Ultraviolet photodissociation action spectroscopy of gas-phase protonated quinoline and isoquinoline cations

Hansen, Christopher S., Blanksby, Stephen J., & Trevitt, Adam J. (2015) Ultraviolet photodissociation action spectroscopy of gas-phase protonated quinoline and isoquinoline cations. Physical Chemistry Chemical Physics, 17(39), pp. 25882-25890.

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The gas-phase photodissociation action spectroscopy of protonated quinoline and isoquinoline cations (quinolineH+ and isoquinolineH+) is investigated at ambient temperature. Both isomers exhibit vibronic detail and wavelength-dependent photoproduct partitioning across two broad bands in the ultraviolet. Photodissociation action spectra are reported spanning 370–285 nm and 250–220 nm and analysed with the aid of electronic structure calculations: TD-DFT (CAM-B3LYP/aug-cc-pVDZ) is used for spectra simulations and CBS-QB3 for dissociation enthalpies. It is shown that the action spectra are afforded predominantly by two-photon excitation. The first band is attributed to both the S1 ← S0 and S2 ← S0 electronic transitions in quinolineH+, with a S1 ← S0 electronic origin assigned at 27900 cm−1. For isoquinolineH+ the S1 ← S0 transition is observed with an assigned electronic origin at 27500 cm−1. A separate higher energy band is observed for both species, corresponding to the S3 ← S0 transition, with origins assigned at 42100 cm−1 and 42500 cm−1 for quinolineH+ and isoquinolineH+, respectively. Franck–Condon absorption simulations provide an explanation for some vibrational structure observed in both bands allowing several normal mode assignments. The nature of the electronic transitions is discussed and it is shown that the excited states active in the reported spectra should be of ππ* character with some degree of charge transfer from the homocycle to the heterocycle.

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ID Code: 96431
Item Type: Journal Article
Refereed: Yes
DOI: 10.1039/c5cp02035b
ISSN: 1463-9076
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > PHYSICAL CHEMISTRY (INCL. STRUCTURAL) (030600)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2016 Royal Society of Chemistry
Deposited On: 30 Jun 2016 01:24
Last Modified: 12 Jul 2016 02:24

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