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Title: The spectroscopy and photochemistry of quinioline structural isomers: (E)- and (Z)-phenylvinylnitrile

Abstract

In Titan’s atmosphere, photochemical pathways that lead to nitrogen heteroaromatics may incorporate photoisomerization of their structural isomers as a final step. (E)- and (Z)-phenylvinylnitrile ((E)- and (Z)-PVN, C{sub 6}H{sub 5} —CH=CHCN) are structural isomers of quinoline that themselves possess extensive absorptions in the ultraviolet, and thus may engage in such photoisomerization pathways. The present study explores the vibronic spectroscopy and photo-induced isomerization of gas-phase (E)- and (Z)-PVN in the 33,600-35,850 cm{sup −1} region under jet-cooled conditions. The S{sub 0}-S{sub 1} origins for (E)- and (Z)-PVN have been identified at 33 827 cm{sup −1} and 33 707 cm{sup −1}, respectively. Isomer-specific UV-UV hole-burning and UV depletion spectra reveal sharp vibronic structure that extends over almost 2000 cm{sup −1}, with thresholds for fast non-radiative decay identified by a comparison between hole-burning and UV depletion spectra. Dispersed fluorescence spectra of the two isomers enable the assignment of many low frequency transitions in both molecules, aided by harmonic frequency calculations (B3LYP/6-311++G(d,p)) and a comparison with the established spectroscopy of phenylvinylacetylene, the ethynyl counterpart to PVN. Both isomers are proven to be planar in both the S{sub 0} ground and S{sub 1} electronic excited states. (E)-PVN exhibits extensive Duschinsky mixing involving out-of-plane modes whose frequenciesmore » and character change significantly in the ππ{sup ∗} transition, which modulates the degree of single- and double-bond character along the vinylnitrile substituent. This same mixing is much less evident in (Z)-PVN. The spectroscopic characterization of (E)- and (Z)-PVN served as the basis for photoisomerization experiments using ultraviolet hole-filling spectroscopy carried out in a reaction tube affixed to the pulsed valve. Successful interconversion between (E) and (Z)-PVN was demonstrated via ultraviolet hole-filling experiments. Photoexcitation of (E)- and (Z)-PVN at their respective S{sub 0}-S{sub 1} origins failed to produce quinoline, a simple polycyclic aromatic nitrogen heterocylcle, within the detection sensitivity of our experiments. Stationary points along the potential energy surface associated with (Z)-PVN → quinoline isomerization showed a barrier of 93 kcal/mol associated with the first step in the isomerization process, slowing the interconversion process at the excitation energies used (96 kcal/mol) to timescales beyond those probed in the present experiment.« less

Authors:
; ; ; ;
Publication Date:
OSTI Identifier:
22493542
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 143; Journal Issue: 7; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; COMPARATIVE EVALUATIONS; EXCITATION; EXCITED STATES; FLUORESCENCE SPECTROSCOPY; HOLES; ISOMERIZATION; ISOMERS; MOLECULES; NITRILES; NITROGEN; PHOTOCHEMISTRY; POTENTIAL ENERGY; RADIATIVE DECAY; SURFACES; ULTRAVIOLET RADIATION

Citation Formats

Mehta-Hurt, Deepali N., Korn, Joseph A., Navotnaya, Polina, Parobek, Alexander P., Clayton, Rachel M., and Zwier, Timothy S., E-mail: zwier@purdue.edu. The spectroscopy and photochemistry of quinioline structural isomers: (E)- and (Z)-phenylvinylnitrile. United States: N. p., 2015. Web. doi:10.1063/1.4928191.
Mehta-Hurt, Deepali N., Korn, Joseph A., Navotnaya, Polina, Parobek, Alexander P., Clayton, Rachel M., & Zwier, Timothy S., E-mail: zwier@purdue.edu. The spectroscopy and photochemistry of quinioline structural isomers: (E)- and (Z)-phenylvinylnitrile. United States. https://doi.org/10.1063/1.4928191
Mehta-Hurt, Deepali N., Korn, Joseph A., Navotnaya, Polina, Parobek, Alexander P., Clayton, Rachel M., and Zwier, Timothy S., E-mail: zwier@purdue.edu. 2015. "The spectroscopy and photochemistry of quinioline structural isomers: (E)- and (Z)-phenylvinylnitrile". United States. https://doi.org/10.1063/1.4928191.
@article{osti_22493542,
title = {The spectroscopy and photochemistry of quinioline structural isomers: (E)- and (Z)-phenylvinylnitrile},
author = {Mehta-Hurt, Deepali N. and Korn, Joseph A. and Navotnaya, Polina and Parobek, Alexander P. and Clayton, Rachel M. and Zwier, Timothy S., E-mail: zwier@purdue.edu},
abstractNote = {In Titan’s atmosphere, photochemical pathways that lead to nitrogen heteroaromatics may incorporate photoisomerization of their structural isomers as a final step. (E)- and (Z)-phenylvinylnitrile ((E)- and (Z)-PVN, C{sub 6}H{sub 5} —CH=CHCN) are structural isomers of quinoline that themselves possess extensive absorptions in the ultraviolet, and thus may engage in such photoisomerization pathways. The present study explores the vibronic spectroscopy and photo-induced isomerization of gas-phase (E)- and (Z)-PVN in the 33,600-35,850 cm{sup −1} region under jet-cooled conditions. The S{sub 0}-S{sub 1} origins for (E)- and (Z)-PVN have been identified at 33 827 cm{sup −1} and 33 707 cm{sup −1}, respectively. Isomer-specific UV-UV hole-burning and UV depletion spectra reveal sharp vibronic structure that extends over almost 2000 cm{sup −1}, with thresholds for fast non-radiative decay identified by a comparison between hole-burning and UV depletion spectra. Dispersed fluorescence spectra of the two isomers enable the assignment of many low frequency transitions in both molecules, aided by harmonic frequency calculations (B3LYP/6-311++G(d,p)) and a comparison with the established spectroscopy of phenylvinylacetylene, the ethynyl counterpart to PVN. Both isomers are proven to be planar in both the S{sub 0} ground and S{sub 1} electronic excited states. (E)-PVN exhibits extensive Duschinsky mixing involving out-of-plane modes whose frequencies and character change significantly in the ππ{sup ∗} transition, which modulates the degree of single- and double-bond character along the vinylnitrile substituent. This same mixing is much less evident in (Z)-PVN. The spectroscopic characterization of (E)- and (Z)-PVN served as the basis for photoisomerization experiments using ultraviolet hole-filling spectroscopy carried out in a reaction tube affixed to the pulsed valve. Successful interconversion between (E) and (Z)-PVN was demonstrated via ultraviolet hole-filling experiments. Photoexcitation of (E)- and (Z)-PVN at their respective S{sub 0}-S{sub 1} origins failed to produce quinoline, a simple polycyclic aromatic nitrogen heterocylcle, within the detection sensitivity of our experiments. Stationary points along the potential energy surface associated with (Z)-PVN → quinoline isomerization showed a barrier of 93 kcal/mol associated with the first step in the isomerization process, slowing the interconversion process at the excitation energies used (96 kcal/mol) to timescales beyond those probed in the present experiment.},
doi = {10.1063/1.4928191},
url = {https://www.osti.gov/biblio/22493542}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 7,
volume = 143,
place = {United States},
year = {Fri Aug 21 00:00:00 EDT 2015},
month = {Fri Aug 21 00:00:00 EDT 2015}
}