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Bridging the gap between the gas and solution phase : solvent specific photochemistry in 4-tert-butylcatechol
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Horbury, Michael D., Baker, Lewis A., Quan, Wen-Dong, Young, Jamie D., Staniforth, Michael, Greenough, Simon E. and Stavros, Vasilios G. (2015) Bridging the gap between the gas and solution phase : solvent specific photochemistry in 4-tert-butylcatechol. Journal of Physical Chemistry A, 119 (50). pp. 11989-11996. doi:10.1021/acs.jpca.5b03621 ISSN 1089-5639.
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Official URL: http://dx.doi.org/10.1021/acs.jpca.5b03621
Abstract
Eumelanin is a naturally synthesized ultraviolet light absorbing biomolecule, possessing both photoprotective and phototoxic properties. We infer insight into these properties of eumelanin using a bottom-up approach, by investigating a subunit analogue, 4-tert-butylcatechol. Utilizing a combination of femtosecond transient electronic absorption spectroscopy and time-re-solved velocity map ion imaging, our results suggest an environmental-dependent relaxation pathway, following irradiation at 267 nm to populate the S1 (1ππ*) state. Gas-phase and non-polar solution-phase measurements reveal that the S1 state decays through coupling onto the S2 (1πσ*) state that is dissociative along the non-intramolecular hydrogen bonded ‘free’ O–H bond. This process is mediated by tunneling beneath an S1/S2 conical intersection and occurs in 4.9 ± 0.6 ps in the gas-phase and 27 ± 7 ps in the non-polar cyclohexane solution. Comparative studies on the deuterated isotopologue of 4-tert-butylcatechol in both the gas- and solution-phase (cyclohexane) reveals an average kinetic isotope effect of ~19 and ~7, respectively, supportive of O–H dissociation mediated by a quantum tunneling mechanism. In contrast, in the polar acetonitrile, the S1 state decays on a much longer timescale of 1.7 ± 0.1 ns. We propose that the S1 decay is now multicomponent, likely driven by internal conversion, intersystem crossing and fluorescence, as well as O–H dissociation. The attribution of conformer driven excited state dynamics to explain how the S1 state decays in the gas- and non-polar solution-phase versus the polar solution-phase, elegantly demonstrates the influence the environment has on the ensuing excited state dynamics.
Item Type: | Journal Article | ||||||
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Subjects: | Q Science > QD Chemistry | ||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry Faculty of Science, Engineering and Medicine > Research Centres > Molecular Organisation and Assembly in Cells (MOAC) |
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Library of Congress Subject Headings (LCSH): | Photochemistry, Ultraviolet radiation, Spectrum analysis | ||||||
Journal or Publication Title: | Journal of Physical Chemistry A | ||||||
Publisher: | American Chemical Society | ||||||
ISSN: | 1089-5639 | ||||||
Official Date: | 27 May 2015 | ||||||
Dates: |
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Volume: | 119 | ||||||
Number: | 50 | ||||||
Page Range: | pp. 11989-11996 | ||||||
DOI: | 10.1021/acs.jpca.5b03621 | ||||||
Status: | Peer Reviewed | ||||||
Publication Status: | Published | ||||||
Access rights to Published version: | Restricted or Subscription Access | ||||||
Date of first compliant deposit: | 26 October 2016 | ||||||
Date of first compliant Open Access: | 26 October 2016 | ||||||
Funder: | Engineering and Physical Sciences Research Council (EPSRC), University of Warwick. Institute of Advanced Study (IAS), Royal Society (Great Britain) | ||||||
Grant number: | EP/F500378/1, EP/J007153 (EPSRC) |
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