynamics have never been directly monitored in solution because of insufficient time resolution. Here we aim to uncover the extraordinary photophysics behind related ultrafast internal conversion processes in a derivative of cyclohexadiene, α -terpinene ( α -TP), solvated in cyclohexane. Transient absorption anisotropy experiments conducted with 20 fs laser pulses at 267 nm expose non-exponential depopulation kinetics for the ππ * electronic state of α -TP. Our data show that population transfer rapidly accelerates within the first 100 fs after photoexcitation. In addition, recurrences in two-dimensional photon echo (2DPE) line shapes reveal strong vibronic coupling in a normal mode near 523 cm ^−1 , which involves torsions of the C=C bonds and hydrogen out-of-plane (HOOP) wagging on a vinyl group. With the support of several experiments, we hypothesize that the excited state wavepacket in α -TP undergoes several recurrences in the C=C stretching coordinate before displacement along the C=C torsion/vinyl HOOP coordinate finally sets it free from the Franck–Condon region of the potential energy surface. The unconfined wavepacket departs the ππ * electronic state by way of a conical intersection with a lower energy excited state. The present observations are made possible by recent improvements to both the time resolution and detection sensitivity of our experimental setup. This work demonstrates that it is now possible to acquire 2DPE signals in the deep ultraviolet, which are comparable with high-quality measurements in the visible spectral region. These technical developments open the door to studies of many beautiful models for elementary chemical dynamics. |
| first_indexed | 2024-03-12T16:52:19Z |
| format | Article |
| id | doaj.art-2196756a01764f608c842488d9b11063 |
| institution | Directory Open Access Journal |
| issn | 1367-2630 |
| language | English |
| last_indexed | 2024-03-12T16:52:19Z |
| publishDate | 2013-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | New Journal of Physics |
| spelling | doaj.art-2196756a01764f608c842488d9b110632023-08-08T11:05:35ZengIOP PublishingNew Journal of Physics1367-26302013-01-0115202500710.1088/1367-2630/15/2/025007Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpineneBrantley A West0Brian P Molesky1Nicholas P Montoni2Andrew M Moran3Department of Physics and Astronomy, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USADepartment of Chemistry, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USADepartment of Chemistry, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USADepartment of Chemistry, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27599, USAPhotoinduced electrocyclic ring opening reactions in conjugated cylcoalkenes are among the most elementary processes in organic chemistry. One prototypical ring opening reaction transforms cyclohexadiene into hexatriene. It is known that a sequence of sub-100 fs internal conversion transitions precedes bond breaking in cyclohexadiene and some of its derivatives. However, these excited state dynamics have never been directly monitored in solution because of insufficient time resolution. Here we aim to uncover the extraordinary photophysics behind related ultrafast internal conversion processes in a derivative of cyclohexadiene, α -terpinene ( α -TP), solvated in cyclohexane. Transient absorption anisotropy experiments conducted with 20 fs laser pulses at 267 nm expose non-exponential depopulation kinetics for the ππ * electronic state of α -TP. Our data show that population transfer rapidly accelerates within the first 100 fs after photoexcitation. In addition, recurrences in two-dimensional photon echo (2DPE) line shapes reveal strong vibronic coupling in a normal mode near 523 cm ^−1 , which involves torsions of the C=C bonds and hydrogen out-of-plane (HOOP) wagging on a vinyl group. With the support of several experiments, we hypothesize that the excited state wavepacket in α -TP undergoes several recurrences in the C=C stretching coordinate before displacement along the C=C torsion/vinyl HOOP coordinate finally sets it free from the Franck–Condon region of the potential energy surface. The unconfined wavepacket departs the ππ * electronic state by way of a conical intersection with a lower energy excited state. The present observations are made possible by recent improvements to both the time resolution and detection sensitivity of our experimental setup. This work demonstrates that it is now possible to acquire 2DPE signals in the deep ultraviolet, which are comparable with high-quality measurements in the visible spectral region. These technical developments open the door to studies of many beautiful models for elementary chemical dynamics.https://doi.org/10.1088/1367-2630/15/2/025007 |
| spellingShingle | Brantley A West Brian P Molesky Nicholas P Montoni Andrew M Moran Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene New Journal of Physics |
| title | Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene |
| title_full | Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene |
| title_fullStr | Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene |
| title_full_unstemmed | Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene |
| title_short | Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene |
| title_sort | nonlinear optical signatures of ultraviolet light induced ring opening in α terpinene |
| url | https://doi.org/10.1088/1367-2630/15/2/025007 |
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